how to adjust the circuit?

[freetofree]

vdd=3, .35um cmos, telescope
____
-o| |o- vb1=2.0850
-o| |o- vb2=1.8474
--- ----
-| |- vb3=904.7771m
--| |-- vin vic=787.48m
------
|- vfb=902.86m

now the tail current NMOS is in linear region, others in active region, how to adjust the circuit so that it can operate in active region?
amazing

 

[A.Anand Srinivasan]

please post your circuit.... what you have described using characters isn't that clear....

 

[iamxo]

you can increase input transistor W/L to decrease Vgs, so the drain voltage of the tail current source transistor increase.

 

[freetofree]

.title simulation of ota
.prot

.model nm nmos level = 49
+ version = 3.11 acm = 3 hdif = 0.5e-6
+ mobmod = 1.000000e+00 capmod = 1.000000e+00 nqsmod = 0.000000e+00
+ tox = 6.500000e-09 cdsc = 1.000000e-10 cdscb = 0.000000e+00
+ cdscd = 3.146578e-03 cit = -1.165567e-03 nfactor = 2.067847e+00
+ xj = 2.000000e-07 vsat = 1.733115e+05 at = 4.587946e+04
+ a0 = 1.208623e+00 ags = 2.664144e-01 a1 = 0.000000e+00
+ a2 = 3.926521e-01 keta = -5.969015e-03 nch = 3.053200e+17
+ k1 = 7.823191e-01 kt1 = -2.968857e-01 kt1l = 6.948321e-09
+ kt2 = -2.439718e-02 k2 = -5.976393e-02 k3 = -2.348052e+00
+ k3b = -2.995700e+00 w0 = 0.000000e+00 nlx = 2.343014e-07
+ dvt0 = 1.904429e+01 dvt1 = 8.095353e-01 dvt2 = 6.252991e-03
+ dvt0w = 0.000000e+00 dvt1w = 0.000000e+00 dvt2w = 0.000000e+00
+ drout = 5.600000e-01 dsub = 5.891755e-01 vth0 = 4.452273e-01
+ ua = -1.085785e-09 ua1 = 2.451017e-09 ub = 2.210053e-18
+ ub1 = -2.617479e-18 uc = 3.755569e-11 uc1 = 2.640885e-13
+ u0 = 3.324764e-02 ute = -1.230449e+00 voff = -8.793706e-02
+ delta = 9.688553e-03 rdsw = 4.385596e+02 prwg = 1.000000e-01
+ prwb = -7.964250e-02 prt = -4.162666e+01 eta0 = 1.722893e-01
+ etab = -5.113721e-02 pclm = 9.585992e-01 pdiblc1 = 2.537726e-12
+ pdiblc2 = -3.312959e-04 pdiblcb = -1.000000e-03 pscbe1 = 5.656369e+08
+ pscbe2 = 1.000000e-03 pvag = 1.000001e-12 wr = 9.107508e-01
+ dwg = -7.427878e-09 dwb = -3.328336e-09 b0 = 1.598826e-07
+ b1 = 5.141988e-17 alpha0 = 0.000000e+00 beta0 = 3.000000e+01
+ elm = 5.000000e+00 cgsl = 0.000000e+00 cgdl = 0.000000e+00
+ ckappa = 6.000000e-01 cf = 9.056200e-11 clc = 1.000000e-07
+ cle = 6.000000e-01 tnom = 2.500000e+01 cgso = 1.590000e-10
+ cgdo = 1.590000e-10 cgbo = 0.000000e+00 xpart = 1.000000e+00
+ rsh = 0.000000e+00 pb = 5.112000e-01 mj = 3.872000e-01
+ mjsw = 3.872000e-01 pbsw = 5.112000e-01 cj = 8.488000e-04
+ cjsw = 4.896000e-10 lint = 2.345145e-09 ll = 1.382235e-09
+ lln = 2.000000e-01 lw = 0.000000e+00 lwn = 0.000000e+00
+ lwl = 0.000000e+00 wint = 1.347400e-07 wl = 0.000000e+00
+ wln = 1.000000e+00 ww = -7.781819e-14 wwn = 1.000000e+00
+ wwl = 0.000000e+00 nlev = 2.000000e+00 kf = 0.500000e-25

.model pm pmos level = 49
+ version = 3.11 acm = 3 hdif = 0.5e-6
+ mobmod = 1.000000e+00 capmod = 1.000000e+00 nqsmod = 0.000000e+00
+ tox = 6.500000e-09 cdsc = 1.000000e-10 cdscb = 0.000000e+00
+ cdscd = 0.000000e+00 cit = 2.849258e-03 nfactor = 0.000000e+00
+ xj = 2.000000e-07 vsat = 1.235253e+05 at = 0.000000e+00
+ a0 = 5.534111e-01 ags = 0.000000e+00 a1 = 0.000000e+00
+ a2 = 4.000000e-01 keta = -4.742392e-03 nch = 1.198869e+17
+ k1 = 5.036882e-01 kt1 = -4.972940e-01 kt1l = 0.000000e+00
+ kt2 = -4.796538e-02 k2 = 1.710970e-02 k3 = -1.532555e+00
+ k3b = -1.426295e-01 w0 = -5.128171e-07 nlx = 1.500000e-07
+ dvt0 = 1.318457e+00 dvt1 = 2.383284e-01 dvt2 = 0.000000e+00
+ dvt0w = 0.000000e+00 dvt1w = 0.000000e+00 dvt2w = 0.000000e+00
+ drout = 3.972895e-01 dsub = 4.287821e-01 vth0 = -7.891688e-01
+ ua = -7.838913e-10 ua1 = 4.158887e-09 ub = 1.416209e-18
+ ub1 = -3.635865e-18 uc = -3.193134e-11 uc1 = 0.000000e+00
+ u0 = 8.644306e-03 ute = 0.000000e+00 voff = -1.619864e-01
+ delta = 1.000000e-02 rdsw = 1.393589e+03 prwg = -7.131702e-02
+ prwb = -9.573077e-02 prt = 0.000000e+00 eta0 = 5.324062e-02
+ etab = 0.000000e+00 pclm = 1.294956e+00 pdiblc1 = 1.272241e-02
+ pdiblc2 = 5.045117e-04 pdiblcb = -8.715370e-03 pscbe1 = 4.803844e+08
+ pscbe2 = 1.000000e-08 pvag = 0.000000e+00 wr = 8.585317e-01
+ dwg = -1.637238e-08 dwb = -3.444345e-09 b0 = 0.000000e+00
+ b1 = 1.000000e-04 alpha0 = 0.000000e+00 beta0 = 3.000000e+01
+ elm = 5.000000e+00 cgsl = 0.000000e+00 cgdl = 0.000000e+00
+ ckappa = 6.000000e-01 cf = 9.056200e-11 clc = 1.000000e-07
+ cle = 6.000000e-01 tnom = 2.500000e+01 cgso = 4.035600e-10
+ cgdo = 4.035600e-10 cgbo = 0.000000e+00 xpart = 1.000000e+00
+ rsh = 0.000000e+00 pb = 9.316000e-01 mj = 4.845000e-01
+ mjsw = 4.845000e-01 pbsw = 9.316000e-01 cj = 1.117000e-03
+ cjsw = 4.764000e-10 lint = 5.034766e-08 ll = 4.395297e-17
+ lln = 1.370692e+00 lw = 0.000000e+00 lwn = 0.000000e+00
+ lwl = 0.000000e+00 wint = 1.924185e-07 wl = 0.000000e+00
+ wln = 1.000000e+00 ww = -9.207185e-13 wwn = 8.342567e-01
+ wwl = 0.000000e+00 nlev = 2.000000e+00 kf = 0.250000e-25

.unprot
.options post probe MEASDGT=7
.global vdd
.op

vpower vdd 0 3


*bias
ibias vdd N7 10u
Mb_M5 N8 vb1 vdd vdd pm W=10u L=1u M=1
Mb_M6 N9 vb1 vdd vdd pm W=10u L=1u M=1
Mb_M7 N10 vb1 vdd vdd pm W=10u L=1u M=1
Mb_M8 N11 vb1 vdd vdd pm W=10u L=1u M=1

Mb_M9 vb1 vb2 N8 vdd pm W=10u L=1u M=1
Mb_M10 N12 vb2 N9 vdd pm W=10u L=1u M=1
Mb_M11 vmi vb2 N10 vdd pm W=10u L=1u M=1
Mb_M12 vbc vb2 N11 vdd pm W=10u L=1u M=1

Mb_M13 vb2 N13 vb1 vdd pm W=12u L=2.4u M=1
Mb_U6 N7 N7 0 0 nm W=12u L=2u M=1

Mb_U7 N12 N12 vb3 0 nm W=12u L=0.6u M=1
Mb_U15 vpp N12 N14 0 nm W=5u L=20u M=1
Mb_U16 vb3 N12 vpp 0 nm W=12u L=4.2u M=1

Mb_U8 N15 N14 0 0 nm W=12u L=0.8u M=2
Mb_M14 N13 N13 vb2 vdd pm W=12u L=0.35u M=1

Mb_U9 vmi vb3 N16 0 nm W=8u L=0.6u M=2
Mb_U10 N16 vmi N15 0 nm W=12u L=0.6u M=2
Mb_U11 N17 vbc 0 0 nm W=12u L=0.8u M=1
Mb_U12 N13 N7 0 0 nm W=12u L=2u M=1
Mb_U13 vbc vpp N17 0 nm W=12u L=0.6u M=2
Mb_U14 N14 vpp N15 0 nm W=12u L=0.6u M=2


*telescope

M_M1 N1 vb1 vdd vdd pm W=10u L=1u M=3
M_M2 N2 vb1 vdd vdd pm W=10u L=1u M=3
M_M3 on vb2 N1 vdd pm W=10u L=1u M=3
M_M4 op vb2 N2 vdd pm W=10u L=1u M=3

M_U1 op vb3 N3 0 nm W=5u L=0.5u M=1
M_U2 on vb3 N4 0 nm W=5u L=0.5u M=1
M_U3 N4 ip N5 0 nm W=5u L=0.5u M=1
M_U4 N3 in N5 0 nm W=5u L=0.5u M=1

M_U5 N5 vfb 0 0 nm W=10u L=.5u M=1


C_C1 on 0 1.1p
C_C2 op 0 1.1p

*stimulation
V_vb vfb 0 902.86m
V_vic in 0 DC 852.5m
V_vid ip in DC 0V AC 1V 0

*.dc v_vic .5 1.5 0.0001
.probe v(on)


.op


.end

 

[ambreesh]

it is difficult to read the netlist, i am assuming that we are talking about the current sink for the differential pair. The following explanation is based on my assumption:

Your NMOS sink is in linear region.
Tou would need to increase the vds across it, which can only be incresed by incresing the gate voltage on the input of the differential pair.
If you cannot do that, thensee if you can redues the vdsat for the current sink.
If that is not possible, change the architecture.

 

[paley]

because your vin > vth + 2*vdsat , your vthn=450mv and vin=787.48mv , so you must redue the vdsat of the current sink and input mos

 

[lijianheng]

Decrease Vgs or increase Vin.

 

[xdy83]

increase the vin !