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ADC12D1600RF calibration

Dan Bay
Prodigy 120 points

Other Parts Discussed in Thread: ADC12D1600, ADC12D1600RF

I have been using a standard ADC12D1600 with great performance in the DESIQ mode. I am sampling with a 1.2GHz clock and an RF either in the 1st or second nyquist zone. The auto cal feature brings all spurs below -60dBm 100% of the time and typically less than -70. I populated a second board with the ADC12D1600RF part expecting to see the same or better performance especially above 2GHz RF input.

What I have found is that the noise is less, the spur level is generally higher, but still around -60dBm. The image around the FS/2 is -58 to -60 after cal in the normal DESIQ mode, but climbs to -30dBm to -50dBm when I go to the DESCLKIQ mode. The high frequency response is 3-4dB better above 2GHz, but the image is horrible. I have tried adjusting the DES timing adjust and I have found that a value of 0 for DTA is best, but that only gets me to around -50dBm.

Is this poor performance expected of this new part or is there something else that can be done?

I have also adjusted the FSR with hardly any change.

Thanks,

Dan

  • 0
    TI__Mastermind 44680 points

    Hi Dan

    Sorry for the delay in a response to this question.

    As you have found, the interleaving spur is significantly higher in DESCLKIQ mode than in DESIQ mode. This is because the I and Q signal paths are internally isolated from each other in the DESCLKIQ mode, but they are internally connected together via the DES Mux in DESIQ mode. This results in better I to Q signal matching in DESIQ mode, and worse matching in DESCLKIQ mode.

    The higher spurs that you see in DESCLKIQ mode are a known consequence of selecting this mode. We really only included this mode to allow people doing pure time domain data capture to have the highest possible input bandwidth. If better interleaving spur performance is required, DESIQ, DESI or DESQ modes should be used.

    It sounds like you have already tried the adjustments that can provide some improvement in spur performance, so there isn't much else that can be done.

    I hope this is helpful.

    Best regards,

    Jim B