Research Of On-chip Time-domain Measurement Circuits Of Quality Factor

As a frequency selective element,oscillator is widely used in the electronic field of consumer,communication,industry and automobile.With advantages in size,weight,power consumption,reliability,sensitivity,etc.,and the features like easier integration,more stable,lower cost,and shorter manufacturing time,the MEMS oscillator has been gradually sharing the market with the quartz oscillator evenly.As an important parameter of the resonant circuit,the quality factor directly represents a number of performance indicators of the resonator,or describe the physical state of a system vibration.For some applications,Q-factor is even directly used as a variable quantity which is associated with the surrounding environment.Besides,the Q-factor indicates the working performance of the oscillator.Therefore,under the circumstance of shrinking circuit geometries and the on-chip application of oscillator has become an inevitable tendency,the research of on-chip time-domain measurement circuits of Q-factor is of great significance.Based on the principle of the time-domain measurement,an electrical method is used for the research of on-chip Q-factor measurement,to solve the bad frequency performance of the discrete circuit,and to improve the narrow range of the measurable Q-factor value.For different application requirements,three types of circuits which can be integrated on-chip are proposed.The circuits are designed and layout completely.The studies included in this paper are giving below:Firstly,a Q-factor measurement circuit is proposed for the resonators,which have only one resonant frequency and the value of Q-factor is on the orders of 10~3.The offset of the OTA cancelled automatically thanks to an original joint of implementation of both peak detector and comparator by a reconfigurable circuit,leading to a high accuracy measurement of Q-factor.The digital control circuit plays an important role in the automatic shift between peak detector and comparator,which makes the system more stable.Besides,the ending block shut the system down when counting finished for saving the power.The post-layout simulation shows that the operating frequency can reach up to 200kHz,which is about 4times higher than the early measurement circuit.And it achieves an accuracy of 0.09%under the typical process,After considering the robustness and process,the accuracy is still within�0.4%.Secondly,another measurement circuit is developed for the resonators,which have more than one resonance frequency.A new compensation method is introduced,not only increases stability but also relaxed restrictions on the OTA maximum DC gain,thereby increasing the comparator accuracy.Besides,the introduction of the compensation resistor cancels the speed limit introduced by OTA,which improve the accuracy theoretically and eliminate the influence of the input signal frequency of the circuit at the same time,so that the frequency of the input signal can be expanded from a single 200kHz to 100kHz~1.5MHz.With a little complex digital control logic circuit to add a power-saving mode,energy saving during the reconfigurable circuit portion off duty,the system reduces power consumption by 7.5%.The post-layout simulation results show that the accuracy of the system rose to�0.2%,but compared to the first circuit,the core circuit area increased by42.6%.In addition,the digital control logic circuits are improved by adding an extra capacitor,which cannot discharge transiently,leads to an automatic passage between the two configurations.And this method shut down the whole part of reconfigurable circuits during the power saving mode.As a result,power consumption of the system reduced by about 23%,but the core circuit area increased by 2.7%.Thirdly,for the measuring requirement of high quality factor,another circuit is proposed in this paper.Get ride of the peak detection circuit,only high performance comparator and digital control circuit are used to implement the Q-factor measurement.So that the coverage of quality factor value and upper limit have been greatly improved.The post-layout simulation results show that the measurable Q-factor can reach up to 10~6,and in the worst case(T=-40?under ss process corner)still meet the 0.01%accuracy specifications.In addition,under the same accuracy,this circuit can cover the Q-factor range from 10~4 to 10~6.While the input signal can still cover the frequency range from100kHz to 1.5MHz.However,the power consumption increases sharply,and the core circuit area compared to the second circuit has an increase of 38.8%.At last,to guide the design of such architecture,a theoretical analysis links the required accuracy and the given Q-factor to the circuit parameters,such as:DC gain of OTA,reference voltage,errors of reconfigurable circuits and stable requirements,has been given in this paper for the first time.