MH88524 데이터 시트보기 (PDF) - Mitel Networks

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MH88524

Dual 2-4 Wire Circuit

Mitel Networks 

Preliminary Information

MH88524

Functional Description

The MH88524 is a Dual 2-4 Wire Circuit used to

interface between ground reference 2-Wire circuitry

and ground referenced 4-Wire circuitry. The device

can accommodate two full duplex audio links.

Hybrid

The 2-4 Wire hybrid circuit separates the ground

reference full duplex signal at JUNi (where i=1 or 2)

of the switched line into receive and transmit ground

referenced signals the RXi (Receive) and TXi

(Transmit). The hybrid also prevents the input signal

at RXi from appearing at TXi. The degree to which

the hybrid minimises the contribution to the RXi

signal at the TXi output is specified as transhybrid

loss. For maximising transhybrid loss, see the

Transhybrid Loss section.

The 4-Wire side can be interfaces to a COIC such as

the MH88631 for use in analog voice switched

systems; or a filter/codec, such as the Mitel MT896X,

for use in digital voice switched systems.

The 2-wire side can be interfaces to a crosspoint

switch such as the MT8816 or a junctor SLIC such

as the MH88510 for use in analog voice switched

systems.

Return Loss at Junctor

The MH88524’s Junctor impedance (Zin) is fixed at

604Ω nominal when RXi and TXi in a feedback loop

as shown in Figure 6, the JUNi impedance will

change, see Return Loss with Interface Circuit.

Return Loss with Interface Circuit

To maximise return loss at Tip-Ring of the Interface

Circuit, the termination impedance at Tip-Ring of the

Interface Circuit (COIC or SLIC) should match the

Interface Circuit’s input impedance (600Ω, 900Ω or

complex). However, with the inclusion of the

MH88524, the interface circuit’s input impedance is

dependent on the JUNi termination resistance. For

optimum return loss the JUNi should be terminated

with 754Ω.

Figure 6, shows, illustrates a typical connection

between an Interface Circuit (MH88631) and the

MH88524. Note how the return loss occurs when

JUNi is terminated with 754Ω.

Figure 8 illustrates a typical connection between two

interface circuits (MH88631), through an MH88524

and two crosspoint switches. Optimum return loss

occurs when JUNi is terminated with 754Ω. Since the

JUNi input/output impedance is 604Ω, the MH88510

JUNC input/output impedance is 604Ω, and the

crosspoint switches resistance are 75W + 75Ω, this

configuration gives optimum return loss.

Transhybrid Loss

THL = log (VRX/VTX)

Transhybrid loss is maximised when the JUNi

termination impedance is 754W. In addition, good

transhybrid loss is indicated in Figure 4 and AC

Electrical Characteristics.

Fixed Transmit and Receive Gain

Transmit Gain (JUNi to TXi, TXi/JUNi) and receive

Gain (RXi to JUNi, JUNi/RXi) are both fixed at 0dBV

providing the MH88524 JUNi impedance is 754Ω.

Application with MT8840, MH88500 and

MH88524

Figure 11 illustrates an application for the

MH88524’s wide bandwidth. The MT8840 requires a

2-4 Wire converter which has good transhybrid loss

at 32kHz. Since the MH88524 operates to 50kHz, it

is ideal for this application. In addition, if a SLIC

(Subscriber Line Interface Circuit) is required, the

MH88500 can also be used since it also has a 604Ω

Junctor and a wide bandwidth.

Mechanical Data See Figure 12.

2-77

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