holdvoltagehasanegativetemperaturecoefficientas:VT(T)=VT(T)+a(T-T)()whereaisthetemperaturecoefficientwithatypicalvalueof-mVKinCMOSLmVtechnology;VT(T)isthevalueofthethresholdvoltageattemperatureT.AsshowninFig.,thevoltageoutputsensorisathresholdvoltagereferencecell.ThepchanneltransistorsP,Pconstituteacurrentmirror.ThecurrentoftransistorNismirroredtotansistorsN,N,andN.ThevoltagedroponthesetransistorsisfedbacktothegateofN.Foreasycalculating,wechooseasamesizeofthetransistorsN,N,andN(BN=BN=BN),andwechooseappropriatesizeoftheothertransistorstoensurethatthetransistorsP,P,N,N,N,andNareallinthestateofsaturation.Thentheoutputvoltagesofthissensorareindirectproportiontothethresholdvoltageandlinearwithtemperatureandtheirvaluesare:VH=VT(+KPKP-KN)=kVT()VL=VT(+KNKP-KN)=kVT()whereisdeterminedbytheratiobetweenthegatesizesofthenchanneltransistorNandN,andistheratioofthegate是接通,晶体管P是关闭,造成电容C放电,以至于使源电流I直到Vc值超过最高限额VH。
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