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PGA460: Calculating BPF coefficients for FREQ_SHIFT=1 mode

Andras Gajdacs
Prodigy 45 points
Part Number: PGA460

Hello,

We are planning on using PGA460 in conjuction with a 320 kHz closed type transducer. This implies that FREQ_SHIFT has to be set to 1, but in this case BPF coefficients need to be set manually.

In order to calculate those coefficients the datasheet should have provided at least:

1) internal sampling rate at which the BPF operate

2) target gain (since the coefficients are 16 bit signed integers, right?)

Please provide these parameters.

Thank you,

Andras

  • 0
    TI__Mastermind 27950 points
    Hi Andras,

    You are correct, the DSP's BPF coefficients are not automatically calculated and written to the BPF_A2_xSB, BPF_A3_xSB, and BPF_B1_xSB registers when FREQ_SHIFT=1 for the high-freq range. We have provided a look-up table and coefficient calculator in the PGA460-Q1 EVM GUI ( www.ti.com/.../slac739 ). You do not need the EVM to use these specific GUI tools, though I do recommend that you use the EVM-GUI to evaluate and optimize your 320kHz. The GUI has been programmed to automatically update the coefficients when FREQ_SHIFT=1, so you do not need to manually do so during initial eval.

    In response to manually calculate these values:
    1) The sample rate of the DSP is the same as the 12-bit ADC of 1MSPS (1us).
    2) Yes, the coefficients are signed 16 bit integers. The coefficients are calculated based on the burst frequency (FREQ parameter) and Band-Pass bandwidth (BPF_BW parameter). Additional details cannot be shared due to the proprietary nature of this integrated DSP.

    The coefficients are nearly ideally linear, but this does not hold true on the PGA460 - especially at the minimum and maximum ends. Thus, I recommend using the GUI's look-up table of values, which are based on a 3rd order polynomial trend, as these have been spot checked with real transducers for better recommended starting values at the high-freq range.