PBL386302QNT Ver la hoja de datos (PDF) - Ericsson

Número de pieza

componentes Descripción

Fabricante

PBL386302QNT

Subscriber Line Interface Circuit

Ericsson  

PBL 386 30/2

+

TIP

ZL

VTR

ZTR

+

EL

-

-

RING

TIPX

RF RP

RF RP

RINGX

+

RHP

G 2-4S

-

IL

VTX

IL

ZT

+

VTX

-

Four-Wire to Two-Wire Gain

From (1), (2) and (3) with EL = 0:

G4 −2

=

VTR

VRX

=

− ZT

ZRX

⋅

ZT

αRSN

ZL

+ G2 − 4S ⋅ ( ZL

+ 2RF

+ 2RP)

PBL 386 30/2

RSN

I L /αRSN

ZRX

+

VRX

-

Figure 8. Simplified ac transmission circuit.

Functional Description

and Applications Informa-

tion

Transmission

General

A simplified ac model of the transmission

circuits is shown in figure 8. Circuit analysis

yields:

VTR

= VTX

G2 − 4S

+ IL

⋅ (2RF

+ 2RP )

(1)

VTX + VRX = IL

ZT ZRX αRSN

(2)

VTR = EL - IL · ZL

(3)

where:

VTX is a ground referenced version of the

ac metallic voltage between the TIPX

and RINGX terminals.

G2-4S is the programmable SLIC two-wire

to four-wire gain (transmit direction).

See note below.

VTR is the ac metallic voltage between

tip and ring.

EL is the line open circuit ac metallic

voltage.

IL is the ac metallic current.

RF is a fuse resistor.

RP is part of the SLIC protection

ZL is the line impedance.

ZT determines the SLIC TIPX to RINGX

impedance at voice frequencies.

ZRX controls four- to two-wire gain.

VRX is the analog ground referenced re-

ceive signal.

αRSN is the receive summing node current

to metallic loop current gain = 200.

Note that the SLICs two-wire to four-wire

gain, G2-4S, is user programmable between

two fix values. Refer to the datasheets for

values on G2-4S.

Two-Wire Impedance

To calculate ZTR, the impedance presented

to the two-wire line by the SLIC including

the fuse and protection resistors RF and RP,

let:

VRX = 0.

From (1) and (2):

ZTR

=

ZT

αRSN ⋅ G 2− 4S

+

2RF

+

2RP

Thus with ZTR, αRSN, G2-4S, RP and RF known:

ZT = αRSN ⋅ G2− 4S ⋅ (Z TR − 2RF − 2RP )

Two-Wire to Four-Wire Gain

From (1) and (2) with VRX = 0:

G2− 4

=

VTX

VTR

=

ZT / αRSN

ZT

αRSN ⋅ G2 − 4S

+

2RF

+ 2RP

For applications where

ZT/(αRSN·G2-4S) + 2RF + 2RP is chosen to be

equal to ZL the expression for G4-2 simplifies

to:

G4 −2

=−

ZT

ZRX

⋅

1

2G2 − 4S

Four-Wire to Four-Wire Gain

From (1), (2) and (3) with EL = 0:

G4 −4

=

VTX

VRX

=

− ZT

ZRX

⋅

G 2− 4S ⋅ ( ZL + 2RF + 2RP)

ZT

αRSN

+ G2 −4 S ⋅ ( ZL

+ 2RF

+

2RP )

Hybrid Function

The hybrid function can easily be imple-

mented utilizing the uncommitted amplifier

in conventional CODEC/filter combinations.

Please, refer to figure 9. Via impedance ZB

a current proportional to VRX is injected into

the summing node of the combination

CODEC/filter amplifier. As can be seen

from the expression for the four-wire to

four-wire gain a voltage proportional to VRX

is returned to VTX. This voltage is converted

by RTX to a current flowing into the same

summing node. These currents can be

made to cancel by letting:

VTX

RTX

+

VRX

ZB

= 0(EL

= 0)

The four-wire to four-wire gain, G4-4, in-

cludes the required phase shift and thus

the balance network ZB can be calculated

from:

ZB

=

−RTX

⋅

VRX

VTX

=

R TX

⋅

ZRX

ZT

⋅

ZT

α RSN

+ G2 −4 S ⋅ (ZL

+ 2RF

+ 2RP )

G2 −4 S ⋅ (ZL + 2RF + 2RP )

10

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