Product description

The CMX673 is a general purpose call progress tone detector for use in Public Switched Telephone System (PSTN) applications.

Call progress detection allows equipment which dials into the PSTN network to monitor the progress of the resulting call: Ringing, Busy, Not Available and Answer states can be determined.

The CMX673 uses advanced digital signal processing techniques to detect tones in the frequency band 315 to 650 Hz.

The detection timing of the CMX673 allows it to operate with almost any call progress system. In particular the ‘stuttered dial tone’ of voice mail messaging systems is supported.

The use of digital processing and small geometry CMOS design techniques allows the CMX673 to offer a complete call progress detector which analyses both frequency and amplitude in a single 8 pin (PDIP) package. This, coupled with industry-leading performance and substantially lower power supply requirements than comparable devices, demonstrates CML’s unique capability in this area.

Read More

Devices are available through our distributors below:


  • SalesNetworkLogo_2
  • Mouser_logo
  • RFMW logo

Block diagram


Technical Portal

No additional information available.


  • Worldwide Tone Compatibility
  • Single and Dual Tones Detected
  • Wide Dynamic Signal Range
  • Fast Response Time
  • Low Power (Line) Operation
  • 3.58MHz Xtal/Clock Oscillator
  • ‘Output Enable’ Multiplexing Facility


  • Worldwide Payphone Systems
  • Telephone Redialing Systems
  • Dialling Modems
  • Banking and Billing Systems
  • Telecom Test Equipment
  • Telecom Security Systems

Power supply requirement

  • 2.7 to 5.5 V

Not quite sure what you’re looking for?
We can tailor an existing product to your unique requirements

Design resources

CMX673: Suggested Applications

The CMX673 is an 8-pin DIP or 16-pin SOIC signal-detector that operates on energy in the frequency band of about 315 to 650 Hz. Its primary use is in the detection of status tones encountered during the progression of a telephone call. These tones include: dial tone, circuits busy, ring tone, station busy and others. Call status is derived by examining the cadence of those tones.

Package: D4 (DW)

16-pin SOIC

Package: E3

20-pin TSSOP

Package: P1

8-pin PDIP

Ask a question

Request a quote