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Design >> Analog Design >> spikes on waveform of digital output of ADC
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Message started by icekalt on Sep 4^th, 2009, 5:05am

Title: spikes on waveform of digital output of ADC
Post by icekalt on Sep 4^th, 2009, 5:05am

Hello,

I have just simulated my ADC with a ramp input signal and the 8-bit outputs are V(b0)..V(b1). In the waveform below, there are some spikes around 0.5 V. what is the cause of this? I reall need explanation

Thx in advanced

Title: Re: spikes on waveform of digital output of ADC
Post by Andrew Beckett on Sep 4^th, 2009, 1:53pm

In the absence of Extra Sensory Perception which would allow me to know what your circuit looks like (particularly the digital output stages of the ADC), I can only suggest that the digital outputs of the ADC can generate glitches, due to either combinational logic, or some sort of timing problem? It could be lots of things...

You didn't even give any clues as to what type of ADC it is. If it's a flash converter, it may be caused by some glitches in the conversion of the thermometer code to a binary output? Almost certainly looking at various other nodes in the circuit and understanding the circuit would allow you to figure this out.

Regards,

Andrew.

Title: Re: spikes on waveform of digital output of ADC
Post by icekalt on Sep 4^th, 2009, 1:55pm

Andrew Beckett wrote on Sep 4^th, 2009, 1:53pm:

In the absence of Extra Sensory Perception which would allow me to know what your circuit looks like (particularly the digital output stages of the ADC), I can only suggest that the digital outputs of the ADC can generate glitches, due to either combinational logic, or some sort of timing problem? It could be lots of things...

You didn't even give any clues as to what type of ADC it is. If it's a flash converter, it may be caused by some glitches in the conversion of the thermometer code to a binary output? Almost certainly looking
at various other nodes in the circuit and understanding the circuit would allow you to figure this out.

Regards,

Andrew.

Type of that ADC is Folding and Interpolating ADC

Title: Re: spikes on waveform of digital output of ADC
Post by Andrew Beckett on Sep 7^th, 2009, 3:15am

It's still likely to be some glitches in the sub-range flash converter thermometer decode, any error correction block, or the output latches/logic. I'm referring to blocks in Fig 3 of http://www.commsdesign.com/main/9810/9810feat2.htm, because we still have virtually no information on your design in which to make an informed diagnosis.

I'm sure if you probed around your design, working back from the output, you ought to be able to find where the glitches are coming from. That's far more likely to be successful than expecting people on a forum to diagnose your problem with such a minimal amount of information to go on!

Best Regards (and good luck),

Andrew.

Title: Re: spikes on waveform of digital output of ADC
Post by Berti on Sep 7^th, 2009, 4:39am

Icekalt, note that different kind of decoders exist (1's counter, ROM etc.). They offered different trade-offs depending on the number of bits, probability for glitches etc.

Cheers