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:
Nov. 04, 1997
Filed:
Dec. 13, 1995
Barrie Gilbert, Portland, OR (US);
Eberhard Brunner, Portland, OR (US);
Analog Devices, , US;
Abstract
A variable gain amplifier uses a differential attenuator to provide a differential input to which a differential input signal is applied. The differential attenuator is comprised of (N-1) .pi. attenuator stages, with each stage forming a pair of attenuator taps for providing an attenuated version of the differential input signal. The differential input forms a high-impedance input, which is essentially floating. Each pair of taps is coupled to the differential inputs of a respective gm stage. The differential outputs of the gm stages are coupled to the differential inputs of a main amplifier, which has a high open-loop gain. The transconductance of each gm stage is controlled by an interpolator which provides a bias current to each of the gm stages in a sequential manner as a gain control voltage is swept from its minimum to its maximum values. The combination of the attenuated input voltage, the varying transconductances produces a gain response that is linear-in-dB relative to the gain control voltage. The output of the main amp is fed back through a gain-setting resistor network through a fixed gm stage.