The HT9170 series are Dual Tone Multi Frequency
(DTMF) receivers integrated with digital
decoder and bandsplit 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