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Photodiode amplifiers for 24 bit ADCs

Question asked by bharris on Mar 3, 2013
Latest reply on Mar 7, 2013 by NeilJ

I would like to interface a photodiode transimpedance amplifier to a 24bit ADC (AD7765, AD776, AD7767 or similar). The largest source of error appears to be the drift of the transimpedance amp (TIA), rather than noise.

We prefer to use a linear amplifier, rather than a logarithmic amplifier. The topology is thus a linear TIA followed by either by a single ended to differential amp stage or by grounding one side of the ADC input if it provides better performance.

Assuming a 40 degree change in temperature, a 0.5uV/degree offset coefficient leads to a 20 uV input.  If both the TIA and the SE to DE stage have a 0.5uV/degree drift coefficient, total drift could be as large as 40uV, which is too big for our application.  For comparison a TIA gain of 5K in a 25kHz bandwidth has less than 2uV RMS noise, using a low noise TIA.

I would very much appreciate recommendations for TIA amplifiers, single-ended to differential amp, and input topology for achieving the lowest possible total error, within a -5 to 65 degree temperature range.

 

System parameters are:

Photocurrent range: 20nA to 1mA

Sampling rate: approximately 30 to 50 kilosamples/sec

Photodiode capacitance: 10pF

Thanks

Bernard Harris

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