Brief Description
The FX621 is a single-chip, low-power CMOS tone detector designed for use in both PABX and general payphone applications for Subscriber Private Metering.
The Decode and Not-Decode band edges are accurately defined by the use of an external 4.433619MHz crystal.

FEATUREs/Applications
● Meets 12kHz and 16kHz SPM Specifications
● Low-Power CMOS [ 3.5 – 5 Volt Operation ]
● Tone Follower and SPM Packet Detection Modes
● Adjustable Input Gain
● PABX, Payphone and Telephone Applications
● General-Purpose Tone Detection
● Crystal Oscillator Stability