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ADC08D1020: Driving the ADC input stage

Antonio Lovascio
Prodigy 30 points
Part Number: ADC08D1020

Hello,

regard ADC08D1020, we are thinking of driving the ADC analog input by using a unique 1:1 50 Ohm balun and split its differential output in two differential lines, one for the ADC input named VinI+/VinI- and other for VinQ+/VinQ-. In other word, the idea is to connect two ADC differential input (VinI+/VinI- and VinQ+/VinQ-) together and driving it with a differential 50 Ohm line, as shown below.

We need to understand if this driving approach is good or there are some warnings which we have to pay attention to.

Many thanks.

Regards,

Antonio L.

  • 0
    TI__Mastermind 43950 points

    Hi Antonio

    That basic approach can probably work, but the tricky part is the signal routing from balun outputs to ADC inputs.

    Can I ask why you want to feed the same signal into both the I and Q channels of the ADC?

    Despite the confusing naming (I and Q inputs), in dual input (non-DES) mode the inputs are sampled simultaneously, not in quadrature, so effectively you just end up with 2 samples of the same signal. The ADC does not have a quadrature sampling capability.

    Best regards,

    Jim B

  • 0 in reply to Jim Brinkhurst1
    Prodigy 30 points

    Hi Jim,

    thank you for reply.

    Regards,

    Antonio L.

  • 0 in reply to Antonio Lovascio
    TI__Mastermind 43950 points

    Hi Antonio

    If you want to minimize the output data rate, you can configure the ADC08D1020 into DES (dual edge sampling) mode. One of the inputs (VINI+/- or VINQ+/-) will be sampled at 2x the input clock rate, and the output data can be 1:4 demuxed from the sample rate. The minimum input clock frequency in this mode is 500 MHz, so the sample rate is 1 GSPS and the output data rate is 250 Mwords on four 8-bit ports.

    In non-DES mode the minimum clock rate is 200 MHz. In this case the VINI and VINQ inputs are each sampled at 200MSPS and the output data rate is 100 Mwords on four 8-bit ports (1:2 demux for I and Q channels).

    I hope this is helpful.

    Best regards,

    Jim B