MOTOROLA CONFIDENTIAL - PROPRIETARY
12
November 20, 2000
6881036B20
Circuit Description
Product Family 38C
the TX VCO, the resulting burst would not meet the world standards for GSM with
respect to bandwidth as shown in Figure 5.
The loop filter acts as a very large capacitor and resistor to introduce a long R-C
time for smoothing. It uses a small capacitor and the very high input impedance of
an op amp buffer. During the TX_EN (Whitecap IC
Pin C1
) period when the
transmitter is preparing to operate, the capacitor charges. On receipt of DM_CS
(Whitecap IC
Pin E2
), when the Transmitter actually fires, the capacitor discharges
through the op amp giving a smooth TX VCO tuning voltage. The support voltage
for the loop filter is V1_FILT (V2 from GCAP II through
Q913
which creates V1_SW.
V1_SW, in turn, creates V1_FILT).
The TX VCO IC produces the required output frequency and is controlled by:
• TX_DCS (TX275 + DCS_SEL through (
Q1101
)
• TX275_GSM (G RX275) (
Q110
)
• TX275_DPCS (G RX275) (
Q2102
)
These signals configure the VCO for correct mode of operation (GSM 900 / 1800 /
1900), support voltage being SF_OUT (Magic IC
Pin C1
).
The TX VCO signal is then fed through buffer amplifier
Q330
, which is supported
by TX275. The TX VCO signal is split, a sample of the output frequency being
directed back to the Magic IC
Pin A3
for use within the TIC part of the Magic IC
to implement the TX phase-locked loop.
Isolation diode
CR330
prevents unstabilized TX VCO output from being amplified
and transmitted.
CR330
is biased on by the exciter voltage from the PAC IC (power
amplifier control IC)
U390
Pin 7
which allows the TX output frequency through to
000716-O
Figure 4. CP_TX Overshoot
000717-O
Figure 5. GSM Bandwidth Standard
Channel 24
Overshoot
Channel 56
Acceptable
3dB
Bandwidth
Unacceptable
3dB
Bandwidth
Summary of Contents for 38C V100
Page 1: ...Level 3 Service Manual Model V100 GSM Technology Product Family 38C Personal Communicator ...
Page 2: ......
Page 73: ...V100 BOARD LAYOUT PAGE 1 2 ...
Page 74: ...V100 BOARD LAYOUT PAGE 2 2 ...
Page 77: ...V100 CONNECTOR SCHEMATICS ...
Page 78: ...V100 DISPLAY SCHEMATICS ...
Page 79: ...V100 FM SCHEMATICS ...
Page 81: ......
Page 83: ......