# Is it normal that a DAC outputs spikes?

I'm using a Raspberry Pi 2 and an AD/DA Board, with no extra circuit. Reading on the internet though, I found that DACs need a low pass filter in their output, and I don't understand if the behaviour of my DAC is normal, and I wonder if I need the low pass filter. Its output goes down to 0V at every sample, is it normal? Is this the reason why low pass filters are used?

Alberto

I tried with a better oscilloscope to analyze the signal, and it's all fine. I'm so sorry if I created a useless thread, but I still have learnt new terms I didn't know before.

• Can you please clarify if you observe an output like 1 0 2 0 3 0 4 0 5 0 6 0... and so on (?) or is it that the DAC outputs a few values and then drops to zero and stays there? Also, is this simulation or an actual DAC in a circuit? – A_A Nov 23 '16 at 8:52
• It goes to zero at every value. The DAC is not simulated, is a DAC8532 by Texas Instruments, controlled by a Raspberry Pi 2 – user25006 Nov 23 '16 at 10:29
• Can I please ask you to add all this information to the body of the question? This is all valuable to answer the question. Also, if you have access to an oscilloscope, can you take a screenshot of the output and include that too? Are you sure it is not a problem with clock synchronisation or the way the DAC is driven by the Raspberry Pi code? Is it on GPIOs which are driven programmatically through the PI's module? The DAC should have provision for what is known as Anti-Imaging filter, have you configured that up? – A_A Nov 23 '16 at 10:31
• If every value goes to zero,then how does the spikes come. Like A_A mentioned can you add a snap of output? – Navin Prashath Nov 23 '16 at 11:49
• Eventhough being quite exciting, this is a hardware biased question. Whether your DAC's output voltage or current goes to zero or jumps to spikes depends on your electrical circuit topology and not on the way you process your signals. The reconstruction lowpass filter would only smooth out your DAC's steppy output voltage. That filter cannot be responsible for any weird electrical behaviour (assuming properly connected) – Fat32 Nov 23 '16 at 14:22