Hi all,
I need to feed an ADC with a 0-5V signal and the circuit I'm using, a photodiode transimpedance circuit with a feedback loop to reject ambient light (see schematic attached) produces an AC signal.
I'm only using a small uprocessor to record the ADC stream so I can't do a whole lot of digital post processing on the signal, apart from a bit of averaging. The photodiode measures scattered light from a LED modulated at 1kHz, which at times can can be very small (photocurrents of the order of 100s of nA). I therefore need a output stage on the output of this circuit that will condition the signal (linearly) over a large range of voltages.
I've read a little bit on half-wave rectifiers but it sounds like they run into problems for small signals, and the linearity drops out. Is a peak detector a possible solution? Are there other options I'm not considering? The device (which is portable) takes measurements periodically (say every 10 or so minutes), so I can ideally run a single measurement over a relative long timescale to get the best result.
Any suggestions welcome! Thanks in advance....
I need to feed an ADC with a 0-5V signal and the circuit I'm using, a photodiode transimpedance circuit with a feedback loop to reject ambient light (see schematic attached) produces an AC signal.
I'm only using a small uprocessor to record the ADC stream so I can't do a whole lot of digital post processing on the signal, apart from a bit of averaging. The photodiode measures scattered light from a LED modulated at 1kHz, which at times can can be very small (photocurrents of the order of 100s of nA). I therefore need a output stage on the output of this circuit that will condition the signal (linearly) over a large range of voltages.
I've read a little bit on half-wave rectifiers but it sounds like they run into problems for small signals, and the linearity drops out. Is a peak detector a possible solution? Are there other options I'm not considering? The device (which is portable) takes measurements periodically (say every 10 or so minutes), so I can ideally run a single measurement over a relative long timescale to get the best result.
Any suggestions welcome! Thanks in advance....
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