Figure 7-4 shows the open-loop gain and phase response of the OPA814. The GBWP of an op amp is measured in the 20‑dB/decade constant slope region of the A_OL magnitude plot. The open-loop gain of 60 dB for the OPA814 is along this 20‑dB/decade slope, and the corresponding frequency intercept is at 250 kHz. Converting 60 dB to linear units (1000 V/V) and multiplying the open-loop gain with the 250-kHz frequency intercept gives the GBWP of OPA814 as 250 MHz. As is inferred from the A_OL Bode plot, the second pole in the A_OL response occurs after A_OL magnitude drops to less than 0 dB (1 V/V). This occurrence results in a phase change of less than 180° at 0‑dB A_OL, indicating that the amplifier is stable in a gain of 1 V/V. Amplifiers such as the OPA814 that are JFET input, low noise, and unity-gain stable can be used as high input-impedance buffers and gain stages with minimal degradation in SNR. The OPA814 has 600 MHz of SSBW in gain of 1‑V/V configuration with approximately 65° of phase margin.

The low input offset voltage and offset voltage drift of the OPA814 make the device an excellent amplifier for high-precision, high input-impedance, wideband data-acquisition-system front-ends. Figure 8-2 shows that the system benefits from the low-noise JFET input stage with picoamperes of input bias current to achieve higher precision at the 1-MΩ input impedance setting, and higher SNR at the 50-Ω input impedance setting simultaneously in a typical data-acquisition front-end circuit.

RL = 100 Ω

Figure 7-4 Open-Loop Gain Magnitude and Phase vs Frequency

RL = 100 Ω

Figure 7-5 Open-Loop Gain Magnitude vs Temperature