Audio level detection - (AGC with comparators)

I'd like to knock up a circuit which monitors an incoming DC voltage & compares it against a reference voltage - if the incoming DC voltage is too high, then the DC voltage output from this particular circuit slews down, & vice versa.

Now, I'm cool with the idea of a comparator - I can set the reference voltage to compare against.

Now then, a comparator is a binary device (in that it outputs either high or low output), firstly, I'd like to slow this transition between high & low etc - I'm cool with the idea of an RC filter on the output of the comparator to do just that. The bit I'm struggling with is how to constrain the voltage limits of the comparator output swing.

I'm looking for the comparator to slew between voltages of about 1.2V maximum & 0.45V minimum.

so, for example ....the 'monitored' incoming DC voltage goes below 'threshold', comparator triggers, & goes high - an RC filter slows the comparator's effective output by slewing up slowly - it slews up to a maximum of 1.2V. Ok, the incoming voltage then drops significantly goes below threshold, comparator triggers & goes low - the RC filter slows the comparator output slew - it slews down to a minimum of 0.45V.

It's this last bit that I've not got sorted - how can I arrange it, so, I can have two 'extremety' output voltages that the comparator output slews between.
Last edited:


2004-12-25 12:24 pm
You need a Window comparator......;)

It is made up of 2 comparators and has 2 levels of input thresholds namely HI and LO forming a window........