0
\$\begingroup\$

I have a signal coming from a photodiode detector, the pulse is really short, so the integration time is very small, and the total power measured is very small (very close to the noise of the detector). I want to take the signal detected by photodiode (a short square pulse with variable amplitude) and stretch the duty cycle from about 1% to 50% at the same amplitude of the pulse being stretched (which changes from pulse to pulse).

Normally i would use a monostable 555 timer, but i'm not sure how to get the amplitude issue worked out.

\$\endgroup\$
1
  • \$\begingroup\$ Can you show us an example of the waveform? \$\endgroup\$ Nov 19, 2022 at 17:37

1 Answer 1

0
\$\begingroup\$

One approach - use the trigger pulse to trigger both a monostable and a sample-and-hold (S/H) circuit. The photodiode pulse triggers the S/H to sample its own trigger signal amplitude. This creates a buffered output voltage scaled to equal trigger pulse amplitude. When the monostable circuit times out, use that trailing edge to reset the S/H, driving its output voltage to near 0 V.

Analog Devices (ADI), Linear Technology (LTI, now a part of ADI), and National Semiconductor (now a part of TI) have many S/H parts.

\$\endgroup\$
1
  • \$\begingroup\$ Be aware that choosing a trigger level is difficult: Pulse amplitude is not detectable below this trigger level, so you'd prefer a low trigger level. Some noise may reach the trigger level and be falsely detected, especially if the trigger level is set too low. \$\endgroup\$
    – glen_geek
    Nov 19, 2022 at 14:29

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.