• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 47 subscribers
  • Views 435 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

non-linear gain with OPA1S2385?

Tanya Roussy
Prodigy 10 points
Other Parts Discussed in Thread: OPA1S2385, OPA1S2385EVM

Hello,

I have been working with the OPA1S2385 with quite high gain (100K), with a photodiode as the input, and it seemed to be working well.

For the application I have in mind, I need a speed of ~4Mhz, so with the Gain Bandwidth limit this means the maximum gain for this stage is about 50.  As such, I started playing around with the gain and found the following:

Rf=100k Vout=230mV p-p

Rf=10k Vout=14mV p-p

Rf=1k Vout=7mV p-p

This looks like non-linear gain for me, and is not promising for a gain of 50!

Can you help me with this?  Have you ever seen anything like this?

Thanks!

Tanya

  • 0
    TI__Mastermind 27715 points

    Hello Tanya,

    It seems like you may be attempting to use the OPA1S2385 outside of its capability. If you consider Figure 6 and Figure 7 of the OPA1S2385 data sheet, which show the small-signal frequency response, you can see that even in a gain of ±10 the device is behaving nonlinearly at 4 MHz.

    Furthermore, Are you doing these tests on the OPA1S2385EVM? A PCB with controlled impedance must be used at high frequencies to properly handle the transmission line effects and preserve performance. If you're not using the EVM, I'll need to see your circuit schematic and PCB layout in order to help you properly troubleshoot this issue.

    Best regards,

    Ian Williams
    Linear Applications Engineer
    Precision Analog - Op Amps