Reduced current antenna circuit

• US 5,493,312 A
• Filed: 05/10/1995
• Issued: 02/20/1996
• Est. Priority Date: 10/26/1993
• Status: Expired due to Fees

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments Deutschland Gesellschaft Mit Beschrã¤Nkter Haftung (Texas Instruments, Inc.)
• Inventors: Knebelkamp, Michael
• Primary Examiner(s): Hajec, Donald T.
• Assistant Examiner(s): Ho, Tan
• Application Number:
  US08/438,602
• Time in Patent Office: 286 Days
• Field of Search: 343/742, 343/744, 343/860, 343/867, 343/866, 340/505, 340/572
• US Class Current: 343/860
• CPC Class Codes: H01Q 23/00 Antennas with active circuits or circuit elements integrated within them or attached to them
• CPC Class Codes: H01Q 7/08 Ferrite rod or like elongated core

Abstract

An alternative resonant circuit configuration reduces the amount of RF current that is switched by the power-stage transistors of a T/R unit and thereby also significantly reduces the reliability risk. A parallel resonant antenna configuration of coils and capacitors reduces the RF current through the output stage push-pull transistor configuration to a small fraction of the RF current experienced by typical series resonant circuits. This circuit offers advantages of low cost, reliable impedance matching while reducing the volume necessary to perform the function.

Claims

1. An antenna resonant circuit of a T/R unit which reduces the amount of current flowing through the output-power stage of the T/R unit comprising:

an output-power stage of a T/R unit;

a low Q series resonant circuit comprised of a series connected capacitor and an inductor for stimulating a main antenna circuit to oscillate with a resonant frequency;

said main antenna circuit comprised of a parallel combination of a second inductor and a second capacitor connected in series with a third capacitor wherein said third capacitor is connected in series with said series connected capacitor and said parallel combination is connected in parallel with said series combination of said third and said series connected capacitor; and

wherein said low Q series resonant circuit is connected in parallel with said output power stage of said T/R unit.

2. The antenna resonant circuit of claim 1, wherein said output power stage comprises a push-pull pair of transistors.

3. The antenna resonant circuit of claim 1, wherein said resonant frequency of said antenna resonant circuit is determined by the values of said second and third capacitors.

4. The antenna resonant circuit of claim 1, wherein the amount of power transferred from the low Q series resonant circuit to the main antenna resonant circuit is determined by the values of the inductor and the capacitor of the low Q series resonant circuit.