Research And Design Of On-chip RC Relaxation Oscillator

As an on-chip integrated clock source,the RC relaxation oscillator is widely used in automotive Bluetooth,smart home,biological transplantation chips,and wireless sensor equipment.In order to provide a stable clock signal,the output frequency stability is an important performance indicator of the RC relaxation oscillator.This article has carried out the research to improve the stability of the output frequency of the on-chip RC relaxation oscillator by compensating the inherent delay of the oscillator.Aiming at the propagation delay of the comparator in the voltage-mode RC relaxation oscillator,by deriving the transfer function of the comparator and analyzing the influence factors of the delay,the result shows that the propagation delay of the comparator is related to its bias current.A new oscillator circuit is proposed that stabilizes the bias current of the comparator and reduces the delay change with temperature,thereby improving the stability of the oscillator output frequency.Under the TSMC 180 nm CMOS process,the chopper topology and the oscillator circuit with the reference current source compensation comparator delay are simulated and verified.The results show that: in the range of-35 ? ? 115 ?,the output frequency temperature coefficient of the chopper topology is 129.6ppm / ?.The output frequency temperature coefficient of the oscillator circuit with compensated comparator delay decreases to 22.15 ppm / ?.Aiming at the loop delay in the current mode RC relaxation oscillator,this paper proposes a compensation method using precharge technology.The charging method of the oscillator circuit is controlled by the digital control circuit.When the charging of one capacitor branch is completed,the digital control circuit is triggered to control the charging current source to precharge the other capacitor branch.After the loop delay,the oscillator output switches,and the digital control circuit again controls the oscillator to return to the normal charging mode.Therefore,the oscillation period of the oscillator during the alternate charging process of the two capacitor branches does not include the loop delay,which eliminates the influence of the loop delay on the output frequency and improves the stability of the oscillator output frequency.Under TSMC 180 nm CMOS process,the current mode oscillator circuit without loop delay elimination and the oscillator circuit with pre-charge technology are simulated and verified.The results show that: in the range of-20??100?,the temperature coefficient of output frequency of current mode oscillator circuit without compensation is 129 ppm / ?,and the temperature coefficient of the output frequency of the oscillator circuit using the precharge technology is reduced to 32ppm/?.The layout design and post-simulation of the voltage-mode RC relaxation oscillator with compensator propagation delay compensation and the current-mode RC relaxation oscillator with precharge technology are carried out using TSMC 180 nm CMOS technology.Due to the influence of layout parasitics and other factors,the performance parameters of the oscillator circuit have slightly changed.Among them,the voltage-mode oscillator circuit's post-simulation result is compared with the pre-simulation result: the output frequency of the oscillator drops from 1.07 MHz to 1.018 MHz,and the temperature coefficient of the output frequency rises from 22.15ppm/ ? to 54ppm/ ?;The current-mode oscillator circuit's post-simulation result is compared with the pre-simulation result:the output frequency of the oscillator drops from 500.2k Hz to 497.3k Hz,and the temperature coefficient of the output frequency rises from 32ppm/? to 46ppm/?.