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PCM1792A

Ali Burak Parım
Prodigy 50 points
Other Parts Discussed in Thread: PCM1792A, PCM1792

Hi,


I am working a project on my internship and I am stuck! Please let me explain.

I am using a PCM1792a on my PC board and I am trying to test the DACs outputs with a sine wave on 1kHz. I mainly sending the sine wave with I2S and controlling the DAC with I2C with STM32f4 Discovery eval board.

I use 24-bit as bit rate and 90kHz as Fs. Stm32f4 is generating a master clock for i2s and its freq is 256fs as default. I did not change the DACs registers, it works as default. Actually, I don't get "playing with register" concept, unfortunately. Although, I am using a main file for generate sine wave with look-up table and importing a codec file actually written for CS43L22 DAC(is on the discovery board), PCM1792A looks like working properly( exept that triangular wave). There are some register definitions and I2C functions of stm32f4 in the codec file.I can see an output on both channels' - and + outputs but not a exact sine wave ( half - wave rectified sine). And the difference of - and + outputs looks like a triangular wave more than a sine.

Any idea why I faced this problem?

My first suspicion is that codec file. Because it is not for PCM1792a and register mapping is different. However, if the problem is that, how I can see half sine waves on the same frequency that I sending from stm32f4? May be I should create or find a codec file for pcm1792 but I am not sure wheather it is necessary. I am not an experienced engineer on field as a bechalor student and I am not good on assuming on codes. I would be appreciated any command.


Many thanks in advance!


Regards,

Burak

  • 0
    TI__Guru 55826 points

    Why do you observe a triangular wave, if the outputs produce a half-sine wave? It looks like there's a measurement setup problem if the sine-waves transform into an observed triangular wave.

    I'm not familiar with the CS43L22 but I'd assume that it's neither register nor address compatible so the register writes that happen in your system are ignored at best or (if it's SPI or by any chance the I2C addresses match (unlikely)) wreak havoc in the DAC setup at worst.

  • 0 in reply to Dominik Hartl11
    Prodigy 50 points

    Sorry for late reply due to weekend.

    "Why do you observe a triangular wave, if the outputs produce a half-sine wave?" That is exactly what I want to know.

    I wanna test again and capture some screen to make my situation more clear for you.

    Here it is. First screen shows the DACs 1st channels + and - outputs as 1 and 2 and "math" wave is dirrefence of them. 2nd one shows the same thing in narrower time domain. And last screen capture shows the DACs output that on the stm32f4 eval board as wave 1 (yellow) and my DACs 1st cahannels + or - output as wave 2 (blue). As you can see all signals are in same frequency. Waveforms of PCM1792As - and + look like half wave rectified sine wave. The difference of them looks like a sharp ended sine or a triangular. It close that I expect but may be little bit sharper than that. Is it more clear or totaly useless?


    If this is normal, I'll continue the progress and solder my filter/gain stage op-amp, ADA4937-2. Then, I can measure that stages outputs. I just wanna be sure there is nothing wrong on DACs outputs.

    My mentor is a busy man and he has not enough time. that is the reason I am asking to you. Sorry for keeping busy you!