MH88632B 데이터 시트보기 (PDF) - Mitel Networks

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MH88632B

Central Office Interface Circuit

Mitel Networks 

Preliminary Information

MH88632B

User defined Input Impedances can be used to

satisfy most national requirements. See Table 1.

All connections should be kept as short as possible.

Network Balance Impedance

The MH88632B’s Network Balance Impedance can

be selected to mirror the Input Impedance, to be

AT&T compromise or set to a user defined value.

Thus, the Network Balance Impedance can comply

with most national requirements.

With NS at logic 0, the Network Balance Impedance

is selected to mirror the Input Impedance of the

device. No connection should be made to NATT, N1

and N2.

To select a Network Balance Impedance equal to

AT&T Compromise (i.e. 350Ω+(1kΩ//210nF) ), NS

should be set to a logic 1 and a direct connection

made between NATT and N1. No connection should

be made to N2.

To set a user defined Network Balance Impedance

NS is set to a logic 1. An impedance network which

is 10 times the required Network Balance Impedance

must be placed between N1 and AGND. Another

impedance network must be placed between N1 and

N2 which is 10 times the selected input impedance

of the device.

For example, to implement a Network Balance

Impedance of 220Ω+(820Ω//115nF), an impedance

network of 2200Ω+(8200Ω//11.5nF) must be

connected between N1 and AGND. An impedance

network equal to 10 times the selected Input

Impedance must be connected between N1 and N2.

See Table 2.

All connections should be kept as short as possible.

2-4 Wire Conversion

The device converts the balanced 2-Wire input,

presented by the line at Tip and Ring, to a ground

referenced signal at TX. This circuit operates with or

without loop current; signal reception with no loop

current is required for on-hook reception enabling the

detection of Caller Line Identification signals.

Conversely the device converts the ground

referenced signal input at RX, to a balanced 2-Wire

signal across Tip and Ring.

The 4-Wire side (TX and RX) can be interfaced to a

filter/codec, such as the Mitel MT896X, for use in

digital voice switched systems.

During full duplex transmission, the signal at Tip and

Ring consists of both the signal from the device to

the line and the signal from the line to the device.

The signal input at RX, being sent to the line, must

not appear at the output TX. In order to prevent this,

the device has an internal cancellation circuit. The

measure of attenuation is Transhybrid Loss (THL).

Programmable Transmit and Receive Gain

The Transmit Gain (GTX) of the MH88632B is the

gain from the balanced signal across Tip and Ring to

the ground referenced signal at TX. It is

programmed by making a connection to GTX1. A

direct connection from GTX1 to GTX0 selects a gain

of 0dB. A direct connection from GTX1 to AGND

selects a gain of +6dB. Other gains can be

programmed by connecting a resistor (RTX) between

GTX1 and AGND. The value of resistor is selected

using the following formulae.

RTX =

5000

10(-GTX/20) - 0.5

GTX = - 20 log(0.5+5000)

RTX

The Receive Gain (GRX) of the MH88632B is the

gain from the ground referenced signal at RX to the

balanced signal across Tip and Ring. It is

programmed by making a connection to GRX1. A

direct connection from GRX1 to GRX0 selects a gain

of 0dB. A direct connection from GRX1 to AGND

selects a gain of +6dB. Other gains can be

programmed by connecting a resistor (RRX) between

GRX1 and AGND. The value of resistor is selected

using the following formulae.

RRX =

5000

10(-GRX/20) - 0.5

GRX = -20 log(0.5+5000)

RRX

For the correct programming of Transmit and

Receive Gains the selected Input Impedance must

match the specified telephone line characteristic

impedance.

2-243

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