DC offset cancellation in VGA (Variable gain amplifer)

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ee_wmxaa

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dc offset cancellation

Hi,all

I am doing a project on designing a variable gain amplifier (VGA)under UWB specification. I have conducted several literature research. I found that they included a dc offset cancellation circuit in most of the previous work. And after adding this circuit, the frequency response of the VGA will look like a bandpass filter. I wonder what is dc offset and why the frequency response looks like a bandpass filter.

Thank you
 

offset cancellation

A DC offset cancellation circuit uses a feedback loop. The bandwidth of this loop can reshape the bandwidth of your amplifier. The design of the loop needs careful design in terms of delay, frequency response and stability.
 
dc cancellation

Hi,vfone

Can you tell me more detail about why the bandwidth will look like a bandpass filter.

Thank you
 

vga amplifer

Applying the offset voltage correction signal to the variable gain amplifier it will adjust the forward gain factor of the VGA and the gain factor of the offset loop amplifier.
Increasing the forward gains tends to change the cut-off frequencies.
Is necessarily to analyze and tune the transfer function of the loop.
 

vga variable gain amplifier filter

ee_wmxaa said:
Hi,vfone

Can you tell me more detail about why the bandwidth will look like a bandpass filter.

Thank you
Click to expand...

Any dc cancellation loop must discriminate between dc and signals because only the dc portion is to be minimized ("cancelled").
However, as there is no lowpass with cutoff at - lets say 1 mikroHz -- some low frequency components are "cancelled" as well. This cannot be avoided and leads to a lower frequency limit of the amplifier. The upper limit is detrermined by the amplifier itself.
 

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