LMH32404-Q1: AC coupled input

David Wende

Part Number: LMH32404-Q1
Other Parts Discussed in Thread: LMH32404

Hi all,

We have an application where the LMH32404 input channels will be driven by balanced detectors.

The detectors will have some non-negligible DC output current, therefore we are thinking of AC coupling the detectors to the LMH32404.

The signal bandwidth is from 200kHz up to 50MHz.

Is there any inherent problem in this approach?

Thanks

David

over 1 year ago

0 Sam Burnett over 1 year ago

TI__Expert 3620 points

Hi David,

It shouldn't be an issue, but have you considered taking advantage of the ambient light cancellation feature?

Best,

Sam

+1 David Wende over 1 year ago in reply to Sam Burnett

Intellectual 620 points

Hi Sam,

Thanks for replying, however as I said we will be using a balanced detector, it will sourcing and sinking current.

The TIA datasheet states that ALC only works when PD is sinking.

In addition, I slightly mis-stated the problem.

In fact, our wanted signal is relatively very small in amplitude and frequency from around 1 MHz upwards but it is riding on an unwanted very large signal of around 200 kHz.

This unwanted signal at 200kHz is the "DC" that I want to block (at least partially) from the TIA input.

Thanks

+1 Sam Burnett over 1 year ago in reply to David Wende

TI__Expert 3620 points

Hi David,

AC coupling with external bias should be fine then, just sounds like you may have to experiment with the capacitor value to get the right amount of filtering. If you want a more rigorous analysis I'll need the photodiode capacitance spec.

Best,

Sam

0 David Wende over 1 year ago in reply to Sam Burnett

Intellectual 620 points

Thanks Sam,

David

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LMH32404-Q1: AC coupled input