OPA3691 Datasheet, PDF (12/25 Pages) Burr-Brown (TI) – Triple Wideband, Current-Feedback OPERATIONAL AMPLIFIER With Disable

TRIPLE ADC BUFFER CHANNEL
The OPAx691 family is ideally suited to single-supply,
wideband ADC driving. A current-feedback op amp is ideal
where high gains with high bandwidths are required. The
wide 3Vp-p output swing with over 150MHz full-power band-
width on a single +5V supply is well suited to the
2Vp-p input range commonly required from modern CMOS
pipelined ADCs. Three channels of very high-speed digitizer
channels are shown in Figure 3 using the OPA3691 driving
three ADS831s (8-bit, 80MSPS CMOS converters). Each
input is AC-coupled into a 50Ω gain resistor that also will act
as a 50Ω impedance match at high frequencies. The amplifier’s
inputs and outputs are centered on the ADC common-mode
input voltage by tying each converter’s V_CM to the noninverting
inputs of the amplifier. This V_CM acts as the swing midpoint
for the input to the converter. Since the ADS831 can operate
with differential inputs, driving into the IN input will give a net
noninverting signal channel even with the amplifiers operat-
ing at an inverting gain of –6. The other input to the ADS831
is tied to this V_CM as well to give an input signal midpoint
equal to V_CM. The 300Ω feedback resistor will be the output
load in this configuration. Harmonic distortion for the OPA3691
will not degrade the converter’s SFDR performance in this
application.
Power-supply
+5V
decoupling not shown.
0.1µF
1/3
OPA3691
0.1µF 50Ω
V₁
300Ω
0.1µF
1/3
OPA3691
0.1µF 50Ω
V₁
300Ω
0.1µF
1/3
OPA3691
300Ω
22Ω
47pF
IN
V_CM
ADS831
IN 8-Bit
80MSPS
300Ω
22Ω
47pF
IN
V_CM
ADS831
IN 8-Bit
80MSPS
300Ω
22Ω
47pF
IN
V_CM
ADS831
IN 8-Bit
80MSPS
WIDEBAND RGB MULTIPLEXER
The OPA3691 is ideally suited to implementing a simple,
very wideband, 2x1 RGB multiplexer. This simple “wired-OR
video multiplexer” can be easily implemented using the
circuit shown in Figure 4.
This circuit uses two OPA3691s where each package accepts
the three RGB component video signals from one of two
possible sources. Each noninverting input is terminated in 75Ω
+5V
V_DIS
+5V
R1
75Ω
U1
1/3
OPA3691
Power-supply
decoupling not shown.
82.5Ω
V_OUT Red
340Ω
402Ω
75Ω Line
G1
75Ω
1/3
OPA3691
340Ω
402Ω
82.5Ω
V_OUT Green
75Ω Line
B1
75Ω
1/3
OPA3691
82.5Ω
340Ω
402Ω
R2
75Ω
–5V
+5V
U2
1/3
OPA3691
82.5Ω
340Ω
402Ω
V_OUT Blue
75Ω Line
G2
75Ω
1/3
OPA3691
340Ω
402Ω
82.5Ω
B2
1/3
75Ω
OPA3691
82.5Ω
0.1µF 50Ω
V₁
300Ω
FIGURE 3. Triple-Channel ADC Driver.
12
340Ω
402Ω
–5V
FIGURE 4. Wideband 2x1 RGB Multiplexer.
www.ti.com
OPA3691
SBOS227A