Interesting GaN power part: A3G26D055N

Straight wires are about 20 nH per inch. There's not enough inductive coupling there to make that vary much.

Cheers

Phil Hobbs

[...]

1. Can you tell us the input voltage noise and corner frequency of the EPC2038?
2. How do you couple the input signal to the gate at +2.5V? See

Figure 2: Transfer Characteristics, page 2

1. What is the bandwidth of the amplifier?

1. What is the input capacitance?

I don't know. Above I have asked if someone has done it :-)

All I have done with it up to now is making a test circuit as a chopper and I have verified that I can solder it to the board. That is not important, just curiosity. Soldering was easy with hot air.

The chopper has the drain at the input, vaguely as a voltage divider. Gate voltage is the LVCmos switching frequency. 5V CMOS would be quite close to killing it. A chopper may profit from low charge injection.

As an amplifier, one could use the circuit that Win used for measuring the transistor noise tables in AOE3. It has a NPN to servo the gate bias. But if you have interest in 1/f and below, you may not be able to tell the difference between servo effects and input noise.

Gerhard

I use them and have done some off-label testing. But I switch them hard and don't care about noise.

The gates are kind of strange. At high gate voltages, there seems to be some longterm damage mechanism slowly increasing gate current.

I'd guess that they are noisy, but numbers would be interesting.

Gerhard Hoffmann snipped-for-privacy@arcor.de wrote:

OK, Thanks.

ISTR Win used a bunch of bipolars to get the noise down to pV/root(Hz) for ribbon microphones. This required an extremely large input coupling capacitor to prevent shorting out the base bias and still pass the low frequencies needed.

I am working on a different approach that DC-couples the input signal to an op amp, or several in parallel for low noise. There is no couping capacitor needed, and the op amp eliminates the risk of blowing out the base due to the high surge current from a power supply. The capacitors in the feedback network need to be insulated or covered to minimize low frequency voltage shift due to random air currents affecting the tempco of the capacitors. Thanks to P. Hobbs for this observation.

I am also working on high attenuation ripple filters for the op amp power supplies. I'd appreciate your comments.

Here is the ASC file for the input stage:

Version 4 SHEET 1 1888 724 WIRE 544 32 480 32 WIRE 672 32 608 32 WIRE 480 112 480 32 WIRE 528 112 480 112 WIRE 672 112 672 32 WIRE 672 112 608 112 WIRE 720 160 576 160 WIRE 864 160 720 160 WIRE 576 176 576 160 WIRE 720 176 720 160 WIRE 864 176 864 160 WIRE 480 192 480 112 WIRE 512 192 480 192 WIRE 544 192 512 192 WIRE 640 208 608 208 WIRE 672 208 672 112 WIRE 672 208 640 208 WIRE 400 224 384 224 WIRE 544 224 400 224 WIRE 384 240 384 224 WIRE 480 256 480 192 WIRE 576 256 576 240 WIRE 784 256 576 256 WIRE 784 272 784 256 WIRE 864 272 864 256 WIRE 384 336 384 320 WIRE 480 368 480 336 WIRE 528 368 480 368 WIRE 576 368 528 368 WIRE 672 368 576 368 WIRE 720 368 720 240 WIRE 720 368 672 368 WIRE 784 368 784 352 WIRE 480 384 480 368 WIRE 576 384 576 368 WIRE 672 384 672 368 WIRE 480 464 480 448 WIRE 576 464 576 448 WIRE 672 480 672 464 FLAG 384 336 0 FLAG 400 224 Vin FLAG 640 208 U1O FLAG 480 464 0 FLAG 528 368 R1C1 FLAG 784 368 0 FLAG 864 272 0 FLAG 512 192 U1N FLAG 576 464 0 FLAG 672 480 0 SYMBOL voltage 384 224 R0 WINDOW 0 33 22 Left 2 WINDOW 3 37 77 Left 2 WINDOW 123 35 103 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 10 SYMATTR Value2 AC 1 SYMBOL opamps\\lt1028 576 144 R0 SYMATTR InstName U1 SYMBOL res 624 96 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 4950 SYMBOL res 464 240 R0 SYMATTR InstName R1 SYMATTR Value 50 SYMBOL cap 464 384 R0 SYMATTR InstName C1 SYMATTR Value 10mf SYMATTR SpiceLine Rser=25m Lser=2n SYMBOL voltage 784 368 M180 WINDOW 0 33 22 Left 2 WINDOW 3 33 44 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value 15 SYMBOL voltage 864 160 R0 WINDOW 0 33 22 Left 2 WINDOW 3 33 44 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V3 SYMATTR Value 15 SYMBOL cap 608 48 M270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName C2 SYMATTR Value 100p SYMBOL cap 560 384 R0 SYMATTR InstName C3 SYMATTR Value 10mf SYMATTR SpiceLine Rser=25m Lser=2n SYMBOL res 656 368 R0 SYMATTR InstName Rleak SYMATTR Value 1e6 SYMBOL diode 704 240 M180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D1 SYMATTR Value 1N4001 TEXT 368 -96 Left 2 ;'Measure Power Supply, Zener, LED Noise TEXT 368 -64 Left 2 !.ac dec 500 1m 1e8\n;.tran 2

Here is the frequency response:

[AC Analysis] { Npanes: 1 { traces: 1 {524290,0,"V(u1o)"} X: ('M',1,0.001,0,1e+008) Y[0]: (' ',0,0.125892541179417,6,125.892541179417) Y[1]: (' ',0,-280,40,80) Volts: (' ',0,0,3,9.99,0.002,10.012) Log: 1 2 0 GridStyle: 1 PltMag: 1 } } [Transient Analysis] { Npanes: 1 { traces: 3 {524290,0,"V(m1s)"} {589828,0,"V(m1g)"} {524291,0,"V(vdc)"} X: (' ',1,0,0.2,2) Y[0]: (' ',1,-0.9,0.9,9) Y[1]: (' ',0,1e+308,30,-1e+308) Volts: (' ',0,0,0,-0.9,0.9,9) Log: 0 0 0 GridStyle: 1 PltMag: 1 PltPhi: 1 0 } }

Here are different versions of the power supply ripple filters.

Version 4 SHEET 1 1888 1296 WIRE -48 48 -64 48 WIRE 16 48 -48 48 WIRE 144 48 16 48 WIRE 288 48 240 48 WIRE 320 48 288 48 WIRE 448 48 320 48 WIRE 576 48 448 48 WIRE 768 48 672 48 WIRE 864 48 768 48 WIRE 896 48 864 48 WIRE -64 64 -64 48 WIRE 768 64 768 48 WIRE 896 64 896 48 WIRE 288 80 288 48 WIRE 16 128 16 48 WIRE 32 128 16 128 WIRE 160 128 112 128 WIRE 192 128 192 112 WIRE 192 128 160 128 WIRE 448 128 448 48 WIRE 464 128 448 128 WIRE 592 128 544 128 WIRE 624 128 624 112 WIRE 624 128 592 128 WIRE 192 144 192 128 WIRE 624 144 624 128 WIRE 768 144 768 128 WIRE -64 160 -64 144 WIRE 288 160 288 144 WIRE 896 160 896 144 WIRE 192 224 192 208 WIRE 624 224 624 208 WIRE -16 256 -64 256 WIRE 144 256 -16 256 WIRE 288 256 240 256 WIRE 320 256 288 256 WIRE 448 256 320 256 WIRE 576 256 448 256 WIRE 768 256 672 256 WIRE 864 256 768 256 WIRE 896 256 864 256 WIRE -64 272 -64 256 WIRE 768 272 768 256 WIRE 896 272 896 256 WIRE 288 288 288 256 WIRE -16 336 -16 256 WIRE 32 336 -16 336 WIRE 160 336 112 336 WIRE 192 336 192 320 WIRE 192 336 160 336 WIRE 448 336 448 256 WIRE 464 336 448 336 WIRE 592 336 544 336 WIRE 624 336 624 320 WIRE 624 336 592 336 WIRE 192 352 192 336 WIRE 624 352 624 336 WIRE 768 352 768 336 WIRE -64 368 -64 352 WIRE 288 368 288 352 WIRE 896 368 896 352 WIRE 192 432 192 416 WIRE 624 432 624 416 WIRE 16 464 16 128 WIRE 144 464 16 464 WIRE 288 464 240 464 WIRE 368 464 288 464 WIRE 400 464 368 464 WIRE 448 464 400 464 WIRE 576 464 448 464 WIRE 736 464 672 464 WIRE 768 464 736 464 WIRE 880 464 768 464 WIRE 896 464 880 464 WIRE 768 480 768 464 WIRE 896 480 896 464 WIRE 368 496 368 464 WIRE 16 544 16 464 WIRE 32 544 16 544 WIRE 160 544 112 544 WIRE 192 544 192 528 WIRE 192 544 160 544 WIRE 208 544 192 544 WIRE 288 544 288 464 WIRE 288 544 272 544 WIRE 448 544 448 464 WIRE 464 544 448 544 WIRE 592 544 544 544 WIRE 624 544 624 528 WIRE 624 544 592 544 WIRE 656 544 624 544 WIRE 736 544 736 464 WIRE 736 544 720 544 WIRE 768 560 768 544 WIRE 368 576 368 560 WIRE 896 576 896 560 WIRE 16 656 16 544 WIRE 144 656 16 656 WIRE 304 656 240 656 WIRE 368 656 304 656 WIRE 400 656 368 656 WIRE 448 656 400 656 WIRE 576 656 448 656 WIRE 736 656 672 656 WIRE 768 656 736 656 WIRE 880 656 768 656 WIRE 896 656 880 656 WIRE 768 672 768 656 WIRE 896 672 896 656 WIRE 368 688 368 656 WIRE 16 736 16 656 WIRE 48 736 16 736 WIRE 160 736 112 736 WIRE 192 736 192 720 WIRE 192 736 160 736 WIRE 208 736 192 736 WIRE 304 736 304 656 WIRE 304 736 288 736 WIRE 448 736 448 656 WIRE 480 736 448 736 WIRE 592 736 544 736 WIRE 624 736 624 720 WIRE 624 736 592 736 WIRE 640 736 624 736 WIRE 736 736 736 656 WIRE 736 736 720 736 WIRE 768 752 768 736 WIRE 368 768 368 752 WIRE 896 768 896 752 WIRE 16 864 16 736 WIRE 144 864 16 864 WIRE 272 864 240 864 WIRE 288 864 272 864 WIRE 352 864 288 864 WIRE 448 864 352 864 WIRE 576 864 448 864 WIRE 720 864 672 864 WIRE 784 864 720 864 WIRE 864 864 784 864 WIRE 896 864 864 864 WIRE 896 880 896 864 WIRE 352 896 352 864 WIRE 784 896 784 864 WIRE 192 944 192 928 WIRE 288 944 288 864 WIRE 624 944 624 928 WIRE 720 944 720 864 WIRE 352 976 352 960 WIRE 784 976 784 960 WIRE 896 976 896 960 WIRE 16 1040 16 864 WIRE 32 1040 16 1040 WIRE 208 1040 112 1040 WIRE 240 1040 240 1008 WIRE 240 1040 208 1040 WIRE 448 1040 448 864 WIRE 464 1040 448 1040 WIRE 640 1040 544 1040 WIRE 672 1040 672 1008 WIRE 672 1040 640 1040 WIRE 240 1056 240 1040 WIRE 672 1056 672 1040 WIRE 240 1136 240 1120 WIRE 672 1136 672 1120 FLAG -64 160 0 FLAG -48 48 VCC FLAG 192 224 0 FLAG 320 48 Q1E FLAG 288 160 0 FLAG 160 128 Q1B FLAG 592 128 Q2B FLAG 768 144 0 FLAG 864 48 Classic FLAG 624 224 0 FLAG 896 160 0 FLAG 400 464 Q7E FLAG 368 576 0 FLAG 160 544 Q7B FLAG 592 544 Q8B FLAG 768 560 0 FLAG 880 464 NPN FLAG 896 576 0 FLAG 352 976 0 FLAG 240 1136 0 FLAG 272 864 Q3C FLAG 208 1040 Q4B FLAG 784 976 0 FLAG 672 1136 0 FLAG 864 864 Sziklai FLAG 640 1040 Q6B FLAG 896 976 0 FLAG 400 656 Q9C FLAG 368 768 0 FLAG 160 736 Q9B FLAG 592 736 Q10B FLAG 768 752 0 FLAG 880 656 PNP FLAG 896 768 0 FLAG 192 432 0 FLAG 320 256 Q11E FLAG 288 368 0 FLAG 160 336 Q11B FLAG 592 336 Q12B FLAG 768 352 0 FLAG 864 256 NegVolt FLAG 624 432 0 FLAG 896 368 0 FLAG -64 368 0 SYMBOL voltage -64 48 R0 WINDOW 0 33 22 Left 2 WINDOW 3 37 77 Left 2 WINDOW 123 35 103 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 15 SYMATTR Value2 AC 1 SYMBOL npn 144 112 R270 WINDOW 0 43 35 VRight 2 WINDOW 3 65 27 VRight 2 SYMATTR InstName Q1 SYMATTR Value 2N3904 SYMBOL res 128 112 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R1 SYMATTR Value 10k SYMBOL cap 176 144 R0 WINDOW 0 34 15 Left 2 WINDOW 3 34 52 Left 2 SYMATTR InstName C1 SYMATTR Value 470uf SYMATTR SpiceLine Rser=17m Lser=10n SYMBOL cap 272 80 R0 WINDOW 0 34 15 Left 2 WINDOW 3 34 52 Left 2 SYMATTR InstName C2 SYMATTR Value 470uf SYMATTR SpiceLine Rser=17m Lser=10n SYMBOL npn 576 112 R270 WINDOW 0 43 35 VRight 2 WINDOW 3 69 25 VRight 2 SYMATTR InstName Q2 SYMATTR Value 2N3904 SYMBOL res 560 112 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 10k SYMBOL cap 608 144 R0 WINDOW 0 34 15 Left 2 WINDOW 3 34 52 Left 2 SYMATTR InstName C3 SYMATTR Value 470uf SYMATTR SpiceLine Rser=17m Lser=10n SYMBOL cap 752 64 R0 WINDOW 0 34 15 Left 2 WINDOW 3 34 52 Left 2 SYMATTR InstName C4 SYMATTR Value 470uf SYMATTR SpiceLine Rser=17m Lser=10n SYMBOL res 880 48 R0 SYMATTR InstName R3 SYMATTR Value 1k SYMBOL res 128 528 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R4 SYMATTR Value 10k SYMBOL cap 272 528 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C5 SYMATTR Value 1000uf SYMATTR SpiceLine Rser=17m Lser=10n SYMBOL cap 352 496 R0 WINDOW 0 34 15 Left 2 WINDOW 3 34 52 Left 2 SYMATTR InstName C6 SYMATTR Value 470uf SYMATTR SpiceLine Rser=17m Lser=10n SYMBOL res 560 528 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R5 SYMATTR Value 10k SYMBOL cap 752 480 R0 WINDOW 0 34 15 Left 2 WINDOW 3 34 52 Left 2 SYMATTR InstName C7 SYMATTR Value 470uf SYMATTR SpiceLine Rser=17m Lser=10n SYMBOL res 880 464 R0 SYMATTR InstName R6 SYMATTR Value 1k SYMBOL pnp 240 928 M270 WINDOW 0 60 59 VLeft 2 WINDOW 3 97 68 VLeft 2 SYMATTR InstName Q3 SYMATTR Value 2N3906 SYMBOL npn 192 1008 R270 WINDOW 0 43 35 VRight 2 WINDOW 3 80 25 VRight 2 SYMATTR InstName Q4 SYMATTR Value 2N3904 SYMBOL res 128 1024 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R7 SYMATTR Value 47k SYMBOL cap 224 1056 R0 WINDOW 0 34 15 Left 2 WINDOW 3 34 52 Left 2 SYMATTR InstName C8 SYMATTR Value 470uf SYMATTR SpiceLine Rser=17m Lser=10n SYMBOL cap 336 896 R0 WINDOW 0 34 15 Left 2 WINDOW 3 34 52 Left 2 SYMATTR InstName C9 SYMATTR Value 470uf SYMATTR SpiceLine Rser=17m Lser=10n SYMBOL pnp 672 928 M270 WINDOW 0 60 59 VLeft 2 WINDOW 3 97 68 VLeft 2 SYMATTR InstName Q5 SYMATTR Value 2N3906 SYMBOL npn 624 1008 R270 WINDOW 0 43 35 VRight 2 WINDOW 3 80 25 VRight 2 SYMATTR InstName Q6 SYMATTR Value 2N3904 SYMBOL res 560 1024 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R8 SYMATTR Value 47k SYMBOL cap 656 1056 R0 WINDOW 0 34 15 Left 2 WINDOW 3 34 52 Left 2 SYMATTR InstName C10 SYMATTR Value 470uf SYMATTR SpiceLine Rser=17m Lser=10n SYMBOL cap 768 896 R0 WINDOW 0 34 15 Left 2 WINDOW 3 34 52 Left 2 SYMATTR InstName C11 SYMATTR Value 470uf SYMATTR SpiceLine Rser=17m Lser=10n SYMBOL res 880 864 R0 SYMATTR InstName R9 SYMATTR Value 1k SYMBOL npn 144 528 R270 WINDOW 0 43 35 VRight 2 WINDOW 3 64 27 VRight 2 SYMATTR InstName Q7 SYMATTR Value 2N3904 SYMBOL npn 576 528 R270 WINDOW 0 43 35 VRight 2 WINDOW 3 63 29 VRight 2 SYMATTR InstName Q8 SYMATTR Value 2N3904 SYMBOL cap 720 528 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C12 SYMATTR Value 1000uf SYMATTR SpiceLine Rser=17m Lser=10n SYMBOL res 304 720 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R10 SYMATTR Value 10k SYMBOL cap 112 720 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C13 SYMATTR Value 1000uf SYMATTR SpiceLine Rser=17m Lser=10n SYMBOL cap 352 688 R0 WINDOW 0 34 15 Left 2 WINDOW 3 34 52 Left 2 SYMATTR InstName C14 SYMATTR Value 470uf SYMATTR SpiceLine Rser=17m Lser=10n SYMBOL res 736 720 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R11 SYMATTR Value 10k SYMBOL cap 752 672 R0 WINDOW 0 34 15 Left 2 WINDOW 3 34 52 Left 2 SYMATTR InstName C15 SYMATTR Value 470uf SYMATTR SpiceLine Rser=17m Lser=10n SYMBOL res 880 656 R0 SYMATTR InstName R12 SYMATTR Value 1k SYMBOL cap 544 720 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C16 SYMATTR Value 1000uf SYMATTR SpiceLine Rser=17m Lser=10n SYMBOL pnp 240 720 M270 WINDOW 0 60 59 VLeft 2 WINDOW 3 97 68 VLeft 2 SYMATTR InstName Q9 SYMATTR Value 2N3906 SYMBOL pnp 672 720 M270 WINDOW 0 60 59 VLeft 2 WINDOW 3 97 68 VLeft 2 SYMATTR InstName Q10 SYMATTR Value 2N3906 SYMBOL cap 176 352 R0 WINDOW 0 34 15 Left 2 WINDOW 3 34 52 Left 2 SYMATTR InstName C17 SYMATTR Value 470uf SYMATTR SpiceLine Rser=17m Lser=10n SYMBOL cap 272 288 R0 WINDOW 0 34 15 Left 2 WINDOW 3 34 52 Left 2 SYMATTR InstName C18 SYMATTR Value 470uf SYMATTR SpiceLine Rser=17m Lser=10n SYMBOL res 560 320 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R13 SYMATTR Value 10k SYMBOL cap 608 352 R0 WINDOW 0 34 15 Left 2 WINDOW 3 34 52 Left 2 SYMATTR InstName C19 SYMATTR Value 470uf SYMATTR SpiceLine Rser=17m Lser=10n SYMBOL cap 752 272 R0 WINDOW 0 34 15 Left 2 WINDOW 3 34 52 Left 2 SYMATTR InstName C20 SYMATTR Value 470uf SYMATTR SpiceLine Rser=17m Lser=10n SYMBOL res 880 256 R0 SYMATTR InstName R14 SYMATTR Value 1k SYMBOL pnp 144 320 R270 WINDOW 0 40 38 VRight 2 WINDOW 3 60 26 VRight 2 SYMATTR InstName Q11 SYMATTR Value 2N3906 SYMBOL pnp 576 320 R270 WINDOW 0 40 38 VRight 2 WINDOW 3 60 26 VRight 2 SYMATTR InstName Q12 SYMATTR Value 2N3906 SYMBOL voltage -64 368 R180 WINDOW 0 33 22 Left 2 WINDOW 3 37 77 Left 2 WINDOW 123 35 103 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value 15 SYMATTR Value2 AC 1 SYMBOL res 128 320 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R15 SYMATTR Value 10k TEXT 200 -96 Left 2 ;'Low Noise Ripple Filter for Opamps TEXT 200 -64 Left 2 !.ac dec 500 1m 1e6 TEXT 120 1216 Left 2 ;Capacitors are Kemet Solid Polymer, 470uF 25V, 17mohm ESR

Here's the PLT files. Watch the wrap:

[AC Analysis] { Npanes: 1 { traces: 5 {524290,0,"V(classic)"} {524291,0,"V(negvolt)"} {524292,0,"V(npn)"} {524293,0,"V(pnp)"} {524294,0,"V(sziklai)"} X: ('M',0,0.001,0,1e+006) Y[0]: (' ',0,1e-012,20,10) Y[1]: (' ',0,-400,80,480) Volts: (' ',0,0,3,5.864,0.001,5.876) Log: 1 2 0 GridStyle: 1 PltMag: 1 } }

Am 18.09.21 um 01:19 schrieb Steve Wilson:

He has a differential version that does not require the huge input capacitor. I have built the single-ended version: <

>

and yes, it features ~70 pV/rt (Hz), like promised. I wanted to use it in the chopper and at 10 KHz the required input capacitor is harmless.

beware of such an event: <

>

I noted a rise of the noise voltage above 500 KHz and in search of the culprit I removed the wet slug tantalum. I was not the tan, it was the routing: <

>

Substituting a mesh removed the effect.

Then I forgot until next week end that the tantalum was removed, and I measured the voltage noise of a lithium battery. Ouch! That stench! And the amplifier was in a alu-cast Hammond box that was closed.

6 screws.

When the op amp has 100 dB pssr, you do not need such extreme external suppression. I'd be ashamed to admit that I need such suppression. It would say that I have a huge source of dirt on my board.

Run such an amplifier from Li batteries. The easiest way to get rid of some ground loops.

Cheers, Gerhard

Thing is, the op amp PSR ain't any 100 dB up at SMPS frequencies. Also of course that 100 dB number is input-referred--if you're running a gain of 100, the output-referred PSR becomes 60 dB even near DC.

Op amps don't care much about somewhat-drifty supply rails, but can use some PSR help above about 1 kHz, which makes cap multipliers an excellent match.

For lab use, I agree.

Cheers

Phil Hobbs

"the father of the AD797" who was that, Gerhard? I'd love to thank him. Popped one of those into the front end of an already-quiet test equipment was the easiest & quickest and substantial improvement I had. This was ca. 1986, not long after it appeared. cheers, RS