XR2206 Waveform Generator

Does the triangle waveform work, or does it have the same problem as the sine wave?

Are you aware that the amplitude for the sine/triangle waveforms is much lower than for the square wave, and depends upon R3 (pin 3)? The datasheet specifies the output as typically 60mV/KOhm (min:max = 40:80).

If both triangle and sine exhibit the same problems, check the circuitry connected to pin 3. If triangle works but sine doesnt, check the switch and resistor between pins 13 and 14.

Hi,

I have supplied my circuit with 22 V. It appears that I'm only getting a triangular wave, even though I have looked at pins 13 and 14 (I could try changing the potentiometer there). The sine/triangular wave is about 10 V p-p with a few volts of offset from the ground. I have been able to vary R3 to change the amplitude to have the sine/ triangular wave max out at 10V p-p. Something is not right with the offset, although I'm not sure what I can do about it.

Cheers,

ssylee

For starters, there is no pot labelled THD. Second, try no load at output (10Meg scope probe is good enough approximation).

Hi Robert,

The THD pot I meant to point out refers to R3 on the diagram. Secondly, I looked at the output with no load at the output, although I don't know what's the impedance of my scope.

ssylee

R3 controls the triangle/sine amplitude. The THD control is the one between pins 13 and 14, labelled RA on the website (it's labelled "THD Adjust" in the data sheet).

Essentially, a lower resistance between pins 13 and 14 rounds off the top of the waveform. If pins 13 and 14 are open-circuit (S1 open), you get a triangle waveform. With a low resistance (S1 closed, RA in effect), the triangle peaks are rounded to give a sine wave (the sine wave should be roughly half the amplitude of the triangle wave for any given value of R3).

My first guess would be that either the IC is faulty or that closing the switch is causing a short between pins 13 and 14, pulling the peaks down to near zero rather than to only half the triangle amplitude.

Are you using the original schematic from page 2, or the version with more complex THD control shown on page 4 (and used for the PCB layout)? Have you made a PCB or is this on breadboard?

In any case, the first thing to check is whether pins 13 and 14 are being shorted when S1 is closed.

You damaged the chip? I looked up that chip number before. The output is suppose to be 6V p-p, either that was a miss print or, yours having that much output is in error! Make sure you have a by pass cap at the Vcc and ground (common). something like a .1 non electrolytic type. and maybe you should try another chip.