Topaz T2688/T200, T2988/T205 L3 Circuit Description
3
Motorola Proprietary Information
also allows the DC offsets of the IQ demodulator to be measured and then cancelled
out. The below matrix shows the truth table for the signals involved and the states of
the receiver path.
Receive
Calibrate
GSM
DCS
RXON1
H
H
L
RXON2
H
H
H
TXON
L
L
L
BS
L
H
Don’t Care
LNA Bias (GSM)
ON
OFF
OFF
LNA Bias (DCS)
OFF
ON
OFF
1
st
Mixer (GSM)
ON
OFF
OFF
1
st
Mixer (DCS)
OFF
ON
OFF
2
nd
Mixer
ON
ON
ON
PGA
ON
ON
ON
I/Q Demodulator
ON
ON
ON
7.
The gain of the Low Noise Amplifiers is approximately 18dB. The amplified signal is
then fed onto
Dual Image rejection SAW (Standing Acoustic Wave) filter U601,
an
identical filter to
U602
. (Loss approximately 2dB).
8.
The output is fed out of the filter on
Pin 7
for GSM and
Pin 5
for DCS, as an
unbalanced output. The discrete circuitry
C604 / C652 / C612 / L605
then split the
signal into 2 balanced signals. (at approxi11dB of input signal)
Figure 1
. U603 Block Schematic
Summary of Contents for TALKABOUT T2688
Page 1: ...T200 T2688 Level 1 2 Service Manual Rev 1 2 ...
Page 4: ...of 51 GSM Field Service Support iv T200 T2688 SECTION 1 GENERAL ...
Page 8: ...of 51 GSM Field Service Support 1 T200 T2688 SECTION 2 T200 DESCRIPTION ...
Page 15: ...of 51 GSM Field Service Support 8 T200 T2688 SECTION 3 FEATURE LIST ...
Page 22: ...of 51 GSM Field Service Support 15 T200 T2688 SECTION 4 DISASSEMBLY PARTS ...
Page 26: ...of 51 GSM Field Service Support 19 T200 T2688 4 5 Exploded Parts Diagram ...
Page 28: ...of 51 GSM Field Service Support 21 T200 T2688 SECTION 5 SIM CARDS AND SECURITY ...
Page 32: ...of 51 GSM Field Service Support 25 T200 T2688 SECTION 6 REPAIR AND TEST PROCEDURES ...
Page 40: ...of 51 GSM Field Service Support 33 T200 T2688 SECTION 7 ACCESSORIES ...
Page 42: ...of 51 GSM Field Service Support 35 T200 T2688 SECTION 8 SALES MODEL NUMBERS ...
Page 46: ...of 51 GSM Field Service Support 39 T200 T2688 SECTION 9 GLOSSARY OF TERMS ...
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