8.3.3 Wide Gain-Bandwidth Product

Figure 6-10 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 AOL 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 8-5 shows the open-loop magnitude (AOL) 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 8-6 shows the AOL magnitude of the

OPA859 as a function of process variation over time. The results show the AOL 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 buffer.

Frequency (Hz)

-15

0

15

30

45

60

75

100k

1M

10M

100M

1G

D404

AOL at 40qC

AOL at 25qC

AOL at +125qC

Figure 8-5. Open-Loop Gain vs Temperature

Frequency (Hz)

-15

0

15

30

45

60

75

100k

1M

10M

100M

1G

D405

AOL (

V

)

AOL (Typ.)

AOL (

V

)

Figure 8-6. Open-Loop Gain vs Process Variation

OPA859

SBOS852A – SEPTEMBER 2018 – REVISED MAY 2025

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