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. 22, 1994
Filed:
Jun. 05, 1992
Juha Pikkarainen, Oulu, FI;
Nokia Mobile Phones, Ltd., Helsinki, FI;
Abstract
A switched capacitor decimator circuit (20) is shown to be useful in a cellular telephone that operates in accordance with a subaudible signalling protocol. The switched capacitor decimator circuit has an input node for inputting a received signal that includes a subaudible signalling component and an interfering voice component. The switched capacitor decimator circuit further has an output node for outputting a signal having an amplified subaudible signalling component and voice component. The circuit includes an operational amplifier (22) having an input and an output and a characteristic DC offset voltage. A first capacitance (Cint) is switchably coupled, at a rate equal to a first frequency, between the input and the output of the operational amplifier. A second capacitance (Cin) is coupled between the input node and the input of the operational amplifier. A gain (G) of the circuit is given by Ncin/Cint, where n is a ratio of the first frequency to a second, lower frequency. The circuit further includes circuitry (C3, C4) for DC offset compensating the switched capacitor decimator circuit such that the DC offset voltage of the operational amplifier appears at the output node amplified only with a gain of unity.