8 Detailed Description

8.1 Overview

The ultra-wide, 900-MHz gain bandwidth product (GBWP) of the OPA859-Q1, 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-Q1 combines multiple features to optimize dynamic performance. In addition to the wide

of 1150 V/µs.

The OPA859-Q1 is offered in a 2-mm × 2-mm, 8-pin WSON package that features a feedback (FB) pin for a

simple feedback network connection between the amplifiers output and inverting input. Excess capacitance on

an amplifiers input pin can reduce phase margin causing instability. This problem is exacerbated in the case of

very wideband amplifiers like the OPA859-Q1. To reduce the effects of stray capacitance on the input node, the

OPA859-Q1 pinout features an isolation pin (NC) between the feedback and inverting input pins that increases

the physical spacing between them thereby reducing parasitic coupling at high frequencies. The OPA859-Q1

also features a very low capacitance input stage with only 0.8-pF of total input capacitance.

8.2 Functional Block Diagram

The OPA859-Q1 is a classic voltage feedback operational amplifier (op amp) with two high-impedance inputs

and a low-impedance output. Standard application circuits are supported, like the two basic options shown in

Figure 8-1 and Figure 8-2. The DC operating point for each configuration is level-shifted by the reference voltage

split-supply applications.

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Figure 8-1. Noninverting Amplifier

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Figure 8-2. Inverting Amplifier

OPA859-Q1

SBOSA59 – FEBRUARY 2021

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