The OPA2830 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 OPA2830 is compensated to provide stable operation with a wide range of resistive loads.

Figure 8-1 shows the ac-coupled, gain of +2 configuration used for the 5V Specifications and Typical Characteristics. 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 8-1, 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. The parallel combination equals the dc resistance at the inverting input (R_F), reducing the dc output offset due to input bias current.

Figure 8-1 AC-Coupled, G = +2, 5V Single-Supply Specification and Test Circuit

Figure 8-2 shows the ac-coupled, gain of +2 configuration used for the 3V Specifications and Typical Characteristics. Voltage swings reported in the Electrical Characteristics are taken directly at the input and output pins. For the circuit of Figure 8-2, 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. The parallel combination equals the dc resistance at the inverting input (R_F), reducing the dc output offset due to input bias current.

Figure 8-2 AC-Coupled, G = +2, 3V Single-Supply Specification and Test Circuit

Figure 8-3 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 8-3, the total effective load is 150Ω || 1.5kΩ. Two optional components are included in Figure 8-3. 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 configuration gives an input bias current canceling 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 printed circuit board (PCB) layouts, this optional capacitor typically improves the 2nd-harmonic distortion performance by 3dB to 6dB.

Figure 8-3 DC-Coupled, G = +2, Bipolar Supply Specification and Test Circuit