MH88632 データシートの表示（PDF） - Mitel Networks

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MH88632

Central Office Interface Circuit

Mitel Networks 

Preliminary Information

MH88632

c) Supervision Features TG & RG (Tip Ground

and Ring Ground Detect Output)

The TG (Tip Lead Ground Detect) output provides a

logic low when the tip lead is at ground (AGND)

potential. The RG (Ring Lead Ground Detect) output

provides a logic low when the Ring lead is at ground

(AGND) potential.

See Table 6 for Loop Ground Status Outputs.

Ground Start Signalling Features

For Ground Start signalling, relay K2 and resistors

R1 and R2, and relay K3 and resistor R3 are

required (See Figure 8). Activation of K2 is controlled

by the logic signal at the BRC (Bias Relay Control)

input while activation of K3 is controlled by the logic

signal at the GRC (Ground Relay Control) input.

K2 is used to engage the bias resistors while K3 is

used to ground the right lead; this is used in ground

start applications for signalling to the central office.

Typical Ground Start Signalling

Protocol

Refer to Figure 8 for Typical LS-GS Application

Circuit.

In the idle state, the system (e.g., PBX control card)

provides a logic high to the BRC input. This activates

the COIC’s second internal relay driver which

activates relay K2. Both contacts of relay K2 close,

which connect the -48VDC supply to Tip (tip lead)

and Ring (ring lead) through bias resistors R1 and

R2.

Depending on which Ground Start protocol is used,

initiating a Ground start call to the central office can

be performed by the following sequence of events.

The system provides a logic low to the GRC input.

this activates the COIC’s third internal relay driver

which activates relay K3. The contacts of relay K3

close, which connects the ring lead to ground

through a current limiting resistor R3.

The Central Office reconizes the ring ground

condition and responds by grounding the tip lead.

The COIC senses the grounded Tip and switched the

TG (Tip Lead Ground Detect) output to a logic low.

The system then applies a logic high to the LRC

(Loop Relay Control) input. This activates the COIC’s

first internal relay driver which activates relay K1.

Both contacts the relay K1 close, which activates the

COIC’s internal circuitry resulting in an active line

termination across Tip and Ring. The system then

provides a logic low to the BRC input. This

deactivates the COIC’s second internal relay driver

which deactivates K2. Both contacts of relay K2

open, which disconnect the bias from Tip and Ring.

The system then provides a logic high to the GRC

input. This deactivates the COIC’s third internal relay

driver which deactivates relay K3. The contact of

relay K3 opens. which disconnects the grounded ring

lead. The voice link is now established.

Receiving a Ground Start call from central office is

performed similarly. The central office can signal the

COIC by either grounding the tip lead or by

grounding the ring lead.

Hybrid

The 2-4 Wire Hybrid circuit separates the balanced

full duplex signal at Tip and Ring of the telephone

line into receive and transmit ground referenced

signals at Rx (Receive) and TX (Transmit) of the

COIC. The hybrid also prevents the input signal at

RX from appearing at TX. The degree to which the

Hybrid minimises the contribution of the RX signal at

the TX output is specified as transhybrid loss. For

maximizing transhybrid loss, see the Network

Balance section.

The 4-Wire side can be interfaced to a filter/codec

such as the Mitel MT896X, for use in digital voice

switched systems.

Line Impedance

The MH88632’s Tip-Ring impedance (Zin) can be set

to 600Ω, 900Ω or to a user selectable value. Thus,

Zin can be set to any international requirements. The

connection to Z1 determines the input impedance.

With Z1 connected to Z600, the line impedance is set

to 600Ω. With Z1 connected to Z900, the line

impedance is set to 900Ω. A user defined impedance

can be selected which is 0.1 times the impedance

between Z1 and Z2. For example, with 2200Ω in

series with 11.5nF in parallel with 8200Ω, all between

Z1 and Z2, the devices line impedance will be 220Ω

in series with 115nF in parallel with 820Ω. See Table

3 and Figures 4 & 5.

2-239

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