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TDMA M3090/M3097:
TX_STEP
SW_QMOD_KEY
DET_800_1900
Description
The RF detect circuit is used to detect the RF amplitude level of the TX signal. RF detect reports back to U201 (DCI) pin 31, using a dc level, for amplitude stabilization.
The RF detect circuit is RF coupled with the TX signal from either band, 800MHz or 1900MHz. The RF input is then converted into a dc level and 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 Q902-A is switched off and Q901 is switched on. Since Q902-A is switched off , the supply to diode CR903 gets cut off thus not forward bias-
ing CR903 and not letting any signal through. By Q901 being switched on, it supplies the desired current to amplifier Q904 and at the same time Q901 also switches
Q902-B on. Having Q902-B on will forward bia s diode CR904, letting the signal through.
When TX_STEP is high Q902-A is switched on and Q901 is switched off. Since Q901 is switched off, the supply to amplifier Q904 is cutoff and also Q902B is
switched off, thus not forwa rd biasing CR904 and not let ting any signal flow through . Having Q902-A on will forward bias diode CR903 lettin g the signal through.
In summary, during high power steps the signal is sent directly to the RF _DET output through CR903. During low power steps the signal passes through amplifier Q904
and then sent to the RF_DET output through CR904.
RF Detect Circuit
TX_STEP
TX_2.75
Q901
CR902
Q902-A
SW_QMOD_KEY
Q904
CR903
Q902-B
CR904
RF_DET
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