模拟集成电路的分析与设计：Chapter 11-Bandgap References.ppt

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,General Consideration,The best references should be:,independent on,supply,;,independent on,temperature,An accurate circuit design needs an accurate voltage or current reference.,In practice,there are several kinds of references exist:,1.Supply-independent biasing;,2.Proportional to absolute temperature(PTAT)reference;,3.Constant-G,m,behavior reference;,4.Temperature independent reference.,Other parameters affecting references may be:output impedance,output noise and power dissipation.,Supply independent biasing(1),Simple current mirror.,I,out,dependent on V,DD,.,Supply independent biasing,(2),I,out,independent on V,DD,but,I,out,is not uniquely defined.,Supply independent biasing,(3),I,out,independent on V,DD,and is uniquely defined.,A resistor is added at source of NMOS.,PMOS mirror,Supply independent biasing,(4),For eliminating body effect!,A resistor is added at source of PMOS.,Supply independent biasing,(5),If M,5,is not added,I,out,=0 satisfy the current mirror,conditon,in this case,all transistor will be in off state,this problem is called“start-up”problem.,When M,5,is added,this will not happen again.,A diode connected transistor is added to the circuit to solve“start-up”problem.,PTAT References,(1),Negative-Temperature Coefficient(TC)voltage:the base-emitter voltage of bipolar transistor:,The TC of V,BE,itself also depends on the temperature;,When T=300,o,K,V,BE,750 mV,V,BE,/T-1.5 mV/,o,K,;,PTAT References,(2),Positive-TC voltage:the difference between two base-emitter voltages:,V,BE,is proportional to absolute temperature T and its TC is independent of the temperature,;,We call this PTAT reference(for example,PTAT voltage or PTAT current).,PTAT References,(3),Add transistors to adjust coefficient:,Bandgap,References,(1),If V,O1,=V,O2,:,At room temperature:,If we can make,ln,n,=17.2,then:,And:,Zero temperature coefficient reference!,Bandgap,References,(2),Why called,bandgap,?:,Let,V,REF,/T=0,we got,:,Therefore:,As T,0,:,Here comes the term“,bandgap,”,Bandgap,References,(3),How to keep V,O1,=V,O2,in reality?,Why not use Op Amp?,Therefore:,If keep ln,n,(1+R,2,/R,3,)=17.2,then,V,out,exhibits zero temperature coefficient!,I,R3,If V,X,V,Y,then:,Bandgap,References,(4),Sometimes use,pnp,as,banndgap,for compatible with CMOS technology:,Bandgap,References,(5),Sometimes due to asymmetries,there exists input offset for op amp,it will affect the reference output:,Bandgap,References,(6),Use this structure can reduce the effect of offset:,Increase this term to reduce the effect of V,OS,Bandgap,References,(7),More practical one:two emitter follower in series and PMOS current sources.,Collectors connected to ground,compatible with CMOS process,PTAT current,(1),PTAT current can be obtained by following structure:,V,X,V,Y,If V,X,=V,Y,then:,Generating a PTAT current reference,PTAT current,(2),A real implementation of PTAT current reference:,PTAT current,(3),Using PTAT current to create a,bandgap,voltage reference:,Case study,(1),The circuit producing PTAT current reference,with two series base-emitter voltages in each branch so as to reduce the effect of MOSFET mismatch:,Case study,(2),Using low-voltage,cascode,to reduce the power-supply dependence;,“self-biased”is introduced to produce V,b1,and V,b2,by itself:,Case study,(3),A zero TC floating voltage is produced by following structure:,I,R6,I,R5,If V,E,=V,F,then:,Proper choice of the resistor ratios and,n,can provides a zero TC of,V,out,Case study,(4),To improve the supply rejection,a local supply(,局部电源）,is used and a regulation circuit(,稳压电路）,is added:,While V,R1,can be a,bandgap,reference produced by Core circuit:,Case study,(5),The overall circuit including“start-up”circuit:,Questions for Chap.11(1),(1)How do the best references should be?,(2)Tell us at least three kinds of reference in practice.,(3)Calculate,I,out,of the circuit in Figure 11.3 and explain why it is a supply independent biasing?,(4)Why add R,S,in Fig.11.3(a)?,(5)Why add M,5,in Fig.11.5?,Questions for Chap.11(2),(6)What is PTAT reference?,(7)Explain briefly why the circuit in Fig.11.8 can be temperature-independent.,Questions for Chap.11(3),Q11.1;,Q11.2;,Q11.7.,