I am doing a project on PPG Blood Pressure capturing. The signal naturally have a slow varying DC offset ( 1-2 V ), while the useful rippling signal range 100-500mV (0-50Hz).
Is a high pass filter useful to remove the varying DC offset? What should be the frequency range?
Thanks a lot
Uhh... Isn't 0Hz = DC???
If you throw in a HP filter, you need to spec a cut off...say f = 1Hz.
Perhaps consider an active HP filter if you need more performance.
D from BC British Columbia Canada
An integrator to adjust the dc offset of the amplifier. I believe it is called servoing. if the voltage is negative the output goes positive if positive it goes negative. the rate of change is if 1 meg resistor and 1 uf cap 1 v per second. the output is summed with the input signal of the amp the input to the integrator is the output of the amp. you might also want to shunt the integrating cap with a very large value resistor to provide some dc feedback.
Bob
That's kinda like what I saw one day on:
Slow signal is fed back for nulling.
D from BC British Columbia Canada
download this
martin
With a more constant DC bias, the best way is to use digital autonulling. Its a one shot deal.
Back in the day I was trying the analog nulling circuit in Art of Electronics. It worked somewhat, but the next circuit I used digital components. 2-20 bit registers and successive approximation chip. it worked very well allthough the bias will skip around the signal unless a LPF is used.
grge
That was 2- 12 bit registers.
greg
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