Datasheet

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SBOS263F − AUGUST 2004 − REVISED AUGUST 2008
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19
APPLICATIONS INFORMATION
WIDEBAND VOLTAGE-FEEDBACK
OPERATION
The OPA830 is a unity-gain stable, very high-speed
voltage-feedback op amp designed for single-supply
operation (+3V to +10V). The input stage supports input
voltages below ground and to within 1.7V of the positive
supply. The complementary common-emitter output stage
provides an output swing to within 25mV of ground and the
positive supply. The OPA830 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 Characteristic
Curves. For test purposes, the input impedance is set to
50Ω with a resistor to ground. Voltage swings reported in
the Electrical Characteristics 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 1.5kΩ resistors at the noninverting
input provide the common-mode bias voltage. Their
parallel combination equals the DC resistance at the
inverting input (R
F
), reducing the DC output offset due to
input bias current.
OPA830
V
S
=+5V
V
OUT
53.6
Ω
V
IN
1.50k
Ω
+V
S
/2
1.50k
Ω
R
L
150
Ω
+V
S
2
6.8
µ
F
+
0.1
µ
F
0.1
µ
F
R
F
750
Ω
R
G
750
Ω
2.5V
Figure 1. AC-Coupled, G = +2, +5V Single-Supply
Specification and Test Circuit
Figure 2 shows the AC-coupled, gain of +2 configuration
used for the +3V Specifications and Typical Characteristic
Curves. For test purposes, the input impedance is set to
50Ω with a resistor to ground. Voltage swings reported in
the Electrical Characteristics are taken directly at the input
and output pins. For the circuit of Figure 2, the total
effective load on the output at high frequencies is
150Ω || 1500Ω. The 1.13kΩ and 2.26kΩ resistors at the
noninverting input provide the common-mode bias
voltage. Their parallel combination equals the DC
resistance at the inverting input (R
F
), reducing the DC
output offset due to input bias current.
OPA830
V
S
=+3V
V
OUT
53.6
Ω
V
IN
2.26k
Ω
1.13k
Ω
R
L
150
Ω
+V
S
3
6.8
µ
F
+
0.1
µ
F
0.1
µ
F
R
F
750
Ω
R
G
750
Ω
+1V
+V
S
/3
Figure 2. AC-Coupled, G = +2, +3V Single-Supply
Specification and Test Circuit
Figure 3 shows the DC-coupled, gain of +2, dual
power-supply circuit configuration used as the basis of the
±5V Electrical Characteristics 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
150Ω with a series output resistor. Voltage swings
reported in the specifications are taken directly at the input
and output pins. For the circuit of Figure 3, the total
effective load will be 150Ω || 1.5kΩ. Two optional
components are included in Figure 3. An additional
resistor (348Ω) is included in series with the noninverting
input. Combined with the 25Ω DC source resistance
looking back towards the signal generator, this gives an
input bias current cancelling resistance that matches the
375Ω source resistance seen at the inverting input (see
the DC Accuracy and Offset Control section). In addition
to the usual power-supply decoupling capacitors to
ground, a 0.01µF capacitor is included between the two
power-supply pins. In practical PC board layouts, this
optional capacitor will typically improve the 2nd-harmonic
distortion performance by 3dB to 6dB.