Embedded DiCAD linear phase shifter for 57–65GHz reconfigurable direct frequency modulation in 90nm CMOS

A digitally controlled artificial dielectric (DiCAD) differential transmission line is designed to perform agile linear phase shift over 100deg with thermometer-coded 16 step control. It also operates with a 16 gain-step VGA to enable re-configurable and direct-frequency modulation at 60 GHz with 256² states (1.1deg angular and 0.0007 magnitude resolutions) and -31 dB static EVM for multiple PSK/QAM modulations. The modulator uses 0.33 mm² core area in 90 nm CMOS and consumes 10 mA at 1 V.

I. Introduction

There is increasing demand for low-cost and highperformance millimeter-wave transmitters for digital communications while direct-frequency modulation is recognized as the most cost-effective solution for such transmitter design. Modern direct frequency modulator's performance is limited by its non-linear phase shifter. Passive phase shifters, for example, utilize bi-phase modulators which receive reflected signals from a variable resistance cold-FET [1] or varactor [2] via a 90° hybrid. Resistance/capacitance variation may change their phase and precise bias controls are necessary to track the nonlinear R-V or C-V relationship. Active phase shifters on the other hand utilize variable-gain amplifiers and multiple passive hybrids/combiners to create the phase shift [3]. In such cases, modulator performance is adversely sensitive to the phase/gain mismatch between amplifiers, differential hybrids and nonlinear phase controls.