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

user4669656
Prodigy 40 points
Part Number: ADC3663

Hello,

   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?

Regards

  • 0
    TI__Expert 8951 points

    Hello,

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

    Regards, Amy

  • 0 in reply to Amy
    TI__Expert 8951 points

    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

  • 0 in reply to Amy
    Prodigy 40 points

    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:

    0x07=0x4B

    0x13=0x01

    delay(1ms)

    0x13=0x0

    0xE=0x8c

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

    0x19=0x10

    0x1B=0x88

    0x24=0x06

    0x25=0x18

    Finally output 40M clk to mclk.

    Regards.

     

  • 0 in reply to user4669656
    TI__Expert 8951 points

    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

    ADC3663_config.txt 
    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