How to express FIR filter output in terms of signal power

Hello everyone...

I am using a Narrow Digital FIR Bandpass filter to filter a signal at the
output of an 8 bit ADC...I calculate the envelope at FIR ouput(I^2 + Q^2)
using the complex outputs of the FIR bandpass filter..I want to express the
FIR output envelope signal in terms of the power of the input signal...how
to do it? What factors do i have to consider? My ADC full scale swing is
870 mV..

Thanks and Regards

Abhijit Kulkarni
Bangalore

abhijitk wrote:
> Hello everyone...
> 
> I am using a Narrow Digital FIR Bandpass filter to filter a signal at the
> output of an 8 bit ADC...I calculate the envelope at FIR ouput(I^2 + Q^2)
> using the complex outputs of the FIR bandpass filter..I want to express the
> FIR output envelope signal in terms of the power of the input signal...how
> to do it? What factors do i have to consider? My ADC full scale swing is
> 870 mV..
> 
> Thanks and Regards
> 
> Abhijit Kulkarni
> Bangalore
> 
> 

The simple way is to calibrate it.  i.e. put in a signal of known power 
e.g. a sinusoid in the passband, and relate the computed output power to 
the input power.  Presumably, any sinusoid in the passband should yield 
a result that tracks its amplitude as a squared function in the computed 
output power, right?  And, any sinisuoid outside the passband will track 
the input amplitude and the filter characteristics.

Fred

abhijitk wrote:
> Hello everyone...
> 
> I am using a Narrow Digital FIR Bandpass filter to filter a signal at the
> output of an 8 bit ADC...I calculate the envelope at FIR ouput(I^2 + Q^2)
> using the complex outputs of the FIR bandpass filter..I want to express the
> FIR output envelope signal in terms of the power of the input signal...how
> to do it? What factors do i have to consider? My ADC full scale swing is
> 870 mV..
> 
> Thanks and Regards

Dhere's not enough information here. You seem to have a single ADC. 
Where do the components of the complex signal come from?

Jerry
-- 
Engineering is the art of making what you want from things you can get.
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