HT9170 is an Dual Tone Multi Frequency (DTMF) receivers integrated with digital decoder and band split filter functions. The HT9170B and HT9170D types supply power-down mode and inhibit mode operations. All types of the HT9170 series use digital counting techniques to detect and decode all the 16 DTMF tone pairs into a 4-bit code output. Highly accurate switched capacitor filters are employed to divide tone (DTMF) signals into low and high group signals. A built-in dial tone rejection circuit is provided to eliminate the need for pre-filtering.
The HT9170 series tone decoders consist of three band pass filters and two digital decode circuits to convert a tone (DTMF) signal into digital code output.