CMOS coupled multivibrators for WMTS applications

In this paper a wideband MOS quadrature oscillator constituted by two multivibrators is presented. Two different forms of coupling, named here as soft and hard, are investigated. Simulations are performed in a 0.13 μm CMOS technology to obtain the tuning range, the synchronization transients, and the influence of mismatches in timing capacitors and charging currents on synchronization. It is found that hard coupling reduces the quadrature error (about 1°, with 5% mismatches in timing capacitors and charging currents) and results in a low phase-noise (about 2 dB improvement) with respect to soft coupling. Either a single multivibrator or coupled multivibrators can be locked to an external synchronizing harmonic frequency, and the locking range is investigated by simulations. The circuit examples for the simulations are oscillators that cover the frequency bands of WMTS.