8 Detailed Description

8.1 Overview

The ultra-wide, 900-MHz gain bandwidth product (GBWP) of the OPA859, combined with the broadband voltage

noise of 3.3 nV/√Hz, produces a viable amplifier for wideband transimpedance applications, high-speed data

acquisition systems, and applications with weak signal inputs that require low-noise and high-gain front ends.

The OPA859 combines multiple features to optimize dynamic performance. In addition to the wide small-signal

bandwidth, the OPA859 has 400 MHz of large-signal bandwidth (VOUT = 2 VPP), and a slew rate of 1150 V/µs.

8.2 Functional Block Diagram

The OPA859 is a classic voltage-feedback operational amplifier (op amp) with two high-impedance inputs and a

low-impedance output. Standard application circuits are supported, such as the two basic options in Figure 8-1

and Figure 8-2. 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 connected to ground in split-supply

applications.

+

±

VIN

RG

VREF

VREF

RF

VSIG

VREF

(1 + RF / RG) × VSIG

VOUT

VS+

VS±

Figure 8-1. Noninverting Amplifier

+

±

VIN

RG

VREF

VREF

RF

VSIG

VREF

±(RF / RG) × VSIG

VOUT

VS+

VS±

Figure 8-2. Inverting Amplifier

OPA859

SBOS852A – SEPTEMBER 2018 – REVISED MAY 2025

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