Browse Prior Art Database

Picosecond Photoconductive Current Source

IP.com Disclosure Number: IPCOM000036739D
Original Publication Date: 1989-Oct-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Arjavalingam, G: AUTHOR [+2]

Abstract

Disclosed is a modification to the picosecond photoconductive optoelectronic probes for testing devices requiring a current pulse to turn on. While retaining the high speed character and the integrated nature of the integrated optoelectronic probes, this disclosure makes them into more ideal current sources.

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Picosecond Photoconductive Current Source

Disclosed is a modification to the picosecond photoconductive optoelectronic probes for testing devices requiring a current pulse to turn on. While retaining the high speed character and the integrated nature of the integrated optoelectronic probes, this disclosure makes them into more ideal current sources.

This modification consists in integrating with the optoelectronic probe a series resistor very close to the contacting gold dot on the side of the coplanar transmission line which is connected to the driving terminal of the device under test. The requirements for this resistor are: 1) that it conform to the geometrical layout of the transmission line to limit the capacitance and inductance to the distributed value of the line itself, and 2) that it must be located as close as possible to the contact point so that the propagation delay to the device is small compared to the pulse width.

The resistance value must be such that, when the device turns on, the line is loaded with an impedance close to its characteristic impedance. Typical values for the impedance are a few ohms, which imply a resistor value slightly less than the line impedance.

The figure shows a typical layout for such an integrated opto electronic current probe. The resistor can be made of p+ polysilicon, which is a process commonly practiced in the bipolar technology. With a typical value for the sheet resistance of 200 L/ , in a 120 L geometry on SOS,...