2-471

RF3133

Rev A4 030527

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 to steep it is difficult

to prevent 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 produce 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 process there is additional squaring of the waveform resulting in higher harmonics. The RF3133 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 harmonics 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.

The RF3133 incorporates many circuits that had previously been required external to the power amplifier. The shaded

area of the diagram below illustrates those components and the following table itemizes a comparison between the

RF3133 Bill of Materials and a conventional solution:

Note: Output power is limited by battery voltage. The relationship in Equation 4 does not limit output power. Equation 4

Component

Conventional

Solution

RF3133

Power Control ASIC

$0.80

N/A

Directional Coupler

$0.20

N/A

Buffer

$0.05

N/A

Attenuator

$0.05

N/A

Various Passives

$0.05

N/A

Mounting Yield

(other than PA)

$0.12

N/A

Total

$1.27

$0.00

From DAC

*Shaded area eliminated with Indirect Closed Loop using RFMD's Integrated Power Control Solution

Traditional Triple-Band PA