44023-1297 <90-00058>
P
AGE
3
CIRCUIT DESCRIPTION
T
he PABX/Trunk Interface Module circuitry consists of three
sections: audio, signaling/control and power regulator.
A
UDIO
S
ECTION
The audio section consists of a receive circuit and a transmit
circuit. Refer to Fig. 1.
Here is a brief description of each of the functional parts of the
circuit:
Receive Circuit
The receive circuit consists of:
♦
A line input (receive) transformer (T1)
♦
Input pad
♦
Summing circuit
♦
Mute FET
♦
Busy and alert tone FETs
♦
Level Control (R5)
♦
Amplifier
♦
Drop output (receive) transformer (T2)
♦
Drop receive/monitor jacks
LINE RCV signals (pins 2 and 4) feed through T1 to the pad.
This pad provides 23 dB of attenuation which prevents
overdriving the mute FET. You can strap the attenuation out in
cases of low line levels (below -5 dBm). Use the summing inputs
in the 440 CMS multi-station package.
External 49020 Tone Supply Subassembly busy and alert tones
connect to pins 36 and 32 respectively. The circuits signaling/
control section operates control FETs for these tones and the
mute. Set the amplifier gain with R5. The drop output feeds
through T2 and the jacks to pins 13 and 7.
Transmit Circuit
The transmit circuit consists of:
♦
Drop transmit/monitor jacks
♦
A drop input (transmit) transformer (T4)
♦
Transmit pad
♦
Mute FET
♦
Off-hook and on-hook tone FETs
♦
Level control (R24)
CONTINUED
. . .
