An LC Voltage-Controlled Oscillator Design for Room Temperature and Cryogenic Operation

An LC voltage-controlled oscillator suitable for operation at cryogenic temperatures is designed. Transistor models modified for cryogenic conditions were used in simulations at the schematic and layout levels. The optimum inductor value has been obtained to achieve the lowest phase noise value. Inverter-based resistive feedback buffers were connected to the differential outputs of the oscillator to facilitate measurements. The fabricated chip was tested, and measurement results were obtained at room temperature and cryogenic conditions. At room temperature, the center frequency is 1.75 GHz, and the phase noise at this frequency is found to be -105 dBc / Hz at a 1 MHz offset frequency. Measurements were carried out at 77 K (-196°C) by immersing the test printed circuit board (PCB) in a container filled with liquid nitrogen (LN2). In this case, the phase noise has been acquired as -108 dBc / Hz for 1.74 GHz at 1 MHz offset frequency. Hence, the design is operational in both environments.