Description
The MT3x7xB 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 MT3x70B 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 MT3x71B, 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 MT327xB and MT337xB can be used with a crystal or a ceramic resonator without additional components. A power-down option is provided for the MT317xB and MT337xB.

FEATUREs
• Wide dynamic range (50 dB) DTMF Receiver
• Call progress (CP) detection via cadence indication
• 4-bit synchronous serial data output
• Software controlled guard time for MT3x70B
• Internal guard time circuitry for MT3x71B
• Powerdown option (MT317xB & MT337xB)
• 4.194304 MHz crystal or ceramic resonator (MT337xB and MT327xB)
• External clock input (MT317xB)
• Guarantees non-detection of spurious tones

APPLICATIONs
• Integrated telephone answering machine
• End-to-end signalling
• Fax Machines