5 V PCM Codec-Filter# Technical Documentation: MC145484SD PCM Codec-Filter
Manufacturer: Motorola (MOT)
Component Type: PCM Codec-Filter with On-Chip Filters
Document Revision: 1.0
---
## 1. Application Scenarios
### 1.1 Typical Use Cases
The MC145484SD is a monolithic, per-channel PCM (Pulse Code Modulation) codec-filter integrated circuit, combining both the encoding (A/D) and decoding (D/A) functions required for digital telephony. Its primary use cases are centered on voice-band signal processing.
* Digital Telephone Subscriber Line Interfaces: It serves as the core analog front-end in subscriber line interface circuits (SLICs) for both wired and wireless telephone handsets and base stations, converting the analog microphone output to a digital PCM stream for transmission, and converting the received digital PCM stream back to an analog signal for the speaker.
* Voice-Over-IP (VoIP) Adapters and Gateways: In early VoIP equipment, the MC145484SD provided the essential interface between the analog telephone line (FXS port) and the digital packet processing system (DSP or host processor).
* Private Branch Exchange (PBX) Line Cards: Used within individual channel cards of digital PBX systems to handle the analog-to-digital and digital-to-analog conversion for each connected telephone extension.
* Digital Answering Machines and Voice Logging Systems: Facilitates the recording of analog voice signals into a digital format for storage and playback.
### 1.2 Industry Applications
This component was predominantly deployed in telecommunications infrastructure and terminal equipment from the late 1980s through the early 2000s.
* Telecommunications: Central office switches, digital loop carriers, channel banks, and ISDN terminal adapters.
* Customer Premises Equipment (CPE): Digital telephones, key telephone systems, and fax machines with digital interfaces.
* Industrial Communication: Intercom systems and dedicated voice communication links requiring robust, standardized µ-law or A-law companding.
### 1.3 Practical Advantages and Limitations
Advantages:
* High Integration: Combines a precision bandpass filter (300 Hz - 3.4 kHz), a switched-capacitor anti-aliasing/reconstruction filter, companding DAC/ADC, and a serial PCM interface into a single 16-pin package (SOIC-16 for MC145484SD), simplifying design and reducing board space.
* Standard Compliance: Fully compliant with ITU-T (formerly CCITT) G.711 recommendations for µ-law (North America/Japan) or A-law (Europe/International) PCM encoding, ensuring interoperability in public telephone networks.
* Low Power Consumption: Designed for power-sensitive applications, typical of line-powered terminal equipment.
* Simplified Analog Design: The on-chip filters eliminate the need for external, precision passive components for anti-aliasing and smoothing, improving reliability and manufacturability.
Limitations:
* Legacy Technology: As a pure PCM codec, it lacks integrated features common in modern voice codecs, such as echo cancellation, DTMF generation/detection, or programmable gain amplifiers, which often require additional external components.
* Fixed Data Rate: Interfaces at standard 64 kbps PCM (8 kHz sampling) and is not designed for variable or lower bit-rate compression algorithms (e.g., ADPCM, G.729).
* Supply Voltage: Typically requires dual supplies (e.g., +5V and -5V), which may not be readily available in modern single-supply systems without additional charge pumps or regulators.
* Interface: Uses a legacy, non-standard serial control interface for power-down and law selection, distinct from the more common I²C or SPI control buses.
---
## 2. Design Considerations
