[Moved]: problem using xr2206 function generator

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hi i am using xr2206 function generator to generate 2 frequency 2500 and 3000 hz (fsk moulation) . but the generate frequency is swing around the require frequency. for example 2400 to 2600 for 2500 hz and i need a almost fixed frequency. can any one help me? by the way i use the circuit that was shown in datasheet.
 

Re: problem using xr2206 function generator

Do you mean this circuit? In which way do you see the output frequency "swinging around"? What's the control signal to the FSK input?

 

Re: problem using xr2206 function generator

yes i exactly use this circuit, i use a digital oscilloscope to see the out put of ic. the input signal come from atmega128 and is a square wave signal. i need 2 frequenies 2500 and 3000 hz but the out put is not fixed. for example for 2500 hz the output is 2400hz to 2600 hz. the rc circuit is a multilayer capacitor and carbonic resistor.
 

The observation is way too vague.

If you'll set the control signal to permanent low or high, how does the output look in each case? If it's not stable as you claim, how does the instability show in the output signal? How do you determine output frequency?

Do you have a stable power supply for XR2206?
 

The multi-layer capacitor is ceramic that is microphonic and its value changes with voltage. Use a film capacitor instead.
Maybe your "carbonic" resistor is very old (carbon composition) or very cheap. Use a name brand modern carbon film or metal film resistor instead.
 

Surely a good suggestion for a high precision design. I don't believe that the observed problems can be related to this point. There must be some trivial problem.
 

I have an XR2206 in my waveform generator. It needs a stable power supply. If you have a wandering supply voltage, then the frequency wanders. This includes ripple on the supply.

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A battery will make a suitable power supply.
 

first of all I'm really tankful for your attention and response
i use a digital oscilloscope for measuring the output signal frequency.
for supplying the ic, i use a minmax 24v regulator and the output is almost regulated and has low voltage ripple.
by changing the value of capacitor and resistor the variation of output frequencies change and a little improve but i don't use other type of capacitor and resistor yet.
when the control signal is permanent low or high the output frequency vary around the desire frequency and it is obvious on scope screen.
 

for supplying the ic, i use a minmax 24v regulator and the output is almost regulated and has low voltage ripple.
do you have output signal in your device with high quality?
would you mind telling me what kind of capacitor and resistor used for generating desire frequency?
are you use just the circuit in data sheet and the result was good?
 

Besides being affected by supply voltage ripple, the circuit can pick up 50 Hz interferences if the oscillator circuit impedance is unsuitable high. Changing the RC values, a metal case around the circuit, or at least a ground plane below it would help.
 

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