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Browse Prior Art Database

High Impedance Low Capacitance Probe

IP.com Disclosure Number: IPCOM000085782D
Original Publication Date: 1976-Jun-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 26K

Publishing Venue

IBM

Related People

Koss, RW: AUTHOR

Abstract

This probe circuit provides required high-input impedance and low-input capacitance necessary for measuring and testing high-speed metal-oxide semiconductor field-effect transistor (MOSFET) integrated circuit performance. The circuit easily measures voltage pulses of up to 15 volts having a response time of less than 10 nanoseconds, over a frequency range of DC to 10 megahertz. Low-input capacitance of 0.5 picofarad provides better performance than probe circuits using FET inputs to provide high-input impedance.

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High Impedance Low Capacitance Probe

This probe circuit provides required high-input impedance and low-input capacitance necessary for measuring and testing high-speed metal-oxide semiconductor field-effect transistor (MOSFET) integrated circuit performance. The circuit easily measures voltage pulses of up to 15 volts having a response time of less than 10 nanoseconds, over a frequency range of DC to 10 megahertz. Low-input capacitance of 0.5 picofarad provides better performance than probe circuits using FET inputs to provide high-input impedance.

The circuit comprises four high-speed, low-gain emitter coupled logic (ECL) differential amplifiers 10, 12, 14 and 16 connected in cascade to provide required negative feedback through a 100K ohm resistor. Input impedance of 1 MEG ohm is provided by a resistor mounted at the probe tip at the end of a short shielded cable 18. The probe voltage output is taken from the output of the first stage and may be coupled by a shielded cable to an oscilloscope.

Each amplifier stage consists of an ECL differential pair having an emitter- follower output. The circuit may be built using a commercially available ECL Quad Line Receiver or Quad Differential Amplifier such as Motorola part number MC 1692.

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