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ADC12D1600RF: 1200 MHz Spur

William Rick
Prodigy 50 points
Part Number: ADC12D1600RF

Hello,

I'm working on debugging a spur which is located right in the center of the passband(At the typical location of the interleaving spur). 

This is strange as we are running only one channel of the ADC in non-DES mode. 

This spur is quite high(~ 20dB above the noise floor), and the level will vary from power up to power up. 

We are running the ADC at 1600MHz, using only the Q Channel. Our RF signal is then centered at 1200 MHz. 

I do not see any spurs at 1200 MHz when I probe the input pins, so I believe this is generated inside the ADC. 

Any ideas where this could be coming from?

Thank You,

Will 

  • 0
    TI__Mastermind 18095 points

    Will:

    Let me see if I understand correctly.  You are injecting 1200 MHz RF tone.  The sampling rate is 1600 MHz in non-interleaved mode.  A signal at 1200 MHz is squarely in the middle of the second Nyquist zone.  I would expect your input signal to show up right in the middle of the band in that situation.

    Perhaps you are not injecting any RF signal and still seeing the spur in the middle.  That would be strange.  Perhaps the device is inadvertently still in DES mode.  Check to see if Q channel outputs a signal with an input at something other that 1200 MHz and check to see if the I channel is working properly.

    --RJH

  • 0 in reply to RJ Hopper
    Prodigy 50 points

    Hi RJH,

    The problem is that we are seeing a spur at 1200 MHz, independent of any RF input to the ADC. 

    When a signal is added, it appears at the expected frequency and is not distorted. (The 1200 MHz spur is always there though.)

    Here is a register dump of the ADC after configuration. I believe it confirms the I channel is powered down, and the device is operating in non-DES. Did I miss anything? 

    Register x0: x0810

    Register x1: x2907

    Register x2: x0000

    Register x3: x4000

    Register x4: xdb4b

    Register x5: xffff

    Register x6: x1c2e

    Register x7: x8142

    Register x8: x0f0f

    Register x9: x0000

    Register xa: x1026

    Register xb: x4000

    Register xc: x0004

    Register xd: x0000

    Register xe: x0001

    Register xf: x001d

    Thank You!

    Will

  • 0 in reply to William Rick
    TI__Mastermind 38790 points

    Hi Will,

    Here are all the registers that need to be written to when in non-DES mode. Other registers may apply to other functions and featured used on the ADC.

    Regards,

    Rob

    ADC12D1620
    0x0 0x2000  // Default value Register 0h Configuration Reg 1
    0x1 0x2907  // Default value Register 1h Reserved
    0x2 0x0000 // Default value Register 2h I-ch Offset
    0x3 0x4000  // Default value Register 3h I-ch FSR
    0x4 0xDB4B  // Default value Register 4h Calibration Adjust
    // Register 0x5 is readback for Calibration Values has no default value
    0x6 0x1C2E  // Default value Register 6h Reserved
    0x7 0x8142  // Default value Register 7h DES Timing Adjust
    0x8 0x0F0F  // Default value Register 8h Reserved
    0x9 0x0000  // Default value Register 9h Reserved
    0xA 0x0000  // Default value Register Ah Q-ch Offset
    0xB 0x4000  // Default value Register Bh Q-ch FSR
    0xC 0x0004  // Default value Register Ch Aperture Delay Coarse Adjust
    0xD 0x0000  // Default value Register Dh Aperture Delay Fine Adjust
    0xE 0x0003  // Default value Register Eh Autosync
    0xF 0x001D  // Default value Register Fh Reserved
    0x0 0x6000  // Change DPS DDR Phase Setting from 0 to 1
    0x0 0xE000  // Change CAL from 0 to 1 to initiate calibration