ZL49021

The ZL49021 is a family of high performance DTMF receivers which decode all 16 tone pairs into a 4-bit binary code. These devices incorporate an AGC for wide dynamic range and are suitable for end-to-end signalling. The ZL49021 provides an early steering (ESt) logic output to indicate the detection of a DTMF signal and requires external software guard time to validate the DTMF digit. The ZL49021, with preset internal guard times, uses a delay steering (DStD) logic output to indicate the detection of a valid DTMF digit. The 4-bit DTMF binary digit can be clocked out synchronously at the serial data (SD) output. The SD pin is multiplexed with call progress detector output. In the presence of supervisory tones, the call progress detector circuit indicates the cadence (i.e., envelope) of the tone burst. The cadence information can then be processed by an external microcontroller to identify specific call progress signals. The ZL49021 can be used with a crystal or a ceramic resonator without additional components. A power-down option is provided for the ZL49021.