RF3159 Просмотр технического описания (PDF) - RF Micro Devices
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RF3159 Datasheet PDF : 26 Pages
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RF3159
• Power variation due to supply voltage:
Output power does not vary due to supply voltage under normal operating conditions. By regulating the collector voltage to the
PA the voltage sensitivity is essentially eliminated. This covers most cases where the PA will be operated. However, as the bat-
tery discharges and VBATT approaches its lower operating limit, the output power from the PA will start to drop. This cannot be
avoided as a certain supply voltage is required to produce full output power. System specifications must allow for this power
decrease.
Switching Transients due to low battery conditions are reduced by the saturation detection circuit in RF3159. The saturation
detection circuit consists of a feedback loop which detects FET saturation. As the FET approaches saturation, the circuit
adjusts the VCC voltage in order to ensure minimum switching transients. The saturation detection circuit is integrated into the
CMOS controller and requires no additional input from the user.
• Power variation due to temperature
RF3159 output power variation due to temperature is largest at low power levels and decreases at the upper power levels. This
follows the ETSI specification limits which allow a larger tolerance over extreme conditions at low power levels. Since output
power is controlled by an analog input, factors other than the power amplifier will have an effect on total system power varia-
tion. The entire system containing the RF3159 should be tested to determine whether compensation is necessary. At high tem-
peratures and low battery voltages, the PA cannot support as high of an output power. In this condition, increasing VRAMP will
not provide more output power, so compensation may not provide the intended result.
• Noise Power
The bias point of the RF3159 is kept constant and the gain in the first stage is always high. This has the effect of maintaining a
consistent noise power which does not increase at reduced output power levels. For that reason, noise power is at its highest
when VRAMP is at its maximum. The RF3159 does not create enough noise in the receive band to cause system receive band
noise power failures, but it may amplify noise from other sources. Care must be taken to prevent noise from entering the power
amplifier.
• Loop Stability and Loop Bandwidth variation across power levels
The design of a proper power control loop involves trade-offs affecting stability, transient spectrum and burst timing. In non-
PowerStar® architectures, backing off power causes gain variation which can affect loop bandwidth. In RF3159 the loop band-
width is determined by VCC regulator bandwidth and does not change over output power. Loop stability is maintained since
amplifier bias voltage is constant.
• Transient Spectrum
Switching transients occur when the up and down power ramps are not smooth enough, or suddenly change shape. If the con-
trol slope of a PA has an inflection point within the output power control range, or if the slope is too steep, switching transients
will result. In RF3159 all stages are kept constantly biased and the output power is controlled by changing the collector voltage
according to Equation 1. Inflection points are eliminated by this design. In addition, the steepness of the power control slope is
reduced because VRAMP actively controls output power over a larger voltage range than many other power amplifiers.
• Harmonics
Harmonics are natural products of high efficiency, saturated power amplifiers. 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 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 pro-
cess, there is additional squaring of the waveform resulting in higher harmonics. The RF3159 has no need for the detector
diode; therefore, the harmonics coming out of the PA should represent maximum power of the harmonics throughout the trans-
mit 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 harmonics. These terminations should be
adjusted to correct problems with harmonics.
Rev A0 DS070102
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