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Original question:

ADS42LB69: Request for ADS42LB69 design review

ADS42LB69: ADS42LB69 Voltage at inputs of ADC

ranjini r
Prodigy 150 points
Part Number: ADS42LB69

The input given is 19dBm 50 ohm RF single ended signal. Can u please have a look at the input circuit and tell what will be the voltage swing at the input of ADC?ADS_Front_end .pdf

  • 0
    TI__Guru* 91947 points

    Ranjini,

    The swing will be around 12.5dBm (-6dBm from resistors and some loss from the transformers depending on the frequency) if the input is less than 20MHz. With a higher input frequency, it will start dropping off due to the low pass filter and the response of the transformer. This can be seen be the attached TINA simulation and the transformer data sheet.

    Regards,

    Jim

  • 0 in reply to jim s
    Prodigy 150 points

    Hi,

    I would like to know if the input given is 21dBm, 50 ohm, 70MHz single ended signal for the same circuit, what would be the voltage swing at the input of ADC?

    And also the maximum swing allowed at the input pin of ADC.

    Regards,

    Ranjini

  • 0 in reply to ranjini r
    TI__Genius 12780 points

    Hi Ranjini,

    For a 70 MHz sinewave, the signal swing at the ADC input (right side of circuit) would be about 1/2 of the input (left side of circuit).

    The nominal ADC input is 2 Vpp differential, so for this configuration, you would need to reduce the input power or provide more attenuation.

    Best Regards,

    Dan