The OPA858IDSGR is a wideband operational amplifier optimized for transimpedance and voltage amplifier applications where the signal of interest is fast, weak, and originates from a high-impedance source. With a gain-bandwidth product of 5.5 GHz, a slew rate of 2000 V/μs, and an input bias current of only 10 pA, the device is positioned for optical time-of-flight (ToF) systems, LIDAR receivers, and other applications requiring the conversion of small photodiode currents into usable voltage signals at bandwidths extending into the hundreds of megahertz.

The OPA858IDSGR is a decompensated amplifier, meaning it is stable only for gains of 7 V/V or greater. This design choice sacrifices unity-gain stability in exchange for higher achievable bandwidth at the noise gains typical of transimpedance configurations. The device operates from a supply voltage range of 3.3 V to 5.25 V and draws a quiescent current of 20.5 mA.

The input stage uses MOSFET devices, which accounts for the exceptionally low bias current of 10 pA. This is a critical specification for photodiode interfacing, where bias current flowing through the source impedance produces a DC offset that can saturate the amplifier or degrade measurement accuracy.

The OPA858IDSGR incorporates several features tailored to the transimpedance amplifier (TIA) configuration.

Feedback Pin. The package includes a dedicated feedback pin (FB) that simplifies the connection of the feedback network between the input and output. This pin placement reduces parasitic capacitance and inductance in the feedback path, which is essential for maintaining stability and bandwidth at gigahertz frequencies.

Wide Input Common-Mode Range. The input common-mode range extends to within 1.4 V of the positive supply and includes the negative supply. This flexibility accommodates both single-supply and split-supply operation, and simplifies interfacing with photodiodes that may be biased at or near ground.

Low Input Capacitance. The common-mode input capacitance of 0.6 pF and differential input capacitance of 0.2 pF are critical for TIA bandwidth. In a photodiode amplifier, the total input capacitance—comprising the photodiode capacitance and the amplifier input capacitance—directly determines the achievable transimpedance bandwidth for a given feedback resistor. Minimizing the amplifier's contribution to this capacitance preserves bandwidth.

Output Stage. The output stage can deliver 105 mA and provides a 2.5 V_PP output swing in TIA configuration, sufficient to drive the inputs of high-speed ADCs directly or through a differential output amplifier such as the THS4541 or LMH5401.

The primary application of the OPA858IDSGR is optical front-end design for time-of-flight and LIDAR systems. In these systems, a short pulse of light is emitted, and the time taken for the reflected pulse to return is measured. The photodiode converts the returning light into a current pulse, which the TIA converts to a voltage for subsequent time-to-digital conversion.

In a typical LIDAR receiver, the OPA858IDSGR might be configured with a feedback resistance in the tens to hundreds of kilohms, producing a transimpedance gain sufficient to raise a 100 μA photocurrent pulse to a 100 mV voltage swing. The 5.5 GHz GBWP supports closed-loop bandwidths in the hundreds of megahertz at these transimpedance gains, enabling the resolution of pulse widths in the nanosecond range.

Beyond LIDAR, the device is applicable to laser distance measurement, optical time-domain reflectometry (OTDR) for fiber optic fault location, level transmitters using optical sensing, distributed temperature sensing, and 3D scanners. The combination of low noise, high bandwidth, and low input bias current makes it a general-purpose solution for high-speed optical signal acquisition.

The OPA858IDSGR is a specialized amplifier that prioritizes bandwidth, noise performance, and low input bias current over unity-gain stability. This trade-off is well matched to transimpedance applications, where the amplifier operates at a noise gain determined by the feedback network and the photodiode capacitance. For engineers designing optical receivers for LIDAR, ToF ranging, or high-speed photodiode instrumentation, the OPA858IDSGR provides a focused set of capabilities that address the central challenges of the application: converting small, fast current pulses into voltage signals without adding noise or limiting bandwidth.