9 Application and Implementation

Note

Information in the following applications sections is not part of the TI component specification,

and TI does not warrant its accuracy or completeness. TI’s customers are responsible for

determining suitability of components for their purposes, as well as validating and testing their design

implementation to confirm system functionality.

9.1 Application Information

The OPA859 offers high input impedance, very high-bandwidth, high slew-rate, low noise, and better than –60

dBc of distortion performance at frequencies up to 100 MHz. These features make this device an excellent

front-end buffer in high-speed data acquisition systems. The wide bandwidth also makes this amplifier an

excellent choice for high-gain active filter systems.

9.2 Typical Applications

9.2.1 TIA in an Optical Front-End System

Figure 9-1 shows the OPA859 configured as a transimpedance amplifier (U1) in a wide-bandwidth, optical front-

end system. A second OPA859 configured as a unity-gain buffer (U2) sets a dc offset voltage to the THS4520.

The THS4520 is used to convert the single-ended transimpedance output of the OPA859 into a differential

output signal. The THS4520 drives the input of the ADS54J64, 14-bit, 1-GSPS analog-to-digital converter (ADC)

that digitizes the analog signal.

+

±

VBIAS

CF

RF

3.5 V

5 V

OPA859

+

±

499

499

499

±

+

499

VOCM = 1.3 V

5 V

+

±

2.95 V

5 V

OPA859

ADS54J64

Low-pass

filter

U1

U2

Figure 9-1. OPA859 as Both a TIA and a Buffer in an Optical Front-End System

9.2.1.1 Design Requirements

The objective is to design a low noise, wideband optical front-end system using the OPA859 as a

transimpedance amplifier. The design requirements are:

• Amplifier supply voltage: 5 V

• TIA common-mode voltage: 3.5 V

• THS4520 gain: 1 V/V

• ADC input common-mode voltage: 1.3 V

• ADC analog differential input range: 1.1 VPP

www.ti.com

OPA859

SBOS852A – SEPTEMBER 2018 – REVISED MAY 2025

Copyright © 2025 Texas Instruments Incorporated

Submit Document Feedback

21

Product Folder Links: OPA859