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A Ingap/Gaas Hbt Wlan Power Amplifierwith Power Detector

In wireless systems, the power amplifier (PA) is one of
the highest energy-consuming components. The efficiency
of the power amplifier is the key reqnirement [I]. To
improve power added efficiency (PAE), an RF power
amplifier can be operated in high efficient modes such as
class-B, class-E, and class-F. However, these high
efficiency amplifiers have nonlinearity, which result in
unacceptable adjacent channel power ratio. In order to
satisfy the linearity requirement, power amplifiers are
typically operated in linear Class-A or Class-AB
configurations [2]. But these power amplifiers have low
power efficiency. The gain should be increased to
improve PAE in the same supply voltage. To increase the
overall power amplifier gain, the number of stages in PA
must be increased. This increases the chip size, as well as
idle bias currents. If the gain of each stage power
transistor is quite high, two-stage configuration achieves
the enough gain. A method to increase gain in a power
transistor is to use a split WC ballasting power transistor
[3]. A power detector to measure the RF output power is
the key requirement for power control. Usually, output
power is monitored at output load, which causes the
degradation of output power [4-SI.
In this paper, the input power of power stage is sensed,
and the power level is indicated by the output voltage of
power detector. The two-stage power amplifier, which
comprises of high gain power transistors, is presented.
(C)
I 2 3 4 3 6 7 8 9 IO
FrequencyfOtk]
Fig.1. (a) Base & emitter ballasting (b) Split WC ballasting
(c) Measured unilateral gain of hvo shuchmes
at same bias condition. (The emitter size is 1920um2)
11. DEVICE CHARACTERISTICS
As in Si BJT, HBT exhibits thermal instability-related
...

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