Dear all:
I'm desingning a system that sends data through the telephone line. I'm using an 1N9270 chip (HM9270) tone decoder to identify the DTMF tones. The valid input signal range level is from 27.5mV to 883mV for this chip. As the impedance of the line is unknown (aprox. 600ohm), the amplitud of the receiving signal may be too week if I don't amplify it enough or too strong if I over amplify it, I don't know how much attenuation the signal will suffer. That's why I need an AGC. I used the LM13600 to build the AGC that is described in the datasheet. It works properly, but the smallest input level signal from which the AGC works fine is 200 mV and I need to control even smaller level signal, let's say, 10 mV. By varying the resistors in the design in the datasheet I got the 200mV. I need that the AGC responds form 10mV to 5V at the input and at the output from 27.5mv to 883mV. I can't vary any further (or at least, I don't know how to vary) the value of the resistors because it causes a distortion at output signal. The frecuency of my signals are from 600Hz to 2500 Hz. Has anyone used this Op. Amp. to build an AGC with these or similiar input signal levels?. Any idea?
Thanks in advance,
Mike Sparrow