MC145481 Datasheet, PDF (1/23 Pages) Motorola, Inc – 3V PCM CODEC-FILTER

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SEMICONDUCTOR TECHNICAL DATA
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MC145481
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 Transcoder, 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
20
1
DW SUFFIX
SOG PACKAGE
CASE 751D
SD SUFFIX
SSOP
20
CASE 940C
1
ORDERING INFORMATION
MC145481DW
MC145481SD
SOG Package
SSOP
PIN ASSIGNMENT
VAG Ref 1
RO– 2
PI 3
PO– 4
PO+ 5
VDD 6
FSR 7
DR 8
BCLKR 9
PDI 10
20 VAG
19 TI+
18 TI–
17 TG
16 Mu/A
15 VSS
14 FST
13 DT
12 BCLKT
11 MCLK
This document contains information on a product under development. Motorola reserves the right to change or discontinue this product without notice.
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MC145481
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