Removal of DC offset without Digital Highpass Filters

dc offset removal

Dear friends,

I'm currently working on a project including AC current and voltage measurement.

The input signal to the ADC is a sine wave shifted by a constant dc offset, as the ADC is unipolar.

inside the microcontroller I need to remove that DC offset to restore the original signal.

my question is, Can I use some technique other than the digital high pass filter to do this, knowing that the controller is AVR 8 bit RISC core?

I'm thinking of this method: I get the maximum and the minimum of the sampled signal, and calculate the offset as minimum + (maximum - minimum)/2
and then subtract the offset of every sample

can I use these method?

thanks a lot, good luck to everyone,

Mohammad

dc removal filter

y u cann't use single capacitor???????

adc dc offset

dear xulfee,

thanks for your reply, the ADC is unipolar, that is, the input analog signal must be positive with respect to the ground, so I added that DC offset to shift the sine wave above zero before the adc. after sampling the shifted sine wave, I need to remove that offset again without using digital filters, that is my issue.

waiting for all your help guys??

remove dc offset

yes the use of a single capacitor will remove the dc componet of the voltage

removing dc offset high sampling rate

Dear,

If you know the dc offset value , subtract it from the all sample points.

if you don't know the dc offset value, find the mean of the sample points then subtract it from all your sample points.

SPHiNX

digital high pass

then just use difference amplifier ,apply ur signal at one input n dc offest in other one,u'll get ur result,anyhow also check single capacitor,wht result it can give u

dc offset high pass filter

The suggestion by Sphynx

"If you know the dc offset value , subtract it from the all sample points"

is correct if you consider an ideal system where the DC offset is known a priori and remains constant in time (thermal variations or aging of components could cause drifts) and keeps the same value on all the units you have to build.
In practice this is never true, so in a real world if you don't want to implement HP digital filtering, probably you will have to SW perform calibration procedure to estimate the dc component independently from the HW and then subtract it to the incoming samples: if the dc component is sufficiently stable could be sufficient doing this only once at start up of the system.
Calibration routines could be performed as "background tasks" avoiding the overload of the CPU due to digital filtering, specially when sample rate is relatively high and/or the HW resources are limited as in a 8-bit MCU.

Regards
Mowgli

dc offset removal in adc

Check out this article from Xilinx

https://www.xilinx.com/support/documentation/white_papers/wp279.pdf

remove dc component filter

You can remove dc offset from signal by
subtracting the average value of the entire signal from each element in the signal