The CD22204 complete dual tone multiple frequency (DTMF) receiver detects a selectable group of 12 or 16 standard digits. No front-end pre-filtering is needed. The only externally required components are an inexpensive 3.579545MHz TV ‘‘colorburst’’ crystal (for frequency reference) and a bias resistor. Extremely high system density is possible through the use of the Alternate Time Base (ATB) output of a crystal connected CD22204 receiver to drive the time bases of up to 10 additional receivers. This is a monolithic integrated circuit fabricated with low power, complementary symmetry CMOS processing. It only requires a single power supply.
The CD22204 employs state-of-the-art ‘‘switched-capacitor’’ filter technology, resulting in approximately 40 poles of filtering and digital circuitry on the same CMOS chip. The analog input is preprocessed by 60Hz reject and bandsplitting filters and then zero-cross detected to provide AGC. Eight bandpass filters detect the individual tones. Digital processing is used to measure the tone and pause durations and provides the correctly coded and timed digital outputs. The outputs interface directly to standard CMOS circuitry and are three-state enabled to facilitate bus oriented architectures.

Features
• No Front End Band Splitting Filters Required
• Single Low Tolerance 5V Supply
• Three-State Outputs for Microprocessor Based Systems
• Detects all 16 Standard DTMF Digits
• Uses Inexpensive 3.579545MHz Crystal
• Excellent Speech Immunity
• Output in 4-Bit Hexadecimal Code
• Excellent Latch-Up Immunity