Datasheet
APPLICATION INFORMATION
WIDEBAND VARIABLE GAIN AMPLIFIER
VCA822
x1
x2
R
200
G
W
R
G+
V
IN
x1
R
G-
-V
IN
I
RG
V
G
V
OUT
FB
R
F
1kW
V
REF
+5V -5V
0.1 Fm
X2Y
Capacitor
â
2.2 Fm2.2 Fm
+
+
20W
20W
20W
V
OUT
+V
IN
VCA822
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..................................................................................................................................... SBOS343C – SEPTEMBER 2007 – REVISED DECEMBER 2008
For test purposes, the input impedance is set to 50 Ω
with a resistor to ground and the output impedance is
set to 50 Ω with a series output resistor. Voltage
OPERATION
swings reported in the Electrical Characteristics table
The VCA822 provides an exceptional combination of
are taken directly at the input and output pins, while
high output power capability with a wideband, greater
output power (dBm) is at the matched 50 Ω load. For
than 40dB gain adjust range, linear in V/V variable
the circuit in Figure 77 , the total effective load is
gain amplifier. The VCA822 input stage places the
100 Ω 1k Ω . Note that for the SO-14 package, there
transconductance element between two input buffers,
is a voltage reference pin, V
REF
(pin 9). For the
using the output currents as the forward signal. As
SO-14 package, this pin must be connected to
the differential input voltage rises, a signal current is
ground through a 20 Ω resistor in order to avoid
generated through the gain element. This current is
possible oscillations of the output stage. In the
then mirrored and gained by a factor of two before
MSOP-10 package, this pin is internally connected
reaching the multiplier. The other input of the
and does not require such precaution. An X2Y™
multiplier is the voltage gain control pin, V
G
.
capacitor has been used for power-supply bypassing.
Depending on the voltage present on V
G
, up to two
The combination of low inductance, high resonance
times the gain current is provided to the
frequency, and integration of three capacitors in one
transimpedance output stage. The transimpedance
package (two capacitors to ground and one across
output stage is a current-feedback amplifier providing
the supplies) of this capacitor enables to achieve the
high output current capability and high slew rate,
low second-harmonic distortion reported in the
1700V/ µ s. This exceptional full-power performance
Electrical Characteristics table. More information on
comes at the price of a relatively high quiescent
how the VCA822 operates can be found in the
current (36mA), but a low input voltage noise for this
Operating Suggestions section.
type of architecture (8.2nV/ √ Hz).
Figure 77 shows the dc-coupled, gain of +10V/V, dual
power-supply circuit used as the basis of the ± 5V
Electrical Characteristics and Typical Characteristics .
Figure 77. DC-Coupled, A
VMAX
= +10V/V, Bipolar Supply Specification and Test Circuit
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