7 Detailed Description

7.1 Overview

The OPA818 is a 13-V supply, 2.7-GHz gain-bandwidth product (GBWP), voltage-feedback operational amplifier

(op amp) featuring a 2.2-nV/√Hz, low-noise, JFET input stage. The OPA818 is decompensated to be typically

stable in gains ≥ 7 V/V. The decompensated architecture allows for a favorable tradeoff of low quiescent current

for a very high GBWP and low distortion performance in high-gain applications. The high voltage capability

combined with a 1400-V/µs slew rate enables applications that require wide output swings (10 VPP at VS = 12

V) for high-frequency signals. Such applications include optical front ends, test and measurement, and medical

systems. The low noise JFET input with pico amperes of bias current makes this device particularly attractive

for high TIA gain applications and test and measurement front ends. The OPA818 also features a power-down

mode that disables the core amplifier for power savings.

The OPA818 is built using TI's proprietary high-voltage, high-speed, complementary, bipolar SiGe process.

7.2 Functional Block Diagram

The OPA818 is a conventional voltage-feedback op amp with two high-impedance inputs and a low-

impedance output. Standard amplifier configurations are supported. Figure 7-1 and Figure 7-2 show two basic

configurations. The dc operating point for each configuration is level-shifted by the reference voltage (VREF),

which is typically set to midsupply in single-supply operation. VREF is typically set to ground in split-supply

applications.

+

–

VIN

RG

VREF

VREF

RF

VSIG

VREF

(1+RF/RG)VSIG

VO

VS+

VS–

Figure 7-1. Noninverting Amplifier

+

–

VIN

RG

VREF

VREF

RF

VSIG

VREF

–(RF/RG)VSIG

VO

VS+

VS–

Figure 7-2. Inverting Amplifier

7.3 Feature Description

7.3.1 Input and ESD Protection

The OPA818 is built using a very high speed complementary bipolar process. The internal junction breakdown

voltages are relatively low for these very small geometry devices. These breakdowns are reflected in Section

6.1. Figure 7-3 shows how all the device pins are protected with internal ESD protection diodes.

These diodes also provide moderate protection to input overdrive voltages beyond the supplies. The protection

diodes typically support 10mA continuous current. Where higher currents are possible (for example, in systems

with ±12V supply parts driving into the OPA818), add current limiting series resistors in series with the two

inputs to limit the current. Keep these resistor values as low as possible because high values degrade both

noise performance and frequency response. There are no back-to-back ESD diodes between VIN+ and VIN–. As

a result, the differential input voltage between VIN+ and VIN– is entirely absorbed by the VGS of the input JFET

differential pair; do not exceed the voltage ratings in Section 6.1.

OPA818

SBOS940B – MAY 2019 – REVISED DECEMBER 2025

www.ti.com

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