VCA810: VCA810

Hi, 

The VCA810 has a max gain of 40dB (100 V/V) when the VC pin is set at -2V. Since you only need 900 V/V and can get 100V/V from the VCA810, I would actually suggest you just follow the first stage with a gain of 9 V/V amplifier instead of using a second VCA. Then you will only need one control voltage signal for the gain and you will get a gain range of 9 V/V to 900 V/V. 

Regards, 

Thanks for the reply Jacob,

My first TIA (transimpedance amplifier) stage has a gain of around ~1000A/V after this, I want a gain of ~900V/V.

So I planned for this design if it is not correct please correct me.

Ravikumar

Hi Ravikumar, 

My concern on your design would be the input SNR. What is the final output voltage swing you are trying to achieve from your signal chain. 

Regards, 

Thanks for the reply Jacob,

The output signal will be in mV's.

I am using Lock-In amplifier for measurements/detection of the signal.

If I use 2 VCA's for dynamic range/control of gain is there any issue?

I have already designed this amplifier for fixed voltage gain as shown in figure.1, and now I want to modify to figure. 2 (2 stages varible voltage gain)

Presentation1.tif

Thanks 

Ravikumar 

Hi Ravikumar, 

If your fixed gain circuits are working, then I believe you should be okay with the VCA stages. You could see up to a few mV of output noise if you are doing no filtering on your signal at max gain, but you can always add some bandpass or lowpass filters to help reduce the noise. 

Regards,