Extended Phase Noise Performance in Mutual Negative Resistance CMOS LC Oscillator for Low Supply Voltages(<Special Section>Analog Circuit and Device Technologies)

A LC oscillator based upon the quadrature magnetic coupling to generate a mutual negative resistance (mu-R) is introduced. The topology offers enhanced optimum phase noise at low supply voltages by enabling extended circuit operation in the current-limited regime through the control of its mutual inductors' coupling factor, k. The principal operation of the mu-R oscillator is described and its comparison with the popular cross-coupled topology is discussed. The capability of the technique is demonstrated via design examples of 1.8GHz oscillators. Simulations show that, by employing inductors with a self-inductance of 2nH, a quality factor of about 7.5 and a coupling k=0.52, the mu-R oscillator exhibits the minimum phase noise of -142dBc/Hz at 3MHz-offset with 18mA bias current and 2V supply. This is 3-dB more than the minimum achievable phase noise in the cross-coupled oscillator with identical component parameters and supply voltage level.