OPA2682 Datasheet, PDF (14/19 Pages) Burr-Brown (TI) – Dual, Wideband, Fixed Gain BUFFER AMPLIFIER With Disable

DIFFERENTIAL ADC DRIVER
The circuit in Figure 3 converts a single-ended input to a
differential signal which drives the ADS823 converter. The
common-mode biasing uses a simple resistor divider con-
nected to the ADC’s reference voltages. Connecting the top
op amp’s R_G to its non-inverting input provides a bias
current path for the non-inverting input. This connection
also improves distortion performance because both op amps
operate with nearly equal noise gains.
MULTIPLEXED VIDEO AMPLIFIER
The multiplexed video amplifier in Figure 4 “wire-ORs” the
two output signals together. The “make-before-break” dis-
able characteristic of the OPA2682N ensures that the output
is always under control. To avoid large switching glitches,
switch during the sync or retrace portions of the video
signal—the two inputs should be almost equal at these
times. Because the output is always under control, the
switching glitches for two 0V inputs are < 20mV. This
circuit also ensures that the maximum differential voltage
across the inputs of the unselected channel do not exceed the
±1.2V Maximum Rating when using standard video signal
levels.
The two output resistors isolate the outputs from each other
when switching between channels. The feedback network of
the disabled amplifier forms part of the output impedance
and attenuates the output signal slightly. The 68.1Ω value
compensates for the attenuation, and still provides good
back-matching for the cable (return loss > 20dB).
0.10µF
V_IN
+5V
400Ω
400Ω
1/2
OPA2682
400Ω
400Ω
0.10µF
1/2
OPA2682
100Ω
50pF
100Ω
50pF
2.5V
FIGURE 3. Wideband, AC-Coupled, Single-Supply A/D Driver.
+5V
+V_S
+In
ADS823
10-Bit
60MSPS
–In
REFT
REFB
(+3.5V) GND (+1.5V)
0.10µF
0.10µF
2kΩ
2kΩ
V_DIS
+5V
2kΩ
+5V
Video 1
75Ω
400Ω
DIS
1/2
OPA2682N
400Ω
400Ω
400Ω
Video 2
75Ω
1/2
OPA2682N
DIS
2kΩ
–5V
V_OUT < 2.6V
68.1Ω
75Ω Cable
RG-59
V_OUT
68.1Ω
FIGURE 4. Two-Channel Video Multiplexer (SO-14 only).
®
OPA2682
14