The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
May. 31, 1994
Filed:
Sep. 21, 1993
Robert A Zimmer, Loveland, CO (US);
Charles E Moore, Loveland, CO (US);
Hewlett-Packard Company, Palo Alto, CA (US);
Abstract
A circuit provides a high impedance input to an operational amplifier by substituting a p-channel field effect transistor for the bias resistor normally used on the input to an operation amplifier. By placing a PFET in place of the bias resistor, a resistance value can be created that is hundreds of times higher, for the same area of silicon within the integrated circuit, as that created with an actual resistor. This PFET has parasitic capacitance which may be significantly offset by connecting the gate of the PFET to the output of a source follower circuit having its input connected to the inverting input of the operational amplifier. The circuit may be still further improved by using a voltage follower amplifier circuit in place of the source follower.