Document
www.DataSheet4U.com
MOTOROLA
SEMICONDUCTOR TECHNICAL DATA
Order this document by MC145481/D
MC145481
Product Preview
3 V PCM Codec-Filter
The MC145481 is a general purpose per channel PCM Codec–Filter with pin selectable Mu–Law or A–Law companding, and is offered in 20–pin SOG and SSOP packages. This device performs the voice digitization and reconstruction as well as the band limiting and smoothing required for PCM systems. This device is designed to operate in both synchronous and asynchronous applications and contains an on–chip precision reference voltage. This device has an input operational amplifier whose output is the input to the encoder section. The encoder section immediately low–pass filters the analog signal with an active R–C filter to eliminate very high frequency noise from being modulated down to the passband by the switched capacitor filter. From the active R–C filter, the analog signal is converted to a differential signal. From this point, all analog signal processing is done differentially. This allows processing of an analog signal that is twice the amplitude allowed by a single–ended design, which reduces the significance of noise to both the inverted and non–inverted signal paths. Another advantage of this differential design is that noise injected via the power supplies is a common–mode signal that is cancelled when the inverted and non–inverted signals are recombined. This dramatically improves the power supply rejection ratio. After the differential converter, a differential switched capacitor filter band– passes the analog signal from 200 Hz to 3400 Hz before the signal is digitized by the differential compressing A/D converter. The decoder accepts PCM data and expands it using a differential D/A converter. The output of the D/A is low–pass filtered at 3400 Hz and sinX/X compensated by a differential switched capacitor filter. The signal is then filtered by an active R–C filter to eliminate the out–of–band energy of the switched capacitor filter. The MC145481 PCM Codec–Filter has a high impedance VAG reference pin which allows for decoupling of the internal circuitry that generates the mid–supply VAG reference voltage to the VSS power supply ground. This reduces clock noise on the analog circuitry when external analog signals are referenced to the power supply ground. The MC145481 PCM Codec–Filter accepts a variety of clock formats, including Short Frame Sync, Long Frame Sync, IDL, and GCI timing environments. This device also maintains compatibility with Motorola’s family of Telecommunication products, including the MC14LC5472 and MC145572 U–Interface Transceivers, MC145474/75 and MC145574 S/T–Interface Transc e i v e r s , M C 1 4 5 5 3 2 A D P C M Tr a n s c o d e r, M C 1 4 5 4 2 2 / 2 6 U D LT – 1 , MC145421/25 UDLT–2, and MC3419/MC33120 SLICs. The MC145481 PCM Codec–Filter utilizes CMOS due to its reliable low–power performance and proven capability for complex analog/digital VLSI functions. Single 2.7 to 5.25 V Power Supply Typical Power Dissipation of 8 mW @ 3 V, Power–Down of 0.01 mW Fully–Differential Analog Circuit Design for Lowest Noise Transmit Band–Pass and Receive Low–Pass Filters On–Chip Active R–C Pre–Filtering and Post–Filtering Mu–Law and A–Law Companding by Pin Selection On–Chip Precision Reference Voltage of 0.886 V for a – 5 dBm TLP @ 600 Ω • Push–Pull 300 Ω Power Drivers with External Gain Adjust
This document contains information on a product under development. Motorola reserves the right to change or discontinue this product without notice. REV 1 7/96
20 1
DW SUFFIX SOG PACKAGE CASE 751D
20 1
SD SUFFIX SSOP CASE 940C
ORDERING INFORMATION
MC145481DW MC145481SD SOG Package SSOP
PIN ASSIGNMENT
VAG Ref RO– PI PO– PO+ VDD FSR DR BCLKR PDI 1 2 3 4 5 6 7 8 9 10 20 19 18 17 16 15 14 13 12 11 VAG TI+ TI– TG Mu/A VSS FST DT BCLKT MCLK
• • • • • • •
© Motorola, Inc. 1996 MOTOROLA
MC145481 1
DataSheet 4 U .com
www.DataSheet4U.com
RO – FREQ PI – + SHARED DAC PO + VDD VSS VAG Ref VAG 1 R* VSS TG TI – TI + – + FREQ ADC –1 VDD R* 0.886 V REF DAC
RECEIVE SHIFT REGISTER
DR
FSR BCLKR Mu/A SEQUENCE AND CONTROL PDI MCLK BCLKT FST
PO –
TRANSMIT SHIFT REGISTER
DT
Figure 1. MC145481 3 V PCM Codec–Filter Block Diagram
DEVICE DESCRIPTION
A PCM Codec–Filter is used for digitizing and reconstructing the human voice. These devices are used primarily for the telephone network to facilitate voice switching and transmission. Once the voice is digitized, it may be switched by digital switching methods or transmitted long distance (T1, microwave, satellites, etc.) without degradation. The name codec is an acronym from ‘‘COder’’ for the analog–to–digital converter (ADC) used to digitize voice, and ‘‘DECoder’’ for the digital–to–analog converter (DAC) used for reconstructing voice. A codec is a single device that does both the ADC and DAC conversions. To digitize intelligible voice requires a signal–to–distortion ratio of about 30 dB over a dynamic range of about 40.