Avago Technologies MGA-71543 - Manual

Revision 07/13/01 @ 4:56 PM Page 1
W-CDMA application using MGA-71543, a Low
Noise Amplifier with Bypass Switch.
_________________________
INTRODUCTION :
The MGA-71543 is a single stage GaAs RFIC
low noise amplifier with an integrated bypass
switch (Figure 1).
Figure 1. MGA-71543. Functional Diagram
The purpose of the switch feature is to prevent
distortion of high signal levels in receiver
applications by bypassing the amplifier.
Furthermore it saves current thus improving
battery life.
One of the two ground leads of the amplifier is
tied to the control leads of the switch to allow
simple control of the bias. Therefore, using one
of the ground leads, it is possible to vary the bias
current (including completely shutting down the
amplifier) by varying the resistor to ground that
is attached to it.
In short, the MGA-71543 is a small LNA/Bypass
Switch MMIC that provides a low Noise figure,
a high gain and high third order input intercept
point (IIP3) especially suitable for the LNA stage
for W-CDMA application.
This application note describes a W-CDMA Low
noise amplifier design using Agilent
Technologies’ MGA-71543.
Design overview and summary:
The board used for this design is shown in
figure2. The schematic of this board is shown
in figure 3. The number of components used
can be reduced in a real application circuit
because some jumpers (0
Ω
resistors), and
bypass capacitors could be eliminated without
performance degradation (some are only used
for ease, if tuning is necessary and also as a
safety to avoid any possible oscillations).
Matching and biasing
A simple series-shunt network of 1.5nH and
4.7nH at the input provides the noise matching
and the necessary DC grounding (of the input
pin). Because the main active device is a
depletion mode FET, source-biasing technique is
used so that only one positive DC supply is
required at the output. The input (gate) is DC
grounded and the source is RF bypassed, while
current setting resistors (R20 or R21) are
attached to ground.
A simple shunt-series network of 3.9nH and
1.8pF at the output does the required matching
for linearity while providing the RF choking and
DC blocking. The output-matching network does
not affect the noise figure, which was already set
by the input matching.
R38 and R25 provide some resistor loading at
low frequency and help stabilize the device at
low frequency. The rest of the components used,
including bypass capacitors (C8, C36, C37, C44,
C47), current setting resistors (R20 or R21),
voltage drop resistor (R24), DC block capacitors,
are all listed in table 1.
Performance Results
It is possible to achieve 3.7dBm of input Third
order intercept Point (IIP3) at 2.1GHz with a
device current of 11mA.
Conclusion
The MGA-71543 can be used for W-CDMA
application with the following typical
performance summary data:
NF Gain IIP3 S11 S22
1.2 15 3.7 13 8
Current = 11mA
Frequency: 2.1GHz
RF IN RF OUT
SW & Bias Control