def _get_psrr_lti(self, op_dict, nf_dict, ser_type, amp_in, cload, cdecap_amp, rsource) -> float:
'''
Returns:
psrr: PSRR (dB)
fbw: Power supply -> output 3dB bandwidth (Hz)
'''
n_ser = ser_type == 'n'
n_amp = amp_in == 'n'
# Supply -> output gain
ckt_sup = LTICircuit()
ser_d = 'vdd' if n_ser else 'reg'
ser_s = 'reg' if n_ser else 'vdd'
inp_conn = 'gnd' if n_ser else 'reg'
inn_conn = 'reg' if n_ser else 'gnd'
tail_rail = 'gnd' if n_amp else 'vdd'
load_rail = 'vdd' if n_amp else 'gnd'
# Passives
if rsource != 0:
ckt_sup.add_res(rsource, 'vbat', 'vdd')
ckt_sup.add_cap(cload, 'reg', 'gnd')
ckt_sup.add_cap(cdecap_amp, 'out', 'reg')
# Series device
ckt_sup.add_transistor(op_dict['ser'], ser_d, 'out', ser_s, fg=nf_dict['ser'], neg_cap=False)
# Amplifier
ckt_sup.add_transistor(op_dict['amp_in'], 'outx', inp_conn, 'tail', fg=nf_dict['amp_in'], neg_cap=False)
ckt_sup.add_transistor(op_dict['amp_in'], 'out', inn_conn, 'tail', fg=nf_dict['amp_in'], neg_cap=False)
ckt_sup.add_transistor(op_dict['amp_tail'], 'tail', 'gnd', tail_rail, fg=nf_dict['amp_tail'], neg_cap=False)
ckt_sup.add_transistor(op_dict['amp_load'], 'outx', 'outx', load_rail, fg=nf_dict['amp_load'], neg_cap=False)
ckt_sup.add_transistor(op_dict['amp_load'], 'out', 'outx', load_rail, fg=nf_dict['amp_load'], neg_cap=False)
if rsource == 0:
num_sup, den_sup = ckt_sup.get_num_den(in_name='vdd', out_name='reg', in_type='v')
else:
num_sup, den_sup = ckt_sup.get_num_den(in_name='vbat', out_name='reg', in_type='v')
gain_sup = num_sup[-1]/den_sup[-1]
wbw_sup = get_w_3db(den_sup, num_sup)
if gain_sup == 0:
return float('inf')
if wbw_sup == None:
wbw_sup = 0
fbw_sup = wbw_sup / (2*np.pi)
psrr = 10*np.log10((1/gain_sup)**2)
return psrr, fbw_sup
def make_ltickt(self, op_dict: Mapping[str, Any], nf_dict: Mapping[str,
int],
cload: float, rload: float, meas_side: str) -> LTICircuit:
ckt = LTICircuit()
inp_conn = 'gnd' if meas_side == 'n' else 'inp'
inn_conn = 'gnd' if meas_side == 'p' else 'inn'
ckt.add_transistor(op_dict['main_in'],
'main_outn',
inp_conn,
'main_tail',
fg=nf_dict['main_in'])
ckt.add_transistor(op_dict['main_in'],
'main_outp',
inn_conn,
'main_tail',
fg=nf_dict['main_in'])
# ckt.add_transistor(op_dict['main_tail'], 'main_tail', 'cmfb_outp', 'gnd', fg=nf_dict['main_tail'])
ckt.add_transistor(op_dict['main_tail'],
'main_tail',
'gnd',
'gnd',
fg=nf_dict['main_tail'])
ckt.add_res(rload, 'main_outn', 'gnd')
ckt.add_res(rload, 'main_outp', 'gnd')
ckt.add_cap(cload, 'main_outn', 'gnd')
ckt.add_cap(cload, 'main_outp', 'gnd')
# ckt.add_transistor(op_dict['cmfb_in'], 'cmfb_out1n', 'gnd', 'cmfb_tail', fg=nf_dict['cmfb_in']*2)
# ckt.add_transistor(op_dict['cmfb_in'], 'cmfb_out1p', 'main_outn', 'cmfb_tail', fg=nf_dict['cmfb_in'])
# ckt.add_transistor(op_dict['cmfb_in'], 'cmfb_out1p', 'main_outp', 'cmfb_tail', fg=nf_dict['cmfb_in'])
# ckt.add_transistor(op_dict['cmfb_tail'], 'cmfb_tail', 'gnd', 'gnd', fg=nf_dict['cmfb_tail'])
# ckt.add_transistor(op_dict['cmfb_load'], 'cmfb_out1n', 'cmfb_out1n', 'gnd', fg=nf_dict['cmfb_load'])
# ckt.add_transistor(op_dict['cmfb_load'], 'cmfb_out1p', 'cmfb_out1p', 'gnd', fg=nf_dict['cmfb_load'])
# ckt.add_transistor(op_dict['cmfb_load_copy'], 'cmfb_outp', 'cmfb_out1n', 'gnd', fg=nf_dict['cmfb_load_copy'])
# ckt.add_transistor(op_dict['cmfb_load_copy'], 'cmfb_outn', 'cmfb_out1p', 'gnd', fg=nf_dict['cmfb_load_copy'])
# ckt.add_transistor(op_dict['cmfb_out'], 'cmfb_outp', 'cmfb_outp', 'gnd', fg=nf_dict['cmfb_out'])
# ckt.add_transistor(op_dict['cmfb_out'], 'cmfb_outn', 'cmfb_outn', 'gnd', fg=nf_dict['cmfb_out'])
# assert False, 'blep'
# ckt.add_transistor(op_dict['cmfb_in'], 'cmfb_outn', 'gnd', 'cmfb_tail', fg=nf_dict['cmfb_in']*2, neg_cap=False)
# ckt.add_transistor(op_dict['cmfb_in'], 'cmfb_outp', 'main_outn', 'cmfb_tail', fg=nf_dict['cmfb_in'], neg_cap=False)
# ckt.add_transistor(op_dict['cmfb_in'], 'cmfb_outp', 'main_outp', 'cmfb_tail', fg=nf_dict['cmfb_in'], neg_cap=False)
# ckt.add_transistor(op_dict['cmfb_tail'], 'cmfb_tail', 'gnd', 'gnd', fg=nf_dict['cmfb_tail'], neg_cap=False)
# ckt.add_transistor(op_dict['cmfb_out'], 'cmfb_outn', 'cmfb_outn', 'gnd', fg=nf_dict['cmfb_out'], neg_cap=False)
# ckt.add_transistor(op_dict['cmfb_out'], 'cmfb_outp', 'cmfb_outp', 'gnd', fg=nf_dict['cmfb_out'], neg_cap=False)
return ckt
def run_main():
interp_method = 'spline'
sim_env = 'tt'
nmos_spec = 'specs_mos_char/nch_w0d5.yaml'
pmos_spec = 'specs_mos_char/pch_w0d5.yaml'
intent = 'lvt'
nch_db = get_db(nmos_spec, intent, interp_method=interp_method,
sim_env=sim_env)
nch_op = nch_db.query(vbs=0, vds=0.5, vgs=0.5)
pprint.pprint(nch_op)
# building circuit
cir = LTICircuit()
cir.add_transistor(nch_op, 'out', 'in', 'gnd', 'gnd', fg=2)
cir.add_res(10e3, 'out', 'gnd')
cir.add_cap(100e-15, 'out', 'gnd')
# get gain/poles/zeros/bode plot
trans_fun = cir.get_transfer_function('in', 'out', in_type='v')
print('poles: %s' % trans_fun.poles)
print('zeros: %s' % trans_fun.zeros)
# note: don't use the gain attribute. For some reason it's broken
print('gain: %.4g' % (trans_fun.num[-1] / trans_fun.den[-1]))
fvec = np.logspace(5, 10, 1000)
_, mag, phase = sig.bode(trans_fun, w=2 * np.pi * fvec)
# get transient response
state_space = cir.get_state_space('in', 'out', in_type='v')
tvec = np.linspace(0, 1e-8, 1000)
_, yvec = sig.step(state_space, T=tvec)
_, (ax0, ax1) = plt.subplots(2, sharex=True)
ax0.semilogx(fvec, mag)
ax0.set_ylabel('Magnitude (dB)')
ax1.semilogx(fvec, phase)
ax1.set_ylabel('Phase (degrees)')
ax1.set_xlabel('Frequency (Hz)')
plt.figure(2)
plt.plot(tvec, yvec)
plt.ylabel('Output (V/V)')
plt.xlabel('Time (s)')
plt.show()
def _get_loadreg_lti(self, op_dict, nf_dict, ser_type, amp_in, cload, cdecap_amp, rsource, vout, iout) -> float:
'''
Returns:
loadreg: Load regulation for peak-to-peak load current variation of 20% (V/V)
'''
n_ser = ser_type == 'n'
n_amp = amp_in == 'n'
vdd = 'vdd' if rsource != 0 else 'gnd'
# Supply -> output gain
ckt = LTICircuit()
ser_d = vdd if n_ser else 'reg'
ser_s = 'reg' if n_ser else vdd
inp_conn = 'gnd' if n_ser else 'reg'
inn_conn = 'reg' if n_ser else 'gnd'
tail_rail = 'gnd' if n_amp else vdd
load_rail = vdd if n_amp else 'gnd'
# Passives
if rsource != 0:
ckt.add_res(rsource, 'gnd', 'vdd')
ckt.add_cap(cload, 'reg', 'gnd')
ckt.add_cap(cdecap_amp, 'out', 'reg')
# Series device
ckt.add_transistor(op_dict['ser'], ser_d, 'out', ser_s, fg=nf_dict['ser'], neg_cap=False)
# Amplifier
ckt.add_transistor(op_dict['amp_in'], 'outx', inp_conn, 'tail', fg=nf_dict['amp_in'], neg_cap=False)
ckt.add_transistor(op_dict['amp_in'], 'out', inn_conn, 'tail', fg=nf_dict['amp_in'], neg_cap=False)
ckt.add_transistor(op_dict['amp_tail'], 'tail', 'gnd', tail_rail, fg=nf_dict['amp_tail'], neg_cap=False)
ckt.add_transistor(op_dict['amp_load'], 'outx', 'outx', load_rail, fg=nf_dict['amp_load'], neg_cap=False)
ckt.add_transistor(op_dict['amp_load'], 'out', 'outx', load_rail, fg=nf_dict['amp_load'], neg_cap=False)
num, den = ckt.get_num_den(in_name='reg', out_name='reg', in_type='i')
transimpedance = num[-1]/den[-1]
loadreg = transimpedance*0.2*iout/vout
return loadreg
def construct_feedback(n_op, p_op, tail_op,
nf_n, nf_p, nf_tail,
cload, cn=165e-15, cp=83e-15, r=70.71e3):
'''
Inputs:
p/n/tail_op: Operating point information for a given device.
NMOS (input), PMOS (active load), or tail device.
nf_n/p/tail: Integer. Number of minimum channel width/length
devices in parallel.
cload: Float. Load capacitance in farads.
cn: Float. Capacitance in farads attached to the negative input
terminal of the amplifier for the filter.
cp: Float. Capacitance in farads attached to the positive input
terminal of the amplifier for the filter.
r: Float. Resistance in ohms used external to the amplifier
for the filter.
Outputs:
Returns the LTICircuit constructed for closed-loop analysis of
the amplifier with the loop broken.
'''
ckt = LTICircuit()
# Left side
ckt.add_transistor(n_op, 'out_copy', 'inp', 'tail', fg=nf_n)
ckt.add_transistor(p_op, 'out_copy', 'out_copy', 'gnd', fg=nf_p)
# Right side
ckt.add_transistor(n_op, 'out', 'inn', 'tail', fg=nf_n)
ckt.add_transistor(p_op, 'out', 'out_copy', 'gnd', fg=nf_p)
# Tail
ckt.add_transistor(tail_op, 'tail', 'gnd', 'gnd', fg=nf_tail)
# Adding additional passives
ckt.add_cap(cload, 'out', 'gnd')
ckt.add_cap(cn, 'inn', 'rmid')
ckt.add_cap(cp, 'inp', 'gnd')
ckt.add_res(r, 'in', 'rmid')
ckt.add_res(r, 'rmid', 'inp')
return ckt
def _get_stb_lti(self, op_dict, nf_dict, ser_type, amp_in, cload, cdecap_amp, rsource) -> float:
'''
Returns:
pm: Phase margin (degrees)
'''
ckt = LTICircuit()
n_ser = ser_type == 'n'
n_amp = amp_in == 'n'
vdd = 'vdd' if rsource != 0 else 'gnd'
# Series device
ser_d = vdd if n_ser else 'reg'
ser_s = 'reg' if n_ser else vdd
ckt.add_transistor(op_dict['ser'], ser_d, 'out', ser_s, fg=nf_dict['ser'], neg_cap=False)
# Passives
ckt.add_cap(cload, 'reg', 'gnd')
ckt.add_cap(cdecap_amp, 'out', 'reg')
if rsource != 0:
ckt.add_res(rsource, 'gnd', 'vdd')
# Amplifier
tail_rail = 'gnd' if n_amp else vdd
load_rail = vdd if n_amp else 'gnd'
inp_conn = 'gnd' if n_ser else 'amp_in'
inn_conn = 'gnd' if not n_ser else 'amp_in'
ckt.add_transistor(op_dict['amp_in'], 'outx', inp_conn, 'tail', fg=nf_dict['amp_in'], neg_cap=False)
ckt.add_transistor(op_dict['amp_in'], 'out', inn_conn, 'tail', fg=nf_dict['amp_in'], neg_cap=False)
ckt.add_transistor(op_dict['amp_tail'], 'tail', 'gnd', tail_rail, fg=nf_dict['amp_tail'], neg_cap=False)
ckt.add_transistor(op_dict['amp_load'], 'outx', 'outx', load_rail, fg=nf_dict['amp_load'], neg_cap=False)
ckt.add_transistor(op_dict['amp_load'], 'out', 'outx', load_rail, fg=nf_dict['amp_load'], neg_cap=False)
# Calculating stability margins
num, den = ckt.get_num_den(in_name='amp_in', out_name='reg', in_type='v')
pm, _ = get_stability_margins(np.convolve(num, [-1]), den)
return pm
def _get_loopgain_lti(self, op_dict, nf_dict, ser_type, amp_in, rsource) -> float:
'''
Returns:
A: DC loop gain
'''
ckt = LTICircuit()
n_ser = ser_type == 'n'
n_amp = amp_in == 'n'
vdd = 'vdd' if rsource != 0 else 'gnd'
# Series device
ser_d = vdd if n_ser else 'reg'
ser_s = 'reg' if n_ser else vdd
ckt.add_transistor(op_dict['ser'], ser_d, 'out', ser_s, fg=nf_dict['ser'], neg_cap=True)
# Passives
if rsource != 0:
ckt.add_res(rsource, 'gnd', 'vdd')
# Amplifier
tail_rail = 'gnd' if n_amp else vdd
load_rail = vdd if n_amp else 'gnd'
inp_conn = 'gnd' if n_ser else 'amp_in'
inn_conn = 'gnd' if not n_ser else 'amp_in'
ckt.add_transistor(op_dict['amp_in'], 'outx', inp_conn, 'tail', fg=nf_dict['amp_in'], neg_cap=False)
ckt.add_transistor(op_dict['amp_in'], 'out', inn_conn, 'tail', fg=nf_dict['amp_in'], neg_cap=False)
ckt.add_transistor(op_dict['amp_tail'], 'tail', 'gnd', tail_rail, fg=nf_dict['amp_tail'], neg_cap=False)
ckt.add_transistor(op_dict['amp_load'], 'outx', 'outx', load_rail, fg=nf_dict['amp_load'], neg_cap=False)
ckt.add_transistor(op_dict['amp_load'], 'out', 'outx', load_rail, fg=nf_dict['amp_load'], neg_cap=False)
# Calculating stability margins
num, den = ckt.get_num_den(in_name='amp_in', out_name='reg', in_type='v')
A = num[-1]/den[-1]
return A
def characterize_casc_amp(env_list,
lch,
intent_list,
fg_list,
w_list,
db_list,
vbias_list,
vload_list,
vtail_list,
vmid_list,
vincm,
voutcm,
vdd,
vin_clip,
clip_ratio_min,
cw,
rw,
fanout,
ton,
k_settle_targ,
scale_min=0.25,
scale_max=20):
# compute DC transfer function curve and compute linearity spec
ndb, pdb = db_list[0], db_list[-1]
results = solve_casc_diff_dc(env_list,
ndb,
pdb,
lch,
intent_list,
w_list,
fg_list,
vbias_list,
vload_list,
vtail_list,
vmid_list,
vdd,
vincm,
voutcm,
vin_clip,
clip_ratio_min,
num_points=20)
vmat_list, ratio_list, gain_list = results
# compute settling ratio
fg_tail, fg_in, fg_casc, fg_load = fg_list
db_tail, db_in, db_casc, db_load = db_list
w_tail, w_in, w_casc, w_load = w_list
fzin = 1.0 / (2 * ton)
wzin = 2 * np.pi * fzin
tvec = np.linspace(0, ton, 200, endpoint=True)
scale_list = []
cin_list = []
for env, vbias, vload, vtail, vmid, vmat in zip(env_list, vbias_list,
vload_list, vtail_list,
vmid_list, vmat_list):
# step 1: get half circuit parameters and compute input capacitance
in_par = db_in.query(env=env,
w=w_in,
vbs=-vtail,
vds=vmid - vtail,
vgs=vincm - vtail)
casc_par = db_casc.query(env=env,
w=w_casc,
vbs=-vmid,
vds=voutcm - vmid,
vgs=vdd - vmid)
load_par = db_load.query(env=env,
w=w_load,
vbs=0,
vds=voutcm - vdd,
vgs=vload - vdd)
cir = LTICircuit()
cir.add_transistor(in_par, 'mid', 'in', 'gnd', fg=fg_in)
cir.add_transistor(casc_par, 'out', 'gnd', 'mid', fg=fg_casc)
cir.add_transistor(load_par, 'out', 'gnd', 'gnd', fg=fg_load)
zin = cir.get_impedance('in', fzin)
cin = (1 / zin).imag / wzin
cin_list.append(cin)
# step 3A: construct differential circuit with vin_clip / 2.
vts, vmps, vmns, vops, vons = vmat[-1, :]
vinp = vincm + vin_clip / 4
vinn = vincm - vin_clip / 4
tail_par = db_tail.query(env=env, w=w_tail, vbs=0, vds=vts, vgs=vbias)
inp_par = db_in.query(env=env,
w=w_in,
vbs=-vts,
vds=vmns - vts,
vgs=vinp - vts)
inn_par = db_in.query(env=env,
w=w_in,
vbs=-vts,
vds=vmps - vts,
vgs=vinn - vts)
cascp_par = db_casc.query(env=env,
w=w_casc,
vbs=-vmns,
vds=vons - vmns,
vgs=vdd - vmns)
cascn_par = db_casc.query(env=env,
w=w_casc,
vbs=-vmps,
vds=vops - vmps,
vgs=vdd - vmps)
loadp_par = db_load.query(env=env,
w=w_load,
vbs=0,
vds=vons - vdd,
vgs=vload - vdd)
loadn_par = db_load.query(env=env,
w=w_load,
vbs=0,
vds=vops - vdd,
vgs=vload - vdd)
cir = LTICircuit()
cir.add_transistor(tail_par, 'tail', 'gnd', 'gnd', fg=fg_tail)
cir.add_transistor(inp_par, 'midn', 'inp', 'tail', fg=fg_in)
cir.add_transistor(inn_par, 'midp', 'inn', 'tail', fg=fg_in)
cir.add_transistor(cascp_par, 'dn', 'gnd', 'midn', fg=fg_casc)
cir.add_transistor(cascn_par, 'dp', 'gnd', 'midp', fg=fg_casc)
cir.add_transistor(loadp_par, 'dn', 'gnd', 'gnd', fg=fg_load)
cir.add_transistor(loadn_par, 'dp', 'gnd', 'gnd', fg=fg_load)
cir.add_vcvs(0.5, 'inp', 'gnd', 'inac', 'gnd')
cir.add_vcvs(-0.5, 'inn', 'gnd', 'inac', 'gnd')
# step 3B: compute DC gain
cir.add_vcvs(1, 'dac', 'gnd', 'dp', 'dn')
dc_tf = cir.get_transfer_function('inac', 'dac')
_, gain_vec = dc_tf.freqresp(w=[0.1])
dc_gain = gain_vec[0].real
# step 3C add cap loading
cload = fanout * cin
cir.add_cap(cload, 'outp', 'gnd')
cir.add_cap(cload, 'outn', 'gnd')
cir.add_vcvs(1, 'outac', 'gnd', 'outp', 'outn')
# step 4: find scale factor to achieve k_settle
# noinspection PyUnresolvedReferences
scale_swp = np.arange(scale_min, scale_max, 0.25).tolist()
max_kset = 0
opt_scale = 0
for cur_scale in scale_swp:
# add scaled wired parasitics
cap_cur = cw / 2 / cur_scale
res_cur = rw * cur_scale
cir.add_cap(cap_cur, 'dp', 'gnd')
cir.add_cap(cap_cur, 'dn', 'gnd')
cir.add_cap(cap_cur, 'outp', 'gnd')
cir.add_cap(cap_cur, 'outn', 'gnd')
cir.add_res(res_cur, 'dp', 'outp')
cir.add_res(res_cur, 'dn', 'outn')
# get settling factor
sys = cir.get_state_space('inac', 'outac')
_, yvec = scipy.signal.step(
sys, T=tvec) # type: Tuple[np.ndarray, np.ndarray]
k_settle_cur = yvec[-1] / dc_gain
# print('scale = %.4g, k_settle = %.4g' % (cur_scale, k_settle_cur))
# update next scale factor
if k_settle_cur > max_kset:
max_kset = k_settle_cur
opt_scale = cur_scale
else:
# k_settle is decreasing, break
break
if max_kset >= k_settle_targ:
break
# remove wire parasitics
cir.add_cap(-cap_cur, 'dp', 'gnd')
cir.add_cap(-cap_cur, 'dn', 'gnd')
cir.add_cap(-cap_cur, 'outp', 'gnd')
cir.add_cap(-cap_cur, 'outn', 'gnd')
cir.add_res(-res_cur, 'dp', 'outp')
cir.add_res(-res_cur, 'dn', 'outn')
if max_kset < k_settle_targ:
raise ValueError('%s max kset = %.4g @ scale = %.4g, '
'cannot meet settling time spec.' %
(env, max_kset, opt_scale))
scale_list.append(opt_scale)
return vmat_list, ratio_list, gain_list, scale_list, cin_list
def design_inv_tia(specs, pch_op_info, nch_op_info, pch_scale):
sim_env = specs['sim_env']
pch_db = specs['pch_db']
nch_db = specs['nch_db']
vgs_res = specs['vgs_res']
vdd = specs['vdd']
rdc_targ = specs['rdc']
f3db_targ = specs['f3db']
pm_targ = specs['pm']
cin = specs['cin']
cl = specs['cl']
scale_min = specs['scale_min']
scale_max = specs['scale_max']
n_scale = specs['n_scale']
rf_min = specs['rf_min']
rf_max = specs['rf_max']
n_rf = specs['n_rf']
pch_ibias = pch_op_info['ibias']
nch_ibias = nch_op_info['ibias']
gmp = pch_op_info['gm'] * pch_scale
gmn = nch_op_info['gm']
gm_tot = gmp + gmn
gdsp = pch_op_info['gds'] * pch_scale
gdsn = nch_op_info['gds']
rop = 1 / gdsp
ron = 1 / gdsn
ro_tot = rop * ron / (rop + ron)
gds_tot = 1 / ro_tot
cgsp = pch_op_info['cgs'] * pch_scale
cgsn = nch_op_info['cgs']
cgs_tot = cgsp + cgsn
cgbp = pch_op_info['cgb'] * pch_scale
cgbn = nch_op_info['cgb']
cgb_tot = cgbp + cgbn
cgdp = pch_op_info['cgd'] * pch_scale
cgdn = nch_op_info['cgd']
cgd_tot = cgdp + cgdn
cggp = pch_op_info['cgg'] * pch_scale
cggn = nch_op_info['cgg']
cgg_tot = cggp + cggn
cdsp = pch_op_info['cds'] * pch_scale
cdsn = nch_op_info['cds']
cds_tot = cdsp + cdsn
cdbp = pch_op_info['cdb'] * pch_scale
cdbn = nch_op_info['cdb']
cdb_tot = cdbp + cdbn
cddp = pch_op_info['cdd'] * pch_scale
cddn = nch_op_info['cdd']
cdd_tot = cddp + cddn
scale_vec = np.linspace(scale_min, scale_max, n_scale)
for scale in scale_vec:
for rf in np.linspace(rf_min, rf_max, n_rf):
# Build circuit
cir = LTICircuit()
cir.add_transistor(pch_op_info,
'out',
'in',
'gnd',
'gnd',
fg=scale * pch_scale)
cir.add_transistor(nch_op_info,
'out',
'in',
'gnd',
'gnd',
fg=scale)
cir.add_res(rf, 'out', 'in')
cir.add_cap(cin, 'in', 'gnd')
cir.add_cap(cl, 'out', 'gnd')
# Get gain/poles/zeros/Bode plot
# Note: any in_type other than 'v' results in current source input
tf = cir.get_transfer_function('in', 'out', in_type='i')
rdc = np.absolute(tf.num[-1] / tf.den[-1])
w3db = get_w_3db(tf.num, tf.den)
f3db = w3db / (2 * np.pi)
cin_tot = cin + cgg_tot * scale
cl_tot = cl + cdd_tot * scale
cgd_scaled = cgd_tot * scale
gm_scaled = gm_tot * scale
gds_scaled = gds_tot * scale
cir_open_loop = LTICircuit()
cir_open_loop.add_vccs(gm_scaled, 'out', 'gnd', 'vt', 'gnd')
cir_open_loop.add_conductance(gds_scaled, 'out', 'gnd')
cir_open_loop.add_cap(cl_tot, 'out', 'gnd')
cir_open_loop.add_res(rf, 'out', 'vr')
cir_open_loop.add_cap(cgd_scaled, 'out', 'vr')
cir_open_loop.add_cap(cin_tot, 'vr', 'gnd')
tf_open_loop = cir_open_loop.get_transfer_function('vt',
'vr',
in_type='v')
pm, gain_margin = get_stability_margins(tf_open_loop.num,
tf_open_loop.den)
pm = pm - 180
if rdc >= rdc_targ and f3db >= f3db_targ and pm >= pm_targ:
ibias = scale * nch_ibias
design = dict(IB=ibias,
Scale=scale,
Rf=rf,
RDC=rdc,
f3dB=f3db,
PM=pm)
return design
def _get_stb_lti(self, op_dict, nf_dict, series_type, rload,
cload) -> float:
'''
Returns:
pm: Phase margins (in degrees)
'''
ckt = LTICircuit()
n_ser = series_type == 'n'
# Series device
ser_d = 'gnd' if n_ser else 'reg'
ser_s = 'reg' if n_ser else 'gnd'
ckt.add_transistor(op_dict['ser'],
ser_d,
'out',
ser_s,
fg=nf_dict['ser'],
neg_cap=False)
# Load passives
ckt.add_res(rload, 'reg', 'gnd')
ckt.add_cap(rload, 'reg', 'gnd')
# TODO include any compensation passives
# Amplifier
inp_conn = 'gnd' if n_ser else 'in'
inn_conn = 'gnd' if not n_ser else 'in'
ckt.add_transistor(op_dict['in'],
'outx',
inp_conn,
'tail',
fg=nf_dict['in'],
neg_cap=False)
ckt.add_transistor(op_dict['in'],
'out',
inn_conn,
'tail',
fg=nf_dict['in'],
neg_cap=False)
ckt.add_transistor(op_dict['tail'],
'tail',
'gnd',
'gnd',
fg=nf_dict['tail'],
neg_cap=False)
ckt.add_transistor(op_dict['load'],
'outx',
'outx',
'gnd',
fg=nf_dict['load'],
neg_cap=False)
ckt.add_transistor(op_dict['load'],
'out',
'outx',
'gnd',
fg=nf_dict['load'],
neg_cap=False)
# Calculating stability margins
num, den = ckt.get_num_den(in_name='in', out_name='reg', in_type='v')
pm, _ = get_stability_margins(np.convolve(num, [-1]), den)
return pm
def design_preamp_string(db_n,
lch,
w_finger,
vdd,
cload,
vin_signal,
vin_shift,
voutcm,
vtail_res,
gain_min,
fbw_min,
rload_res,
vb_n,
itail_max=10e-6,
error_tol=.01):
"""
Designs a preamplifier to go between the comparator and TIA, stringing them
together.
Inputs:
Outputs:
"""
# Estimate vth for use in calculating biasing ranges
vthn = estimate_vth(db_n, vdd, 0)
vincm = (vin_signal + vin_shift) / 2
vtail_min = .15 # TODO: Avoid hardcoding?
vtail_max = vin_signal - vthn
vtail_vec = np.arange(vtail_min, vtail_max, vtail_res)
best_op = None
best_itail = np.inf
for vtail in vtail_vec:
op_tail = db_n.query(vgs=voutcm, vds=vtail, vbs=vb_n)
# The "mean" of the input devices
op_in = db_n.query(vgs=vincm - vtail,
vds=voutcm - vtail,
vbs=vb_n - vtail)
# Calculate the max tail size based on current limit
# and size input devices accordingly
nf_in_min = 2
nf_in_max = int(round(itail_max / 2 / op_in['ibias']))
nf_in_vec = np.arange(nf_in_min, nf_in_max, 1)
for nf_in in nf_in_vec:
amp_ratio_good, nf_tail = verify_ratio(op_in['ibias'] / 2,
op_tail['ibias'], nf_in,
error_tol)
if not amp_ratio_good:
continue
itail = op_tail['ibias'] * nf_tail
rload = (vdd - voutcm) / (itail / 2)
# Input devices too small
if op_in['gm'] * nf_in * rload < gain_min:
continue
# Check small signal parameters with symmetric circuit
ckt_sym = LTICircuit()
ckt_sym.add_transistor(op_in, 'outp', 'gnd', 'tail', fg=nf_in)
ckt_sym.add_transistor(op_in, 'outn', 'inp', 'tail', fg=nf_in)
ckt_sym.add_transistor(op_tail, 'tail', 'gnd', 'gnd', fg=nf_tail)
ckt_sym.add_res(rload, 'outp', 'gnd')
ckt_sym.add_res(rload, 'outn', 'gnd')
ckt_sym.add_cap(cload, 'outp', 'gnd')
ckt_sym.add_cap(cload, 'outn', 'gnd')
num, den = ckt_sym.get_num_den(in_name='inp',
out_name='outn',
in_type='v')
num_unintent, den_unintent = ckt_sym.get_num_den(in_name='inp',
out_name='outp',
in_type='v')
gain_intentional = num[-1] / den[-1]
gain_unintentional = num_unintent[-1] / den_unintent[-1]
gain = abs(gain_intentional - gain_unintentional)
wbw = get_w_3db(num, den)
if wbw == None:
wbw = 0
fbw = wbw / (2 * np.pi)
if fbw < fbw_min:
print("(FAIL) BW:\t{0}".format(fbw))
continue
if gain < gain_min:
print("(FAIL) GAIN:\t{0}".format(gain))
continue
print("(SUCCESS)")
if itail > best_itail:
continue
# Check once again with asymmetric circuit
vin_diff = vin_signal - vin_shift
voutn = voutcm - gain * vin_diff / 2
voutp = voutcm + gain * vin_diff / 2
op_signal = db_n.query(vgs=vin_signal - vtail,
vds=voutn - vtail,
vbs=vb_n - vtail)
op_shift = db_n.query(vgs=vin_shift - vtail,
vds=voutp - vtail,
vbs=vb_n - vtail)
ckt = LTICircuit()
ckt.add_transistor(op_shift, 'outp', 'gnd', 'tail', fg=nf_in)
ckt.add_transistor(op_signal, 'outn', 'inp', 'tail', fg=nf_in)
ckt.add_transistor(op_tail, 'tail', 'gnd', 'gnd', fg=nf_tail)
ckt.add_res(rload, 'outp', 'gnd')
ckt.add_res(rload, 'outn', 'gnd')
ckt.add_cap(cload, 'outp', 'gnd')
ckt.add_cap(cload, 'outn', 'gnd')
num, den = ckt.get_num_den(in_name='inp',
out_name='outn',
in_type='v')
num_unintent, den_unintent = ckt.get_num_den(in_name='inp',
out_name='outp',
in_type='v')
gain_intentional = num[-1] / den[-1]
gain_unintentional = num_unintent[-1] / den_unintent[-1]
gain = abs(gain_intentional - gain_unintentional)
wbw = get_w_3db(num, den)
if wbw == None:
wbw = 0
fbw = wbw / (2 * np.pi)
if fbw < fbw_min:
print("(FAIL) BW:\t{0}".format(fbw))
continue
if gain < gain_min:
print("(FAIL) GAIN:\t{0}".format(gain))
continue
print("(SUCCESS)")
if itail < best_itail:
best_itail = itail
best_op = dict(nf_in=nf_in,
nf_tail=nf_tail,
itail=itail,
rload=rload,
gain=gain,
fbw=fbw,
voutcm=voutcm,
vtail=vtail,
cin=op_signal['cgg'] * nf_in)
if best_op == None:
raise ValueError("No viable solutions.")
return best_op
def characterize_casc_amp(env_list,
fg_list,
w_list,
db_list,
vbias_list,
vload_list,
vtail_list,
vmid_list,
vcm,
vdd,
vin_max,
cw,
rw,
fanout,
ton,
k_settle_targ,
verr_max,
scale_res=0.1,
scale_min=0.25,
scale_max=20):
# compute DC transfer function curve and compute linearity spec
results = solve_casc_diff_dc(env_list,
db_list,
w_list,
fg_list,
vbias_list,
vload_list,
vtail_list,
vmid_list,
vdd,
vcm,
vin_max,
verr_max,
num_points=20)
vin_vec, vmat_list, verr_list, gain_list = results
# compute settling ratio
fg_in, fg_casc, fg_load = fg_list[1:]
db_in, db_casc, db_load = db_list[1:]
w_in, w_casc, w_load = w_list[1:]
fzin = 1.0 / (2 * ton)
wzin = 2 * np.pi * fzin
tvec = np.linspace(0, ton, 200, endpoint=True)
scale_list = []
for env, vload, vtail, vmid in zip(env_list, vload_list, vtail_list,
vmid_list):
# step 1: construct half circuit
in_params = db_in.query(env=env,
w=w_in,
vbs=-vtail,
vds=vmid - vtail,
vgs=vcm - vtail)
casc_params = db_casc.query(env=env,
w=w_casc,
vbs=-vmid,
vds=vcm - vmid,
vgs=vdd - vmid)
load_params = db_load.query(env=env,
w=w_load,
vbs=0,
vds=vcm - vdd,
vgs=vload - vdd)
circuit = LTICircuit()
circuit.add_transistor(in_params, 'mid', 'in', 'gnd', fg=fg_in)
circuit.add_transistor(casc_params, 'd', 'gnd', 'mid', fg=fg_casc)
circuit.add_transistor(load_params, 'd', 'gnd', 'gnd', fg=fg_load)
# step 2: get input capacitance
zin = circuit.get_impedance('in', fzin)
cin = (1 / zin).imag / wzin
circuit.add_cap(cin * fanout, 'out', 'gnd')
# step 3: find scale factor to achieve k_settle
bin_iter = BinaryIterator(scale_min,
None,
step=scale_res,
is_float=True)
while bin_iter.has_next():
# add scaled wired parasitics
cur_scale = bin_iter.get_next()
cap_cur = cw / 2 / cur_scale
res_cur = rw * cur_scale
circuit.add_cap(cap_cur, 'd', 'gnd')
circuit.add_cap(cap_cur, 'out', 'gnd')
circuit.add_res(res_cur, 'd', 'out')
# get settling factor
sys = circuit.get_voltage_gain_system('in', 'out')
dc_gain = sys.freqresp(w=np.array([0.1]))[1][0]
sgn = 1 if dc_gain.real >= 0 else -1
dc_gain = abs(dc_gain)
_, yvec = scipy.signal.step(
sys, T=tvec) # type: Tuple[np.ndarray, np.ndarray]
k_settle_cur = 1 - abs(yvec[-1] - sgn * dc_gain) / dc_gain
print('scale = %.4g, k_settle = %.4g' % (cur_scale, k_settle_cur))
# update next scale factor
if k_settle_cur >= k_settle_targ:
print('save scale = %.4g' % cur_scale)
bin_iter.save()
bin_iter.down()
else:
if cur_scale > scale_max:
raise ValueError(
'cannot meet settling time spec at scale = %d' %
cur_scale)
bin_iter.up()
# remove wire parasitics
circuit.add_cap(-cap_cur, 'd', 'gnd')
circuit.add_cap(-cap_cur, 'out', 'gnd')
circuit.add_res(-res_cur, 'd', 'out')
scale_list.append(bin_iter.get_last_save())
return vmat_list, verr_list, gain_list, scale_list
itrim = 0
else:
vos_base = idiff_trim_base*rload
nf_trim = ceil(vos_targ/vos_base)
itrim = (op_trim_on['ibias']+op_trim_off['ibias'])*nf_trim
# LTICircuit simulation
circuit = LTICircuit()
circuit.add_transistor(op_in, 'outp', 'gnd', 'tail', fg=nf_in)
circuit.add_transistor(op_in, 'outn', 'inp', 'tail', fg=nf_in)
circuit.add_transistor(op_trim_on, 'outn', 'gnd', 'gnd', fg=nf_trim)
circuit.add_transistor(op_trim_off, 'outp', 'gnd', 'gnd', fg=nf_trim)
circuit.add_transistor(op_tail, 'tail', 'vmirr', 'gnd', fg=nf_tail)
circuit.add_transistor(op_mirr, 'vmirr', 'vmirr', 'gnd', fg=nf_mirr)
circuit.add_transistor(op_dummy, 'gnd', 'gnd', 'vmirr', fg=nf_dummy)
circuit.add_res(rload, 'outp', 'gnd')
circuit.add_res(rload, 'outn', 'gnd')
circuit.add_cap(cload, 'outp', 'gnd')
circuit.add_cap(cload, 'outn', 'gnd')
circuit.add_cap(dac_cap, 'tail', 'gnd')
num, den = circuit.get_num_den(in_name='inp', out_name='outn', in_type='v')
num_unintentional, den_unintentional = circuit.get_num_den(in_name='inp', out_name='outp', in_type='v')
gain_intentional = num[-1]/den[-1]
gain_unintentional = num_unintentional[-1]/den_unintentional[-1]
gain = abs(gain_intentional-gain_unintentional)
wbw = get_w_3db(num, den)
if wbw == None:
wbw = 0
fbw = wbw/(2*np.pi)
if fbw < bw_min:
cond_print("Bandwidth fail: {}".format(fbw), debugMode)
def verify_TIA_inverter_SS(n_op_info, p_op_info, nf_n, nf_p, rf, cpd, cload,
rdc_min, fbw_min, pm_min):
"""
Inputs:
n/p_op_info: The MOSDBDiscrete library for the NMOS and PMOS
devices in the bias point for verification.
nf_n/p: Integer. Number of channel fingers for the NMOS/PMOS.
rf: Float. Value of the feedback resistor in ohms.
cpd: Float. Input capacitance not from the TIA in farads.
cload: Float. Output capacitance not from the TIA in farads.
rdc_min: Float. Minimum DC transimpedance in ohms.
fbw_min: Float. Minimum bandwidth (Hz).
pm_min: Float. Minimum phase margin in degrees.
Outputs:
Returns two values
The first is True if the spec is met, False otherwise.
The second is a dictionary of values for rdc (DC transimpedance, V/I),
bw (bandwidth, Hz), and pm (phase margin, deg) if computed. None otherwise.
"""
# Getting relevant small-signal parameters
gds_n = n_op_info['gds'] * nf_n
gds_p = p_op_info['gds'] * nf_p
gds = gds_n + gds_p
gm_n = n_op_info['gm'] * nf_n
gm_p = p_op_info['gm'] * nf_p
gm = gm_n + gm_p
cgs_n = n_op_info['cgs'] * nf_n
cgs_p = p_op_info['cgs'] * nf_p
cgs = cgs_n + cgs_p
cds_n = n_op_info['cds'] * nf_n
cds_p = p_op_info['cds'] * nf_p
cds = cds_n + cds_p
cgd_n = n_op_info['cgd'] * nf_n
cgd_p = p_op_info['cgd'] * nf_p
cgd = cgd_n + cgd_p
# Circuit for GBW
circuit = LTICircuit()
circuit.add_transistor(n_op_info, 'out', 'in', 'gnd', fg=nf_n)
circuit.add_transistor(p_op_info, 'out', 'in', 'gnd', fg=nf_p)
circuit.add_res(rf, 'in', 'out')
circuit.add_cap(cpd, 'in', 'gnd')
circuit.add_cap(cload, 'out', 'gnd')
# Check gain
num, den = circuit.get_num_den(in_name='in', out_name='out', in_type='i')
rdc = num[-1] / den[-1]
if abs(round(rdc)) < round(rdc_min):
print("GAIN:\t{0} (FAIL)".format(rdc))
return False, dict(rdc=rdc, fbw=None, pm=None)
# Check bandwidth
fbw = get_w_3db(num, den) / (2 * np.pi)
if fbw < fbw_min or np.isnan(fbw):
print("BW:\t{0} (FAIL)".format(fbw))
return False, dict(rdc=rdc, fbw=fbw, pm=None)
# Check phase margin by constructing an LTICircuit first
circuit2 = LTICircuit()
"""circuit2.add_transistor(n_op_info, 'out', 'in', 'gnd', fg=nf_n)
circuit2.add_transistor(p_op_info, 'out', 'in', 'gnd', fg=nf_p)
circuit2.add_cap(cpd, 'in', 'gnd')
circuit2.add_cap(cload, 'out', 'gnd')
circuit2.add_res(rf, 'in', 'break')
# Cancel Cgd to correctly break loop
circuit2.add_cap(-cgd, 'in' , 'out')
circuit.add_cap(cgd, 'in', 'break')"""
circuit2.add_conductance(gds, 'out', 'gnd')
circuit2.add_cap(cgs + cpd, 'in', 'gnd')
circuit2.add_cap(cds + cload, 'out', 'gnd')
circuit2.add_cap(cgd, 'in', 'out')
circuit2.add_res(rf, 'in', 'out')
loopBreak = circuit2.get_transfer_function(in_name='in',
out_name='out',
in_type='i')
pm, gainm = get_stability_margins(loopBreak.num * gm, loopBreak.den)
if pm < pm_min or np.isnan(pm):
print("PM:\t{0} (FAIL)\n".format(pm))
return False, dict(rdc=rdc, fbw=fbw, pm=pm)
print("SUCCESS\n")
return True, dict(rdc=rdc, fbw=fbw, pm=pm)
def design_inv_tia(specs, pch_op_info, nch_op_info, pch_scale):
sim_env = specs['sim_env']
pch_db = specs['pch_db']
nch_db = specs['nch_db']
vgs_res = specs['vgs_res']
vdd = specs['vdd']
isw = specs['isw']
ber_targ = specs['ber']
voff = specs['voff']
snr_like_targ = specs['snr_like']
pmos_noise_scale = specs['pmos_noise_scale']
# rdc_targ = specs['rdc']
noise_const = specs['noise_const']
tper = specs['tper']
f_factor = specs['f_factor']
# f3db_targ = specs['f3db']
f3db_targ = f_factor * 1 / tper
pm_targ = specs['pm']
cin = specs['cin']
cl = specs['cl']
scale_min = specs['scale_min']
scale_max = specs['scale_max']
n_scale = specs['n_scale']
rf_min = specs['rf_min']
rf_max = specs['rf_max']
n_rf = specs['n_rf']
pch_ibias = pch_op_info['ibias']
nch_ibias = nch_op_info['ibias']
gmp = pch_op_info['gm'] * pch_scale
gmn = nch_op_info['gm']
gm_tot = gmp + gmn
gammap = pch_op_info['gamma']
gamman = nch_op_info['gamma']
gdsp = pch_op_info['gds'] * pch_scale
gdsn = nch_op_info['gds']
rop = 1 / gdsp
ron = 1 / gdsn
ro_tot = rop * ron / (rop + ron)
gds_tot = 1 / ro_tot
cgsp = pch_op_info['cgs'] * pch_scale
cgsn = nch_op_info['cgs']
cgs_tot = cgsp + cgsn
cgbp = pch_op_info['cgb'] * pch_scale
cgbn = nch_op_info['cgb']
cgb_tot = cgbp + cgbn
cgdp = pch_op_info['cgd'] * pch_scale
cgdn = nch_op_info['cgd']
cgd_tot = cgdp + cgdn
cggp = pch_op_info['cgg'] * pch_scale
cggn = nch_op_info['cgg']
cgg_tot = cggp + cggn
cdsp = pch_op_info['cds'] * pch_scale
cdsn = nch_op_info['cds']
cds_tot = cdsp + cdsn
cdbp = pch_op_info['cdb'] * pch_scale
cdbn = nch_op_info['cdb']
cdb_tot = cdbp + cdbn
cddp = pch_op_info['cdd'] * pch_scale
cddn = nch_op_info['cdd']
cdd_tot = cddp + cddn
scale_vec = np.linspace(scale_min, scale_max, n_scale)
for scale in scale_vec:
for rf in np.linspace(rf_max, rf_min, n_rf):
# Build circuit
cir = LTICircuit()
cir.add_transistor(pch_op_info,
'out',
'in',
'gnd',
'gnd',
fg=scale * pch_scale)
cir.add_transistor(nch_op_info,
'out',
'in',
'gnd',
'gnd',
fg=scale)
cir.add_res(rf, 'out', 'in')
cir.add_cap(cin, 'in', 'gnd')
cir.add_cap(cl, 'out', 'gnd')
# Get gain/poles/zeros/Bode plot
# Note: any in_type other than 'v' results in current source input
tf = cir.get_transfer_function('in', 'out', in_type='i')
rdc = np.absolute(tf.num[-1] / tf.den[-1])
w3db = get_w_3db(tf.num, tf.den)
f3db = w3db / (2 * np.pi)
if f3db >= f3db_targ:
# Noise
in_gmp = noise_const * gammap * gmp
in_gmn = noise_const * gamman * gmn
in_rf = noise_const / rf
tf_gm = cir.get_transfer_function('out', 'out', in_type='i')
dc_gm = tf_gm.num[-1] / tf_gm.den[-1]
wo2_gm = tf_gm.den[-1] / tf_gm.den[0]
woQ_gm = tf_gm.den[-1] / tf_gm.den[1]
wz_gm = tf_gm.num[-1] / tf_gm.num[0]
von_gmp = pmos_noise_scale * in_gmp * dc_gm**2 * woQ_gm / 4 * (
wo2_gm / wz_gm**2 + 1)
von_gmn = in_gmn * dc_gm**2 * woQ_gm / 4 * (wo2_gm / wz_gm**2 +
1)
cir.add_vccs(1, 'out', 'in', 'vn', 'gnd')
tf_rf = cir.get_transfer_function('vn', 'out', in_type='v')
dc_rf = tf_rf.num[-1] / tf_rf.den[-1]
wo2_rf = tf_rf.den[-1] / tf_rf.den[0]
woQ_rf = tf_rf.den[-1] / tf_rf.den[1]
wz_rf = tf_rf.num[-1] / tf_rf.num[0]
von_rf = in_rf * dc_rf**2 * woQ_rf / 4 * (wo2_rf / wz_rf**2 +
1)
von = von_gmp + von_gmn + von_rf
# Signal
vo = isw * rdc
snr_like = (vo - voff) / np.sqrt(von)
if snr_like >= snr_like_targ:
cin_tot = cin + cgg_tot * scale
cl_tot = cl + cdd_tot * scale
cgd_scaled = cgd_tot * scale
gm_scaled = gm_tot * scale
gds_scaled = gds_tot * scale
# Build open loop circuit for phase margin
cir_open_loop = LTICircuit()
cir_open_loop.add_vccs(gm_scaled, 'out', 'gnd', 'vt',
'gnd') # ***
cir_open_loop.add_conductance(gds_scaled, 'out', 'gnd')
cir_open_loop.add_cap(cl_tot, 'out', 'gnd')
cir_open_loop.add_res(rf, 'out', 'vr')
cir_open_loop.add_cap(cgd_scaled, 'out', 'vr')
cir_open_loop.add_cap(cin_tot, 'vr', 'gnd')
tf_open_loop = cir_open_loop.get_transfer_function(
'vt', 'vr', in_type='v')
pm, gm = get_stability_margins(tf_open_loop.num,
tf_open_loop.den)
pm = pm - 180
if pm >= pm_targ:
ibias = scale * nch_ibias
design = dict(IB=ibias,
Scale=scale,
Rf=rf,
RDC=rdc,
f3dB=f3db,
PM=pm,
Von_Rf=von_rf,
Von_gmp=von_gmp,
Von_gmn=von_gmn,
Von=von,
SNR_Like=snr_like)
return design
def design_inverter_tia_lti(db_n, db_p, sim_env,
vg_res, rf_res,
vdd, cpd, cload,
rdc_min, fbw_min, pm_min,
vb_n, vb_p):
"""
Designs a transimpedance amplifier with an inverter amplifier
in resistive feedback. Uses the LTICircuit functionality.
Inputs:
db_n/p: Databases for NMOS and PMOS device characterization data,
respectively.
sim_env: Simulation corner.
vg_res: Float. Step resolution when sweeping gate voltage.
rf_res: Float. Step resolution when sweeping feedback resistance.
vdd: Float. Supply voltage.
cpd: Float. Input parasitic capacitance.
cload: Float. Output load capacitance.
rdc_min: Float. Minimum DC transimpedance.
fbw_min: Float. Minimum bandwidth (Hz).
pm_min: Float. Minimum phase margin.
vb_n/p: Float. Back-gate/body voltage of NMOS and PMOS, respectively.
Raises:
ValueError: If unable to meet the specification requirements.
Returns:
A dictionary with the following key:value pairings:
vg: Float. Input bias voltage.
nf_n: Integer. NMOS number of channel fingers.
nf_p: Integer. PMOS number of channel fingers.
rf: Float. Value of feedback resistor.
rdc: Float. Expected DC transimpedance.
fbw: Float. Expected bandwidth (Hz).
pm: Float. Expected phase margin.
ibias: Float. Expected DC bias current.
"""
ibn_fun = db_n.get_function('ibias', env=sim_env)
ibp_fun = db_p.get_function('ibias', env=sim_env)
# Get sweep values (Vg, Vd)
vg_min = 0
vg_max = vdd
vg_vec = np.arange(vg_min, vg_max, vg_res)
nf_n_vec = np.arange(1, 20, 1) # DEBUGGING: Is there a non-brute force way of setting this?
# Find the best operating point
best_ibias = float('inf')
best_op = None
for vg in vg_vec:
vdd_vd_ratio = vdd/vg
#print("\nVD/VG: {}".format(vg))
n_op_info = db_n.query(vgs=vg, vds=vg, vbs=vb_n-0)
p_op_info = db_p.query(vgs=vg-vdd, vds=vg-vdd, vbs=vb_p-vdd)
# Find ratio of fingers to get desired output common mode
ibias_n = n_op_info['ibias']
ibias_p = p_op_info['ibias']
pn_match = abs(ibias_n/ibias_p)
pn_ratio = pn_match/(vdd_vd_ratio - 1) # DEBUGGING: Won't be exact
if pn_ratio == 0:
continue
# Sweep the number of fingers to minimize power
for nf_n in nf_n_vec:
nf_p = int(round(nf_n * pn_ratio))
if nf_p <= 0:
continue
ibias_error = abs(abs(ibias_p)*nf_p-abs(ibias_n)*nf_n)/(abs(ibias_n)*nf_n)
if ibias_error > 0.05:
continue
print("N/P: {}/{} fingers".format(nf_n, nf_p))
# Finding amplifier ss parameters
inv = LTICircuit()
inv.add_transistor(n_op_info, 'out', 'in', 'gnd', fg=nf_n)
inv.add_transistor(p_op_info, 'out', 'in', 'gnd', fg=nf_p)
inv_num, inv_den = inv.get_num_den(in_name='in', out_name='out', in_type='v')
A0 = abs(inv_num[-1]/inv_den[-1])
gds_n = n_op_info['gds'] * nf_n
gm_n = n_op_info['gm'] * nf_n
cgs_n = n_op_info['cgs'] * nf_n
cgd_n = n_op_info['cgd'] * nf_n
cds_n = n_op_info['cds'] * nf_n
cgb_n = n_op_info.get('cgb', 0) * nf_n
cdb_n = n_op_info.get('cdb', 0) * nf_n
cdd_n = n_op_info['cdd'] * nf_n
cgg_n = n_op_info['cgg'] * nf_n
gds_p = p_op_info['gds'] * nf_p
gm_p = p_op_info['gm'] * nf_p
cgs_p = p_op_info['cgs'] * nf_p
cgd_p = p_op_info['cgd'] * nf_p
cds_p = p_op_info['cds'] * nf_p
cgb_p = p_op_info.get('cgb', 0) * nf_p
cdb_p = p_op_info.get('cdb', 0) * nf_p
cdd_p = p_op_info['cdd'] * nf_p
cgg_p = p_op_info['cgg'] * nf_p
gm = abs(gm_n) + abs(gm_p)
gds = abs(gds_n) + abs(gds_p)
ro = 1/gds
cgs = cgs_n + cgs_p
cds = cds_n + cds_p
cgb = cgb_n + cgb_p
cdb = cdb_n + cdb_p
cgd = cgd_n + cgd_p
cdd = cdd_n + cdd_p
cgg = cgg_n + cgg_p
# Assume Rdc is negative, bound Rf
rf_min = max(rdc_min*(1+A0)/A0 + ro/A0, 0)
rf_vec = np.arange(rf_min, rdc_min*5, rf_res)
# Sweep values of Rf to check f3dB and PM spec
for rf in rf_vec:
# Circuit for GBW
circuit = LTICircuit()
circuit.add_transistor(n_op_info, 'out', 'in', 'gnd', fg=nf_n)
circuit.add_transistor(p_op_info, 'out', 'in', 'gnd', fg=nf_p)
circuit.add_res(rf, 'in', 'out')
circuit.add_cap(cpd, 'in', 'gnd')
circuit.add_cap(cload, 'out', 'gnd')
# Determining if it meets spec
num, den = circuit.get_num_den(in_name='in', out_name='out', in_type='i')
rdc = num[-1]/den[-1]
if abs(rdc) < rdc_min-1e-8:
print("RDC: {0:.2f} (FAIL)\n".format(rdc))
continue
else:
print("RDC: {0:.2f}".format(rdc))
fbw = get_w_3db(num, den)/(2*np.pi)
if fbw < fbw_min or isnan(fbw):
print("BW: {} (FAIL)\n".format(fbw))
break # Increasing Rf isn't going to help
else:
print("BW: {}".format(fbw))
# Circuit for phase margin
# miller = (1-gm*rf)/(ro+rf)*ro
circuit2 = LTICircuit()
circuit2.add_conductance(gds, 'out', 'gnd')
circuit2.add_cap(cgg+cpd, 'in', 'gnd')
circuit2.add_cap(cdd+cload, 'out', 'gnd')
circuit2.add_cap(cgd, 'in', 'out')
circuit2.add_res(rf, 'in', 'out')
loopBreak = circuit2.get_transfer_function(in_name='out', out_name='in', in_type='i')
pm, gainm = get_stability_margins(loopBreak.num*gm, loopBreak.den)
if pm < pm_min or isnan(pm):
print("PM: {} (FAIL)\n".format(pm))
continue
else:
print("PM: {}\n".format(pm))
if ibias_n*nf_n < best_ibias:
best_ibias = ibias_n*nf_n
best_op = dict(
vg=vg,
nf_n=nf_n,
nf_p=nf_p,
rf=rf,
rdc=rdc,
fbw=fbw,
pm=pm,
ibias=best_ibias)
if best_op == None:
raise ValueError("No solutions.")
return best_op
def _get_psrr_lti(self, op_dict, nf_dict, series_type, amp_in, rload,
cload) -> float:
'''
Outputs:
psrr: PSRR (dB)
fbw: Power supply -> output 3dB bandwidth (Hz)
'''
n_ser = series_type == 'n'
n_amp = amp_in == 'n'
# Supply -> output gain
ckt_sup = LTICircuit()
ser_d = 'vdd' if n_ser else 'reg'
ser_s = 'reg' if n_ser else 'vdd'
inp_conn = 'gnd' if n_ser else 'reg'
inn_conn = 'reg' if n_ser else 'gnd'
tail_rail = 'gnd' if n_amp else 'vdd'
load_rail = 'vdd' if n_amp else 'gnd'
ckt_sup.add_transistor(op_dict['ser'],
ser_d,
'out',
ser_s,
fg=nf_dict['ser'],
neg_cap=False)
ckt_sup.add_res(rload, 'reg', 'gnd')
ckt_sup.add_cap(rload, 'reg', 'gnd')
ckt_sup.add_transistor(op_dict['in'],
'outx',
inp_conn,
'tail',
fg=nf_dict['in'],
neg_cap=False)
ckt_sup.add_transistor(op_dict['in'],
'out',
inn_conn,
'tail',
fg=nf_dict['in'],
neg_cap=False)
ckt_sup.add_transistor(op_dict['tail'],
'tail',
'gnd',
tail_rail,
fg=nf_dict['tail'],
neg_cap=False)
ckt_sup.add_transistor(op_dict['load'],
'outx',
'outx',
load_rail,
fg=nf_dict['load'],
neg_cap=False)
ckt_sup.add_transistor(op_dict['load'],
'out',
'outx',
load_rail,
fg=nf_dict['load'],
neg_cap=False)
num_sup, den_sup = ckt_sup.get_num_den(in_name='vdd',
out_name='reg',
in_type='v')
gain_sup = num_sup[-1] / den_sup[-1]
wbw_sup = get_w_3db(num_sup, den_sup)
# Reference -> output gain
# ckt_norm = LTICircuit()
# ser_d = 'gnd' if n_ser else 'reg'
# ser_s = 'reg' if n_ser else 'gnd'
# inp_conn = 'in' if n_ser else 'reg'
# inn_conn = 'reg' if n_ser else 'in'
# ckt_norm.add_transistor(op_dict['ser'], ser_d, 'out', ser_s, fg=nf_dict['ser'], neg_cap=False)
# ckt_norm.add_res(rload, 'reg', 'gnd')
# ckt_norm.add_cap(rload, 'reg', 'gnd')
# ckt_norm.add_transistor(op_dict['in'], 'outx', inp_conn, 'tail', fg=nf_dict['in'], neg_cap=False)
# ckt_norm.add_transistor(op_dict['in'], 'out', inn_conn, 'tail', fg=nf_dict['in'], neg_cap=False)
# ckt_norm.add_transistor(op_dict['tail'], 'tail', 'gnd', 'gnd', fg=nf_dict['tail'], neg_cap=False)
# ckt_norm.add_transistor(op_dict['load'], 'outx', 'outx', 'gnd', fg=nf_dict['load'], neg_cap=False)
# ckt_norm.add_transistor(op_dict['load'], 'out', 'outx', 'gnd', fg=nf_dict['load'], neg_cap=False)
# num_norm, den_norm = ckt_norm.get_num_den(in_name='in', out_name='reg', in_type='v')
# gain_norm = num_norm[-1]/den_norm[-1]
if gain_sup == 0:
return float('inf')
if wbw_sup == None:
wbw_sup = 0
fbw_sup = wbw_sup / (2 * np.pi)
psrr = 10 * np.log10((1 / gain_sup)**2)
return psrr, fbw_sup
def meet_spec(self, **params) -> List[Mapping[str, Any]]:
"""To be overridden by subclasses to design this module.
Raises a ValueError if there is no solution.
"""
### Get DBs for each device
specfile_dict = params['specfile_dict']
in_type = params['in_type']
l_dict = params['l_dict']
th_dict = params['th_dict']
sim_env = params['sim_env']
# Databases
db_dict = {
k: get_mos_db(spec_file=specfile_dict[k],
intent=th_dict[k],
lch=l_dict[k],
sim_env=sim_env)
for k in specfile_dict.keys()
}
### Design devices
vdd = params['vdd']
vincm = params['vincm']
cload = params['cload']
gain_min, gain_max = params['gain_lim']
fbw_min = params['fbw']
ibias_max = params['ibias']
optional_params = params['optional_params']
# Pulling out optional parameters
vstar_min = optional_params.get('vstar_min', 0.2)
res_vstep = optional_params.get('res_vstep', 10e-3)
error_tol = optional_params.get('error_tol', 0.01)
n_in = in_type == 'n'
# Estimate threshold of each device
vtest = vdd / 2 if n_in else -vdd / 2
vb = 0 if n_in else vdd
vth_in = estimate_vth(is_nch=n_in,
vgs=vtest,
vbs=0,
db=db_dict['in'],
lch=l_dict['in'])
vth_tail = estimate_vth(is_nch=n_in,
vgs=vtest,
vbs=0,
db=db_dict['tail'],
lch=l_dict['tail'])
# Keeping track of operating points which work for future comparison
viable_op_list = []
# Sweep tail voltage
vtail_min = vstar_min if n_in else vincm - vth_in
vtail_max = vincm - vth_in if n_in else vdd - vstar_min
vtail_vec = np.arange(vtail_min, vtail_max, res_vstep)
print(f'Sweeping tail from {vtail_min} to {vtail_max}')
for vtail in vtail_vec:
voutcm_min = vincm - vth_in if n_in else 0
voutcm_max = vdd if n_in else vincm - vth_in
voutcm = optional_params.get('voutcm', None)
if voutcm == None:
voutcm_vec = np.arange(voutcm_min, voutcm_max, res_vstep)
else:
voutcm_vec = [voutcm]
# Sweep output common mode
for voutcm in voutcm_vec:
in_op = db_dict['in'].query(vgs=vincm - vtail,
vds=voutcm - vtail,
vbs=vb - vtail)
ibias_min = 2 * in_op['ibias']
# Step input device size (integer steps)
nf_in_max = int(round(ibias_max / ibias_min))
nf_in_vec = np.arange(2, nf_in_max, 2)
for nf_in in nf_in_vec:
ibias = ibias_min * nf_in
ibranch = ibias / 2
res_val = (vdd -
voutcm) / ibranch if n_in else voutcm / ibranch
# Check gain, bandwidth
ckt_half = LTICircuit()
ckt_half.add_transistor(in_op,
'out',
'in',
'gnd',
fg=nf_in,
neg_cap=False)
ckt_half.add_res(res_val, 'out', 'gnd')
ckt_half.add_cap(cload, 'out', 'gnd')
num, den = ckt_half.get_num_den(in_name='in',
out_name='out',
in_type='v')
gain = -(num[-1] / den[-1])
wbw = get_w_3db(num, den)
if wbw == None:
wbw = 0
fbw = wbw / (2 * np.pi)
if gain < gain_min or gain > gain_max:
print(f'gain: {gain}')
break
if fbw < fbw_min:
print(f'fbw: {fbw}')
continue
# Design tail to current match
vgtail_min = vth_tail + vstar_min if n_in else vtail + vth_tail
vgtail_max = vtail + vth_tail if n_in else vdd + vth_tail - vstar_min
vgtail_vec = np.arange(vgtail_min, vgtail_max, res_vstep)
print(f'vgtail {vgtail_min} to {vgtail_max}')
for vgtail in vgtail_vec:
tail_op = db_dict['tail'].query(vgs=vgtail - vb,
vds=vtail - vb,
vbs=0)
tail_success, nf_tail = verify_ratio(
in_op['ibias'] * 2, tail_op['ibias'], nf_in,
error_tol)
if not tail_success:
print('tail match')
continue
viable_op = dict(nf_in=nf_in,
nf_tail=nf_tail,
res_val=res_val,
voutcm=voutcm,
vgtail=vgtail,
gain=gain,
fbw=fbw,
vtail=vtail,
ibias=tail_op['ibias'] * nf_tail,
cmfb_cload=tail_op['cgg'] * nf_tail)
viable_op_list.append(viable_op)
print("\n(SUCCESS)")
print(viable_op)
self.other_params = dict(
in_type=in_type,
l_dict=l_dict,
w_dict={k: db.width_list[0]
for k, db in db_dict.items()},
th_dict=th_dict)
# assert False, 'blep'
return viable_op_list
def design_preamp(db_n,
db_p,
lch,
w_finger,
vdd,
cload,
vin_signal,
vin_shift,
voutcm_res,
vtail_res,
gain_min,
fbw_min,
rload_res,
vb_p,
vb_n,
itail_max=10e-6,
error_tol=.01):
"""
Designs a preamplifier to go between the comparator and TIA.
Inputs:
db_n/p: Database with NMOS/PMOS info
lch: Float. Channel length (m)
w_finger: Float. Width of a single finger (m)
vdd: Float. Supply voltage (V)
cload: Float. Load capacitance (F)
vin_signal: Float. Input bias voltage (V).
vin_shift: Float. Gate bias voltage for the non-signal-facing input
device (V).
voutcm_res: Float. Resolution for output common mode voltage sweep
(V).
vtail_res: Float. Resolution for tail voltage of amplifying
and offset devices for sweep (V).
gain_min: Float. Minimum gain (V/V)
fbw_min: Float. Minimum bandwidth (Hz)
rload_res: Float. Load resistor resolution for sweep (ohms)
vb_n/p: Float. Body/back-gate voltage (V) of NMOS and PMOS devices.
itail_max: Float. Max allowable tail current of the main amplifier (A).
error_tol: Float. Fractional tolerance for ibias error when computing
device ratios.
Raises:
ValueError if there is no solution given the requirements.
Outputs:
nf_in: Integer. Number of fingers for input devices.
nf_tail: Integer. Number of fingers for tail device.
itail: Float. Tail current of main amp (A).
rload: Float. Load resistance (ohm).
gain: Float. Amp gain (V/V).
fbw: Float. Bandwidth (Hz).
voutcm: Float. Output common mode voltage (V).
cin: Float. Approximation of input cap (F).
Notes:
Under construction.
"""
# Estimate vth for use in calculating biasing ranges
vthn = estimate_vth(db_n, vdd, 0)
vincm = (vin_signal + vin_shift) / 2
voutcm_min = vin_signal - vthn
voutcm_max = vdd
voutcm_vec = np.arange(voutcm_min, voutcm_max, voutcm_res)
vtail_min = .15 # TODO: Avoid hardcoding?
vtail_max = vin_signal - vthn
vtail_vec = np.arange(vtail_min, vtail_max, vtail_res)
best_op = None
best_itail = np.inf
# Sweep output common mode voltage
for voutcm in voutcm_vec:
# Sweep tail voltage
for vtail in vtail_vec:
op_tail = db_n.query(vgs=voutcm, vds=vtail, vbs=vb_n)
# The "mean" of the input devices
op_in = db_n.query(vgs=vincm - vtail,
vds=voutcm - vtail,
vbs=vb_n - vtail)
# Calculate the max tail size based on current limit
# and size input devices accordingly
nf_in_min = 2
nf_in_max = int(round(itail_max / 2 / op_in['ibias']))
nf_in_vec = np.arange(nf_in_min, nf_in_max, 2)
for nf_in in nf_in_vec:
amp_ratio_good, nf_tail = verify_ratio(op_in['ibias'] / 2,
op_tail['ibias'], nf_in,
error_tol)
if not amp_ratio_good:
continue
itail = op_tail['ibias'] * nf_tail
rload = (vdd - voutcm) / (itail / 2)
# Check small signal parameters with symmetric circuit
ckt_sym = LTICircuit()
ckt_sym.add_transistor(op_in, 'outp', 'gnd', 'tail', fg=nf_in)
ckt_sym.add_transistor(op_in, 'outn', 'inp', 'tail', fg=nf_in)
ckt_sym.add_transistor(op_tail,
'tail',
'gnd',
'gnd',
fg=nf_tail)
ckt_sym.add_res(rload, 'outp', 'gnd')
ckt_sym.add_res(rload, 'outn', 'gnd')
ckt_sym.add_cap(cload, 'outp', 'gnd')
ckt_sym.add_cap(cload, 'outn', 'gnd')
num, den = ckt_sym.get_num_den(in_name='inp',
out_name='outn',
in_type='v')
num_unintent, den_unintent = ckt_sym.get_num_den(
in_name='inp', out_name='outp', in_type='v')
gain_intentional = num[-1] / den[-1]
gain_unintentional = num_unintent[-1] / den_unintent[-1]
gain = abs(gain_intentional - gain_unintentional)
wbw = get_w_3db(num, den)
if wbw == None:
wbw = 0
fbw = wbw / (2 * np.pi)
if fbw < fbw_min:
print("(FAIL) BW:\t{0}".format(fbw))
continue
if gain < gain_min:
print("(FAIL) GAIN:\t{0}".format(gain))
continue
print("(SUCCESS)")
if itail > best_itail:
continue
# Check once again with asymmetric circuit
vin_diff = vin_signal - vin_shift
voutn = voutcm - gain * vin_diff / 2
voutp = voutcm + gain * vin_diff / 2
op_signal = db_n.query(vgs=vin_signal - vtail,
vds=voutn - vtail,
vbs=vb_n - vtail)
op_shift = db_n.query(vgs=vin_shift - vtail,
vds=voutp - vtail,
vbs=vb_n - vtail)
ckt = LTICircuit()
ckt.add_transistor(op_shift, 'outp', 'gnd', 'tail', fg=nf_in)
ckt.add_transistor(op_signal, 'outn', 'inp', 'tail', fg=nf_in)
ckt.add_transistor(op_tail, 'tail', 'gnd', 'gnd', fg=nf_tail)
ckt.add_res(rload, 'outp', 'gnd')
ckt.add_res(rload, 'outn', 'gnd')
ckt.add_cap(cload, 'outp', 'gnd')
ckt.add_cap(cload, 'outn', 'gnd')
num, den = ckt.get_num_den(in_name='inp',
out_name='outn',
in_type='v')
num_unintent, den_unintent = ckt.get_num_den(in_name='inp',
out_name='outp',
in_type='v')
gain_intentional = num[-1] / den[-1]
gain_unintentional = num_unintent[-1] / den_unintent[-1]
gain = abs(gain_intentional - gain_unintentional)
wbw = get_w_3db(num, den)
if wbw == None:
wbw = 0
fbw = wbw / (2 * np.pi)
if fbw < fbw_min:
print("(FAIL) BW:\t{0}".format(fbw))
continue
if gain < gain_min:
print("(FAIL) GAIN:\t{0}".format(gain))
continue
print("(SUCCESS)")
if itail < best_itail:
best_itail = itail
best_op = dict(nf_in=nf_in,
nf_tail=nf_tail,
itail=itail,
rload=rload,
gain=gain,
fbw=fbw,
voutcm=voutcm,
vtail=vtail,
cin=op_signal['cgg'] * nf_in)
if best_op == None:
raise ValueError("No viable solutions.")
return best_op