MGA-86576 データシートの表示（PDF） - Avago Technologies
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MGA-86576 Datasheet PDF : 6 Pages
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The use of lumped inductors is not desired since they
tend to radiate and cause undesired feedback. Moving the
bypass capacitor, C1, down the microstripline towards the
Vdd terminal, as shown in Figure 9, will improve the gain
below 2 GHz by trading off some high end gain. A mini-
mum value of 10 Ω for R1 is recommended to de-Q the
bias decoupling network, although 100 Ω will provide the
highest circuit gain over the entire 1.5 to 8 GHz frequency
range. Vdd will have to be increased accordingly for higher
values of R1. For operation in the 2 to 6 GHz frequency
range, a 10 pF capacitor may be used for DC blocking on
the output microstripline. A larger value such as 27 pF is
more appropriate for operation at 1.5 GHz.
Table 1 provides the approximate inductor length for
minimum noise figure at a given frequency for the circuit
board shown in Figure 7.
Table 1. L1 Length vs. Frequency for Optimum Noise Figure.
Frequency
GHz
Length
Inches
1.5
0.70
1.8
0.60
2.1
0.50
2.4
0.40
2.5
0.30
3.0
0.20
3.7
0.10
4.0
0.05
Figure 9. Complete MGA-86576 Demonstration Amplifier.
Ground (Pins 2 and 4)
Ground pins should attach directly to the backside ground
plane by the shortest distance possible using the design
hints suggested in the earlier section. Liberal use of plated
through vias is recommended.
RF Input (Pin 1)
A 50 Ω microstripline can be used to feed RF to the de-
vice. A blocking capacitor in the 10 pF range will provide
a suitable DC block in the 2 to 6 GHz frequency range.
Although there is no voltage present at pin 1, it is highly
suggested that a DC blocking capacitor be used to prevent
accidental application of a voltage from a previous ampli-
fier stage.With no further input matching, the MGA-86576
is capable of noise figures as low as 2 dB in the 2 to 6 GHz
frequency range. Since Γo is not 50 Ω, it is possible to de-
sign and implement a very simple matching network in
order to improve noise figure and input return loss over a
narrow frequency range. The circuit board layout shown
in Figure 7 provides an option for tuning for a low noise
match anywhere in the 1.5 to 4 GHz frequency range. For
optimum noise figure performance in the 4 GHz frequency
range, L1 can be a 0.007 inch diameter wire 0.080 inches
in length as shown in Figure 9. Alternatively, L1 can be
replaced by a 0.020 inch wide microstripline whose length
can be adjusted for minimum noise figure in the 1.5 to 4
GHz frequency range.
7 Volt Bias for Operation at Higher Temperatures
The MGA-86576 was designed primarily for 5 volt op-
eration over the -25 to +50°C temperature range. For
applications requiring use to +85°C, a 7 volt bias supply
is recommended to minimize changes in gain and noise
figure at elevated temperature. Figure 10 shows typical
gain, noise figure, and output power performance over
temperature at 4 GHz with 7 volts applied. With a 7 volt
bias supply, output power is increased approximately 1.5
dB. Other parameters are relatively unchanged from 5 volt
data. S‑parameter and noise parameter data for 7 volts are
available upon request from Avago.
25
POWER GAIN
20
15
10
P1dB
5
NOISE FIGURE
0
-40 -30 -20 -10 0 25 50 85 125
TEMPERATURE °C
Figure 10. Gain, NF50, and P1dB vs. Temperature at 4
GHz with 7 Volt Bias Supply.
MGA-86576 fig 10
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