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Bandwidth/Demodulation Bandwidth

Question asked by jejo86 on Jan 7, 2013
Latest reply on Jan 15, 2013 by jejo86

hi,

i am interested in one of the following quadrature demodulators: ADL5387, AD8348

 

i am trying to build a laser rangefinder with an amplitude modulated laser at 300MHz. so the optical detector outputs a sine wave at 300MHz with random phase, depending on the distance of the object. the phase can change slowly, when the object comes closer or moves away from the rangefinder, or there can be quick jumps in the phase if the rangefinder moves along a wall and detects an edge. i need to determine the phase of this sine wave to get the current distance of the object.

 

since the phase is random and can make great jumps the bandwidth of my signal is basically infinite.

 

what happens if i use my signal with the above mentioned demodulators? the AD8348 has a demodulation bandwidth of 75MHz, the ADL5387 has a demodulation bandwidth of approx. 240MHz. does this mean that i have to make sure that the input signal bandwidth is not greater than 75MHz respectively 240MHz by filtering the signal with a bandpass at 300MHz+-37,5MHz (300MHz+-120MHz)? or does the demodulator simply clip off any signals beyond the 75MHz (240MHz) after the signal is in the baseband and the filtering in beforehand would be unnecessary effort?

 

thanks

jejo86

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