Low noise, high bias voltage on picoAmp TIA's input, howto?

I've been thinking about a more complicated solution, and the one that comes to mind would use a 4046 to generate a roughly 5MHz clock and a cheap programmable logic device - the XC2C64A-7VQG44C comes to mind, though it isn't all that cheap - to divide this down to generate two roughly 100kHz non-over-lapping drive waveforms for the MOSFets, plus a square wave to drive one of the phase comparators on the 4046, to lock it to the nominally 100kHz sine wave coming out of a one turn winding on the transformer (L5 in the "simple' circuit).

Divide by fifty is a six-stage binary counter, so the XC2C64A with it's 64 cells is bigger than necessary. The ICT PA7024 which I used back in 1992 would probably be quite big enough.

The tank circuit doesn't do anything silly if you drive it off-resonance - the peak voltages move away from 90 degrees and 270 degrees, which the phase comparator can detect and use to lock the actual operating frequency to the resonant frequency, even if moves as the inductor warms up

I finally got around to reading the "zero ripple" paper

more carefully and it looks as if they want to run a Baxandall-like inverter a bit below resonance, which sort of works, but the centre tap voltage sits at 0V for an appreciable period each cycle, and peaks higher ( 46.14V in the example circuit below - versus 37.7V for an ideal Baxandall converter) while the current through the feed inductor peaks a bit higher.

My ripple cancelling scheme doesn't work as well either but there's not a lot in it. It strikes that you could start the converter at a frequency that is guaranteed to be below the resonant frequency - 17% below the on-tolerance value should be enough for the circuit we've been looking at - and monitor the length of time that the centre tap stays close to the negative rail with something relatively slow (like a cheap single chip microprocessor) and inch it up until it gets close to value you'd see at the resonant frequency, and stick with that.

Version 4 SHEET 1 1944 1396 WIRE -1888 -848 -2000 -848 WIRE -1776 -848 -1824 -848 WIRE -1632 -848 -1776 -848 WIRE 1712 -848 -1632 -848 WIRE -1632 -784 -1632 -848 WIRE -1632 -672 -1632 -704 WIRE -656 -464 -704 -464 WIRE -272 -464 -656 -464 WIRE 16 -464 -208 -464 WIRE 464 -464 96 -464 WIRE 624 -464 464 -464 WIRE -1632 -368 -1632 -608 WIRE -544 -368 -1632 -368 WIRE -384 -368 -544 -368 WIRE -704 -304 -704 -464 WIRE -672 -304 -704 -304 WIRE -384 -304 -384 -368 WIRE -384 -304 -592 -304 WIRE -240 -304 -384 -304 WIRE 624 -304 624 -464 WIRE 624 -304 -160 -304 WIRE 1872 -224 1872 -288 WIRE -2000 -112 -2000 -848 WIRE -1776 144 -1776 -848 WIRE -400 176 -624 176 WIRE 960 176 -320 176 WIRE 1072 176 960 176 WIRE 1200 176 1136 176 WIRE 1280 176 1200 176 WIRE 1424 176 1360 176 WIRE 1584 176 1488 176 WIRE 1792 176 1584 176 WIRE -624 288 -624 176 WIRE -400 288 -624 288 WIRE -288 288 -400 288 WIRE 912 288 -208 288 WIRE 1072 288 912 288 WIRE 1200 288 1200 176 WIRE 1200 288 1136 288 WIRE -1632 384 -1632 -368 WIRE 320 384 -1456 384 WIRE 1792 384 1792 176 WIRE 624 400 624 -304 WIRE -1456 480 -1456 384 WIRE 320 480 320 384 WIRE 432 480 320 480 WIRE 576 480 512 480 WIRE 1584 480 1584 176 WIRE -1632 512 -1632 448 WIRE -704 560 -704 -304 WIRE -912 640 -1008 640 WIRE -752 640 -832 640 WIRE -1008 816 -1008 640 WIRE -2000 1088 -2000 -32 WIRE -1776 1088 -1776 208 WIRE -1776 1088 -2000 1088 WIRE -1632 1088 -1632 576 WIRE -1632 1088 -1776 1088 WIRE -1456 1088 -1456 560 WIRE -1456 1088 -1632 1088 WIRE -1008 1088 -1008 896 WIRE -1008 1088 -1456 1088 WIRE -704 1088 -704 656 WIRE -704 1088 -1008 1088 WIRE -400 1088 -400 288 WIRE -400 1088 -704 1088 WIRE 624 1088 624 496 WIRE 624 1088 -400 1088 WIRE 1264 1088 1264 592 WIRE 1264 1088 624 1088 WIRE 1584 1088 1584 544 WIRE 1584 1088 1264 1088 WIRE 1664 1088 1584 1088 WIRE 1792 1088 1792 464 WIRE 1792 1088 1664 1088 WIRE 1824 1088 1792 1088 WIRE 1920 1088 1824 1088 WIRE -2000 1120 -2000 1088 WIRE 1664 1136 1664 1088 WIRE 1824 1184 1824 1088 WIRE 960 1216 960 176 WIRE 1104 1216 960 1216 WIRE 1296 1216 1168 1216 WIRE 912 1344 912 288 WIRE 1104 1344 912 1344 WIRE 1296 1344 1296 1216 WIRE 1296 1344 1168 1344 WIRE 1376 1344 1296 1344 WIRE 1504 1344 1456 1344 WIRE 1664 1344 1664 1200 WIRE 1664 1344 1568 1344 WIRE 1824 1344 1824 1264 WIRE 1824 1344 1664 1344 FLAG -2000 1120 0 FLAG -544 -368 Vct FLAG -656 -464 tank- FLAG 1264 512 CancellingV FLAG 464 -464 tank+ SYMBOL ind2 -688 -288 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 4 56 VBottom 2 SYMATTR InstName L1 SYMATTR Value 0.176m SYMATTR Type ind SYMATTR SpiceLine Rser=0.088 Cpar=10p SYMBOL ind2 -256 -288 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 4 56 VBottom 2 SYMATTR InstName L2 SYMATTR Value 0.176m SYMATTR Type ind SYMATTR SpiceLine Rser=0.022 SYMBOL cap -208 -480 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 46 32 VTop 2 SYMATTR InstName C1 SYMATTR Value 2.2n SYMBOL res 464 480 M90 WINDOW 0 -26 11 VBottom 2 WINDOW 3 22 8 VTop 2 SYMATTR InstName R1 SYMATTR Value 22 SYMBOL nmos 576 400 R0 SYMATTR InstName M1 SYMATTR Value Si3440DV SYMBOL nmos -752 560 R0 SYMATTR InstName M2 SYMATTR Value Si3440DV SYMBOL res -880 640 M90 WINDOW 0 -18 21 VBottom 2 WINDOW 3 19 15 VTop 2 SYMATTR InstName R2 SYMATTR Value 22 SYMBOL ind2 -1648 -800 R0 SYMATTR InstName L7 SYMATTR Value 2.2m SYMATTR SpiceLine Ipk=5A Rser=0.8 Rpar=100k Cpar=10p SYMBOL diode 1072 192 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D1 SYMATTR Value RFU02VS8S SYMBOL diode 1072 304 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D2 SYMATTR Value RFU02VS8S SYMBOL diode 1168 1200 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D3 SYMATTR Value RFU02VS8S SYMBOL diode 1168 1328 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D4 SYMATTR Value RFU02VS8S SYMBOL cap 1568 480 R0 SYMATTR InstName C2 SYMATTR Value 10n SYMBOL cap 1648 1136 R0 WINDOW 3 17 75 Left 2 SYMATTR Value 10n SYMATTR InstName C3 SYMBOL res 1792 416 R0 SYMATTR InstName R4 SYMATTR Value 47k SYMBOL res 1824 1216 R0 SYMATTR InstName R5 SYMATTR Value 47k SYMBOL cap -1792 144 R0 SYMATTR InstName C4 SYMATTR Value 1µ SYMBOL ind2 -416 192 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 4 56 VBottom 2 SYMATTR InstName L4 SYMATTR Value 12.2m SYMATTR Type ind SYMATTR SpiceLine Rser=10 Cpar=10p SYMBOL ind2 -192 272 R90 WINDOW 0 4 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName L3 SYMATTR Value 12.2m SYMATTR Type ind SYMATTR SpiceLine Rser=10 Cpar=10p SYMBOL zener -1616 448 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D5 SYMATTR Value 1N5375B SYMBOL FerriteBead -1632 544 R180 SYMATTR InstName L15 SYMATTR Value 12µ SYMATTR SpiceLine Ipk=3 Rser=0.0118 Rpar=870 Cpar=1.1p SYMBOL ind2 1360 1360 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 -6 69 VBottom 2 SYMATTR InstName L9 SYMATTR Value 153m SYMATTR SpiceLine Rser=1 Cpar=10p SYMBOL voltage -2000 -128 R0 WINDOW 123 0 0 Left 0 WINDOW 39 24 44 Left 2 SYMATTR SpiceLine Rser=1 SYMATTR InstName V1 SYMATTR Value 24 SYMBOL ind2 1376 160 R90 WINDOW 0 4 56 VBottom 2 WINDOW 3 48 56 VTop 2 SYMATTR InstName L8 SYMATTR Value 153m SYMATTR SpiceLine Rser=1 Cpar=10p SYMBOL FerriteBead 1456 176 R90 WINDOW 0 -16 0 VBottom 2 SYMATTR InstName L11 SYMATTR Value 12µ SYMATTR SpiceLine Ipk=3 Rser=0.0083 Rpar=880 Cpar=715f SYMBOL FerriteBead 1536 1344 R90 WINDOW 0 -16 0 VBottom 2 SYMATTR InstName L12 SYMATTR Value 12µ SYMATTR SpiceLine Ipk=3 Rser=0.0083 Rpar=880 Cpar=715f mfg="Würth Elektronik" pn="74275010 WE-UKW 6050" SYMBOL FerriteBead -1632 -640 R180 SYMATTR InstName L16 SYMATTR Value 12µ SYMATTR SpiceLine Ipk=3 Rser=0.0118 Rpar=870 Cpar=1.1p SYMBOL FerriteBead -1856 -848 R90 WINDOW 0 -16 0 VBottom 2 SYMATTR InstName L13 SYMATTR Value 12µ SYMATTR SpiceLine Ipk=3 Rser=0.0083 Rpar=880 Cpar=715f SYMBOL ind2 1248 496 R0 SYMATTR InstName L14 SYMATTR Value 153m SYMBOL voltage -1008 800 R0 WINDOW 123 0 0 Left 0 WINDOW 39 24 44 Left 2 SYMATTR SpiceLine Rser=1 SYMATTR InstName V2 SYMATTR Value PULSE(0 8 0u 25n 25n 5.95u 12u 11000) SYMBOL voltage -1456 464 R0 WINDOW 123 0 0 Left 0 WINDOW 39 24 44 Left 2 SYMATTR SpiceLine Rser=1 SYMATTR InstName V3 SYMATTR Value PULSE(0 8 6u 25n 25n 5.95u 12u 11000) SYMBOL res 48 -464 M90 WINDOW 0 -26 11 VBottom 2 WINDOW 3 22 8 VTop 2 SYMATTR InstName R3 SYMATTR Value 33 TEXT -1920 1144 Left 2 !.tran 0 10m 0m 10n TEXT -1792 1208 Left 2 !K1 L1 L2 L3 L4 0.99 TEXT -856 1144 Left 2 !.ic I(L7=1u) I(L1=1u) V(Bias)=5) TEXT -848 1208 Left 2 !K2 L7 L8 L9 L14 0.99