DAC unfiltered output

ameer · ‎2015-10-30

Posted on October 30, 2015 at 16:12

Hi every 1.

I am trying to implement the sine wave generator on STM32F3 which is actually working fine but the problem is that the

output waveform is not identical to the real time function generator because its not getting proper reconstruction i think.

If i pass the generated signal to the OPAMP it actually dies and shows 0 volt at the output which is not my requirement.

Is there any technique either hardware based or software based to improve this waveform.

Also attached is the snapshot of the generated signal which is showing on my self made oscilloscope.

Thanks in advance. 🙂

#dac #stm32f3 #filter

waclawek.jan · ‎2015-10-30

Posted on October 30, 2015 at 16:32

This looks more like irregular output of the samples.

Do you use Timer+DMA? Are there any length interrupts in the program?

Switching on the opamp should not kill the signal, you are doing something wrong .

JW

ameer · ‎2015-10-30

Posted on October 30, 2015 at 16:42

Yes i used TIM6 interrupt with DAC1 and DMA. I dont think its coding issue because when i passed the signal through low pass filter the output samples got regular shape.

But still opamp kills the waveform by the way i am using opamp in inverting buffer mode. Should i add additional reconstruction circuitiry ??

AvaTar · ‎2015-10-30

Posted on October 30, 2015 at 17:58

But still opamp kills the waveform ...

Have you read the datasheet carefully ?

The DAC has an output impedance of about 1 Megaohm in unbuffered mode, or 15kOhm in buffered mode. Enabling the buffered mode introduces up to 200mV offset to the rails (i.e. up to 400mV loss in output range).

You need to take this fact into consideration when designing external circuitry. I guess your feedback resistors for gain adjustment are ''killing'' the DAC output.