RF2444 データシートの表示（PDF） - RF Micro Devices
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RF2444 Datasheet PDF : 16 Pages
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RF2444
Theory of Operation
RF Micro Devices
2.4 GHz ISM Chipset
IL = 3-4 dB
2.4 to 2.483 GHz
Gain
Select
RF2444
SSOP-16 EPP
Filter
2.4 to 2.483 GHz
LNA
Dual Gain Modes
-5 dB and +10 dB
RX
15 dB Gain
SAW
IL = 10 dB max
Discrete
Pin Diode
RF2517
SSOP-28
Dual
Frequency
Synthesizer
RF
VCO
IF
VCO
RX
15 dB
IF Amp
-15 dB to 35 dB Gain
TX
15 dB
TX
+45°
-45°
RF2126
23 dBm or 33 dBm
External PA
Figure 1. Entire Chipset Functional Block Diagram
10 dBm
PA Driver
IL = 3-4 dB
2.4 to 2.483 GHz
Σ
15 dB Gain
Range
VGC2
VGC1
RF2938
TQFP-48 EPP
RSSI
OUT Q
DATA Q
Base Band Amp.
Active Selectable LPF
(fC = 1 MHz to 40 MHz)
0-30 dB Gain
OUT I
DATA I
Filter
I INPUT
Filter
Selectable LPF
Q INPUT
The RF2444 contains the LNA/Mixer for this chipset.
The LNA is made from two stages including a common
8
emitter amplifier stage with a power gain of 13dB and
an attenuator which has an insertion loss of 3dB in
high gain mode, and 17dB in low gain mode. The
attenuator was put after the LNA so that system noise
figure degradation would be minimized. A single gain
stage was used prior to the image filter to maximize
IP3 which minimizes the risk of large out-of-bad signals
jamming the desired signal.
The mixer on the RF2444 is also two stages. The first
stage is a common emitter amp used to boost the total
power gain prior to the lossy SAW filter, to convert to a
differential signal to the input of the mixer, and to
improve the noise figure of the mixer. The second
stage is a double balanced mixer whose output is dif-
ferential open collector. It is recommended that a “cur-
rent combiner” is used (as shown in figure 2) at the
mixer output to maximize conversion gain, but other
loads can also be used. The current combiner is used
to do a differential to single ended conversion for the
SAW filter. C1, C2 and L1 are used to tune the circuit
for a specific IF frequency. L2 is a choke to supply DC
current to the mixer that is also used as a tuning ele-
ment, along with C3, to match to the SAW filter’s input
impedance. RL is the SAW filter’s input impedance.
The mixer power conversion gain is +19dB when R1 is
set to 1kΩ. The conversion gain can be adjusted up
~5dB or down ~7dB by changing the value of R1.
Once R1 is chosen, L2 and C3 can be used to tune the
output for the SAW filter.
VCC
C1
C2 L2
L1
R1
Open Collector
Mixer Output
C3
OUT
RL
Figure 2. Current Combiner for Mixer Load
The cascaded power gain of the LNA/Mixer is 29dB,
which after insertion loss in the image filter (~3dB) and
IF SAW filter (~10dB), still gives 16dB of gain prior to
the IF amps. Because of this, the noise figure of the IF
amps should not significantly degrade system noise
figure.
The LNA input should be matched for a good return
loss for optimum gain and noise figure. To allow the
designer to match each of these ports, 2-port s-param-
eter data is available for the LNA, and 1-port data is
available for MIXER IN and LO IN.
8-58
Rev A3 010717
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