RF3158PCBA-41X RFMD [RF Micro Devices], RF3158PCBA-41X Datasheet - Page 20

• Manufacturer Part Number: RF3158PCBA-41X
• Description: QUAD-BAND GSM/EDGE/GSM850/EGSM900 /DCS/PCS POWER AMPLIFIER MODULE
• Manufacturer: RFMD [RF Micro Devices]

RF3158
• Harmonics
• Multimode Operation
20 of 26
Harmonics are natural products of high efficiency, saturated power amplifiers. An ideal, class 'E', saturated power ampli-
fier will produce a perfect square wave. Looking at the Fourier transform of a square wave reveals high harmonic content.
Although this is common to all saturated power amplifiers, there are other factors that contribute to harmonic content as
well. With many power control methods, a peak power detector is used to rectify and sense forward power. Through the
rectification process, there is additional squaring of the waveform resulting in higher harmonics. The RF3158 has no
need for the detector diode; therefore, the harmonics coming out of the PA should represent maximum power of the har-
monics throughout the transmit chain. This is based on proper harmonic termination of the transmit port. The receive
port termination on antenna switch as well as the harmonic impedance from the switch itself will have an impact on har-
monics. These terminations should be adjusted to correct problems with harmonics.
When a GSM TDMA frame contains bursts of different modulation types (EDGE, GSM), a linear EDGE power amplifier
must be ramped down, the mode changed, and the power ramped back up again during the guard period between
bursts. This requires precise timing of control signals with less room for margin when compared to multiple timeslots with
the same modulation. The RF3158 is designed to operate in different modes in adjacent timeslots provided that the con-
trol signals are properly applied. The system must be capable of controlling the RF input drive timing separately from the
V
MODE
and V
RAMP
control signals. Failure to provide the proper timing will produce switching transients.
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at ([phone] or [e-mail].
Rev A2 DS070615