I am building a 16 channel multiplexer which will deliver the input from 16 microphones to a single ADC. I am clocking the ADC at 1.6 MHz and therefore sampling each audio channel at 100 kHz.
The ADC resolution is 12 bits, I cannot change the ADC because I am modifying a design, not starting from scratch. The ADC range is 2V. This is the microphone I am using:
I am realising this using 5 LMH6574 4:1 multiplexer chips, 4 used for the 16 mic lines then the fifth for the 4 outputs to produce a single output - The select lines for the first four are driven from a 2 bit binary up counter - a second up counter runs the 5th chip at CLK/4.
My question is this: Is it better to use an audio pre-amplifier for each channel - before being put through the multiplexer - or use a single pre-amplifier after the multiplexer stage?
I assume that if a single pre-amplifier is used it must have a bandwidth of at least 1.6 MHz, is this correct? - Will a high frequency pre-amp cause a loss in quality at the audio frequencies (compared with a hifi pre-amp chip)?
I also assume that the settling time of this amplifier is the all important factor, are there any rules/common practices defining what percentage I should be within (2%,1% 0.01% etc)?