TDMA T2290/T2297:
Exciter
B14
Description
After the desired transmit informati on is modul ated with a TX carrier frequency, enough signal power needs to be provided for RF transmission through the antenna. The
exciter stage is used to relieve amplifi cation of the final stage PA. This reduces excess heat dissipati on and overloading of the final stage PA.
In 800MHz mode, the TX signal passses through FL452 and then is a mplified by Q401. Q401 is driven on by supp ling D through Q475-A. Q475-A can be
switched on or off via the 800KEY line. In 8 00MHz TX mode, 800KEY is low. Thi s state brings the gate of Q475-A to a low level, causing Q475-A to switch on.
There are two operating modes in the 800MHz band, a nalog and digital . In 800MHz mode Q810 is switched on with a low level of the gate. The output of Q810 will then
be used to provide the biasi ng voltage for the final st age PA(U801).
The 800BIAS voltage level determines the operating condition of the fina l stage PA. A l ower voltage level at 800BIAS denotes digital mode and a higher voltage level
denotes analog mode. In analog mode, A_D is pulled high caus ing Q811 t o be switched off. This state causes a voltage drop across R811, thus, having a lower voltage
level at 800BIAS. In digital mode A_D is pulled low causing Q811 to be switched on. During this state R8 11 is bypassed an d 800BIAS will ha ve a higher voltage level.
In 1900MHz mode, the TX signal is ampli fied by Q411. Q411 is driv en on by suppling D through Q475-B. Q475-B can be switch ed on or off via the
1900KEY line. In 1 900MHz mode, 1900KEY is low. This s tate brings the gate of Q475-B to a low level, causi ng Q475-B to switch on.
1900BIAS provides the proper biasing voltage for the final stage PA(U901). 1900BIAS is supplied from TX_2.75. In 1900MHz mode, having 1900KEY low will swit ch
Q910 on.
Q411
1900_OUT
800_OUT
FL452
FL454
D
1900KEY
Q475-B
D
Q475-A
Q401
800KEY
CR810-B
CR910-B
1900_PA_IN
800_PA_IN
CR910-A
TX_2.75
Q910
1900BIAS
CR810-A
TX_2.75
Q810
800BIAS
Q811
A_D
R811
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 ...