Dual PLLs for 46/49 MHz Cordless Telephones# Technical Documentation: MC145167P Phase-Locked Loop (PLL) Frequency Synthesizer
Manufacturer: Motorola (now part of NXP Semiconductors)
Component Type: CMOS PLL Frequency Synthesizer with Prescaler
Package: 16-Pin DIP (MC145167P)
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## 1. Application Scenarios
### Typical Use Cases
The MC145167P is a monolithic CMOS integrated circuit designed as a programmable frequency synthesizer for phase-locked loop (PLL) systems. Its primary function is to generate stable, programmable RF or local oscillator (LO) signals by comparing a divided version of a voltage-controlled oscillator (VCO) output with a precise reference frequency.
Primary Operational Modes:
* Frequency Synthesis in Communication Equipment: The device serves as the core control element in PLLs, where its programmable divider (N counter) allows the generation of multiple discrete frequencies from a single, stable reference oscillator (e.g., a crystal).
* Channel Selection: By loading different binary values into its internal registers via a serial data interface, the output frequency can be stepped in precise increments, enabling channel selection in radios, scanners, and transceivers.
* Frequency Translation: It is commonly used in up-conversion and down-conversion stages within superheterodyne receivers and transmitters.
### Industry Applications
* Land Mobile Radio (LMR): Used in handheld transceivers, base stations, and repeater systems for public safety, commercial, and amateur radio bands (VHF/UHF).
* Cordless Telephones: Provides the channel selection logic for the handset and base unit.
* Wireless Data Links: Found in low-power telemetry, remote control, and industrial sensor networks.
* Test and Measurement Equipment: Employed in signal generators and frequency counters as a programmable clock source.
* Broadcast Equipment: Can be used in FM or TV tuners for precise local oscillator generation (though largely superseded by more integrated solutions for consumer applications).
### Practical Advantages and Limitations
Advantages:
* High Integration: Combines a reference oscillator amplifier, a programmable reference divider (R counter), a programmable main divider (N counter), and phase detector in one package, reducing component count.
* CMOS Technology: Offers low power consumption, making it suitable for battery-operated portable devices.
* Serial Programming: The 3-wire serial interface (Data, Clock, Enable) simplifies microcontroller interfacing and reduces pin count on the controlling device.
* Dual-Modulus Prescaler: The internal prescaler (e.g., 64/65 or 128/129, depending on variant) allows high-frequency VCO operation while maintaining fine frequency resolution.
* Wide Operating Voltage: Typically operates from 3V to 9V, offering design flexibility.
Limitations:
* Maximum Frequency: The maximum input frequency at the `f_in` pin (from the VCO via the prescaler) is limited (typically in the order of tens of MHz for the CMOS prescaler). This restricts its use in very high-frequency (e.g., GHz) applications without an external, higher-speed prescaler.
* Phase Detector Limitations: The phase/frequency detector output is a digital triplet state output. It requires an external passive loop filter to convert it to a smooth DC control voltage for the VCO. Design of this filter is critical for stability and lock time.
* Spurious Emissions: Improper loop filter design or board layout can lead to reference sidebands or other spurious signals on the VCO output.
* Obsolescence Risk: As a legacy CMOS PLL, it may have limited availability compared to modern fractional-N or delta-sigma synthesizer ICs with superior phase noise and
