OPA3693 Datasheet, PDF (15/29 Pages) Burr-Brown (TI) – Triple, Ultra-Wideband, Fixed-Gain, VIDEO BUFFER with Disable

OPA3693
www.ti.com
SBOS353 – DECEMBER 2006
APPLICATION INFORMATION
WIDEBAND BUFFER OPERATION
The OPA3693 gives the exceptional ac performance
of a wideband current-feedback op amp with a highly
linear output stage. It features internal R_F and R_G
resistors, making it a simple matter to select a gain
of +2V/V, +1V/V, or –1V/V with no external resistors.
Requiring only 13mA/ch supply current, the
OPA3693 output swings to within 1V of either supply
with > 650MHz small-signal bandwidth and >
250MHz delivering 7V_PP into a 100Ω load. This low
output headroom in a very high-speed amplifier gives
remarkable single +5V operation. The OPA3693
delivers 2V_PP swing with > 400MHz bandwidth
operating on a single +5V supply. The primary
advantage of a current-feedback fixed-gain video
buffer (as opposed to a slew-enhanced, low-gain,
stable voltage-feedback implementation) is a higher
slew rate with lower quiescent power and output
noise.
Figure 42 shows the dc-coupled, gain of +2V/V, dual
power-supply circuit configuration used as the basis
for the ±5V Electrical Characteristics table and
Typical Characteristics curves. For test purposes, the
input impedance is set to 50Ω with a resistor to
ground and the output impedance is set to 50Ω with
a series output resistor. Voltage swings reported in
the specifications are taken directly at the input and
output pins while load powers (dBm) are defined at a
matched 50Ω load. For the circuit of Figure 42, the
total effective load is 100Ω || 600Ω = 85.7Ω. The
disable control line (DIS) is typically left open to
ensure normal amplifier operation. In addition to the
usual power-supply decoupling capacitors to ground,
a 0.01µF capacitor can be included between the two
power-supply pins. This optional added capacitor
typically improves the 2nd-harmonic distortion
performance by 3dB to 6dB.
Figure 43 shows the DC-coupled, gain of +1V/V
buffer configuration used as a starting point for the
gain of +5V Typical Characteristic curves. In this
case, the inverting input resistor, R_G, is left open
giving a very broadband gain of +1V/V performance.
While the test circuit shows a 50Ω input resistor, a
buffer application is typically transforming from a
source that cannot drive a heavy load to a 100Ω
load, such as shown in Figure 43. The noninverting
input impedance of the OPA3693 is typically
100kΩ || 2pF. Driving directly into the noninverting
input provides this very light load to the source.
However, the source must provide the noninverting
input bias current required by the input stage to
operate. An alternative approach to a gain of +1
buffer is described in the Wideband Unity-Gain
Buffer section of this data sheet.
+5V
50W Source
V_I
50W
0.1mF
6.8mF
1/3
OPA3693
R_F
300W
DIS
50W
V_O
50W Load
R_G
300W
0.1mF
6.8mF
-5V
Figure 42. DC-Coupled, G = +2, Bipolar-Supply,
Specification and Test Circuit
+5V
50W Source
V_I
50W
0.1mF
6.8mF
1/3
OPA3693
R_F
300W
DIS
50W
V_O
50W Load
R_G
300W
Open
-5V
0.1mF
6.8mF
Figure 43. DC-Coupled, G = +1V/V,
Bipolar-Supply, Specification and Test Circuit
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