Hi everyone. I am implementing the attached transimpedance amplifier circuit and I have a few issues with it that I would like to resolve. When the LED is incident on the photodiode, the output of the circuit follows the input frequency of the LED. When I remove the LED, the output shows pulses at a frequency of about 2k Hz, and it remains 2k everytime I remove the LED. I am unsure what is causing this, my guess is that it has something to do with the dc-coupling capacitor circuit. This makes it difficult to distinguish when the LED is on or off. I would expect that when there is no light on the PD there should be no current flowing so the output should remain at some constant DC value, not any type of frequency.
In addition, when the frequency of the LED falls below 1 kHz, the output becomes noisy (shakes on the oscilloscope) and remains at a frequency of about 1.3k Hz, and hence does not follow the frequency of the LED. It seems the circuit does not work at low frequencies. Could it be that the dc blocking capacitor is blocking the signal at low frequencies because at these low frequencies the signal approaches DC? Any suggestions on how to alleviate these issues would be great. Thanks!
In addition, when the frequency of the LED falls below 1 kHz, the output becomes noisy (shakes on the oscilloscope) and remains at a frequency of about 1.3k Hz, and hence does not follow the frequency of the LED. It seems the circuit does not work at low frequencies. Could it be that the dc blocking capacitor is blocking the signal at low frequencies because at these low frequencies the signal approaches DC? Any suggestions on how to alleviate these issues would be great. Thanks!
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