V1.0 Page 15 of 38 ICM MP CC ST
A35-A36-A40 Company Confidential 09/01
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 Notes
phase locked loop and is accomplished via the SMARTI(D400).
The 2
nd
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) and PCN_TX_VCOENQ(TDMA-Timer K12) into
the different modes.
The required voltage VCC_2,8 is provided by N430
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