Motorola MTR2000 T5544 Instruction / Field Service Manual page 201

Note
68P81096E28-C
09/30/05
The output of the gain adjust circuitry is fed through a 2-pole low-pass fil-
ter and into the inputs of two amplifiers. The outputs of the amplifiers are
fed to two transistors which are connected in a push-pull configuration to
drive the primary of the audio transformer. The audio signal is induced
into the secondary and output to the landline system (via the wire-trap ter-
minal connector) as balanced audio.
4-Wire Voice Audio Path (Refer to Figure 4)
For 4-wire configurations, phone line connections are made at the wire-
trap terminal connector on the station backplane. Landline-to-Station sig-
nals are connected at Line 1 Audio. Station-to-Landline signals are con-
nected at Line 2 Audio.
Voice audio signals sent to/from the station via 4-wire copper pair are pro-
cessed by the 4-wire audio path on the WIB (Line 1 Audio & Line 2 Audio).
The 4-wire audio path operates as follows:
Landline-to-Station balanced audio (Line 1 Audio) is input to the primary
of an audio transformer. The signal is induced into the transformer sec-
ondary and fed to a buffer. (Note that jumpers in parallel with the trans-
former primary and secondary provide for selectable impedance
matching. Refer to Figure 2 for impedance matching information.)
The buffer feeds the audio signal to the pre-emphasis and gain adjust cir-
cuitry. To compensate for line losses, the gain adjust circuitry provides
coarse adjustment for eight levels of gain adjust (5, 10, 15, 20, 25, 30, 35, and
40dB), which is under the control of the SCM (via the SPI latch).
The output of the gain adjust circuitry is de-emphasized and then fed to an
A/D converter in the PCM codec, which digitizes the audio signal into a
PCM output. This output is fed serially to the DSP ASIC on the SCM,
which provides a memory-mapped interface with the DSP and other SCM
audio circuitry (refer to the Station Control Module section).
Station-to-Landline audio is input to the WIB as PCM data (WL 1/2 RXD)
and fed to a D/A converter in the PCM codec, which takes the PCM data
and converts it to an analog audio signal. The audio signal is fed to the
gain adjust circuitry. Under control of the SCM (via the SPI latch), the gain
adjust circuitry provides four coarse levels of gain (0dB, -6dB, -12dB, and
-20dB). The output of the gain adjust circuitry is fed through a 2-pole low-
pass filter and into the inputs of two amplifiers (line drivers).
The outputs of the amplifiers are fed to two transistors which are connect-
ed in a push-pull configuration to drive the primary of an audio trans-
former. The audio signal is induced into the secondary and output to the
landline system (via the wire-trap terminal connector on the backplane) as
balanced audio.
The outputs of the amplifiers are fed to two transistors which are connect-
ed in a push-pull configuration to drive the primary of an audio trans-
CLN1204 Wireline Interface Board
7