OPA2634 Datasheet, PDF (10/17 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 +10V). The input stage supports input voltages
below ground, and to within 1.2V of the positive supply. The
complementary 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 opera-
tion 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
R_G
0.1µF 750Ω
R_F
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 > 60MHz 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 information on driving
capacitive loads.
SINGLE-SUPPLY ADC INTERFACE
The front page shows a DC-coupled, single-supply, dual
ADC (Analog-to-Digital Converter) driver circuit. Many
systems are now requiring +3V supply capability of both the
10
+V_S = 3V
6.8µF
+
2.26kΩ
0.1µF
374Ω
V_IN
57.6Ω
1/2
OPA2634
R_G
562Ω
R_F
750Ω
V_OUT
R_L
150Ω
+V_S
2
FIGURE 2. DC-Coupled Signal—Resistive Load to Supply
Midpoint.
ADC and its driver. The OPA2634 provides excellent per-
formance 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 followed by a
simple real pole at the output. It has a –3dB frequency of
5MHz, and a –60dB stopband starting at 12MHz.
100Ω
215Ω
680pF
1% Resistors
5% Capacitors
V_IN
680pF 10pF 20Ω
56pF
1/2
OPA2634
68.1Ω
210Ω
V_OUT
191Ω
150pF
1/2
OPA2634
205Ω
330pF
115Ω
93.1Ω
220pF
20Ω 18pF 330pF
48.7Ω
FIGURE 3. Inverse Chebyshev Anti-Aliasing Filter.
OPA2634
SBOS098A