LDO用NMOS作为调整管，怎样减小NMOS的衬偏效应？

想用NMOS的源级跟随器＋运放构成LDO电路，Typical输入3.3V，输出1.8V。电源波动±10%，仿真时发现，如果输入电压为2.97V，这时NMOS调整管gate端电压已经达到2.97V，导致OP内部输出端PMOS位于深线性区，LDO不能正常工作。所用工艺为SMIC 180nm,正常情况下Vth=0.7V，现在由于NMOS调整管S端电压为1.8V左右，衬偏效应导致NMOS Vth=1.3V左右。因此，请教各位有没有什么办法减小NMOS调整管的Vth，使LDO在输入电压为2.97V时也能正常工作?谢谢！注意：所用工艺为单肼工艺，所有NMOS共用一个P衬底。

Nmos调整管的不是一般都有个charge pump来抬栅电压的吗

多谢回复！
我这个LDO比较简单，不会采用charge pump来提高栅压，如果没有其他好的办法来解决上述问题，我就使用PMOS来做了。

比较简单的办法是用native nmos

晶圆厂没有提供耗尽型device，考虑使用PMOS了。谢谢回复

1. pmos
2. charge_pump + Nmos
3. isolation Nmos
4. native nmos (very low Vth)
5. nmoswsizelarge ...

Native NMOS is instrinic device in process. It's there already. Question is whether foundry provide the simulation model or not. As far as I know, SMIC0.18um should have this model.

************************************************************************************
*1.8V NATIVE NMOS MODEL*
************************************************************************************
*
.model nnt18 NMOS
+LEVEL= 49
*
* GENERAL PARAMETERS
*
+CALCACM= 1
+LMIN= 4.5E-7LMAX= 1.0E-5WMIN= 1.9E-7
+WMAX= 1.0E-4TNOM= 25.0VERSION= 3.24
+TOX= '3.87E-09+DTOX_NNT18'TOXM= 3.87E-09XJ= 1.6000000E-07
+NCH= 4.4440000E+16LLN= 1.0000000LWN= 1.0000000
+WLN= 1.0000000WWN= 1.0000000LINT= 3.2000000E-08
+LL= 0.00LW= 0.00LWL= 0.00
+WINT= 0.00WL= 0.00WW= 0.00
+WWL= 0.00MOBMOD= 1BINUNIT= 2
+XL= '2.5E-8+DXL_NNT18'XW= '0.00+DXW_NNT18'DWG= 0.00
+DWB= 0.00
* DIODE PARAMETERS
+ACM= 12LDIF= 7.00E-08HDIF= 2.0E-07
+RSH= 7.08RD= 0RS= 0
+RSC= 1RDC= 1
*
* THRESHOLD VOLTAGE PARAMETERS
*
+VTH0= '-0.015+DVTH_NNT18'LVTH0= 2.8000000E-08K1= 9.6053920E-02
+K2= -2.5212668E-02K3= -0.5717283DVT0= 1.0000000E-02
+DVT1= 0.00DVT2= -1.0000000E-02DVT0W= -9.0000010E-02
+DVT1W= 1.3570372E+05DVT2W= 0.00NLX= 4.3929600E-07
+W0= 0.00K3B= -0.8582231PVTH0= '0+DPVTH0_NNT18'
*
* MOBILITY PARAMETERS
*
+VSAT= 1.3500000E+05LVSAT= -1.8200000E-02WVSAT= 1.0000000E-04
+PVSAT= 3.6000000E-09UA= 9.6000000E-10LUA= -5.0000000E-17
+PUA= -3.0000002E-23UB= 2.1696805E-18UC= -2.2999993E-11
+WUC= -3.5000000E-17PUC= 2.0000000E-23RDSW= 1.2000000E+02
+PRWB= 0.00PRWG= 0.00WR= 1.0000000
+U0= 6.1000000E-02WU0= 2.2000000E-09PU0= -1.0000000E-16
+A0= 1.5500000KETA= -2.9847301E-03A1= 0.00
+A2= 0.9800000AGS= 1.5000000B0= 0.00
+B1= 0.00
*
* SUBTHRESHOLD CURRENT PARAMETERS
*
+VOFF= -0.1100000NFACTOR= 1.0000000CIT= 1.9915700E-04
+CDSC= 0.00CDSCB= 0.00CDSCD= 0.00
+ETA0= 8.0000000E-02LETA0= 4.0000000E-08PETA0= 5.0000000E-14
+ETAB= -1.0000000E-02PETAB= 8.0000000E-15DSUB= 0.5600000
*
* ROUT PARAMETERS
*
+PCLM= 1.6000000PDIBLC1= 1.0000000E-02PDIBLC2= 0.1200000
+PDIBLCB= 5.7750700E-02DROUT= 0.5600000PSCBE1= 6.4335600E+08
+PSCBE2= 1.0000000E-20PVAG= 0.00DELTA= 1.0000000E-02
+ALPHA0= 9.3800000E-09ALPHA1= 1.0385719E-02BETA0= 5.8915170
*
* TEMPERATURE EFFECTS PARAMETERS
*
+KT1= -0.2961084KT2= 1.0000000E-03AT= 2.0456400E+04
+UTE= -1.6500000WUTE= -1.1000000E-09UA1= 3.8350100E-09
+WUA1= -2.0736400E-16PUA1= 6.0000000E-23UB1= -7.4901900E-18
+WUB1= -1.7708197E-26UC1= -6.6000000E-11KT1L= -7.4000000E-15
+PRT= 0.00
*
* NOISE PARAMETERS
*
+NOIMOD= 2NOIA= 4.4361E+20NOIB= 1.0074E+04
+NOIC= 2.9928E-13EM= 1.039E+06EF= 9.075E-01
*
* CAPACITANCE PARAMETERS
*
+CJ= '1.45E-04+DCJ_NNT18'MJ= 0.334PB= 0.538
+CJSW= '1.63E-10+DCJSW_NNT18'MJSW= 0.0689PBSW= 0.563
+CJSWG= '6.60E-11+DCJSWG_NNT18'MJSWG= 0.0689PBSWG= 0.563
+TCJ= 0.00246TCJSW= 0.00122TCJSWG= 0.00122
+TPB= 0.00277TPBSW= 0.00204TPBSWG= 0.00204
+JS= 5.2E-06JSW= 1.0E-13NJ= 1.0651
+XTI= 3NQSMOD= 0ELM= 5
+CGDO= '2.66E-10+DCGDO_NNT18'CGSO= '2.66E-10+DCGSO_NNT18' TLEVC= 1
+CAPMOD= 3XPART= 1CF= 0.00
+ACDE= 0.64MOIN= 24NOFF= 2.50
*
************************************************************************************
*3.3V NATIVE NMOS MODEL*
************************************************************************************
*
.model nnt33 NMOS
+LEVEL= 49
*
* GENERAL PARAMETERS
*
+CALCACM= 1
+LMIN= 1.0E-6LMAX= 1.0E-5WMIN= 1.9E-7
+WMAX= 1.0E-4TNOM= 25.0VERSION= 3.24
+TOX= '6.65E-09+DTOX_NNT33' TOXM= 6.65E-09XJ= 1.6000000E-07
+NCH= 5.5313000E+15LLN= 1.0000000LWN= 1.0000000
+WLN= 1.0000000WWN= 1.0000000LINT= 6.4999990E-08
+LL= 0.00LW= 0.00LWL= 0.00
+WINT= 0.00WL= 0.00WW= 0.00
+WWL= 0.00MOBMOD= 1BINUNIT= 2
+XL= '-1.5E-8+DXL_NNT33'XW= '0.00+DXW_NNT33'DWG= 0.00
+DWB= 0.00
* DIODE PARAMETERS
+ACM= 12LDIF= 6.50E-08HDIF= 2.05E-07
+RSH= 7.08RD= 0RS= 0
+RSC= 1RDC= 1
*
* THRESHOLD VOLTAGE PARAMETERS
*
+VTH0= '-9.1E-02+DVTH_NNT33' LVTH0= -7.0000000E-08PVTH0= '1.0000000E-14+DPVTH0_NNT33'
+K1= 9.0587460E-02K2= -9.5673000E-03K3= -8.8000000
+DVT0= 0.00DVT1= 0.00DVT2= 0.00
+DVT0W= 0.00DVT1W= 0.00DVT2W= 0.00
+NLX= 0.00W0= 0.00K3B= -2.4000001
* MOBILITY PARAMETERS
*
+VSAT= 1.1500000E+05LVSAT= -2.0000000E-02WVSAT= -1.7000001E-02
+PVSAT= 2.1000000E-08UA= 3.2000000E-10LUA= 1.8461700E-17
+WUA= -3.0000001E-17PUA= 1.5000001E-23UB= 2.1500000E-18
+LUB= 1.0000000E-27WUB= -1.5000000E-25UC= 1.6885901E-11
+WUC= -1.8830001E-17RDSW= 2.8000000E+02PRWB= 0.00
+PRWG= 0.00WR= 0.8500000U0= 4.9435450E-02
+LU0= 1.6700000E-09WU0= 2.0000000E-10PU0= 1.0000000E-15
+A0= 1.0500000KETA= -1.0000000E-03WKETA= -1.0000000E-09
+A1= 0.00A2= 0.9800000AGS= 1.3000000
+B0= 0.00B1= 0.00
*
* SUBTHRESHOLD CURRENT PARAMETERS
*
+VOFF= -0.1080000NFACTOR= 1.0000000CIT= 1.7250000E-04
+CDSC= 0.00CDSCB= 0.00CDSCD= 0.00
+ETA0= 5.8832400E-02LETA0= 3.45000000E-07ETAB= -5.0000000E-02
+DSUB= 0.5600000
*
* ROUT PARAMETERS
*
+PCLM= 0.6000000PDIBLC1= 2.0000000E-02PDIBLC2= 3.5568000E-02
+PDIBLCB= 5.9980500E-02DROUT= 0.5600000PSCBE1= 5.0000000E+08
+PSCBE2= 1.0000000E-07PVAG= 0.00DELTA= 1.0000000E-02
+ALPHA0= 1.3993774E-08ALPHA1= -3.0000000E-03BETA0= 4.6188860
+LBETA0= 1.6556398E-06
*
* TEMPERATURE EFFECTS PARAMETERS
*
+KT1= -0.2122575KT2= 5.0000000E-04AT= 1.6500000E+04
+UTE= -1.4421700WUTE= 5.0000000E-08UA1= 3.3785630E-09
+PUA1= -1.0000000E-23UB1= -6.1694750E-18UC1= -4.6000000E-11
+WUC1= -3.0000001E-17KT1L= -7.3966800E-09PRT= 0.00
*
* NOISE PARAMETERS
*
+NOIMOD= 2NOIA= 6.01E+20NOIB= -1.05E+04
+NOIC= 3.20E-13EM= 1.33E+06EF= 9.46E-01
*
* CAPACITANCE PARAMETERS
*
+CJ= '0.000148+DCJ_NNT33'MJ= 0.344PB= 0.542
+CJSW= '2.16E-10+DCJSW_NNT33'MJSW= 0.149PBSW= 0.536
+CJSWG= '1.25E-10+DCJSWG_NNT33'MJSWG= 0.149PBSWG= 0.536
+TPB= 0.00264TPBSW= 0.00262TPBSWG= 0.00262
+TCJ= 0.00255TCJSW= 0.00108TCJSWG= 0.00108
+JS= 5.2E-06JSW= 1.0E-13NJ= 1.0651
+XTI= 3NQSMOD= 0ELM= 5
+CGDO= '1.34E-10+DCGDO_NNT33'CGSO= '1.34E-10+DCGSO_NNT33' TLEVC= 1
+CAPMOD= 3XPART= 1CF= 0.00
+ACDE= 0.45MOIN= 24NOFF= 2.3177
*

1.8V*+/-10%=+0.18V
使用charge pump还是可能做到(当然要看负载电流)
还能有较好的PSRR

LDO都是PMOS输出的吧，NMOS是实现不了low dropout的，只能叫regulator

仅作为电容来用

多谢！

找到了，nnt33.仿真能满足要求，非常感谢！