Electronics > Beginners
Generating precise outputs from a comparator
(1/4) > >>
guymo:
Hello,

I am trying to design an analog circuit to perform frequency addition for sawtooth waves. Given two sawtooths running 0 - 5V, if we sum the voltages, detect when the sum crosses 5V, and subtract 5V in that case, we get a new sawtooth wave whose frequency is the sum of the input wave frequencies.

The obvious way to do this is to use a comparator and somehow clip or set the output voltages to be 0V and 5V. Obviously a certain amount of precision is desirable and ultimately I'd like to be able to chain a bunch of these stages which calls for more precision and a low parts count if possible.

So: what's the best way to get precise voltage outputs from a comparator?

Ideas I have had:

-  use an LM311 with a 5V reference for the pull-up; I'm not sure if the 0V output will be precise and there will be loading issues for the pull-up.
-  use a rail-to-rail op amp powered from 0V and 5V. This seems quite a good approach although there is some danger that the input waves go beyond the power supply rails of this component and perhaps give it trouble
-  run the comparator output through a CMOS IC (inverter for instance) powered from 0 and 5V
-  clip the outputs of a regular comparator with some sort of shunt reference -- but what? I've played with a TL431 and didn't get very good results
-  use a precision clipping circuit. Parts count is going up at this point...

Any advice or ideas welcomed! I'm posting in Beginners because I basically don't know what I am doing...

D-Jack:
So the output should be: (wave1 + wave2) or (wave1+wave2)-5v?
And can you use dual supply op-amp or must it be single supply?
guymo:

--- Quote from: D-Jack on July 04, 2018, 11:16:24 pm ---So the output should be: (wave1 + wave2) or (wave1+wave2)-5v?
And can you use dual supply op-amp or must it be single supply?

--- End quote ---

Yes, overall output will be wave1+wave2 if that does not exceed 5V, and wave1+wave2-5V otherwise.

The system as a whole will be running on good old fashioned +/-15V dual supplies.
Giaime:
As far as output accuracy goes, I have obtained best results with CMOS ICs, especially when run in parallel. Their low RDS(on) for the output stages help to reduce loading effects: I use them for precision PWM DACs.
Of course they cannot be more accurate than the power supply rail they're being powered with.
Zero999:
What issues did you have with the TL431?
Navigation
Message Index
Next page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod