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ADS5296A: Driving the Input stage

David Wende
Intellectual 630 points
Part Number: ADS5296A
Other Parts Discussed in Thread: VCA2615

Hello TI.

Two questions:

Firstly:

I noticed that the EVM for this device uses back-back transformers at the input stage.

This idea is not mentioned in the data sheet.

Please tell me why the EVM uses this method. What are the benefits?

Secondly:

I would like to drive this ADC from a variable gain stage that can accept a single ended input.

Frequency response from 200kHz up to 100MHz with maximum gain about 30 V/V.

I can set this variable gain manually (don't need AGC).

What would be your recommendation?

Thank you

  • 0
    TI__Intellectual 1590 points

    Hi David,

    Apologies for delayed response. I hope you are doing well. Please find my responses for your queries below-

    First Question-

    On EVM we use transformers to convert single ended inputs (coming from external rf signal sources) to differential output signals. Since main purpose of the EVM is to demonstrate ADC performance, we use this simple passive circuits to convert the input signals to differential. But this approach doesn't add any advantage in terms of noise and signal gain. 

    Second Question-

    I see one part, VCA2615, close to your requirement. 

    VCA2615 data sheet, product information and support | TI.com

    Could you give more detail like, do you wish to have gain stage+ anti-alias filter in a single chip, how many channels do you intend to have, min and max range of the gain you wish to have ?

    Regards,

    Kalyan

  • 0 in reply to Bellala Kalyan
    Intellectual 630 points

    Hi Kalyan,

    My design is closed, but thanks for your answer.

    My question though was not "why you use transformer on EVB", but rather, why are you using back-to-back transformers.

    Thanks