24-GHz in-phase/quadrature direct-down converter with integrated quadrature couplers and baluns in standard 0.18 μm cmos technology

A novel monolithic CMOS radio frequency (RF) direct-down converter architecture is described, that comprises three miniature quadrature couplers (QCs), three miniature baluns and two sub-harmonic mixers (SHMs) for direct-down conversion. The SHMs in conjunction with the QCs and baluns are used to eliminate local oscillator (LO) self-mixing. The circuit was fabricated in a standard 0.18 m CMOS process for 24 GHz applications. At an RF of 24 GHz and intermediate frequency (IF) of 100 MHz, the RF direct-down converter exhibits an amplitude mismatch of only 0.6 dB, a phase mismatch of only 3.53 , a voltage gain of 1.5 dB, and an third-order input intercept point (IIP3) of 6.5 dBm while dissipating 10.05 mW from a 1.5 V supply. In addition, excellent isolations were also achieved. The corresponding LO-to-IF, RF-to-IF, LO-to-RF and 2LO-to-RF isolations are 45.7, 46.5, 61.1 and 60 dB, respectively, at 24 GHz. The chip area was only 1.017 × 0.717 mm², that is, 0.729 mm², excluding the test pads.