Not much info on this subject to be found in Google, so I decided to give this forum a try.

My project involves the "loading effect" of a metallic object upon a free-running LC oscillator. This means that the amplitude - and to a lesser extent the frequency - of the oscillator changes as the object gets closer to the inductance.

My oscillator produces a 40Vpp sine wave. Before applying the peak detector I subtract 37V DC so the peak is 3V maximum. This is like "zooming in" into the peaks, which allows to detect small amplitude variations of the order of a millivolt in the 40V range.

You would assume that the amplitude of the oscillator (the envelope after peak detection) would be constant if the power supply is well regulated. Well, this is not the case, instead, the amplitude behaves like a "random walk" (Brownian motion) drifting up and down in what appears to be huge "pink noise" also known as "flicker noise" or "1/f" noise. In this case the drift is in the order of the 100's of millivolts, so large it buries the signal.

Google taught me that flicker noise is the integral of white noise, and since the LC circuit is in fact an integrator, any noise injected by the power supply or the components of the oscillator will result in 1/f noise.

I've tried to remedy this by using a battery as a power supply + big capacitor, since regulators are noisy. The drift is a bit less but still remains.

Any ideas on how to minimize this annoying effect?

Attached: LTSpice simulation. I've added the white noise source BV to show what the effect looks like (plot V(peak)) as it happens in the real circuit without BV.

My project involves the "loading effect" of a metallic object upon a free-running LC oscillator. This means that the amplitude - and to a lesser extent the frequency - of the oscillator changes as the object gets closer to the inductance.

My oscillator produces a 40Vpp sine wave. Before applying the peak detector I subtract 37V DC so the peak is 3V maximum. This is like "zooming in" into the peaks, which allows to detect small amplitude variations of the order of a millivolt in the 40V range.

You would assume that the amplitude of the oscillator (the envelope after peak detection) would be constant if the power supply is well regulated. Well, this is not the case, instead, the amplitude behaves like a "random walk" (Brownian motion) drifting up and down in what appears to be huge "pink noise" also known as "flicker noise" or "1/f" noise. In this case the drift is in the order of the 100's of millivolts, so large it buries the signal.

Google taught me that flicker noise is the integral of white noise, and since the LC circuit is in fact an integrator, any noise injected by the power supply or the components of the oscillator will result in 1/f noise.

I've tried to remedy this by using a battery as a power supply + big capacitor, since regulators are noisy. The drift is a bit less but still remains.

Any ideas on how to minimize this annoying effect?

Attached: LTSpice simulation. I've added the white noise source BV to show what the effect looks like (plot V(peak)) as it happens in the real circuit without BV.