Design of Quadrature Output Two-stage Differential Ring VCO

A 3.8GHz ring oscillator with the two-stage differential structure for PLL is presented. The circuit includes three parts: control voltage-current conversion unit, ring oscillator, and output buffer: control voltage-current conversion unit uses low-threshold transistors to increase the tuning range of the oscillator; to optimize the phase noise of the oscillator, a positive feedback mechanism is introduced into the delay cell, improve the rising and falling speed of the circuit waveform; the output buffer shapes the oscillator output waveform so that the output waveform reaches the rail-to-rail output swing. The simulation results show that the tuning range of the oscillator is 110MHz~7.5GHz, the gain is 6.06GHz/V, the phase noise at 3.8GHz frequency is -94.9dBc/Hz@1MHz, and the power consumption is 7. 56mW.