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:
Feb. 27, 2001
Filed:
Sep. 30, 1999
Marc E. Goldfarb, Atkinson, NH (US);
Wyn T. Palmer, North Andover, MA (US);
Analog Devices, Inc., Norwood, MA (US);
Abstract
A filter having a semiconductor chip and a low pass filter section on the chip. The low pass filter section includes a filter transconductor and a filter capacitor connected to the filter capacitor. The low pass filter section has a cut-off frequency related to the transconductance, gm,, of the filter transconductor and the capacitance of the filter capacitor. A gm control circuit having a control circuit transconductor is provided. The gm control circuit includes a first oscillator for producing a reference frequency. The first oscillator has a portion thereof on the chip and an off-chip capacitor and off-chip resistor. The reference frequency is a function of the capacitance of the off-chip capacitor and the resistance of the off-chip resistor. A second oscillator is on the chip and produces a variable frequency. The second oscillator has an on-chip capacitor. The variable frequency is a function of the capacitance of the on-chip capacitor and on-chip transconductor, gm,, such variable frequency is controlled by a control circuit transconductor control signal. A control loop is provided. The control loop is responsive to a difference between the reference frequency and the variable frequency and such loop produces the a feedback signal to drive the variable frequency towards the reference frequency.