Excuse me for resuscitating this topic, but I was wondering if anyone could elaborate further on the following concept (see excerpt below) generously provided by MooseFET?
My original post was about how to design a _zero_ delay LP filter for geomagnetic signals below 50Hz.
I am hoping for a bit more detail to assist me in coming up with a workable schematic.
Glenn Kenroy
******"The first step is to make a PLL that locks onto the 60Hz. You want the VCO in the PLL to be running at many times the 60Hz frequency. I am going to suggest 7200 times, but faster is likely better. 7200 times just makes the explanation easier.
Important frequencies:
60*8*3*5 = 72007200 / 15 = 60*8
7200 / 3 = 5*60*8 7200 / 5 = 3*60*8I will assume that you have the PLL locked to the 60Hz.
You will be making the same circuit 3 times. It uses the CD4051 The 8 times the frequency goes to a counter that makes the CD4051 scan through a group of capacitors.
Each of the 8 outputs of the CD4051 connects to one end of a capacitor. The other end of the capacitor is grounded.
If the common point is fed with a resistor. This makes a circuit that will charge up the capacitors until they match the 60Hz input waveform."
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