Using a TI LM7171 Model in LTspice

Hi sallyfrach ,

I took a look at your simulation and here are my thoughts:

• This is a voltage input Op-Amp, hence, the input should be voltage not a current, if you do so follow your circuit diagram where in you use current as an input, it would take use the common mode input resistance and multiply it to your current in which case this would be your input voltage instead. My suggestion here is use your current source and place a resistor parallel, if it is 1uA, 1MOhms parallel resisitance will show 1V input. Please determine your your target input voltage first.
•  As per my investigation, there seems to be a problem with the Model File you are using, you may want to check with the owner of the model, since this is not an ADI product, I really can't make further investigation with the model. I may suggest here using High frequency Op-Amps like LT1222 which I think really is your target of operation based on the frequency you are trying to use.
• In my investigation of the model, I tried simulating its Large Signal Response but it does not follow as shown in the datasheet, which is in fact a problem with the model. Please double check with the owner.
• If you would want to share with us your target application, maybe I could redirect you to the Op-Amps forum so you could ask for the closest part that we do have similar to the operation of the LM7171.

I hope this notes help.

Best Regards,

Earl

Hi sallyfrach ,

I took a look at your simulation and here are my thoughts:

• This is a voltage input Op-Amp, hence, the input should be voltage not a current, if you do so follow your circuit diagram where in you use current as an input, it would take use the common mode input resistance and multiply it to your current in which case this would be your input voltage instead. My suggestion here is use your current source and place a resistor parallel, if it is 1uA, 1MOhms parallel resisitance will show 1V input. Please determine your your target input voltage first.
•  As per my investigation, there seems to be a problem with the Model File you are using, you may want to check with the owner of the model, since this is not an ADI product, I really can't make further investigation with the model. I may suggest here using High frequency Op-Amps like LT1222 which I think really is your target of operation based on the frequency you are trying to use.
• In my investigation of the model, I tried simulating its Large Signal Response but it does not follow as shown in the datasheet, which is in fact a problem with the model. Please double check with the owner.
• If you would want to share with us your target application, maybe I could redirect you to the Op-Amps forum so you could ask for the closest part that we do have similar to the operation of the LM7171.

I hope this notes help.

Best Regards,

Earl

I'm using LT17.1.15 and have ran your circuit without any issues except some initial waveform distortion in the range of 0-20uS. I then chose to run it for 30uS and ignore the first 20uS of data. Over that range the waveform was a clean sinewave. It was 2 volts P_P centered on a DC level of 2.98 volts. I agree with EarlJohn that you should use a different OA. If you look at the LM7171 data sheet you'll notice that Vos and Ibias are large and that explains the DC level of 2.98 volts. Here's my circuit file:

TESTBED for LM7171
V1 1 0 15
V2 0 2 15
R1 4 3 1MEG
R2 0 3 10K
X_U2 0 4 1 2 3 LM7171
.LIB LM7171.lib
I1 4 0 SINE(0 1u 300K 0 0 0)
.TRAN 10n 30u 20u 1n

Hi Earl, 

Thank you very much for your help! I appreciate your support. 

In my breadboard circuit I finally see a signal when I add a resistor in parallel with my current source - thank you for the suggestion! I will try the LT1222 op-amp as well and see if it operates better under these conditions. 

Thanks again, 

Sally