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We've built this transimpedance amplifier circuit to receive 10kHz pulses from a laser. The laser is driven by a square wave signal generator and is pulsing correctly. We expected to see a square wave at the output (yellow plot on the oscilloscope), the green is the voltage at the inverting input of the opamp. Why are we seeing these strange spikes at the beginning and end of each period? Our goal is to push the frequency to 1MHz, but we see this strange behavior even at the low frequencies. Thanks!

schematic

simulate this circuit – Schematic created using CircuitLab

enter image description here

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    \$\begingroup\$ It is better to use the scope's screen shot capability than take a photo, and if you do take a photo keep it straight. \$\endgroup\$
    – Kevin White
    Feb 23, 2022 at 2:13
  • \$\begingroup\$ IN- should always equal IN+, i.e. 0V. The spikes on it are where the opamp is slew rate limiting so the output cannot control the voltage at IN-. \$\endgroup\$
    – user16324
    Feb 23, 2022 at 14:53

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The slew rate of an LM358 is around 0.3V/µs, and it only has a typical bandwidth of 700kHz. It takes around 40µs for that opamp to change its output voltage by 12V. Replace it with a more modern and capable opamp.

The jump at switch-on is the reverse current from the 2.2nF capacitor charging up. That capacitor value seems high for this design; I'd go with more like 100pF.

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