ADL5202 abnormal peak at output

Hello,

 

Issue:
When changing the amplitude
of input signal to certain value from zero, abnormal peak of a few period is observed at the beginning of output amplitude changing to certain value from zero.

Condition:

Gain is set by Parallel I/F transparent mode.

Gain is fixed to max.

Input signal is 128MHz sine wave.

Output level is 0dBm in 150 ohm.

Measured by FET probe contacting at 150 ohm termination (>>See the attachment please).

Application circuit:

Similar to Figure 55. Wideband ADC Interfacing Example Featuring One-Half of the ADL5202 and the AD9268 which is described in datasheet.

Request:

1. Could you please tell me the ways to solve this issue?

2. Could you please provide the transmission function of the internal ac-coupled feedback path? The feedback path is described in p.18 of datasheet. Would like to examine if excess compensation causes this issue.

 

Best Regards,

ADL5202abnormalpeakatoutput.xlsx
  • Hi, Katsu,

        The pulse response measured is the combined result of three contributors:

    1. The amplifier's frequency response, especially peaking, which was not observed (datasheet fig. 9 & fig. 39);

    2. High pass filter response from ac coupling circuit (pull-up inductor and dc block cap); and

    3. Pulse response of the test probe (seems to be flat base on the input waveform).

        I would think it is created by the high pass circuit.  You can try changing the DC  block cap and pull-up inductor values to see if the peaking can be adjusted.

    Benjamin

  • Hi Benjamin,

    Thanks for the suggestion. Do you have recommendation to pull-up inductor and dc block cap values? Which is better way to start with, reducing inductor?

    Does the internal ac-coupled feedback path have nothing to do with the pulse response?

    Best Regards,
    katsu

  • Hi, Katsu,   I understand you are using this circuit below:

    The designer and I would like to get some clarifications:

    -- Are you using the circuit with the component values as shown,

    -- Are you using the 1:3 transformer to interface to a Sig Gen, if so, what is the model number?

    -- What is the physical distance between the transformer, ADL5202, Filter, and AD9268, and if they were connected with microsrrips (we were wondering if the peaking could be caused by transmission line reflections);

        Thanks!

    Benjamin

  • Hi Benjamin,

    Give me a moment to confirm the items you requested.

    Best Regards,
    katsu

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