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PCM5122EVM-U DAC produces tones in the pass-band.

John Lindsay
Prodigy 20 points
Other Parts Discussed in Thread: PCM5122, SRC4392

Hi

I am testing a PCM5122 using the Evaluation board and feeding 192kHz SPDIF audio into the Coax input and monitoring the Output on a Prism Sound Dscope Audio analyser.

The SRC on the Evaluation board is configured to recover clock and data from the SPDIF and output 4 wire I2S data at 192kHz to the DAC which is running in Hardware mode.

With a 1kHz tone @ -2dBFS the THD is around -84dB.

When I increase the frequency of the input sine wave the tones in the pass-band increase in magnitude which effects the THD by around 25dB.

If I run the DAC in Software mode are there any registers or settings which could improve this behaviour?

Or is there anything obvious I am doing wrong!

Many Thanks

John

  • 0
    TI__Mastermind 27990 points
    Hi John,

    What are your jumper settings on the EVM? Are you using scripts or the GUI to configure the SRC4392? At what frequency is the THD being increased by 25 dB?

    Justin
  • 0
    Prodigy 20 points

    Hi

    The board is jumpered and a script is run to recover the clocks from the SPDIF input and feed this to the SCK input of the PCM5122 along with BCK, LRCK and DATA.

    SW3 is set HHL for 24.576 crystal

    W5 is 2-3 to route RXCLK to SCK.

    SCLK, BCK, DIN and LRCK are jumpered along with XSMT.

    The following script is run to setup the SRC

    # Scrtipt for PCM5122 EVM - SP/DIF in (RCA) - Analogue out

    # RESET RESET THIS IS MASTER RESET FOR SRC

    # Page 0 = DEFAULT for Control

    # Write to page 0

    w E0 7F 00

    # Register 01, Bit 7 = 1 resets to default

    d 100

    w E0 01 80

    # Delay 0.1 sec to allow part to reset

    d 100

    # Register 01, Bit 7 = 0 for normal operation

    w E0 01 00

    d 100

    #----- GPO1 Rx INternal Sync clk ----#

    w E0 1B 0E

    #----- Setup Port A ------#

    # 24bit I2S, Master mode, DIR source, at mute

    w E0 03 69

    # Use RxCko as Port A Master clock

    # w E0 04 0B # for SP/DIF @ 48k or below

    # w E0 04 09 # for SP/DIF @ 96kHz

    w E0 04 08 # for SP/DIF @ 192kHz

    #----- Setup DIR ------#

    #DIR Config 1

    # Input source: RX2 - S/PDIF RCA (default)

    w E0 0D 09

    #DIR Config 2 - Enable RxCko

    w E0 0E 11

    #----- PLL Configuration -----#

    # Set P=2, J=8, D=0

    w E0 0F 22

    w E0 10 1B

    w E0 11 A3

     

    # Unmute Port A Output

    w E0 03 29 # disable mute, ensure i2s format

    # Disable All Function power down (all blocks set by local control)

    w E0 01 3F

    The THD at 1kHz is around -84dB, at 1kHz but has dropped to -68dB at 70kHz. at all frequencies I see spikes in the passband that look to be some form of alias or harmonic.

    e.g. at 70k there is a spike at ~34k

    at 10kHz there are spikes at 20k and 30k

    Regards

    John

  • 0 in reply to John Lindsay
    TI__Mastermind 27990 points
    Hi John,

    Could you try the high attenuation filter setting for the DSP prgram, in register 43 its:

    00011: High attenuation x8/x4/x2 interpolation filter with de-emphasis

    Test what effect this has on the performance. Since the part hcan have a range of operating frequencies and many different output filters, the performance at high frequency will change depending on settings both within the part and the passives chosen outside the part.

    Justin