TDMA T2290/T2297:
RF Detect/A_D Switch
B18
Description
The RF detect circuit is use d to detect the RF amplitud e level of the TX signal. RF detect reports back to U1800(DCI) pin 31, using a dc level, for amplitude stabi lization. The RF
detect circuit is RF coupled with the TX sign al from either band, 8 00MHz or 1900MHz. The RF input is then conver ted into a dc level an d sent to the RF_DETECT line. There are
two stages in the RF detect circuit which are used to increase the dynamic range of the RF detect output. The two stages are controlled by the TX_STEP line input. TX _STEP is
high when power steps 0 through 5 are used . TX_STEP is low when power steps 6 through 10 are used .
When TX_STEP is low Q503-A is switched on and Q503-B is swi tched off. Q501 inverts the state of Q503-B. This operation forward biases diode CR504. A t the same time it cuts
off the supply to diode CR502, th us not forward biasing CR502. Whe n TX_STEP is hig h Q503-A is switc hed off and Q503 -B is switched on . This operation cuts off the supply to
diode CR504. At the same time current is supplied to amplifier Q502 and CR502. During low power steps the signal is se nt directly to the RF _DET output through CR504. During
high power steps the signal passes through amplifier Q502 and then sent to the RF _DET output through CR502.
Proper PA loads need to be defined when op erating in 80 0MHz analog and 800MHz digit al mode. This is done by making Load B active or inactive on the PA output path. When
transmitting in 800MHz an alog mode, LOAD A is use d and LOAD B is bypassed. LOAD B is bypassed by allowing CR8 22 to be forward biased. Forward biasing CR822 w ill pro-
vide a ground state at the anode side, thus allowing only LOAD A(C823) to be present.
CR822 is forward biase d by having a supply voltage present at the AD_SW line. When the A_D line is pulled d own, Q505 is switched on, forcing the base of Q821 low. PNP tran-
sistor Q821 will then b e switched on, allowin g the output(AD_SW) to be pulled high from SW _QMOD_KEY.
In 800MHz digital mode, CR821 i s not forward biased, thus having CR821 in an open state. Dur ing this state LOAD A and LOAD B are used for the PA load. To have CR822 in an
open state, AD_SW is not pulled high by SW_QMOD_KEY. The AD_SW state is determined by the A_D line . Having a high state at A_D would switch Q505 off, thus not switch-
ing Q821 oon.
CR504
Q502
CR502
CR503
SW_QMOD_KEY
TX_STEP
TX_2.75
RF_DET
Q501
Q503-B
Q503-A
TX_STEP
TL800
TL801
TL900
TL901
TX_800
TX_1900
TX_800
TX_1900
SW_QMOD_KEY
Load
A
Load
B
CR822
A_D
Q505
Q821
SW_QMOD_KEY
Содержание T2290
Страница 1: ...DIGITAL WIRELESS TELEPHONE Service Manual Level 3 Release 1 TDMA T2290 T2297 ...
Страница 26: ... 2000 Motorola Inc TDMA T2290 T2297 Cellular Overview 16 ...
Страница 40: ...Motorola Confidential Proprietary TDMA T2290 T2297 TDMA Test Mode NAM Programming 30 ...
Страница 68: ...Disassembly TDMA T2290 T2297 Keypad Removal Motorola Confidential Proprietary 58 ...