OPA3692IDBQT Datasheet, PDF (11/26 Pages) Texas Instruments – Triple, Wideband, Fixed Gain Video BUFFER AMPLIFIER With Disable

APPLICATIONS INFORMATION
WIDEBAND BUFFER OPERATION
The OPA3692 gives the exceptional AC performance of a
wideband, current-feedback op amp with a highly linear,
high-power output stage. It features internal R_F and R_G
resistors that make it easy to select a gain of +2, +1, or
–1 without external resistors. Requiring only 5.1mA/ch quies-
cent current, the OPA3692 swings to within 1V of either
supply rail and delivers in excess of 160mA at room tempera-
ture. This low output headroom requirement, along with
supply voltage independent biasing, gives remarkable +5V
single-supply operation. The OPA3692 will deliver greater
than 200MHz bandwidth driving a 2Vp-p output into 100Ω on
a +5V single supply. Previous boosted output stage amplifi-
ers have typically suffered from very poor crossover distor-
tion as the output current goes through zero. The OPA3692
achieves a comparable power gain with much better linearity.
Figure 1 shows the DC-coupled, gain of +2, dual power-
supply circuit configuration used as the basis of the ±5V
Electrical and Typical Characteristics. 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 1, the total effective load will be 100Ω || 804Ω = 89Ω.
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 0.1µF capacitor
can be included between the two power-supply pins. This
optional capacitor typically improves the 2nd-harmonic dis-
tortion performance by 3dB to 6dB.
Figure 2 shows the AC-coupled, gain of +2, single-supply
circuit configuration used as the basis of the +5V Electrical and
50Ω Source
V_IN
50Ω
+5V
DIS
0.1µF
6.8µF
1/3
OPA3692
50Ω Load
50Ω
R_F
402Ω
R_G
402Ω
0.1µF
6.8µF
–5V
FIGURE 1. DC-Coupled, G = +2, Bipolar Supply, Specifica-
tion and Test Circuit.
Typical Characteristics. Though not a rail-to-rail design, the
OPA3692 requires minimal input and output voltage headroom
compared to other very wideband, current-feedback op amps.
It will deliver a 3Vp-p output swing on a single +5V supply with
greater than 150MHz bandwidth. The key requirement of
broadband single-supply operation is to maintain input and
output signal swings within the usable voltage ranges at both
the input and the output. The circuit in Figure 2 establishes an
input midpoint bias using a simple resistive divider from the
+5V supply (two 806Ω resistors). The input signal is then AC-
coupled into this midpoint voltage bias. The input voltage can
swing to within 1.5V of either supply pin, giving a 2Vp-p input
signal range centered between the supply pins. The input
impedance matching resistor (57.6Ω) used for testing is ad-
justed to give a 50Ω input match when the parallel combination
of the biasing divider network is included. The gain resistor
(R_G) is AC-coupled, giving the circuit a DC gain of +1, which
puts the input DC bias voltage (2.5V) on the output as well.
Again, on a single +5V supply, the output voltage can swing to
within 1V of either supply pin while delivering more than 120mA
output current. A demanding 100Ω load to a midpoint bias is
used in this characterization circuit. The new output stage used
in the OPA3692 can deliver large bipolar output currents into
this midpoint load with minimal crossover distortion, as shown
by the +5V supply, 3rd-harmonic distortion plots. Although
Figure 2 shows a single +5V operation, this same circuit is
suitable for applications up to a single +12V supply.
+V_S +5V
50Ω Source
0.1µF
V_IN
57.6Ω
806Ω
806Ω
0.1µF
6.8µF
1/3
OPA3692
DIS
V_O 100Ω
R_F
402Ω
V_S/2
R_G
402Ω
0.1µF
FIGURE 2. AC-Coupled, G = +2, Single-Supply Specification
and Test Circuit.
VIDEO RGB AMPLIFIER
The front page shows an RGB amplifier based on the
OPA3692. The package pinout supports a signal flow-through
printed circuit board (PCB). The internal resistors simplify the
PCB even more, while maintaining good gain accuracy. For
systems that need to conserve power, the total supply current
for the disabled OPA3692 is only 450µA.
This triple op amp could also be used to drive triple video ADCs
to digitize component video.
OPA3692
11
SBOS228E
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