ad5539jq Analog Devices, Inc., ad5539jq Datasheet - Page 15

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

REV. B
The transient response of the signal channel at V
V
driving a 75
mately 7 ns.
A few final circuit details: in general, the control amplifier com-
pensation capacitor for Pin 2, C
of 3000 pF (3 nF) to provide both circuit stability and maximum
control bandwidth. However, if the maximum control bandwidth
is not needed, then it is advisable to use a larger value of C
with typical values between 0.01 and 0.1 F. Like many aspects
of design, the value of C
will lower the high frequency distortion, reduce the high fre-
quency crosstalk and improve the signal channel phase response.
Conversely, lower values of C
channel bandwidth at the expense of degraded linearity in the
output response when amplitude modulating a carrier signal.
The control channel bandwidth will vary in inverse proportion to
the value of C
C
Both the bandwidth and pulse response of the control channel
can be further increased by using a feedforward capacitor, C
with a value between 5 and 20 percent of C
fully adjusted to give the best pulse response for a particular step
input applied to the control channel. Note that since C
nected between a linear control input (Pin 1) and a logarith-
Y
C
= V
of 0.01 F and a V
OUT
= + or –1 V is shown in Figure 46; with the VCA
C
load. The rise and fall times are both approxi-
, providing a typical bandwidth of 2 MHz with a
X
voltage of +1.7 volts.
C
will be a tradeoff: higher values of C
C
will provide a higher control
C
, must have a minimum value
Figure 47. An Analog Multiplier Video Switch
C
. C
ff
X
should be care-
= +2 V,
ff
is con-
C
,
ff
,
C
–15–
Figure 46. Transient Response of the Voltage-Controlled
Amplifier V
mic node, the settling time of the control channel with a pulse
input will vary with different control input step levels.
Diode D1 clamps the logarithmic control node at Pin 2 of the
AD539, (preventing this point from going too negative); this
diode helps decrease the circuit recovery time when the control
input goes below ground potential.
THE AD539/5539 COMBINATION AS A FAST, LOW
FEEDTHROUGH, VIDEO SWITCH
Figure 47 shows how the AD539/5539 combination can be used
to create a fast video speed switch suitable for many high fre-
X
= +2 Volts, V
Y
= 1 Volt
AD5539