I am working on designing a circuit that subtracts two DC outputs from the photodiode ends with series resistors. For this, I am planning to use the basic differential amplifier connected to the photodiode pair as shown in the figure below. I have few questions on how to arrive at the specs for the DA design.
First the ICMR: In the DA design, ICMR limits are decided by the M9, and (M1/M2) mosfets' saturation. But how do I know if this is the adequate ICMR for the circuit? Does the definition related to the photodiode output voltages?
The output capacitance: I am clueless about the output capacitor and its value. Since I need to measure the difference between the DC voltages (xgain) at the output, I think this capacitor should be able to store the DC charge like a bank.
Since, we're looking for DC frequencies, Is there any effect on the measurement by the capacitance? If I am using a DC probe at the output, what value of capacitance is best?
-Rakesh.
I recommend using Micro-Cap (http://www.spectrum-soft.com/download/download.shtm). All EE's at Emerson used Micro-cap, even though it cost $4,000 each. There are no other electronic SPICE modeling programs even close to Micro-Cap capability.
Micro-Cap is now free. Andy Thompson, owner of Spectrum Software, has retired.
Micro-Cap does worst case analysis --- changing the tolerances of components --- changing the temperature --- etc. And it is easy to use.
I have used Micro-Cap for all of my electronic designs since 2001. When I tested prototypes, they worked exactly as the model predicted.
The website --- https://NDAcademy.FoxPing.com/ --- 2.8 Electronic Cascade RC Filters --- and --- 7.2 Electronic SPICE Models --- provide examples.
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