General Description

The 78A207 is a single-chip, Multi-Frequency (MF) receiver that can detect all 15 tone-pairs, including ST and KP framing tones. This receiver is intended for use in equal access applications and thus meets both Bell and CCITT R1 central office register signaling specifications.
The 78A207 employs state-of-the-art switched capacitor filters in CMOS technology. The receiver consists of a bank of channel-separation bandpass filters followed by zero-crossing detectors and frequency-measurement bandpass filters, an amplitude check circuit, a timer and decoder circuit, and a clock generator. The device does not attempt to identify strings of digits by the KP (key pulse) and ST (stop) tone pairs.
No anti-alias filtering is needed if the input signal is band-limited to 26 KHz. The only external component required is an inexpensive television "color burst" 3.58 MHz crystal.

The outputs interface directly with standard CMOS or TTL circuitry and are three-state enabled to facilitate bus-oriented architecture.


  • Meets Bell and CCITT R1 specifications
  • 20-pin plastic DIP
  • Single low-tolerance 5V supply
  • Detects all 15 tone-pairs including ST and KP                                 
  • Long KP capability
  • Built-in amplitude discrimination
  • Excellent noise tolerance
  • Outputs in either "n of 6" or hexadecimal code
  • Three-state outputs, CMOS-compatible and TTL-compatible