phase shift in inverting opamp

John Larkin · 2018-05-05T16:03:31+00:00

I need an instrument input amp with 1M input impedance and -0.5 gain, and very low phase shift out to 100 KHz. I'm not sure what sorts of parasitic shunt capacitance I'll see on the resistors, theoretically 1M input and 500K feedback. My board stackup may affect the shunt capacitances some. Maybe if I use 2x500K instead of 1M, things will work out automatically. Good news: my preferred opamp, AD8034, now has a model built-into LT Spice. So I'll buy more ADI parts because they acquired LTC and LT Spice. Version 4 SHEET 1 880 680 WIRE -768 -128 -800 -128 WIRE -752 -128 -768 -128 WIRE -592 -128 -624 -128 WIRE -576 -128 -592 -128 WIRE -320 -128 -448 -128 WIRE -144 -128 -256 -128 WIRE -48 -128 -144 -128 WIRE 144 -128 16 -128 WIRE 304 -128 144 -128 WIRE 496 -128 368 -128 WIRE -800 -80 -800 -128 WIRE -624 -80 -624 -128 WIRE -800 48 -800 0 WIRE -624 48 -624 0 WIRE -448 48 -448 -128 WIRE -400 48 -448 48 WIRE -288 48 -400 48 WIRE -144 48 -144 -128 WIRE -144 48 -208 48 WIRE -80 48 -144 48 WIRE 144 48 144 -128 WIRE 144 48 0 48 WIRE 288 48 144 48 WIRE 496 48 496 -128 WIRE 496 48 368 48 WIRE -448 144 -448 48 WIRE 144 192 144 48 WIRE 176 192 144 192 WIRE 496 208 496 48 WIRE 496 208 240 208 WIRE 560 208 496 208 WIRE 592 208 560 208 WIRE 176 224 144 224 WIRE -448 320 -448 224 WIRE 144 352 144 224 FLAG 144 352 0 FLAG -448 320 0 FLAG -624 48 0 FLAG -800 48 0 FLAG -768 -128 +12 FLAG 208 176 +12 FLAG -592 -128 -12 FLAG 208 240 -12 FLAG -400 48 GEN FLAG 560 208 OUT SYMBOL res -96 64 R270 WINDOW 0 -45 60 VTop 2 WINDOW 3 -55 61 VBottom 2 SYMATTR InstName R1 SYMATTR Value 500K SYMBOL res 272 64 R270 WINDOW 0 -37 60 VTop 2 WINDOW 3 -41 61 VBottom 2 SYMATTR InstName R2 SYMATTR Value 500K SYMBOL voltage -448 128 R0 WINDOW 123 64 135 Left 2 WINDOW 39 0 0 Left 2 WINDOW 0 77 60 Left 2 WINDOW 3 35 99 Left 2 SYMATTR Value2 AC 1 SYMATTR InstName V1 SYMATTR Value SINE(0 1 1k) SYMBOL voltage -624 -96 R0 SYMATTR InstName V2 SYMATTR Value -15 SYMBOL voltage -800 -96 R0 SYMATTR InstName V3 SYMATTR Value...

May 05, 2018 22 Replies

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Steve Wilson 8 years ago

It would be nice to give it a try.

Did you ever post a schematic? Google Groups has a few of your posts, but no references to a schematic. Any data such as risetime, amplitude, rep rate?

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Phil Hobbs 8 years ago

It was a customer gig, so they own the work product. In general terms, it was a single-diode sampler with pHEMT switches driven by LVDS line receivers (as recommended by JL). The FWHM was about 100-150 ps depending on the version, and eventually the position uncertainty was a small fraction of an inch.

Those aren't SOTA numbers except that the BOM cost for my bit was only about $2 +- 40 cents, depending on the version--the pHEMTs were more expensive than the SiGe BJT alternatives but switched faster. IIRC Chester & Co cleaned up the impulse response of the transducer enough that they could get excellent results with cheaper transistors, but I haven't seen the final result.

A fun gig, for sure.

Cheers

Phil Hobbs

Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com

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Steve Wilson 8 years ago

Thanks. Very interesting.

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