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Integrated transformer balun with enhanced common-mode rejection for radio frequency, microwave, and millimeter-wave integrated circuits

  • US 9,330,832 B2
  • Filed: 02/13/2013
  • Issued: 05/03/2016
  • Est. Priority Date: 02/13/2013
  • Status: Active Grant
First Claim
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1. A transformer balun, comprising:

  • a first winding of at least one turn forming a primary coil, having first and second differential leads oriented in a first direction and connected at a center tap of the primary coil, the primary coil formed in a first conductive layer over a substrate and the first differential lead of the primary coil being grounded, the second differential lead providing a first terminal of the balun; and

    a second winding of at least one turn forming a secondary coil, having a third and fourth differential leads providing second terminals of the balun, oriented in a second direction offset by an angle of substantially ninety degrees from the first direction and connected at a center tap of the secondary coil, the secondary coil formed in a second conductive layer separated by an insulating layer from the first conductive layer, the first and second windings capacitively and inductively coupled forming an equivalent return-path inductance in both the third and fourth differential leads of the balun;

    wherein the primary coil and the secondary coil form a transformer balun wherein having;

    the first differential lead of the primary coil being a half-coil with a second segment and a fourth segment, that are substantially grounded and the second differential lead of the primary coil being a half-coil with a first segment and a third segment, that are a substantially higher impedance and provide the first terminal of the balun;

    the third differential lead of the secondary coil being a half-coil with a third segment parallel to and capacitively and inductively coupling with the higher impedance third segment of the primary coil, and a fourth segment parallel to and capacitively and inductively coupling with the grounded fourth segment of the primary coil, the third differential lead providing a first one of the second terminals of the balun;

    the fourth differential lead of the secondary coil being a half-coil with first segment parallel to and capacitively and inductively coupling with the higher impedance first segment of the primary coil, and a second segment parallel to and capacitively and inductively coupling with the grounded second segment of the primary coil, the fourth differential lead providing a second one of the second terminals of the balun;

    whereby aggregate impedances in the third differential lead and in the fourth differential lead of the secondary coil are substantially equivalent, to maximize common mode rejection.

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