I'm building an light communication device(pretty much lifi) using AM and am mostly done with every part except for demodulating the signal. The signal looks like with a 1.8432MHz carrier wave(serial communication at 115200Hz). The receiver consists of a photodiode, amplifiers, filters, and it requires an envelope detector or a circuit that outputs high when theres a AC signal present.
I've tried using a
- A full and half bridge rectifier(with capacitor)
A lot of signal is suppressed with this can capacitor just shunts everything to ground.
- Envelope detector (https://en.wikipedia.org/wiki/Envelope_detector#/media/File:Simple_envelope_detector.svg, basically peak detector):
It produces a lot of voltage spikes from capacitor discharging and does not really produce any recognizable demodulated wave
- A diode and transistor
Transistor has quite a high breakdown voltage at 0.7V and the capacitor's response time is way too fast
- A diode and capacitor
This circuit works for low signal frequencies but fails at higher signal frequencies
I'm also considering using a slow op-amp with response time faster than signal but slower than carrier wave, would it be reasonable? If so how should I build the circuit. Will there be any better options?
I have access to basic resistors, capacitors, some transistors and diodes, other components would have to be sourced.