Low pass filter analog Picoscope 5000

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Low pass filter analog Picoscope 5000

Post by spintinas » Wed Feb 28, 2018 8:51 pm

Hello, I have a question about picoscope analog hardware low pass filtering. I image my signal from amplifier to pisoscope, and there was plenty of noise, so I apply 10Hz low pass analog filter from Picoscope and my signal was clear. Now, I want to design this filter in my analog circuit, but exactly i didn't know which order this filter of Picoscope is. It is first order simple RC filter or what? With my analog circuit i want to get similar noise rejection as with Picoscope.

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Re: Low pass filter analog Picoscope 5000

Post by Martyn » Thu Mar 01, 2018 1:17 pm

Filter details

The lowpass filtering algorithm is chosen according to the ratio of the selected cut-off frequency (fC) to the sampling rate (fS), as follows:

fC ÷ fS

0.0 to 0.1 uses a Moving average
A moving average filter is used for low cut-off frequencies. The length of the filter is adjusted to achieve the selected cut-off frequency, which is defined as the first minimum in the frequency response. There is significant signal leakage above the cut-off frequency. This filter changes a vertical edge into a linear slope.

0.1 to < 0.5 uses a FIR
A finite impulse response filter is used for medium to high cut-off frequencies. This has a monotonic roll-off above the cut-off frequency and therefore suffers from less leakage than the moving average filter.

You can force PicoScope to use one or other of the filter types by adjusting the Samples control in the Capture Setup toolbar to make the ratio fC/fS fall into one of the two ranges shown in the table. As the table shows, the cut-off frequency must be below half the sampling frequency.
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