AD811 Analog Devices, AD811 Datasheet - Page 17

• Manufacturer Part Number: AD811
• Description: High Performance Video Op Amp
• Manufacturer: Analog Devices

Specifications of AD811

• -3db Bandwidth: 140MHz
• Slew Rate: 2.5kV/µs
• Vos: 500µV
• Ib: 2µA
• # Opamps Per Pkg: 1
• Input Noise (nv/rthz): 1.9nV/rtHz
• Vcc-vee: 9V to 36V
• Isy Per Amplifier: 16mA
• Packages: DIP,LCC,SOIC

To generate the 1 V dc needed for the 1−G term, an AD589
reference supplies 1.225 V ± 25 mV to a voltage divider consist-
ing of resistors R2 through R4. Potentiometer R3 should be
adjusted to provide exactly 1 V at the X1 input.
In this case, an arrangement is shown using dual supplies of
±5 V for both the AD834 and the AD811. Also, the overall gain
is arranged to be unity at the load when it is driven from a
reverse-terminated 75 Ω line. This means that the dual VCA has
to operate at a maximum gain of +2, rather than +4 as in the
VCA circuit of Figure 47. However, this cannot be achieved by
lowering the feedback resistor because below a critical value
(not much less than 500 Ω) the AD811’s peaking may be
unacceptable. This is because the dominant pole in the open-
loop ac response of a current feedback amplifier is controlled
this feedback resistor. It would be possible to operate at a gain of
×4 and then attenuate the signal at the output. Instead, the
signals have been attenuated by 6 dB at the input to the AD811;
this is the function of R8 through
Figure 49 is a plot of the ac response of the feedback keyer when
driving a reverse-terminated 50 Ω cable. Output noise and
adjacent channel feedthrough, with either channel fully off and
the other fully on, is about −50 dB to 10 MHz. The feedthrough
R11.
Rev. E | Page 17 of 20
by
at 100 MHz is limited primarily by board layout. For V
the −3 dB bandwidth is 15 MHz when using a 137 Ω resistor for
R14 and 70 MHz with R14 = 49.9 Ω. For more information on
the design and operation of the VCA and video keyer circuits,
refer to the application note “Video VCAs and Keyers: Using the
AD834 and AD811” by Brunner, Clarke, and Gilbert, available
on the Analog Devices, Inc. website at www.analog.com.
–10
–20
–30
–40
–50
–60
–70
–80
–90
10
0
10k
Figure 49. A Plot of the AC Response of the Video Keyer
100k
GAIN
ADJACENT CHANNEL
FEEDTHROUGH
FREQUENCY (Hz)
1M
R14 = 137Ω
10M
R14 = 49.9Ω
100M
AD811
G
= 1 V,