How to solve the problem of DAC glitches?

[stsiligg]

I atempt to construct a signal with 17 different voltages. What someone can observe at the signal are glitces at the begining of each analog voltage and more specifically more stressfull when the amplitude of previous voltage has big difference from the amplitude of current voltage. Is there anybody who can help me?See this image to understand what I mean

 

[jonashat]

DAC glitces

What is the architecture of the DAC?
Do you use binary weighted elements?

 

[stsiligg]

Re: DAC glitces

The architecture of the DAC is TTL(DAC0830) and ofcourse the inpput datas are binary.

 

[jonashat]

DAC glitces

I though it was a DAC you're designing.
Usually, glitches happen when you transfer between digital codes due to mismatches between elements.

However, a good design should ensure the minimum transition between different input digital codes. Sorry, no clue here

 

[Siniša]

Re: DAC glitces

If you zoom in on the glitches you would likely see that it contains suppresed oscillation on one frequency that coasts to 0 after few ηs or µs. What happens is on every sharp edge you have wide spectrum of frequencies depending on speed of your output and when that pulse hits any resonant circuit it will excite it at it's resonance frequency, same like when hammer hits the bell. Bigger difference in voltage level, harder hammer hits the bell, sort of speak. Also, if wave travels along trace or cable that has one impedance and hits difference in impedance, portion of that wave will bounce back. If you have two or more of this impedance "bumps" , wave will bounce between them until all the waves are absorbed, like waves in pond after you throw rock in it. If you disconnect everything from output of your DAC and measure that output with good calibrated probe and scope, you should see very clean edges. If you still see this what is often called "ringing", problem likely lies in the DAC itself.

Added after 13 minutes:

I just saw that you posted which DAC you use, in case of DAC0830 you have setling time of 1µs, so if your scope scale shown is 200µs/div, 1µs is about right for this DAC. Disregard my previous post as this is beacuse of your DAC. You could try using low pass filter or/and DAC with faster setling time, or you could disconnect your DAC output with switch before changing level and turn it on after DAC has settled on new level. If parasitic capacitance is not enough to hold level for period when you disconnect DAC, add small capacitor.

 

[Vamsi Mocherla]

DAC glitces

Hey the glitches in a DAC also arise because of the timing mismatch. If you are doing a design for the DAC, then you go to the internals and look for a more optimum switching scheme.

The glitches are very high in case of a larger voltage changes because the node capacitances need to be discharged/charged to the next level. If you cannot provide the currents for charging/discharging a node, then you will notice these glitches.

 

[vijayviswam]

Re: DAC glitces

I would like to know the architecture used for this DAC.. ? Is it a binary weighted DAC or unary ? I think it is a Binary DAC dac because the biggest glitches happen when it changes from lower level to upper, that is lot of switches need to change their state.We can reduce the glitch power by converting some of the upper bits to unary architecture by using a thermometer code style or matrix method.

 

[neo79]

DAC glitces

hi there, suppose your dac is a resistive type,do you have a low pass filter before you taking the output? normally without buffer, you will see glithes without doubt

 

[rajavel]

Re: DAC glitces

hi ,
u can use a deglitching circuits or you can choose proper segmatation between Unary & binary to have minimal glitches.

rgds
raags

 

[mists]

DAC glitces

who can give a example of deglitching circuits, thanks!

 

[fguihot]

Re: DAC glitces

I atempt to construct a signal with 17 different voltages. What someone can observe at the signal are glitces at the begining of each analog voltage and more specifically more stressfull when the amplitude of previous voltage has big difference from the amplitude of current voltage. Is there anybody who can help me?See this image to understand what I mean

Hi !!!

What is the max desired frequency of your output signal ???
You could use RC filter to cut the frequency above the max output frequency.
You could also use a lone Resistor, using the load input capacitor (usually 7-15 pF) as the C.
Could you post an zoom image of the glitch ????
How do you measure it ? Is the line terminated ? is the probe at the output of the DAC, or at the load ???
Good luck !!!

 

[mahgoub]

DAC glitces

use thermometer code to reduce glitches

 

[fashion]

DAC glitces

maybe you can use gray code to reduce it