Re: LDO again
paulux said:
I guess the problem may be due to the saturation region of pass device. But accurate analysis of the problem could only be possible if the detailed schematics are available.
yes, the problem is, opamp's input transistors goes into triode region for the highest Vin=3.63V but for the smallest 1.3V is in the saturation. Opamp's gain is small then. How to assure quite constant voltage gain under different supply conditions.
thanks and regards
The circuit:
.PARAM W1=4u
.PARAM W3=4u
.PARAM W5=4u
.PARAM LM=4u
.PARAM LM1=4u
.PARAM W78=4u
.PARAM W6=10u
.PARAM VCM=0
.PARAM POWER=1.3V
.GLOBAL vdd gnd
VDD vdd gnd POWER
VCM 2 gnd vcm
Vin 1 2 ac=1
CL 3 gnd 40p (temporary)
XOP 1 2 3 OPAMP1
******************************************************
.SUBCKT OPAMP1 in+ in- out
M1 out in- S vdd CMOSP W=W1 L=LM
M2 2 in+ S vdd CMOSP W=W1 L=LM
M3 2 2 gnd gnd CMOSN W=W3 L=LM
M4 out 2 gnd gnd CMOSN W=W3 L=LM
M5 S bias vdd vdd CMOSP W=W5 L=LM
M6 bias bias vdd vdd CMOSP W=W6 L=LM1
M7 bias bias tst gnd CMOSN W=W78 L=LM1
M8 tst tst gnd gnd CMOSN W=W78 L=LM1
.ends