A Silicon Monolithic Phase-Inverter Rat-Race Coupler Using Spiral Coplanar Striplines and Its Application in a Broadband Gilbert Mixer

Abstract

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper realized a broadband uniplanar phase-inverter rat-race coupler using a standard silicon process, and then analyzed this coupler under a lossy condition. A phase inverter is employed in this coupler, not only to extend the operation bandwidth, but also to generate balanced outputs by providing equal lossy paths, while symmetrical spiral-shaped coplanar striplines (CPSs) are also utilized to shrink the coupler size, as well as to construct a phase inverter in the middle of one of spiral CPSs. The lossy CPS, when designed as a distortionless line, has a real characteristic impedance, and thus, perfect port matching of the coupler can be achieved at the center frequency. The operation frequency of this silicon monolithic rat-race coupler with the size of 0.5 <formula formulatype="inline"><tex>${\hbox {mm}}^{2}$</tex></formula> is extremely wide and ranges from 5 to 23 GHz. The dissipated loss, transmission coefficient, and isolation of the rat-race coupler are approximately 5.5, <formula formulatype="inline"><tex>$-$</tex></formula>8, and below <formula formulatype="inline"> <tex>$-$</tex></formula>25 dB, respectively. In addition, a wideband Gilbert micromixer with an integrated uniplanar phase-inverter rat-race coupler at the local oscillator port is demonstrated using 0.35-<formula formulatype="inline"><tex>$\mu{\hbox {m}}$</tex></formula> SiGe BiCMOS technology. This mixer works from 2.5 to 13 GHz with 12-dB conversion gain, <formula formulatype="inline"><tex>$-$</tex></formula>16-dBm <formula formulatype="inline"><tex>${\rm IP}_{1\ {\rm dB}}$</tex></formula>, <formula formulatype="inline"><tex>$-$</tex></formula>4-dBm <formula formulatype="inline"> <tex>${\rm IIP}_{3}$</tex></formula>, and 14-dB noise figure. The chip size of the mixer with an integrated coupler is approximately 1.4 mm <formula formulatype="inline"> <tex>$\times$</tex></formula> 1.4 mm. </para>