ad5539jq Analog Devices, Inc., ad5539jq Datasheet - Page 14

• Manufacturer Part Number: ad5539jq
• Description: Ultrahigh Frequency Operational Amplifier
• Manufacturer: Analog Devices, Inc.

Figure 42 shows the oscilloscope response of the generator
alone, set up to simulate the ideal test circuit error signal
(Figure 43).
Figure 42. The Oscilloscope Response Alone Directly
Driven by the Test Generator. Vertical Scale: 5 ns/div.;
Horizontal Scale: 500 V/div
A 50 MHz VOLTAGE-CONTROLLED AMPLIFIER
Figure 44 is a circuit for a 50 MHz voltage-controlled amplifier
(VCA) suitable for use in high quality video-speed applications.
This circuit uses the AD5539 as an output amplifier for the
AD539, a high bandwidth multiplier. The outputs from the two
signal channels of the AD539 are applied to the op amp in a
subtracting configuration. This connection has two main advan-
tages: first, it results in better rejection of the control voltage,
particularly when over-driven (V
it provides a choice of either noninverting or inverting responses,
using either input V
output of the op amp will equal:
AD5539
Figure 44. A Wide Bandwidth Voltage-Controlled Amplifier
V
OUT
=
V
Y1
X
or V
V
2V
Y 1 –
Y2
V
, respectively. In this circuit, the
Y 2
X
< 0 or V
for V
X
> 0
X
> 3.3 V). Secondly,
–14–
Hence, the gain is unity at V
to +3.3 V, the maximum gain in this configuration is about
4.3 dB. (Note: If Pin 9 of the AD539 is grounded, rather than
connected to the output of the 5539N, the maximum gain be-
comes 10 dB.)
The bandwidth of this circuit is over 50 MHz at full gain, and is
not substantially affected at lower gains. Of course, when V
zero (or slightly negative, to override the residual input offset)
there is still a small amount of capacitive feedthrough at high
frequencies; therefore, extreme care is needed in laying out the
PC board to minimize this effect. Also, for small values of V
the combination of this feedthrough with the multiplier output
can cause a dip in the response where they are out of phase.
Figure 45 shows the ac response from the noninverting input,
with the response from the inverting input, V
tical. Test conditions: V
+10 mV to +3.16 V; this is with a 75
feedthrough at V
Figure 45. AC Response of the VCA at Different Gains
V
Y
Figure 43. A Simulated Ideal Test Circuit Error Signal
= 0.5 V RMS
X
= –10 mV is also shown.
Y1
= 0.5 V rms for values of V
X
= +2 V. Since V
load on the output. The
Y2
X
, essentially iden-
can overrange
X
from
REV. B
X
X
is
,