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AC photodiode amplifier design question - synchronous demodulation

Question asked by PeterT on Sep 11, 2015
Latest reply on Sep 29, 2015 by PeterT

Hello,

 

I asking advice on the following issue.

 

I need to design a photodiode amplifier with the following characteristics:

 

- photovoltaic mode

- AC signal with with few kHz

- very low noise

- high gain required

- photodiode properies: capacitace ~ 2000 pF , Rs=3000 MOhm

- amplifier output to be fed to ADA2200 Synchronous Demodulator -> AD779x ADC

- eventually DC servo to compensate offset due to ambient light

 

 

As this thread points out the opamp input bias current for AC applications only results in a DC offset.

 

https://ez.analog.com/message/122455#122455

 

 

- Is my interpretation correct that as long as the induced offset is not too large I can choose a low voltage noise opamp with an appropriate bandwith ?

 

- Is there a better way to deal with the DC component of the signal ( due to ambient light ) than using a DC servo circuit as it might introduce a lot of noise ?

 

- What opamps would be suitable for this kind of application ?

 

 

 

Any advice is highly appreciated!

 

Thanks!

Peter

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