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ADS5404: Interleaving Spur, Auto-correction is nonfunctional

Jordan Kubica
Prodigy 20 points
Part Number: ADS5404

Hi,

I am testing ADS5404 operation on a custom PCB at 500MSPS. I am using a 4MHz test CW signal to drive a single data converter channel.

I have enabled DC correction to remove the spurs at DC and Fs/2 as mentioned on page 23 of the datasheet. I have also enabled auto correction which I understand is supposed to reduce the Fs/2 - Fin spur to around 80dbc, however in my case it is consistently at ~42dbc. I have attached time and frequency domain plots of the ADC data.

I have also run the test with auto correction disabled. The resulting plots are indistinguishable.

I have read back the values of the ADC registers during operation, listed below. Are there any known usage conditions or implementation details which could cause the autocorrection to have no effect?

addr: 0x0 value: 0x8000
addr: 0x1 value: 0x8202
addr: 0x2 value: 0x780
addr: 0x3 value: 0xb18
addr: 0xe value: 0x0
addr: 0xf value: 0x0
addr: 0x1a value: 0xb18
addr: 0x2b value: 0x4b
addr: 0x2c value: 0x0
addr: 0x37 value: 0x0
addr: 0x38 value: 0xffdf
addr: 0x3a value: 0x481b
addr: 0x66 value: 0xfff
addr: 0x67 value: 0xfff

  • 0
    TI__Mastermind 29220 points

    Hi,

    no, I don't know of a reason the autocorrection should be nonfunctional.   Do you have the ability to monitor the current draw to the device?  On the EVM I can see a significant increase in current consumption when the autocorrection is enabled.   If you do not see any change in current consumption then that would be one indication that something is wrong with the configuration.   Are you also asserting a reset pulse to the device after power up so we can know that the SPI register space is starting out with all default values?    I don't know what I am looking at with your FFT plot.    With 500Msps, Nyquist would be 250MHz of course, and with Fin = 4MHz I would expect to see the Fs/2 - Fin spur at 246MHz.   You seem to have something large out there around 120 to 130MHz, but that would not be the interleaving spur. I don't know what that is, but if it is not the interleaving spur then it would not be affected by the interleaving correction. 

    Regards,

    Richard P.

  • 0 in reply to Richard Prentice
    Prodigy 20 points

    Hi Richard, thanks for the response!

    I have double-checked the reset process and measured the power consumption for the board, which increases by about 0.25W when I enable autocorrection. So it looks like the chip is responding to configuration.

    I might be barking up the wrong tree regarding interleaving. I saw another post on this forum which dealt with offset spurs at Fs/4 where I am seeing them, but it looks that was an interleave-by-4 device whereas the ADS5404 is only interleave-by-2. I will look into other possible causes.