LDO transient performance enhancement circuit understanding

[promach]

For the following LDO circuit, how does the transient performance enhancement circuit sub-block in green color works ?

[promach]

For this LDO circuit , I have pretty good transient output voltage V(vout) for a 100k sine input on Vin.

But it goes very bad when I use 1MEG sine input on Vin.

Any advice ?







LDO.asc

Code: [Select]

Version 4
SHEET 1 3764 1620
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FLAG 432 1280 0
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FLAG 3536 704 Vout
IOPIN 3536 704 Out
FLAG 688 1136 0
FLAG 704 976 Vref
FLAG -416 80 Vin
FLAG 3360 1264 Vfb
FLAG -272 1248 0
FLAG 160 1248 0
FLAG -64 1568 0
FLAG -272 944 0
FLAG 160 944 0
SYMBOL pmos4 48 128 R0
WINDOW 123 62 94 Left 2
SYMATTR Value2 L=0.18u W=6u m=2
SYMATTR InstName M2
SYMATTR Value PM
SYMBOL pmos4 1488 384 R0
WINDOW 123 56 100 Left 2
SYMATTR Value2 L=0.18u W=6u m=4
SYMATTR InstName M7
SYMATTR Value PM
SYMBOL pmos4 544 384 M0
WINDOW 123 -11 101 Left 2
SYMATTR Value2 L=0.18u W=6u m=4
SYMATTR InstName M8
SYMATTR Value PM
SYMBOL pmos4 1968 160 R0
WINDOW 123 56 100 Left 2
SYMATTR Value2 L=0.18u W=6u m=2
SYMATTR InstName M9
SYMATTR Value PM
SYMBOL pmos4 944 640 R0
WINDOW 123 56 100 Left 2
SYMATTR Value2 L=0.18u W=6u m=4
SYMATTR InstName M10
SYMATTR Value PM
SYMBOL nmos4 544 1232 M0
WINDOW 123 56 100 Left 2
SYMATTR Value2 L=0.18u W=6u m=8
SYMATTR InstName M11
SYMATTR Value NM
SYMBOL nmos4 752 1232 R0
WINDOW 123 -43 119 Left 2
SYMATTR Value2 L=0.18u W=6u m=2
SYMATTR InstName M12
SYMATTR Value NM
SYMBOL pmos4 1280 896 M0
WINDOW 0 43 30 Left 2
WINDOW 123 56 100 Left 2
SYMATTR InstName M13
SYMATTR Value2 L=0.18u W=6u m=4
SYMATTR Value PM
SYMBOL pmos4 752 896 R0
WINDOW 0 43 30 Left 2
WINDOW 123 56 100 Left 2
SYMATTR InstName M15
SYMATTR Value2 L=0.18u W=6u m=4
SYMATTR Value PM
SYMBOL nmos4 1280 1232 M0
WINDOW 123 56 100 Left 2
SYMATTR Value2 L=0.18u W=6u m=2
SYMATTR InstName M16
SYMATTR Value NM
SYMBOL nmos4 1488 1232 R0
WINDOW 123 -39 112 Left 2
SYMATTR Value2 L=0.18u W=6u m=8
SYMATTR InstName M17
SYMATTR Value NM
SYMBOL voltage -512 256 R0
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 0
SYMATTR Value2 AC 1
SYMATTR InstName Vin
SYMATTR Value SINE(3.3 1 1MEG)
SYMBOL cap 1936 912 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C1
SYMATTR Value 1p
SYMBOL res 3456 992 R0
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL res 3456 1376 R0
SYMATTR InstName R2
SYMATTR Value 10k
SYMBOL pmos4 1968 688 R0
WINDOW 123 56 100 Left 2
SYMATTR Value2 L=0.18u W=6u m=8
SYMATTR InstName M18
SYMATTR Value PM
SYMBOL cap 1824 640 R0
SYMATTR InstName C2
SYMATTR Value 1p
SYMBOL pmos4 2432 128 M0
WINDOW 123 -77 116 Left 2
SYMATTR Value2 L=0.18u W=6u m=8
SYMATTR InstName M19
SYMATTR Value PM
SYMBOL pmos4 3424 128 R0
WINDOW 123 56 100 Left 2
SYMATTR Value2 L=0.18u W=6u m=2000
SYMATTR InstName M20
SYMATTR Value PM
SYMBOL pmos4 2416 656 M270
WINDOW 123 56 100 Left 2
SYMATTR Value2 L=0.18u W=6u m=1
SYMATTR InstName M22
SYMATTR Value PM
SYMBOL pmos4 2464 720 R0
WINDOW 123 56 100 Left 2
SYMATTR Value2 L=0.18u W=6u m=1
SYMATTR InstName M21
SYMATTR Value PM
SYMBOL pmos4 3104 128 R0
WINDOW 123 56 100 Left 2
SYMATTR Value2 L=0.18u W=6u m=8
SYMATTR InstName M23
SYMATTR Value PM
SYMBOL nmos4 3104 1040 R0
WINDOW 123 56 100 Left 2
SYMATTR Value2 L=0.18u W=6u m=8
SYMATTR InstName M24
SYMATTR Value NM
SYMBOL nmos4 2832 1040 M0
WINDOW 123 -77 114 Left 2
SYMATTR Value2 L=0.18u W=6u m=2
SYMATTR InstName M25
SYMATTR Value NM
SYMBOL nmos4 2560 1040 M0
WINDOW 123 -77 114 Left 2
SYMATTR Value2 L=0.18u W=6u m=2
SYMATTR InstName M26
SYMATTR Value NM
SYMBOL pmos4 2736 128 R0
WINDOW 123 56 100 Left 2
SYMATTR Value2 L=0.18u W=6u m=2
SYMATTR InstName M27
SYMATTR Value PM
SYMBOL voltage 688 992 M0
SYMATTR InstName Vref
SYMATTR Value DC 1.1V
SYMBOL nmos4 -160 1200 M0
WINDOW 123 56 100 Left 2
SYMATTR Value2 L=0.18u W=6u m=2
SYMATTR InstName M1
SYMATTR Value NM
SYMBOL nmos4 48 1200 R0
WINDOW 123 -43 119 Left 2
SYMATTR Value2 L=0.18u W=6u m=2
SYMATTR InstName M3
SYMATTR Value NM
SYMBOL nmos4 -160 896 M0
WINDOW 123 56 100 Left 2
SYMATTR Value2 L=0.18u W=6u m=2
SYMATTR InstName M4
SYMATTR Value NM
SYMBOL nmos4 48 896 R0
WINDOW 123 -43 119 Left 2
SYMATTR Value2 L=0.18u W=6u m=2
SYMATTR InstName M5
SYMATTR Value NM
SYMBOL pmos4 -160 128 M0
WINDOW 123 -77 116 Left 2
SYMATTR Value2 L=0.18u W=6u m=1
SYMATTR InstName M6
SYMATTR Value PM
SYMBOL res -192 1360 M0
SYMATTR InstName R3
SYMATTR Value 22k
TEXT 64 32 Left 2 !.lib mosfet_018.lib
TEXT 344 32 Left 2 !.tran 100u
TEXT 520 32 Left 2 !;.ac dec 100 1 1g


[promach]

Why does the transient simulation around 10us have a lot of noise ?

Where is the actual root cause for such deterministic noise at 10us after simulation starts ? And any idea how to eliminate it entirely from the noise source ?