Switched-Current Circuit Theory And Fault Diagnosis

With the development of microelectronics,more and more attention has been paid to the advantages of switched-current(SI) technique.The SI circuits have become very important analog-digital interface circuits of mixed-signal systems and chip systems. The upsurge of research in the academic front of international circuit has been raised.In this paper, switched-capacitor technique is simplely introduced at first.Then high performance SI memory cells are presented in detail.After that,this paper introduces the basic unit structure of the SI circuits.The MOS transistor used in the SI circuits as switch and storage transistor is not perfect. The implementation makes actual performance of MOS transistor not as well as that of the ideal model. In order to design SI circuits successfully and to meet the analog performance the system required,the most important is how to control the errors of SI.This paper introduces the errors in SI memory cell,such as mismatch error, conductance ratio error,settling error,noise error,charge-injection error,and some equations are given.Charge-injection error is the main factor which affects the performance of SI circuits.After theoretical analysis of this error,a new memory cell circuit is proposed.This circuit uses CMOS switch and cascoded mirror.HSPICE simulation demonstrates the proposed circuit can improve the accuracy of SI circuit by reducing the clock-feedthrough error results from charge injection.This paper introduces the basic concept and methods of fault diagnosis of analog circuit. Then the general process of the direct current fault dictionary method is introduced in detail. According to this guilding ideology, the author diagnoses the faults of the memory cell circuit without MOS switch.In order to reduce the effects on the output current by charge injection error, MOS switch is cancelled.The fault model which used has four fault type:gate-source short,gate-drain short,drain open,source open.On the condition of single fault occurring in the circuit, faults are located through the difference of error current. HSPICE simulation demonstrates that some faults can be located correctly, others have close error current.So this experiment can't distinguish all faults.