ADPCM Megafunction

ADPCM Megafunction
Solution Brief 8
December 1996, ver. 1
Target Applications:
Communications
Digital Signal Processing
Features
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Family: FLEX 10K
Vendor:
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Integrated Silicon Systems, Ltd.
29 Chlorine Gardens
Belfast, BT9 5DL,
Northern Ireland
Tel.
44 1232-664-664
Fax
44 1232-669-664
E-mail Info@ISS-DSP.com
WWW http://www.ISS-DSP.com
Fully compliant with G.721, G.723, G.726, G.726a, G.727, and G.727a CCITT
standards
Parameterized number of duplex channels
Supports both A- and µ-law pulse code modulation (PCM) coding and 5-, 4-, 3-,
and 2-bit coding rates
Optimized for the FLEX® 10K device architecture
Supports up to 16 full duplex channels, 32 encode channels, or 32 decode channels
Ideal for a variety of applications
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Digital circuit multiplication equipment (DCME) overload voice channels
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DCME data modem signals
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Packetized speech systems
General Description
The adaptive pulse code modulation (ADPCM) megafunction performs multi-channel
duplex ADPCM coding in telecommunications applications. Most of the applications
of the G.726 standard are in overload channel communication, i.e., carrying voice and
data modem signals in DCME, particularly for modems operating in excess of 4,800
kbits per second. Most of the applications of the G.727 standard are in converting Aand µ-law PCM channels to and from variable-rate embedded ADPCM channels. The
primary use of the megafunction in the G.727 and G.726 standard is for packetized
speech systems, operating in accordance with the packetized voice protocol (PVP).
The ADPCM megafunction, which is optimized for the Altera® FLEX 10K architecture,
combines the algorithm and architecture research of ISS with the performance and
implementation advantages of the FLEX 10K family. The ADPCM megafunction is
designed in a hierarchical manner to enable the high-quality implementation achieved
in the lower-level blocks, such as multipliers and adders, to be carried through to the
higher-level encoder and decoder blocks.
The megafunction ensures that products incorporating ADPCM can be delivered to
market quickly and efficiently, and is parameterized to meet the target application
operating requirements. The megafunction can be utilized for multi-channel encoding,
multi-channel decoding, and multi-channel duplex coding. See Figures 1 and 2.
Figure 1. ADPCM Encoder Block Diagram
Output
Reconstructed
Signal
Calculator
Input
Input PCM
Format
Conversion
Difference
Signal
Computation
Adaptive
Quantizer
Inverse
Adaptive
Quantizer
Adaptive
Predictor
Quantizer
Scale Factor
Adaptation
Adaption
Speed Control
Tone
& Transition
Detector
Altera Corporation
A-SB-008-01
ALTERA MEGAFUNCTION
MEGAFUNCTION PARTNERS
ALTERA
PARTNERS PROGRAM
PROGRAM
SB 8: ADPCM Megafunction
Figure 2. ADPCM Decoder Block Diagram
Input
Inverse
Adaptive
Quantizer
Reconstructed
Signal
Calculator
Output PCM
Format
Conversion
Synchronous
Coding
Adjustment
Output
Adaptive
Predictor
Quantizer
Scale Factor
Adaptation
Adaptation
Speed Control
Tone &
Transition
Detector
Coding Rates & Standards
The ADPCM megafunction supports:
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All four coding rates (5-, 4-, 3-, and 2-bit), six CCITT standards (G.721, G.723,
G.726, G.726a, G.727, G.727a), and both A- and µ-law PCM formats
Single coding rates and standards
Multiple coding rates and standards
When instantiating the ADPCM megafunction, the control bits can be used to select the
desired coding rate. Depending on the coding rate selected, the function may use less
logic. The Altera MAX+PLUS® II software will automatically minimize the design,
removing any unused logic.
The G.726 standard is a fixed ADPCM algorithm for conversion to and from 64 kbits
per second and 40, 32, 24, and 16 kbits per second. The algorithms of the G.727 standard
quantize the signal into core and enhancement bits. The core bits are used for precision
while the enhancement bits are used to reduce the quantization noise in the
reconstructed signal. The core bits must reach the decoder, but the enhancement bits
can be discarded to alleviate congestion. (The G.726a and G.727a represent
modifications to the standards.)
Performance & Utilization
Table 1 shows the performance and typical utilization of the ADPCM megafunction.
Table 1. ADPCM Performance & Utilization (for a EPF10K100-3 device)
Function
Speed
Architecture
Logic Cells
EABs
16-channel ful-duplex ADPCM,
covering all 6 CCITT Standards
5.12 MHz
FLEX 10K
3,963
5
®
2610 Orchard Parkway
San Jose, CA 95134-2020
(408) 894-7000
http://www.altera.com
2
Copyright  1996 Altera Corporation. Altera, AMPP, MAX+PLUS, MAX+PLUS II, FLEX, and FLEX 10K are trademarks and/or service marks
of Altera Corporation in the United States and other countries. Other brands or products are trademarks of their respective holders. The
specifications contained herein are subject to change without notice. Altera assumes no responsibility or liability arising out of the application
or use of any information, product, or service described herein except as expressly agreed to in writing by Altera Corporation. Altera customers
are advised to obtain the latest version of device specifications before relying on any published information and before placing orders for
products or services. All rights reserved.
Altera Corporation