I'm using AD8542 to create relaxation oscillator with the schematic below
But it has problem with temperature. Frequency out is drift about 4-5Hz/*C.
Can you help me to reduce this effect?
The AD8542 is a nonprecision op amp and Vos, Ibias, etc. varies a lot with temperature,
so use a better op amp.
Use a single.
Use a bipolar
You didn't say what the tempco is for the resistors and cap. Even with a perfect op amp,
the frequency will vary with changes in the resistors and capacitors.
Thank Harryh for your reply.
I used NP0 type capacitor and resistor with 25ppm/*C.
Can you suggest partnumber of suitable opamp to replace AD8542?
ADA4051-1 might not be fast enough. Try it first.
If not fast enough, the AD8538.
Also, put a styroform "box" or shield over the board to reduce air currents.
I will try and show the results later.
I've tried with AD8535 and AD8552 but the problem is not fixed.
The output is still effected by temperature. And I found new problem.
With the same circuit (just change opamp), there are the different frequency output
- With AD8542: Fout ~ 5050Hz, drift about 4-5Hz/*C
- With AD8552: Fout ~ 4800Hz, drift about 5-6Hz/*C
- With AD8538: Fout ~ 5170Hz, drift about 4-5Hz/*C
An R-C oscillator will never be as good as a quartz oscillator.
The op amps have different input capacitances which are in parallel with your
180 pF cap. Make the 180pF ten times bigger and the 563k ten times smaller and
see what happens.
What temp range are you using for testing? 25C to 125C?? 25C to 35C??
Above 80C, other imperfections kick in.
Also try reducinig the hysteresis and change R3 to 1 meg.
How solid is your 3.3V?
Also try 5.0V.
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