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The counter and mode settings of the synthesizer are also programmed via 3-wire interface.
D. TX APC Part
The AD8315[U412] is a dual band RF power controller for RF power amplifiers operating in the
850MHz to 2GHz range.
The AD8315[U412] controls the power output of the selected RF channel. RF power is controlled by
driving the RF amplifier power control pins and sensing the resultant RF output power via a
directional coupler. The RF sense voltage is peak detected using an on-chip Schottky diode.
This detected voltage is compared to the DAC voltage at the VSET pin to control the output power.
An internal input signal[TXRAMP] is applied to the positive input of the AD8315 amplifier during the
TXEN mode and a directional coupler near the antenna feeds a portion of the RF output signal back
to the AD8315 peak detector converts this signal to a low frequency feedback signal that balances
the amplifier when this signal equals the RAMP input signal level.
E. Power Amplifier
The PF08107B[U409] is Dual band amplifier for E-GSM(880 to 915MHz) and DCS1800(1710 to
1785MHz). The efficiency of module is the 50% at nominal output power for E-GSM and the 43% at
32dBm for DCS1800. This module should be operated under the GSM burst pulse. To avoid
permanent degradation, CW operation should not be applied. To avoid the oscillation at no input
power, before the input is cut off, the control voltage Vapc should be control to less than 0.5V.
We have to improve thermal resistance, the through holes should be layouted as many as possible
on PCB under the module. And to get good stability, all the GND terminals and the metal cap should
be soldered to ground plane of PCB.
Figure 3-3. Synthesizer Block diagram
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3. TECHNICAL BRIEF
f
ref
13MHz
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