9.1 Overview

The ultra-wide, 5.5-GHz gain bandwidth product (GBWP) of the OPA858, combined with the broadband voltage noise of 2.5 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 OPA858 combines multiple features to optimize dynamic performance. In addition to the wide, small-signal bandwidth, the OPA858 has 600 MHz of large signal bandwidth (V_OUT = 2 V_PP) and a slew rate of 2000 V/µs.

The OPA858 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 OPA858. To reduce the effects of stray capacitance on the input node, the OPA858 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 OPA858 also features a very low capacitance input stage with only 0.8-pF of total input capacitance.