A Transformer-Based Poly-Phase Network for Ultra-Broadband Quadrature Signal Generation

This paper presents a transformer-based poly-phase network to generate fully differential quadrature signals with low loss, compact area, and high-precision magnitude and phase balance over an ultra-wide bandwidth. A fully differential high-coupling 8-port folded transformer-based quadrature hybrid serves as the basic building block for the poly-phase unit stage to achieve significant size reduction and low loss. Multiple poly-phase unit stages can be cascaded to form the multistage poly-phase network to substantially extend the quadrature signal generation bandwidth. The designs of the high-coupling transformer-based quadrature hybrid, the poly-phase unit stage, and the multistage transformer-based poly-phase network are presented with the closed-form design equations in this paper. As a proof-of-concept design, a 3-stage transformer-based poly-phase network is implemented in a standard 65 nm bulk CMOS process with a core area of 772 μm × 925 μm. Measurement results of this poly-phase network over 3 independent samples demonstrate that the output In-Phase and Quadrature (I/Q) magnitude mismatch is less than 1 dB from 2.8 GHz to 21.8 GHz with a passive loss of 3.65 dB at 6.4 GHz. The measured output I/Q phase error is less than 10 ^° from 0.1 GHz to 24 GHz. The effective Image Rejection Ratio (IRR) based on the measured I/Q balancing is more than 30 dB from 3.7 GHz to 22.5 GHz. The 3-stage transformer-based poly-phase network design achieves high-quality quadrature signal generation over a first-ever one-decade bandwidth together with low-loss and compact area.