TDMA T2290/T2297:
TX Offset Oscillator
B10
Description
The offset oscillator frequency is controlled by U110(ZIF/SYN) via
TXCP_OUT
. The operating frequency will depend on the dc biasing of CR300. The offset oscillator
frequency is 157.32MHz in 800MHz mode, an d 192.36MHz in 1900MHz mode.
The two operating frequencies are controlled by the 800*_1900 line. A high state at 800*_1900 will switch Q351 on. This condition will bypass path to ground for C316,
thus C316 is not be active with the tank circuit. During this state, the TX offset oscillator will operate at 192.36MHz. A low state at 800*_1900 will switch Q351 off.
This condition will allow C316 to remain active with the tank circuit. Duri ng this state the TX offset oscillator will operate at 157.32MHz.
The
TXCP_ADA
is a loop filter adapt output. During a high current state R308 will be grounded. This will increase the loop filter bandwidth by decreasing the amount
of resistance at the discharge path of C303. During low curent conditions R308 will not be grounded. This will decrease the loop filter bandwidth by increasi ng the
amount of resistance at the discharge path of C303.
LP_SWITCH
control comes from U110. In Analog mode, the input to Q301 becomes high causing it to switch on. This condition will complete the filter circuit path
to ground, thus allowing the filter ciruitry to become active on the VCO_STEER line . This filter circuit is used to improve phase noise due to stringent adjacent channels
in Analo g mode.
In analog mode the FM signal comes from U1800(DCI) pin 39 and is modulated directly in the offset oscillator. The offset oscillat or with the FM then enters U301
(QMOD). The Quadmod (U301) will fe ed back the offset frequency to U110 for proper PLL(Phase Locked Loop) operation.
Q391
Tank
Ckt
TXCP_OUT
TXCP_ADA
U110
ZIF-SYN
IC
CR301
CR300
U1800
DCI
LP_SWITCH
VCO_FDBK
Q301
U301
MERLIN TX
U1907
Q351
C316
800*_1900
FM
Loop
Filter
Summary of Contents for T2290
Page 1: ...DIGITAL WIRELESS TELEPHONE Service Manual Level 3 Release 1 TDMA T2290 T2297 ...
Page 26: ... 2000 Motorola Inc TDMA T2290 T2297 Cellular Overview 16 ...
Page 40: ...Motorola Confidential Proprietary TDMA T2290 T2297 TDMA Test Mode NAM Programming 30 ...
Page 68: ...Disassembly TDMA T2290 T2297 Keypad Removal Motorola Confidential Proprietary 58 ...