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LTC6268-10 Oscilloscope Differential Probe

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 ProbeLTC6268-10 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 PrototypeLTC6268-10 Oscilloscope Differential Probe Prototype

 

 


Software

LTspice

LTspice® software is a powerful, fast and free simulation tool, schematic capture and waveform viewer with enhancements and models for improving the simulation of switching regulators. Click here to download LTspice

To launch a ready to run LTspice demonstration circuit for this part:

  • Step 1: If you have not installed LTspice on this computer, download and install LTspice
  • Step 2: Once LTspice is installed, click on the link(s) below to launch the simulation
  • Step 3: If LTspice does not automatically open after clicking the link above, you can instead run the simulation by right clicking on the link and selecting "Save Target As." After saving the file to your computer, start LTspice and open the demonstration circuit by selecting 'Open' from the 'File' menu

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