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參數資料

型號：	L9313
英文描述：	Line Interface and Line Access Circuit Full-Feature SLIC and Ringing for TR-57 Applications
中文描述：	線路接口和線路接入電路全功能SLIC和敲響訓練班- 57應用
文件頁數：	33/40頁
文件大小：	746K
代理商：	L9313

Data Sheet

September 2001

Full-Feature SLIC and Ringing Relay for TR-57 Applications

L9313 Line Interface and Line Access Circuit

Agere Systems Inc.

ac Applications

(continued)

Codec Types

(continued)

First-Generation Codecs

These perform the basic filtering, A/D (transmit), D/A

(receive), and

-law/A-law companding. They all have

an op amp in front of the A/D converter for transmit

gain setting and hybrid balance (cancellation at the

summing node). Depending on the type, some have

differential analog input stages, differential analog

output stages, +5 V only or

5 V operation, and

-law/A-law selectability. These are available in single

and quad designs. This type of codec requires continu-

ous time analog filtering via external resistor/capacitor

networks to set the ac design parameters. An example

of this type of codec is the Agere T7504 quad 5 V only

codec.

This type of codec tends to be the most economical in

terms of piece part price, but tends to require more

external components than a third-generation codec.

Further, ac parameters are fixed by the external R/C

network so software control of ac parameters is diffi-

cult.

Third-Generation Codecs

This class of devices includes all ac parameters set

digitally under microprocessor control. Depending on

the device, it may or may not have data control latches.

Additional functionality sometimes offered includes

tone plant generation and reception, PPM generation,

test algorithms, and echo cancellation. Again, this type

of codec may be +5 V only or

5 V operation, single

quad or 16-channel, and

-law/A-law or 16-bit linear

coding selectable. Examples of this type of codec are

the Agere T8536/7 (5 V only, quad, standard features),

T8533/4 (5 V only, quad with echo cancellation), and

the T8531/36 (5 V only 16-channel with self-test).

ac Interface Network

The ac interface network between the L9313 and the

codec will vary depending on the codec selected. With

a first-generation codec, the interface between the

L9313 and codec actually sets the ac parameters. With

a third-generation codec, all ac parameters are set dig-

itally, internal to the codec; thus, the interface between

the L9313 and this type of codec is designed to avoid

overload at the codec input in the transmit direction,

and to optimize signal to noise ratio (S/N) in the receive

direction.

Because the design requirements are very different

with a first- or third-generation codec, the L9313 is

offered with two different receive gains. Each receive

gain was chosen to optimize, in terms of external com-

ponents required, the ac interface between the L9313

and codec.

With a first-generation codec, the termination imped-

ance is set by providing gain shaping through a feed-

back network from the SLIC VITR output to the SLIC

RCVN/RCVP inputs. The L9313 provides a transcon-

ductance from T/R to VITR in the transmit direction and

a single ended to differential gain in the receive direc-

tion, from either RCVN or RCVP to T/R. Assuming a

short from VITR to RCVN or RCVP, the maximum

impedance that is seen looking into the SLIC is the

product of the SLIC transconductance times the SLIC

receive gain, plus the protection resistors. The various

specified termination impedance can range over the

voiceband as low as 300

up to over 1000

. Thus, if

the SLIC gains are too low, it will be impossible to syn-

thesize the higher termination impedances. Further, the

termination that is achieved will be far less than what is

calculated by assuming a short for SLIC output to SLIC

input. In the receive direction, in order to control echo,

the gain is typically a loss, which requires a loss net-

work at the SLIC RCVN/RCVP inputs, which will

reduce the amount of gain that is available for termina-

tion impedance. For this reason, a high-gain SLIC is

required with a first-generation codec.