So I am outputting up to 3, 0-5V signals from three separate DACs. The issue I have come into is that I would like to combine all three signals to form a single output of the same amplitude. Currently the only way I have been able to achieve combining them is with a Summing amp with 1/3 gain on each input so that when they are combined the output is the same amplitude again. As you would expect though, when only one source is provided the output is 1/3 of the needed output amplitude. (inverted)
I then also looked at the LM3900 multi-channel audio mixer IC (http://www.circuitstoday.com/multi-channel-audio-mixer-using-lm3900)
But I am not sure if this accounts for the issue I am trying to fix. Does anyone know if the LM3900 outputs a constant signal amplitude irregardless of the input signal strength?
Best Answer
What you need is an Automatic Gain Control (AGC) to keep the output level constant regardless of input level. A possible candidate is the Maxim MAX9814 which combines a microphone preamplifier and an AGC function with 20 dB of range. Since you have 3 inputs, which presumably have about the same level, then the maximum input level change is from 1 input active to all 3 inputs active or a factor of 3 which is about 10 dB. Thus the MAX9814 should be easily able to handle this range.