MC145481

MOTOROLA

1

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 Trans-

ceivers, MC145532 ADPCM Tr anscoder, MC145422/26 UDLT –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.

Order this document

by MC145481/D

MOTOROLA

SEMICONDUCTOR TECHNICAL DATA

PIN ASSIGNMENT

MC145481

DW SUFFIX

SOG PACKAGE

CASE 751D

ORDERING INFORMATION

MC145481DW

SOG Package

MC145481SD

SSOP

20

1

VDD

PO–

PI

RO–

VAG Ref

PDI

BCLKR

DR

FSR

PO+

5

4

3

2

1

10

9

8

7

6

14

15

16

17

18

19

20

11

12

13

Mu/A

TG

TI–

TI+

VAG

MCLK

BCLKT

DT

FST

VSS

SD SUFFIX

SSOP

CASE 940C

20

1

REV 1

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