• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 30 subscribers
  • Views 117 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

PCM3168A: Clarification on the Sampling Rate

Suhas M V
Prodigy 30 points
Part Number: PCM3168A

Tool/software:

Hi Team,

I am currently working with the PCM3168A audio codec and we are planning to use the PCM3168A codec as a replacement part to the obsolete codec in the existing design. We are looking for the below settings to match the configuration settings of the previous codec to have a consistent performance:
-System clock of 8.192MHz
-Sampling Freq. of 32KHz
-Single rate
-Slave mode operation
-I2C interface
While referring to the datasheet of PCM3168A, I encountered some discrepancies regarding the sampling rate mode (Single vs. Dual Rate Mode) and the appropriate register settings for this configuration.
 
Queries:
1. Register Configuration for 32 kHz Sampling Rate
 Section 9.3.5 (Sampling Mode Description) states that 256xFs corresponds to Dual Rate Mode, but Table 3 (System Clock Frequencies for Common Audio Sampling Rates) lists 256xFs as supported in Single Rate Mode   as well. Could you please clarify whether Single Rate Mode is valid for 256xFs, or if Dual Rate Mode must be used in all cases?
 
2. Automatic vs. Manual Selection of Sampling Rate Mode
 If the PCM3168A is in Auto Mode, will it always default to Dual Rate Mode for 256xFs, or can it operate in Single Rate Mode under certain conditions?
 If manual selection is required, what is the recommended approach to ensure proper operation at 32 kHz?
3. Impact of Selecting Single vs. Dual Rate Mode at 256xFs
 Are there any differences in filter behaviour, oversampling, or performance characteristics when operating at 256xFs in Single vs Dual Rate Mode? If both Single and Dual Rate Modes are technically possible at 256xFs,   what are the specific conditions under which each should be used?
Regards,
Suhas
  • 0
    TI__Genius 12965 points

    Hi Suhas,

    Single rate mode should be valid for 256xFs and 32kHz sampling rate. It seems like dual rate mode is for higher sampling rates to enable lower OSRs. However, with your high system clock and low sampling rate, the device should be fine for single rate mode. It seems that in auto mode, it will automatically select dual rate mode for 256x system clock, but you can select single rate mode with i2c with register 0x40 and SRDA bits shown in table 14 for DAC, and register 0x50 SRAD bits for ADC shown in table 22. 

    Single vs dual rate mode affect the passband of the device with the digital filters, shown in this screenshot of the ADC filters (section 8.15.1):

    Single rate mode puts the device into 128x OSR operation at the ADC/DAC modulator clock, which will ensure that the filters work as intended with the most amount of clock cycles needed for operation. Dual rate mode puts the device into 64x OSR, so the filters and internal DSP systems would have less cycles to work with, but would be potentially less power needed as well. This mode would be better suited for systems where the system clock does not get to 128x the sampling rate, or for sampling rates above 48k. In your scenario, 256x input ratio should be fine for a low sampling rate and is still a higher input clock than 128x OSR so there will be a divider internally to get to 128 OSR at the mod clock.

    Let me know if you have more questions.

    Best,
    Mir