Efficienc Enhancement - Linear CMOS RF Power Amplifiers for Wireless Applications - page 11

Fig. 2.3 Dynamic supply RF power amplifier block diagram

2.3.2.1 A Note on the Name of the Technique

This technique is also known under other names: envelopetracking ( ET )[ 5 , 17 , 33 ],
bias adaption [ 6 , Chap. 8], and envelope following ( EF )[ 29 , 30 ]. However, the
name envelope tracking is employed by Staudinger et al. in [ 31 ] to define a system
in which the supply voltage of the PA is varied according to the long-term rms value
of the input RF signal envelope. The name bias adaption might suggest that the PA
operates in different classes according to the envelope amplitude, which is not the
case. Although envelope following ,usedin[ 30 , 31 ], could be an alternative name
and a subclassification in wideband , average , and step for ET exists [ 35 ], in this
topic we use the term dynamic supply to avoid confusion.

2.3.2.2 Works on Dynamic Supply PAs (Refer also to Table 2.1 )

Hanington et al. developed a boost converter using GaAs HBTs operating at
a switching frequency of 10 MHz to improve the efficiency of a GaAs MEtal
Semiconductor FET (MESFET) power amplifier operating at 4 GHz [ 11 ] and
950 MHz [ 12 ]. In [ 11 ], the supply voltage of the PA could be varied from 5 to
9 V which allowed the global efficiency of the PA to be improved by 45% (includ-
ing 74% efficiency of the DC-DC converter). The PA attained an output power of
22 dBm (158 mW) with an efficiency of 43% at an IMD3 of 30 dBc. In [ 12 ], the

supply voltage could be varied from 3 to 10 V, thereby improving the overall PA ef-
ficiency by 64% (74% DC-DC converter efficiency included). At 20 dBm (100 mW)
output power, the efficiency was 14% and the ACPR was kept below the maximum
IS-95 4 level of

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26 dBc (30 kHz main channel bandwidth).
In [ 2 , 24 ], the power supply voltage of a GaAs MESFET power amplifier can
take two values (4 or 8 V), depending on the instantaneous value of the RF input

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4 IS-95—Interim Standard 95 (CDMA).