參數(shù)資料
型號: PEF24902
英文描述: ISDN Line Interface
中文描述: ISDN線路接口
文件頁數(shù): 19/73頁
文件大?。?/td> 1618K
代理商: PEF24902
PEB 2466
PEF 2466
Functional Description
Hardware Reference Manual
10
2001-02-20
3
Functional Description
The telephone subscriber loop is a bi-directional two-wire line. The Subscriber Line
Interface Circuit (SLIC) on the network side converts the two-wire interface to a four-wire
interface with separate receive and transmit signals, which connect to the SICOFI
4-μC.
The SLIC can be either a transformer or an electronic circuit with operational amplifiers.
It must have a defined input impedance towards the subscriber line for maximum signal
power transfer and return loss. The requirements for the input impedance vary from
country to country and demand impedance matching to the different environments.
Country-specific adaptations are also required for the transhybrid loss, which is a loss
between the transmit and the receive ports of the two-wire to four-wire hybrid.
3.1
DSP-based Architecture
The impedance matching and transhybrid balancing functions are performed by loop
filters between the transmit path (analog to PCM) and the receive path (PCM to analog).
The filter characteristics must be adjusted according to the local requirements of each
market.
In the analog domain, filters must be optimized in hardware; this is generally
both tedious and time-consuming. This is not the case with the DSP-based SICOFI
4-
μC four-channel codec. Its integrated signal processor implements the impedance
matching and transhybrid balancing functions as digital, programmable filters. It also
performs frequency response corrections and level adjustments to enable the design of
a truly universal and internationally applicable telephone linecard. Transmission
characteristics and frequency behavior are enhanced by the accuracy of the digital
filters, which do not fluctuate over temperature or with age.
As an additional benefit of its DSP-based architecture, the PEB 2466 also provides two
tone generators per channel. An on-chip level-metering unit allows line-characterization
without extra hardware; it can also be used to detect specific tones, e.g., modem tones.
3.2
Programming and Control
A very simple Microcontroller Interface is used to program the SICOFI
4-μC functions.
The same port provides access to 28 general purpose I/O pins of the Signaling Interface.
This allows efficient and convenient monitoring and control of other linecard functions,
such as on-/off-hook detection, ground-key detection, switching of ring signals and test
relays. The Serial Microcontroller Interface provides a programming and control
interface and is generic and non-proprietary for use with any microcontroller. It can be
implemented with as few as three signal lines, since the data receive and data transmit
pins may be strapped together.
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