Processing/Sampling IF(IQ) signals

Himadri Guest 2014-11-11 13:13 #3879014

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Signal Characteristics: The IF (I/Q) signal consists of a DC component 
and an AC component.

DC Component: 2.52V; AC Component: 1.72 – 2.04 V (V P-P); BW: 20Hz - 
500kHz; Power: 20dB

Requirement: Now I want to digitize this signal for further processing. 
I prefer a sampling at 1 MSPS with ADC and then porting digital data to 
PC using a FPGA over SPI interface.

Problem: The problem is, the signal with DC and AC component ranges from 
3.5V to -1.5V with 2.5V from DC and almost 1V from positive cycle or 
negative cycle of the AC signal. Now I can use a coupled capacitor to 
block the Dcand use the AC for processing. My choice of ADC reference 
voltage is almost 2V-2.5V (for good resolution usability of ADC) so the 
signal can be amplified. But this signal have a negative part which I 
think is not good for a linear behavious for the ADC, as it has no 
negative reference voltage level. ADC reference is from 1V-5V. Using a 
rectifier is not a good choice from my view.

Question: How can I digitize this signal? Also comment on my views if 
not correct as I have only theoretical knowledge and never worked on a 
practical project.

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foo Guest 2014-11-11 13:28 #3879032

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Himadri wrote:
> comment on my views if
> not correct

So it is.

>DC Component: 2.52V; AC Component: 1.72 – 2.04 V (V P-P);

Vpp means peakt to peak voltage, i.e. the maximim amplitude ist 1.02V.
When added to the DC voltage then the mininum Voltage is +2,52V - 1.02V 
= +1,5V and teh maximum volatge is +2.52V + 1.02V = 3.54V.

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