The two stage differential trans impedance amplifier above allows for current to voltage conversion with elimination of common mode noise. While both stages can provide gain, I choose to provide gain in stage 1 and have stage 2 as a differential follower. I wanted to bring the output voltage to about 500 mV. I selected a 20k resistor in the feedback path to provide an estimated output voltage of 1.7 volt. The second stage will act as a differential follower such that the following is observed. I chose R1 = Rf = R2 = Rg = 50k.
To test the operation of the trans impedance stage I performed the following. I drove the CLK1,2 lines on the POX board with +5v square waves from two function generators. I then use micro controller to program DAC3/4. This allowed modification of brightness of LED in probe. I then turned on the probe and observed the output from S1out, S2out, and AmpOut. As I was driving with a square wave I expected to see the same waveform (freq) on scope. I found the amplitude was below my expectations and actually was around 750mV.
The capacitors CTI1, CIT2 are implemented for stability concerns. The challenge is to prevent oscillation from occurring causing overshoot and ringing. I am preparing notes on this with details to our implementation. I will also include in these notes details on elimination of common noise and why differential amplifier is preferred selection.
I'm starting to look into software and have found some good links on DC removal for DC subtraction. Today I played with implementation in MATLAB. A 1D IIR filter can be implemented easily in MATLAB. Once we have good result in this respect we can transition development to LABVIEW environment.
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