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1、上页上页下页下页返回返回模拟电子技术基础模拟电子技术基础3 Basic FET Amplifiers 3.3.1 DC analysis of FET circuit1DC circuit of J-FETIDQUSQ=IDQ RSUGSQ=IDQ RS+_GRSRDRDDV TGSQUDQIDSQU+_上页上页下页下页返回返回模拟电子技术基础模拟电子技术基础2GS(off)GSQDSSDQ)1(UUII SDQGSQRIU Input equationsI-V equations of J-FETSolve these two equations to acquire IDQThe Q-po
2、int voltage is：DQSDDDDSQ)(IRRVU GR+_SRDRDDV TGSQUDQIDSQU+_上页上页下页下页返回返回模拟电子技术基础模拟电子技术基础Example In this circuit，VDD=18V，RD=3k，RS=1k、RG=1M，FET parameters is IDSS=7mA、UGS(off)=8V。Please determine UGSQ、IDQandUDSQ。+_GRSRDRDDV TGSQUDQIDSQU+_2GS(off)GSQDSSDQ)1(UUII Solution The I-V equation of J-FET isSDQGS
3、QRIU 上页上页下页下页返回返回模拟电子技术基础模拟电子技术基础UGSQ=2.9 VV4.6V)13(9.218DSQ UIDQ=2.9 mA1DQGSQ IU2GSQDQ)81(7UI Therefore:Therefore:上页上页下页下页返回返回模拟电子技术基础模拟电子技术基础2DC circuit of MOSFETDDG2G1G2GQVRRRU (1)DC analysisDQSSQIRU 2GS(th)GSQDQ)(UUKI +_G2RSRDRDDV TGSQUDQIDSQU+_G1RGQU+_+SQU上页上页下页下页返回返回模拟电子技术基础模拟电子技术基础So)(SDDQDDD
4、SQRRIVU SQGQGSQUUU +_G2RSRDRDDV TGSQUDQIDSQU+_G1RGQU+_+SQU上页上页下页下页返回返回模拟电子技术基础模拟电子技术基础3Common-source FET amplifier+GRSRDRDDV T_SC1C+2C+iuLR_+ou上页上页下页下页返回返回模拟电子技术基础模拟电子技术基础3.3.2 Equivalent AC circuit of FETAccording to the principle of FETAccording to the principle of FETiD=f(uGS，uDS)DS0DSDGS0GSDDddd
5、GSDSuuiuuiiuu iG=0FETGiSiGSuDSu Digds上页上页下页下页返回返回模拟电子技术基础模拟电子技术基础DS0DSDGS0GSDDdddGSDSuuiuuiiuu 0GSDmDS uuigTrans-conductorTrans-conductor0DSDdsdsGS1 uuirgThereforeTherefore DSdsmDd1ddurugiGS 上页上页下页下页返回返回模拟电子技术基础模拟电子技术基础DSdsmDd1ddurugiGS dsdsgsmd1urugi FETGiSiGSuDSu DigdsEquivalent circuit of FET gsd
6、gsugsmugdsrdsu上页上页下页下页返回返回模拟电子技术基础模拟电子技术基础Simplified gsdgsugsmugdsuEquivalent circuit of FET gsdgsugsmugdsrdsu上页上页下页下页返回返回模拟电子技术基础模拟电子技术基础3.3.3 Three types of FET circuit1Common-source FET circuitAC circuit+GRSRDRDDV T_SC1C+2C+iuLR_+ou gsdgsugsmugou iuGRiiDRLR上页上页下页下页返回返回模拟电子技术基础模拟电子技术基础gsiUU )/(LDg
7、smoRRUgU ThereforeioUUAu gsLDgsm)/(URRUg LmRg DLL/RRR a.Determine gain Auou gsdgsugsmug iuGRiiDRLR上页上页下页下页返回返回模拟电子技术基础模拟电子技术基础GiRR b.Determine input resistor RiiR gsdgsugsmug iuGRiiDRLRou上页上页下页下页返回返回模拟电子技术基础模拟电子技术基础Definition of Ro Li0oRUIURThereforeDoRR Equivalent circuitc.Determine output resistor
8、 Determine output resistor Roou gsdgsugsmug iuGRiiDRLR gsdgsugsmugu 0i uGRDRoRi上页上页下页下页返回返回模拟电子技术基础模拟电子技术基础2.Common-drain FET circuitAC circuitouGRSRDDV T_1C+2C+iuLR+_ gsdgsugsmugou iuGRiiSRLR上页上页下页下页返回返回模拟电子技术基础模拟电子技术基础LmLm1RgRg )/(LSgsmoRRUgU ThreforeioUUAu SLL/RRR ogsiUUU )/()/(LSgsmgsLSgsmRRUgUR
9、RUg gsdgsugsmugou iuGRiiSRLRa.Determine gain Au上页上页下页下页返回返回模拟电子技术基础模拟电子技术基础Input resistorGiRR iR gsdgsugsmugou iuGRiiSRLRb.Determine input resistor Ri上页上页下页下页返回返回模拟电子技术基础模拟电子技术基础 gsdgsugsmugou iuGRiiSRLR gsdgsugsmugu iuGRSRioRc.Determine output resistor Determine output resistor RoEquivalent circuit
10、上页上页下页下页返回返回模拟电子技术基础模拟电子技术基础gsmSUgRUI UU gsOutput resistormS11gR IUR omS1111gR mS1/gR gsdgsugsmugu 0i uGRSRioR上页上页下页下页返回返回模拟电子技术基础模拟电子技术基础3.Common-gate FET circuit+_T+_+G1RG2R1Ciu2CSRLRouDDV 3C+DR上页上页下页下页返回返回模拟电子技术基础模拟电子技术基础Equivalent circuit+_DRiuSRLRou+gsmuggsd_gsu+_T+_+G1RG2R1Ciu2CSRLRouDDV 3C+DR
11、上页上页下页下页返回返回模拟电子技术基础模拟电子技术基础Therefore)/(LDgsmoRRUgU gsiUU )/(LDmioRRgUUAu a.Determine voltage gain+_DRiuSRLRou+gsmuggsd_gsu+上页上页下页下页返回返回模拟电子技术基础模拟电子技术基础iiiIUR gsmSiiUgRUI ThereforeSinceimSiUgRU mS11gR mS1/gR ii+_DRiuSRLRou+gsmuggsd_gsu+iRb.Determine input resistor Ri上页上页下页下页返回返回模拟电子技术基础模拟电子技术基础thereforethereforeD0oLsRIURRU c.Determine output resistor RoEquivalent Equivalent circuitcircuit+_DRiuSRLRou+gsmuggsd_gsu+_DRiuSRu+gsmuggsd_gsu+ioRSinceugs=ui=0