Differential 45° Phase-Shifted Lo Signal Generation to Enable Subharmonic IQ Modulation for Broadband 6G Communication in the D-Band

This work presents a broadband generation of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{4 5}^{\circ}$</tex> phase-shifted signals in the W-Band in a 90 nm SiGe BiCMOS technology. It is designed for IQ modulation in the D-Band, where the use of subharmonic system architectures is beneficial with regard to efficient signal generation. However, the subharmonic factor, which is two for this work, reduces the required phase shift for IQ modulators from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{9 0}^{\boldsymbol{\circ}}$</tex> to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{4 5}^{\boldsymbol{\circ}}$</tex>. Our approach utilizes an integrated Lange Coupler to generate <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{4 5}^{\boldsymbol{\circ}}$</tex> phase-shifted signals by adding the Lange Coupler's in-phase and quadrature output signals. Accepting a phase error of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\pm 5^{\circ}$</tex> a relative bandwidth of 51.5% is achieved at a center frequency of 83.5 GHz, which represents the highest published operating frequency for an integrated generation of a 45° phase shift. Embedded into a subharmonic IQ modulator, a sideband suppression of more than <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$25 dB$</tex> is achieved over a bandwidth of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$60 GHz$</tex>, covering a large portion of the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$D$</tex> band.