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4.5 Transmitter
4.5.1 Transmitter: Modulator and Up-conversion Loop
The Axx modulation is based on the principle of the up-conversion modulation
phase locked loop and is accomplished via the SMARTI(D400).
nd
The 2
local oszillator provides the quadratic modulator with the TX IF signals
(1696MHz divided by 4 = 424MHz).
This resulting GMSK RF signal is compared in a phase detector with the down mixed
GMSK RF signal from the TX-VCO to get a control voltage for the TX-VCO.
Down mixing, is done in an internal mixer.
To close the loop, the control voltage (output of phase detector) is connected to the
switchable TX-VCO (Z570) after passing a low pass filter.
The TX-VCO, a "two in one" VCO is switched with the EGOLD+ signals
GSM_TX_VCOENQ
(TDMA-Timer J13)
the different modes.
The required voltage
VCC_2,8
1.LO
1285-1361 MHz
880-915 MHz
1710-1785 MHz
TX-VCO
4513
V1.0
A35-A36-A40
and PCN_TX_VCOENQ
is provided by
N430
424 MHz
TP
4512
Page 15 of 38
Company Confidential
(TDMA-Timer K12)
: 4
424 MHz
I Q
Phase
424 MHz
Detector
Mod ulator
Mod Signal
4511
Notes
into
2.LO
1696 MHz
ICM MP CC ST
09/01
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