DELAY CELL FOR HIGH SPEED AND LOW NOISE RING OSCILLATOR

摘要

PURPOSE: A delay cell for a high speed and low noise ring oscillator is provided to realize a high speed and low noise in a PLL circuit by a differential amplifier and a diode transistor. CONSTITUTION: A delay cell comprises a differential amplifier(50) and a voltage clamping circuit(40) connected to the differential amplifier. The differential amplifier amplifies a differential input to a pair of differential input transistors(51,52) according to adjustment of oscillation frequencies of a current flowing in a ring oscillator by adjusting currents flowing through PMOS and NMOS transistors(53,54,55) using control voltages(PBIAS,NBIAS) defined by a bias circuit, respectively. The voltage clamping circuit facilitates interfacing with other circuits at high frequencies by causing a predetermined number of diode transistors(41,42) not to be connected to either of power supply lines while limiting the outputs of the diode transistors within the range of power voltages.