8.3.2 FET-Input Architecture With Wide Gain-Bandwidth Product

Figure 8-4 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 AOL 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 AOL Bode plot, the second pole in the AOL response

occurs after AOL magnitude drops to less than 0 dB (1 V/V). This occurrence results in a phase change of less

than 180° at 0

‑dB AOL, indicating that the amplifier will be 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 9-2 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.

Frequency (Hz)

-20

-195

-10

-180

0

-165

10

-150

20

-135

30

-120

40

-105

50

-90

60

-75

70

-60

80

-45

90

-30

100

-15

110

0

120

15

1k

10k

100k

1M

10M

100M

1G

AOL Magnitude (dB)

AOL Phase ()

RL = 100 Ω

Figure 8-4. Open-Loop Gain Magnitude and Phase

vs Frequency

RL = 100 Ω

Figure 8-5. Open-Loop Gain Magnitude

vs Temperature

8.4 Device Functional Modes

The OPA814 has a single functional mode and is operational when the power-supply voltage is greater than 6 V.

The maximum power supply voltage for the OPA814 is 12.6 V (±6.3 V). The OPA814 can be operated on both

single and dual supplies.

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OPA814

SBOSA14 – APRIL 2023

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