OPA2634 Datasheet, PDF (10/16 Pages) Burr-Brown (TI) – Dual, Wideband, Single-Supply OPERATIONAL AMPLIFIER

APPLICATIONS INFORMATION
WIDEBAND VOLTAGE FEEDBACK OPERATION
The OPA2634 is a unity-gain stable, very high-speed, volt-
age-feedback op amp designed for single-supply operation
(+3V to +5V). The input stage supports input voltages below
ground, and within 1.2V of the positive supply. The comple-
mentary common-emitter output stage provides an output
swing to within 30mV of ground and 140mV of the positive
supply. It is compensated to provide stable operation with a
wide range of resistive loads.
Figure 1 shows the AC-coupled, gain of +2 configuration
used for the +5V Specifications and Typical Performance
Curves. For test purposes, the input impedance is set to 50Ω
with a resistor to ground. Voltage swings reported in the
Specifications are taken directly at the input and output pins.
For the circuit of Figure 1, the total effective load on the
output at high frequencies is 150Ω || 1500Ω. The 1.50kΩ
resistors at the non-inverting input provide the common-
mode bias voltage. Their parallel combination equals the DC
resistance at the inverting input, minimizing the DC offset.
+V_S = 5V
6.8µF
+
1.50kΩ
0.1µF
+
0.1µF
V_IN
53.6Ω
1.50kΩ
1/2
OPA2634
0.1µF 750Ω
750Ω
V_OUT
R_L
150Ω
+V_S
2
FIGURE 1. AC-Coupled Signal—Resistive Load to Supply
Midpoint.
Figure 2 shows the DC-coupled, gain of +2 configuration
used for the +3V Specifications and Typical Performance
Curves. For test purposes, the input impedance is set to 50Ω
with a resistor to ground. Though not strictly a “rail-to-rail”
design, this part comes very close, while maintaining excel-
lent performance. It will deliver up to 2.8Vp-p on a single
+3V supply with > 100MHz small-signal bandwidth. The
374Ω and 2.26kΩ resistors at the input level-shift V_IN so
that V_OUT is within the allowed output voltage range when
V_IN = 0. See the Typical Performance Curves for informa-
tion on driving capacitive loads.
SINGLE-SUPPLY ADC INTERFACE
The front page shows a DC-coupled, single-supply, dual
ADC driver circuit. Many systems are now requiring +3V
+V_S = 3V
6.8µF
+
2.26kΩ
0.1µF
+
374Ω
V_IN
57.6Ω
1/2
OPA2634
V_OUT
R_L
150Ω
562Ω
750Ω
+V_S
2
FIGURE 2. DC-Coupled Signal—Resistive Load to Supply
Midpoint.
supply capability of both the ADC and its driver. The
OPA2634 provides excellent performance in this demanding
application. Its large input and output voltage ranges, and
low distortion, support converters such as the ADS900
shown in this figure. The input level-shifting circuitry was
designed so that V_IN can be between 0V and 0.5V, while
producing a 1V to 2V at the output pin for the ADS900.
ANTI-ALIASING FILTER
Figure 3 shows an anti-aliasing filter, with a 5th-order
Inverse Chebyshev response, based on a single OPA2634.
This filter cascades two 2nd-order Sallen-Key sections with
transmission zeros, and a real pole section. It has a –3dB
V_IN
V_OUT
680pF
100Ω 215Ω
680pF
10pF 20Ω
56pF
68.1Ω
1% Resistors
5% Capacitors
1/2
OPA2634
210Ω
330pF
191Ω
150pF
1/2
220pF
OPA2634
205Ω
115Ω
93.1Ω
20Ω 18pF
330pF
48.7Ω
FIGURE 3. Inverse Chebyshev Anti-Aliasing Filter.
®
OPA2634
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