op-amp circuit wont work

You can't troubleshoot something that isn't there. The schematic image is only a part of the user interface - the problem lies elsewhere.

RL

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Jim Thompson wrote:

I don't mean to interrupt you guys but can anyone help me figure this out, I'm kinda stuck here, thanks

"I have a follow up question about this circuit, I'm really interested in being able to measure 50uV at the input, by adding gain and seeing something at the output.... I was thinking with a gain of 21, this would get me 1.05mV at the output and I could work with that. But, when I apply zero volts at the input I get 20mV at my output. In the datasheet it says the offset voltage is below 10uV... why am I seeing this 20mV? I tried just connecting both input pins to ground and still get 20mV at the output.... also, is there any particular range of resistors that I should use in my feedback? I mean, if I want a gain of 21, I need a ratio of 20 from R2/R1.... does it matter if I use 20k/1k or 200k/10k or 2k/100?"

Hi panfilero, the resistors you choose could make a difference in terms of bais current error or noise.

I don't know that LT opamp. How about using a 'regular' opamp as a transimpedance amp to measure the current. Currents from 50 uA to 100 uA are no big deal at all. (I've measured pA with a TIA and a Gig-ohm resistor) A 100k ohm resistor in the feedback would give 10 Volts on the output for 100uA of current.

George H.

Step 1 can also be done inside LTSpice with View/Spice Netlist

By following your steps 2 and 3.

thanks john

Version 4 SHEET 1 880 680 WIRE 288 -192 176 -192 WIRE 0 -128 -160 -128 WIRE 176 -128 176 -192 WIRE 0 -32 0 -128 WIRE 176 -16 176 -48 WIRE -160 48 -160 -128 WIRE 288 96 288 -192 WIRE 0 144 0 48 WIRE 32 144 0 144 WIRE 160 144 32 144 WIRE 0 160 0 144 WIRE 496 160 352 160 WIRE 656 160 496 160 WIRE 672 160 656 160 WIRE 160 176 112 176 WIRE 672 192 672 160 WIRE 240 256 240 224 WIRE 240 256 208 256 WIRE 0 272 0 240 WIRE 112 272 112 176 WIRE 112 272 0 272 WIRE 208 272 208 256 WIRE 288 272 288 224 WIRE 320 272 320 224 WIRE 320 272 288 272 WIRE 0 304 0 272 WIRE 672 304 672 272 WIRE 288 320 288 272 WIRE 288 320 96 320 WIRE 256 336 256 224 WIRE 368 336 256 336 WIRE 496 336 496 160 WIRE 496 336 448 336 WIRE 96 384 96 320 WIRE 256 416 256 336 WIRE 96 512 96 464 WIRE 256 608 256 496 FLAG 176 -16 0 FLAG 672 304 0 FLAG 96 512 0 FLAG -160 48 0 FLAG 0 304 0 FLAG 656 160 Vout FLAG 208 272 0 FLAG 256 608 0 FLAG 32 144 Vin SYMBOL voltage 176 -144 R0 WINDOW 123 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 5 SYMATTR SpiceLine Rser=3D.000001 SYMBOL Opamps\\LTC2053 272 160 R0 SYMATTR InstName U1 SYMBOL res 240 400 R0 SYMATTR InstName R1 SYMATTR Value 1K SYMATTR SpiceLine tol=3D1 pwr=3D0.1 SYMBOL res 352 352 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 0 56 VBottom 0 SYMATTR InstName R2 SYMATTR Value 200k SYMATTR SpiceLine tol=3D1 pwr=3D0.1 SYMBOL res -16 144 R0 SYMATTR InstName R3 SYMATTR Value 1 SYMBOL res 656 176 R0 SYMATTR InstName R4 SYMATTR Value 500000000 SYMATTR SpiceLine tol=3D1 pwr=3D0.1 SYMBOL voltage 96 368 R0 WINDOW 123 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value -5 SYMATTR SpiceLine Rser=3D.0001 SYMBOL current 0 -32 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName I1 SYMATTR Value -0.017 TEXT -120 592 Left 0 !.tran 0 0.25 0 .01 uic

I second this; the op amp (-) node takes the input current and has a feedback resistor from the output, then a second (match to the feedback) resistor goes from (+) to ground.

sight"

Traveling? I hear Oslo is beautiful this time of year. Everything's just so RIGHT.

mike

I owe you an apology. It *appeared* that it could be done, but I was wrong. Too much is missing from that netlist to give a schematic. I did not try it before submitting the suggestion. Dang me. Sorry.

Your steps are the best route.

John S

And, you are a true gentleman for writing that. I believe in admitting my mistakes, whether minor or major.

Cheers, John S