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Serious low frequency jitter in an RC OSC

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lhlbluesky

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i have designed a rc osc (type: capacitor charging and discharging) used in a power IC (and i used binary-based calibration for charging current), when i tested the osc output frequency, i found the low frequency jitter is serious(about 5%), that is ,smaller than 50Hz, i'm very confused. what caused the low frequency jitter of rc osc? is it flicker noise? but how? or any other reasons? does anyone have met the same problem? pls help me.

thanks all.
 

Re: low jitter rc osc problem

Ripple voltage on the power supply could account for this. Many oscillator circuits change frequency when you raise or lower the supply voltage.

Can you set your oscilloscope so that a trace is triggered by the mains waveform?

Another factor is that your capacitor may carry substantial current, if it is a large value. As a result it might alter volt levels on neighboring components as it charges and discharges.

A smaller value capacitor will draw less current because you would put a higher resistance in series, to yield a given oscillating frequency.
 
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