Failed diode function generator

Thread Starter

jjm212

Joined Apr 18, 2022
2
Why would a diode function generator output a distorted waveform at high frequencies(>50kHz)? In theory and simulation, it should be fine, but when testing, the diode fails to perform properly at higher frequencies. Any ideas?
1650323983860.png
 

Audioguru again

Joined Oct 21, 2019
4,685
The extremely important peak-to-peak input voltage and power supply voltages are missing.
You did not post the distorted waveform.

Since diodes in the feedback path produce rock music severe fuzz (distortion) then the distortion you have is probably normal.
 

Thread Starter

jjm212

Joined Apr 18, 2022
2
I cant upload additional files because this is a part of a school project; if you have any insights on why a diode may fail at higher frequency with a triangular waveform input and a sinusoidal waveform for the attempted output, and where on a spec sheet of such a diode might that be covered, it would be appreciated.
 

drjohsmith

Joined Dec 13, 2021
394
I cant upload additional files because this is a part of a school project; if you have any insights on why a diode may fail at higher frequency with a triangular waveform input and a sinusoidal waveform for the attempted output, and where on a spec sheet of such a diode might that be covered, it would be appreciated.
as some one says on here
in theory , theory is the same as practice !!

This isn't home work by some chance ?

In your simulation
have you model the diode characteristics
whats the different between the model of the diode and the real diode and wiring / circuit
 

MrChips

Joined Oct 2, 2009
26,099
A triangle to sine wave converter using diodes is a crude approximation.
A diode is a non-linear device. It is used with an op-amp to create a logarithmic conversion.

1650400604693.png


The way to convert from a triangular wave to a sine wave is with a low pass filter to attenuate all frequencies higher that the fundamental frequency. This only works for a narrow range of frequencies.

The log amplifier circuit behaves as a compression circuit because it compresses the amplitude as the voltage gets higher. This works from DC to a moderate frequency. At higher frequencies the capacitance of the diode has to be taken into consideration.
 

Audioguru again

Joined Oct 21, 2019
4,685
Maybe the LM318 opamp was a fake one from ebay that has a poor high frequency response. A 741 opamp produces very poor waveforms above 9kHz.
A "switched-capacitor lowpass filter" IC can remove all the harmonics of a squarewave or triangle waveform resulting in an excellent sinewave.
 

crutschow

Joined Mar 14, 2008
29,792
What's the amplitude of the input signal?

Can't you post a picture of the distorted output you are getting, so we can give you more than just WAGs about the source of the problem?
 
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