A linearized current-controlled oscillator for ultra-low power wideband and cognitive radios

Measurement results of a linear current-controlled oscillator (CCO) is presented. Output frequency of a ring oscillator is sensed by a linear CMOS switched-capacitor frequency-detector (SCFD) that operates well over the frequency range of the oscillator operation. The feedback is completed by controlling the supply current of the ring oscillator using a negative impedance converter(NIC). This simple low-power circuit does not use operational amplifiers or resistors. The linearization technique is applicable to all types of oscillators. A prototype of this CCO is fabricated in TSMC 0.18μm CMOS process and it has a power consumption less than 3.6 mW in the frequency range of 140 MHz to 1.15 GHz from a supply voltage of 1.8 V. The measured phase noise is -93.44 dBc/Hz at 1 MHz offset from the carrier at the frequency of 501.13 MHz. It achieves 0.12% linearity over the entire tuning range. This CCO can be readily used in ultra-low power wideband and cognitive radios. A method of improving the settling time by a simple circuit modification of the frequency-detector is discussed with supporting post-layout simulation results.