9.3.3 Wide Gain-Bandwidth Product

Figure 10 shows the open-loop magnitude and phase response of the OPA859. Calculate the gain bandwidth product of any op amp by determining the frequency at which the A_OL is 40 dB and multiplying that frequency by a factor of 100. The open-loop response shows the OPA859 to have approximately 63° of phase-margin when configured as a unity-gain buffer.

Figure 51 shows the open-loop magnitude (A_OL) of the OPA859 as a function of temperature. The results show approximately 5° of phase-margin variation over the entire temperature range. Semiconductor process variation is the naturally occurring variation in the attributes of a transistor (Early-voltage, β, channel-length and width) and other passive elements (resistors and capacitors) when fabricated into an integrated circuit. The process variation can occur across devices on a single wafer, or, across devices over multiple wafer lots over time. Typically the variation across a single wafer is tightly controlled. Figure 52 shows the A_OL magnitude of the OPA859 as a function of process variation over time. The results show the A_OL curve for the nominal process corner and the variation one standard deviation from the nominal. The simulated results show less than 2° of phase-margin difference within a standard deviation of process variation when the amplifier is configured as a unity-gain bufffer.

Figure 51. Open-Loop Gain vs Temperature

Figure 52. Open-Loop Gain vs Process Variation