Motorola 38C V100 Service Manual page 14

Circuit Description
10
is amplified through tuned transistor amplifier Q252 before being used to mix with
the received frequencies through the emitters of the dual mixer transistor Q450.
The mixer produces sum and difference signals consisting of RX frequency plus RX
VCO frequency and RX frequency minus RX VCO frequency. The difference signal
is fed to SAW (surface acoustic wave) filter FL457. The purpose of the SAW filter
is to provide comprehensive removal of harmonics created during the mixing
process.
The resulting 400 MHz IF signal is passed to isolation amplifier Q480. The isolation
amplifier couples the analog IF signal to the following circuit which has a different
ground and also protects the base-band signals from stray RF. The isolation
amplifier is supported by Magic IC U200 Pin C7 SW_VCC.
Figure 2. IF Isolation Amplifier Operation
The IF signal is then passed to the Magic IC U200 Pin A7 PRE IN where it is
demodulated using external 800 MHz varactor diode CR249 (RX local oscillator set
up), which is driven by from Magic IC U200 Pin A9 LO2_CP.
The demodulated signal is converted internally to base-band digital form and
passed along the RX SPI bus to the Whitecap IC.
The RX SPI signal is made up of BDR (base-band data receive), BFSR (Base-band
Frame Synch Receive) and BCLKR (base-band clock receive), fed from Magic IC
Pin G8, Pin G9, and Pin F7 respectively.
The Whitecap IC U800 receives these signals on Pin A3, Pin D4, and Pin B4.
Within the Whitecap IC the signal is digitally processed to reduce Baud rate and
remove error correction bits.
The resulting digital signal is fed down the DIG_AUD_SPI bus to the GCAP II U900,
where it is converted to analog form and distributed to the correct outputs:
The Alert is generated within the Whitecap IC, given the appropriate data from the
incoming signal or SMS, and is fed to the alert pads LS1. This signal is supported
by ALRT_VCC, which is generated from B+ through Q903.
For the headset only, the SPKR signal is used from GCAP II Pin H6. The output is
fed out to the headset jack J504 Pin 3.
Transmit
Analog voice is fed from the Aux Microphone attached to the headset and is routed
from Pin 1 of the headset jack J504 to GCAP II, Pin H3.
Within the GCAP II, the analog audio is converted to digital and clocked out onto
the DIG_AUD SPI bus to the Whitecap IC U800.
MOTOROLA CONFIDENTIAL - PROPRIETARY
November 20, 2000
Isolation
Amp
MAGIC
IC
U200
Product Family 38C
Base-band
Signal
101001010100
000714-O
000714-O
6881036B20