ADC3424: Analogue Input Insertion Loss

Corrin MacKenzie

Part Number: ADC3424

Hi guys,

I'm designing a 4 channel amplifier with ADC circuit using the ADC3424 and in the datasheet it recommends an input circuit that it says should be designed to minimise insertion loss. Would it be sensible to change the values of the two resistors connected to VCM (circled in red)? And what is the maximum these should be?

over 4 years ago

0 dBrock over 4 years ago

TI__Genius 12780 points

Hi Corrin,

These resistors provide 50 ohm (differential) termination for most typical test equipment (signal generator, AWG, etc...). If your source driver has a different source impedance, then these resistors can be changed accordingly.

For example, if you are using a low impedance driver (like an op amp), then these resistors can be changed to a higher value (maybe 100 ohms to 1k ohms?), so that most of the voltage input will not be attenuated.

Best Regards,

Dan

0 Corrin MacKenzie over 4 years ago in reply to dBrock

Prodigy 20 points

Hi Dan,

Thanks, I'm using a variable gain amplifier for my input which does have an op-amp as it's output stage so I have increased these resistors and the insertion loss has definitely reduced. But does this mean I should also re-design my anti-alias filter to match the low impedance input?

Kind regards

Corrin

0 dBrock over 4 years ago in reply to Corrin MacKenzie

TI__Genius 12780 points

Hi Corrin,

Yes, you may need to change some component values since the data sheet only covers the 50 ohm input impedance case.

Best Regards,

Dan

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ADC3424: Analogue Input Insertion Loss