Figure 8-5 shows the open-loop gain and phase response of the OPA817. 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 OPA817 is along this 20 dB/decade slope and the corresponding frequency intercept is at 400 kHz. Converting 60 dB to linear units (1000 V/V) and multiplying it with the 400 kHz frequency intercept gives the GBWP of OPA817 as 400 MHz. As can be inferred from the A_OL Bode plot, the second pole in the A_OL response occurs after A_OL magnitude drops below 0 dB (1 V/V). This results in phase change of less than 180° at 0 dB A_OL indicating that the amplifier will be stable in a gain of 1 V/V. Amplifiers like OPA817 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. It has 800 MHz of SSBW in gain of 1V/V configuration with approximately 55° phase margin.

The low input offset voltage and offset voltage drift of OPA817 makes it a very suitable amplifier for high precision, high input impedance, wideband data acquisition system front-ends. As Figure 9-2 shows, the system benefits from the low noise JFET input stage with pico-amperes of input bias current to achieve higher precision at 1-MΩ input impedance settings and higher SNR at 50-Ω input impedance setting simultaneously in a typical data acquisition front-end circuit.