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ADC3663: The baseline changes after DLL PDN is turned on or when MCLK is switched

Part Number: ADC3663


   I have two questions that contribute to the same phenomenon.

1.The manual states that turning on DLL PDN when Fs is less than 40M can improve the SNR, but when I turn it on, the baseline of data collection will change every time I restart it, and the change range is several mv or even tens of mv. This phenomenon does not occur when the DLL PDN is not enabled.

2.Another problem is when I change the sample rate by changing the mclk frequency, the baseline also changes, which doesn't happen when the mclk frequency doesn't change.

  What are the possible causes of the above problems?


  • Hello,

    I am checking on this and will get back with you soon.

    Regards, Amy

  • Hello,

    I tested a ADC3663EVM in the lab to confirm that setting the DLL PDN would improve the SNR for sampling rates less than 40 MSPS. I immediately saw around 0.5 dB improvement in SNR when setting register 0x11 to 0x04. 

    If you share more details of your setup and data captures, this would help identify the issue you are seeing.

    Regards, AmyADC3663-SNR_improvement.pdf

  • Hello,

    Does the data baseline change after each data sampling restart? My phenomenon is that the baseline has changed.

    At a sampling rate of 20MSPS, my register setup steps and values are as follows:






    0x11=0x1(0x5 when DLL PDN enable)





    Finally output 40M clk to mclk.



  • Hello,

    I set the ADC3663EVM back up in the lab and saw no change to the baseline data after restarting the board. The document I posted above was the data I saw consistently with around 0.5 dB improvement in SNR when setting register 0x11 to 0x04. 

    Are you using a front-end amplifier? I noticed that you are setting register 0x11 to 0x05 (instead of 0x04) for the DLL PDN enable. This would also enable the auto-zero feature, which would only be relevant for a front-end amplifier configuration. Try setting this register to 0x04.

    I also included below the configuration file of register writes that I used, which you can compare with your configuration. If you continue to have issues please provide more details of your data captures.

    Regards, Amy

    0x7	0x0
    0x8	0x0
    0x9	0x0
    0xd	0x0
    0xe	0x0
    0x11	0x4
    0x13	0x0
    0x14	0x0
    0x15	0x0
    0x16	0x0
    0x19	0x10
    0x1a	0x0
    0x1b	0x0
    0x1e	0x0
    0x20	0x0
    0x21	0xf0
    0x22	0xf
    0x24	0x0
    0x25	0x0
    0x26	0x22
    0x27	0x0
    0x2a	0x0
    0x2b	0x0
    0x2c	0x0
    0x2d	0x0
    0x2e	0x0
    0x31	0x0
    0x32	0x0
    0x33	0x0
    0x34	0x0
    // Bit Mapping Registers 0x39 to 0x88. For future development.
    0x39	0x46
    0x3a	0x4c
    0x3b	0x4e
    0x3c	0x54
    0x3d	0x56
    0x3e	0x5c
    0x3f	0x5e
    0x40	0x64
    0x41	0x66
    0x42	0x6c
    0x43	0x6
    0x44	0xc
    0x45	0xe
    0x46	0x14
    0x47	0x16
    0x48	0x1c
    0x49	0x1e
    0x4a	0x24
    0x4b	0x26
    0x4c	0x2c
    0x4d	0x47
    0x4e	0x4d
    0x4f	0x4f
    0x50	0x55
    0x51	0x57
    0x52	0x5d
    0x53	0x5f
    0x54	0x65
    0x55	0x67
    0x56	0x6d
    0x57	0x7
    0x58	0xd
    0x59	0xf
    0x5a	0x15
    0x5b	0x17
    0x5c	0x1d
    0x5d	0x1f
    0x5e	0x25
    0x5f	0x27
    0x60	0x2d
    0x61	0x42
    0x62	0x48
    0x63	0x4a
    0x64	0x50
    0x65	0x52
    0x66	0x58
    0x67	0x5a
    0x68	0x60
    0x69	0x62
    0x6a	0x68
    0x6b	0x2
    0x6c	0x8
    0x6d	0xa
    0x6e	0x10
    0x6f	0x12
    0x70	0x18
    0x71	0x1a
    0x72	0x20
    0x73	0x22
    0x74	0x28
    0x75	0x43
    0x76	0x49
    0x77	0x4b
    0x78	0x51
    0x79	0x53
    0x7a	0x59
    0x7b	0x5b
    0x7c	0x61
    0x7d	0x63
    0x7e	0x69
    0x7f	0x3
    0x80	0x9
    0x81	0xb
    0x82	0x11
    0x83	0x13
    0x84	0x19
    0x85	0x1b
    0x86	0x21
    0x87	0x23
    0x88	0x29
    0x8f	0x0
    0x92	0x0