Operation in Saturation for
Higher Output Power
For applications such as pre-
driver and driver stages in trans-
mitters, the MGA-81563 can be
operated in saturation to deliver
up to 50 mW (17 dBm) of output
power. The power added effi-
ciency increases to 45% at these
power levels.
There are several design consider-
ations related to reliability and
performance that should be taken
into account when operating the
amplifier in saturation.
First of all, it is important that the
stage preceding the MGA-81563
not overdrive the device. Refer-
ring to the “Absolute Maximum
Ratings” table, the maximum
allowable input power is
+13 dBm. This should be regarded
as the input power level above
which the device could be perma-
nently damaged.
Driving the amplifier into satura-
tion will also affect electrical
performance. Figure 18 presents
the Output Power, Third Order
Intercept Point (Output IP
3)
, and
Power Added Efficiency (PAE) as
a function of Input Power. This
data represents performance into
a 50
Ω
load. Since the output
impedance of the device changes
when driven into saturation, it is
possible to obtain even more
output power with a “power
match.” The optimum impedance
match for maximum output power
is dependent on frequency and
actual output power level and can
be arrived at empirically.
50
PAE
40
30
20
10
0
-10
-20
Power
IP
3
-15
-10
-5
0
5
10
Like other active devices, the
intermodulation products of the
MGA-81563 increase as the device
is driven further into nonlinear
operation. The 3rd, 5th, and 7th
order intermodulation products of
the MGA-81563 are shown in
Figure 19 along with the funda-
mental response. This data was
measured in the test circuit in
Figure 10.
Pout, 3rd, 5th, 7th HARMONICS (dBm)
30
20
10
0
-10
-20
-30
-40
-50
-60
-30 -15
-10
5th
7th
3rd
Pout
Pout and IP
3
(dBm), PAE (%)
POWER IN (dBm)
Figure18.OutputPower,IP
3
,and
Power-Added-Efficiencyvs.Input
Power. (V
d
=3.0V)
As the input power is increased
beyond the linear range of the
amplifier, the gain becomes more
compressed. Gain as a function of
either input or output power may
be derived from Figure 18. Gain
compression renders the amplifier
less sensitive to variations in the
power level from the preceding
stage. This can be a benefit in
systems requiring fairly constant
output power levels from the
MGA-81563.
Increased efficiency (45% at full
output power) is another benefit
of saturated operation. At high
output power levels, the bias
supply current drops by about
15%. This is normal and is taken
into account for the PAE data in
Figure 18.
Noise figure and input impedance
are also affected by saturated
power operation. As a guideline,
the input impedance is lowered,
resulting in an improvement in
input VSWR of approximately 20%.
-5
0
5
10
15
FREQUENCY (GHz)
Figure19.IntermodulationProducts
vs.InputPower.(V
d
=3.0V)
Operation at Bias Voltages
Other than 3 Volts
While the MGA-81563 is designed
primarily for use in +3 volt
applications, the internal bias
regulation circuitry allows it to be
operated with any power supply
voltage from +1.5 to +5 volts.
Performance of Gain, Noise
Figure, and Output Power over a
wide range of bias voltage is
shown in Figure 20. As can be
seen, the gain and NF are fairly
flat, but an increase in output
power is possible by using higher
voltages. The use of +5 volts
increases the P
1dB
by 2 dBm.
6-203
AGILENT [ AGILENT TECHNOLOGIES, LTD. ]
