We are evaluating AD9276 as medical ultrasound AFE. one question related to CW demodulation architecture on page27 of datasheet need to consult experts of ADI.
On page 27, it mentions two architecture of implementing CW sum and demodulation.
A. traditional method : V-I amp --- passive delay line ---- summing (current) ---and demod.----ADC
B. Better one as in AD9276: Demod each channel individually ---- then phase shift (delay) ----summing ----ADC
The difference is the sequence of demodulation and summing.
For A, “The dynamic range of the demodulator can limit the achievable dynamic range.”(quote datasheet page27), is the disadvantage.
For B ,“Because the dynamic range expansion from beamforming (i.e. the summing technique to enhance SNR ) occurs after demodulation, the demodulator dynamic range has little effect on the output dynamic range”(quote datasheet page27), is better according to datasheet.
I may not understand this very well.
Firstly, a good demodulator (like AD8339) has very high Dynamic Range, seems not likely to limit the achievable dynamic range?
Second, would you explain with a calculation example on how could modulator affect the dynamic range if placed after summing? I do found the concept that "summing all N channels signal will improve SNR by 10*log(N) times", but I do not know how to take modulator parameter into calculation.
Any advice is appreciated, thanks!
[edited by: XYanalog at 1:02 AM (GMT 0) on 8 Jul 2020]