The LTC6268-10 is a single 4GHz FETinput operational amplifier with extremely low input bias current and low input capacitance. It also features low input-referred current noise and voltage noise making it an ideal choice for high speed transimpedance amplifiers, and high-impedance sensor amplifiers. It is a decompensated op amp that is gain-of-10 stable.
LTC6268-10 Oscilloscope Differential Probe
This circuit uses two LT6268-10 high-frequency amplifiers to realize a fully differential oscilloscope probe with >100MHz bandwidth and 100kilohm input resistance. The input stage is a modified differential amplifier configuration with 100:1 attenuation on the inputs to allow wide common-mode swings. Additionally, the inputs are ac-coupled to provide high-voltage dc blocking. The first-stage IC re-amplifies the signal by 10:1 as does the single-ended output stage, for a composite gain of 1:1. A back-termination resistor provides stability when driving a cable to the 1Megohm oscilloscope input port, and is AC-coupled to remove the 2.5V output-stage bias. The circuit is powered from 5V, which is easily derived from a 9V battery with an LDO (like LT1761-5). Due to the wide bandwidth amplifiers and the relatively high resistances being used, stray capacitance control and careful layout is vital. Additionally, a 'gimmick' feedback capacitor may be needed to adjust the damping of the amplifiers to avoid oscillation and to achieve best time-response.
LTC6268-10 Oscilloscope Differential Probe Prototype
Tools & Simulations
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