构成镜像恒流源的参考回路.ppt

E CR I RT 1T 2 E C 、R和T 1-构成镜像恒流源的参考回路 I R称为参考电流基本镜像恒流源 r o≈r ce2≈∞ R ER UEI C BE CR??? 1U BE1= U BE2= U BE若β 1=β 2=β I B1=I B2=I B、I C1=I C2=I C BCRIII2 1??)2 21(/21 2??????? R RCI II当β>>1 时,可得 R EII CRC?? 2 输出电流 I C2与参考电流I R是镜像关系相对误差? 2 2 2?? C CRI II +U BEQ - 接放大器 r o I RI C2 I B2I B12I BI C1 BCII2 2??) 21( 2??? CI E CR I RT 1T 2I C2T 3I C3T 4I C4T nI C(n+1) ( n+1) I BI B2I B1I B3I B4I Bn 相对误差?)1(? T1 ~ T3 的参数相同β1= β2= β3= β>>1 U BE1 =U BE2 =U BE 31BCRIII??????1 32 ECII)2 21()1( 21 2 2??????????? R R CI II E CR I RT 1T 2+U BEQ - T 3I C1I B3I E3????1 2 22 BCII I C2 I C1=I C2???1 33 EBIII B2I B1 232 BEII????????1 2 II ? 22 BCII?相对误差????????????1 22 2 2 2 2C CRI II 由于电路中接了共集电极管 T 3,对分流电流 I B3的放大作用, 从而使误差减小了( 1+β)倍,精度提高了(1+β)倍。 r o≈r ce2≈∞ r o ) 21( 2??? CI BCII2 2?? BCRIII2 1?? R UUEI BE BE CR???)2 21(/21 2??????? R RCI IIR EII CRC?? 2相对误差? 2 2 2?? C CRI II E CR I RT 1T 2 ( cascade) β 1=β 2=β 3=β 4 >>1 U BE1 =U BE2 =U BE3 =U BE4 =U BET 3T 4+U BEQ - +U BEQ - I C1I C2 I B2I B1I B2I B12I BI R ? 22 CBII?思考:对照 P202 式 4-5-17 ,为何不同? ( Wilson )恒流源(反馈型,高输出阻抗精密恒流源) R ER UUEI C BE BE CR???? 12232 E CII????设T l ~T 3完全匹配 I R =I C1 +I B2 = I C1 +I C2/β( U BE1 = U BE3 = U BE)I C3 =I E2 -2I B 2 221 C CEI II??????? 2212 RIII??????? 22 22 222 212 22 C C CIII????????????????????????????????2 2 22 2??? C CRI II 相对误差 22 1 ce orr?? E CR I RI C2 I C1T 1T 2I C2 I RI