RF3166DPCBA-410 datasheet(12/14 Pages) RFMD

12 / 14 page

12 of 14

RF3166D

Rev A2 061006

7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical

support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.

An often overlooked problem in PA control loops is that a delay not only decreases loop stability it also affects the burst timing

when, for instance the input power from the VCO decreases (or increases) with respect to temperature or supply voltage. The

burst timing then appears to shift to the right especially at low power levels. The RF3166 is insensitive to a change in input

power and the burst timing is constant and requires no software compensation.

Switching transients occur when the up and down ramp of the burst is not smooth enough or suddenly changes shape. If the

control slope of a PA has an inflection point within the output power range or if the slope is simply too steep it is difficult to pre-

vent switching transients. Controlling the output power by changing the collector voltage is as earlier described based on the

physical relationship between voltage swing and output power. Furthermore all stages are kept constantly biased so inflection

points are nonexistent.

Harmonics are natural products of high efficiency power amplifier design. An ideal class “E” saturated power amplifier will pro-

duce a perfect square wave. Looking at the Fourier transform of a square wave reveals high harmonic content. Although this is

common to all power amplifiers, there are other factors that contribute to conducted harmonic content as well. With most

power control methods a peak power diode detector is used to rectify and sense forward power. Through the rectification pro-

cess there is additional squaring of the waveform resulting in higher harmonics. The RF3166 address this by eliminating the

need for the detector diode. Therefore the harmonics coming out of the PA should represent the maximum power of the har-

monics throughout the transmit chain. This is based upon proper harmonic termination of the transmit port. The receive port

termination on the T/R switch as well as the harmonic impedance from the switch itself will have an impact on harmonics.

Should a problem arise, these terminations should be explored.

RF3166DPCBA-410 Datasheet(PDF) 12 Page - RF Micro Devices