| 摘要 |
PURPOSE:To drastically improve the output signal quality by incorporating all of required filters without considerably enlarging the circuit scale of a DTMF transmission/reception circuit made of an integrated circuit and reducing the unnecessary sent signal level of the output. CONSTITUTION:The DTMF transmission/reception circuit is provided with DTMF signal modulating/demodulating circuit 26 and 4, a band-pass filter 22 which separates a low group frequency component of a DTMF signal at the time of receiving the DTMF signal, a low-pass filter 16 which separates a high group frequency component of the DTMF signal, and a high-pass filter 11, and the DTMF signal is transmitted through the low-pass filter 16 at the time of transmitting the DTMF signal, and filters used for transmission/reception are partially shared. |
