PGA970: Waveform Generation

Hi Thevindra Anand,

Thevindra Anand said:

1. Previously I inquired on the dependency of the modulator clock on waveform. Have you discovered anything on the dependency?

Cole was not able to find additional detail.  There may be something that is happening in the GUI that takes place to complete the turn on process of the waveform generator.  You could check the individual settings by following the steps in the datasheet in section 7.5.6.

Thevindra Anand said:

2. In the firmware code, SPI programming code was not provided. Will I be able to attain them?

The SPI communication is fixed within the processor.  The specifics of writing to the SPI will depend on the hardware you are using. The datasheet gives examples of the SPI transaction as well as the timing.

Thevindra Anand said:

3. In the pga970_waveform.c file, the waveform testing was provided for 5kHz, 10kHz, 15kHz and 20kHz. May I know what are the 16-bit values of the waveformTable and the formula in constructing the table size and waveform table value other than the provided frequency of waveform testing?

There is information in the datasheet, but there is a clue when reviewing the data in the pga970_waveform.c file.  Note that the table length for 5kHz is 50, and 25 for 10kHz and 12 for 20kHz.  So the table length will depend on the fixed update rate of the DAC (1MHz or 1us period).  The table values are 1/4 waveform LUT (see section 7.5.6): 

For example, to generate a sine wave of amplitude amp and frequency freq, calculate waveform table values using the formula: amp × sin(2πfreq × (0.5 μs + n1
μs)), n = 0..N. N is the number of 1-μs samples in a quarter-sine wave.

Keep in mind that the DAC is 14-bit and not 16.

Best regards,

Bob B