RF7115PCBA-41X 데이터 시트보기 (PDF) - RF Micro Devices
부품명
상세내역
제조사
RF7115PCBA-41X Datasheet PDF : 22 Pages
| |||
RF7115
Where PPA is the output power from the PA, PLOSS the insertion loss and PIN the input power to the PA. The RF7115 improves
the effective efficiency by minimizing the PLOSS term in the equation. An ASM may have a typical loss of 1.2dB in LB and 1.4dB
in high band. To be added to this is trace losses and mismatch losses. A post PA loss of 1.5dB in LB and 1.8dB in HB is com-
mon. With the integration of a low loss pHEMT switch and matching network in the same module, higher system efficiency can
be achieved.
Output power does not vary due to supply voltage under normal operating conditions if VRAMP is sufficiently lower than VBATT.
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 battery discharges and approaches its lower power range the maximum output power
from the PA will also drop slightly. In this case, it is important to also decrease VRAMP to prevent the power control from induc-
ing switching transients. These transients occur as a result of the control loop slowing down and not regulating power in accor-
dance with VRAMP. The relationship for VRAMPMAX based on VBATT is expressed in equation 3.
VRAMPMAX
=
3--
8
×
VBATT
+
0.15
≤
1.5V
(Eq. 3)
The components following the power amplifier often have insertion loss variation with respect to frequency. Usually, there is
some length of microstrip that follows the power amplifier. There is also a frequency response found in directional couplers
due to variation in the coupling factor over frequency, as well as the sensitivity of the detector diode. Since the RF7115 does
not use a directional coupler with a diode detector, these variations do not occur. Also the TX/RX switch with low pass filters
that usually follows the PA may contribute to frequency variation. The TX/RX switch incorporated in the RF7115 is very broad-
band and does not contribute to frequency roll off. Traditionally working with PA modules, some matching network is necessary
between the PA output and the input of the TX/RX switch in order to get best possible performance. This work no longer has to
be carried out, as this matching network is included in the RF7115.
Noise power in PA's where output power is controlled by changing the bias voltage is often a problem when backing off of out-
put power. The reason is that the gain is changed in all stages and according to the noise formula (Equation 4),
FTOT
=
F1
+
F-----2----–-----1-
G1
+
G--F---1-3----⋅-–--G--1--2--
(Eq. 4)
the noise figure depends on noise factor and gain in all stages. Because the bias point of the RF7115 is kept constant the gain
in the first stage is always high and the overall noise power is not increased when decreasing output power.
Power control loop stability often presents many challenges to transmitter design. Designing a proper power control loop
involves trade-offs affecting stability, transient spectrum and burst timing.
The RF7115 loop bandwidth is determined by internal bandwidth and does not change with respect to power levels. This
makes it easier to maintain loop stability with a high bandwidth loop since the bias voltage and collector voltage do not vary. 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 RF7115 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 prevent switching transients. Controlling the out-
put 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 inflexion 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 RF7115 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.
Rev A0 DS060808
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
13 of 22
Share Link: 