电子科技大学：《模拟集成电路分析与设计 Analysis and Design of Analog Integrated Circuit》课程教学资源（课件讲稿）Chapter 02 Amplifiers, source followers and cascodes

Analysis and Design of Analog Integrated Circuits UQSTC Chapter2 Amplifiers,source followers and cascodes ---Single-transistor amplifiers ---Source followers ---Cascode 2019/9/3 UESTC Luo Ping

Analysis and Design of Analog Integrated Circuits 2019/9/3 UESTC Luo Ping 1 Chapter2 Amplifiers, source followers and cascodes --- Single-transistor amplifiers --- Source followers --- Cascode

Analysis and Design of Analog Integrated Circuits Operational amplifier 1:B Current mirror Differential pair 8年g年089导8g年年 Operational VOUT amplifier is the most versatile circuit block. Current mirror Single- transistor amplifier First stage:a differential pair loaded by a current source. Second stage:a single-transistor amplifier with a DC current source as load. 2019/9/3 UESTC-Luo Ping

Analysis and Design of Analog Integrated Circuits 2019/9/3 UESTC – Luo Ping 2 Operational amplifier is the most versatile circuit block. First stage: a differential pair loaded by a current source. Second stage: a single-transistor amplifier with a DC current source as load

Analysis and Design of Analog Integrated Circuits UQSTC Types of Single Transistor Amplifiers VCC VCC Rc Rc Rc VIN VOUT VOUT VOUT VOUT 0 0 VIN Q RE RE VIN O Common Emitter Common Base Common Collector Emitter Degeneration ◆VDD AVDD VDD RD> RD RD VIN VOUT VOUT VOUT VOUT p VIN 0 Rs Rs VIN Common Source Common Gate Common Drain Source Degeneration 2019/9/3 UESTC-Luo Ping 3

Analysis and Design of Analog Integrated Circuits 2019/9/3 UESTC – Luo Ping 3 Types of Single Transistor Amplifiers

Analysis and Design of Analog Integrated Circuits 2.1 Single-transistor amplifiers One single transistor can be used as an amplifier,a source follower or a cascode.Moreover,gain boosting can be applied by a cascode,which is little more than a cascode combined with an amplifier. With two transistors two more configurations can be differential pair and the current mirror.Combined,they give rise to a full four-transistor differential voltage and current amplifier. 2019/9/3 UESTC-Luo Ping

Analysis and Design of Analog Integrated Circuits 2019/9/3 4 One single transistor can be used as an amplifier, a source follower or a cascode. Moreover, gain boosting can be applied by a cascode, which is little more than a cascode combined with an amplifier. With two transistors two more configurations can be differential pair and the current mirror. Combined, they give rise to a full four-transistor differential voltage and current amplifier. UESTC – Luo Ping 2.1 Single-transistor amplifiers

Analysis and Design of Analog Integrated Circuits UQSTC An amplifier is normally loaded by a DC current source. In this way the maximum gain can be obtained. Single-transistor amplifier Vout VGS out 9mVGS ros Ay gmTDs= 2 los VEL_2VEL VGs-VT IDs Ves-VT Ay≈100 if VEL÷10 V and VGS-V-=0.2v For large gain Av,we must choose VGs-V as small as possible and L as large as possible. L=(4-5)*Lmin.VGS-Vr=0.15-0.2V. 2019/9/3 UESTC-Luo Ping 5

Analysis and Design of Analog Integrated Circuits 2019/9/3 UESTC – Luo Ping 5 An amplifier is normally loaded by a DC current source. In this way the maximum gain can be obtained. For large gain Av, we must choose VGS-VT as small as possible and L as large as possible. L=(4~5)*Lmin. VGS-VT =0.15~0.2V

Analysis and Design of Analog Integrated Circuits UQSTC MOST or bipolar amplifier Ve=4V/um,L=2.5um,VeL=10. MOST Ay= (Ves-V)/2 Av=100)fVEL≈1 o v and VGs-V≈o.2y Bipolar Ay= VE kT/q 3 vs 2 stages for 106 Ay≈1000)ifVE÷26 V since kT1g=26mv 9m= IcE VE kT/q IcE 2019/9/3 UESTC-Luo Ping 6

Analysis and Design of Analog Integrated Circuits 2019/9/3 UESTC – Luo Ping 6 VE=4V/um, L=2.5um, → VEL=10

Analysis and Design of Analog Integrated Circuits UQSTC Gain,Bandwidth and Gain-bandwidth Avo =gmTps Vout 1 BW= in 2元rDsCL GBW= 9m For all single-stage 2πCL Operational amplifiers The product of the low-frequency gain and the bandwidth is called the Gain- Bandwidth product---GBW. GBW depends on the transistor transconductance and the load capacitance, not on the output resistance. 2019/9/3 UESTC-Luo Ping

Analysis and Design of Analog Integrated Circuits 2019/9/3 UESTC – Luo Ping 7 The product of the low-frequency gain and the bandwidth is called the Gain￾Bandwidth product ---GBW. GBW depends on the transistor transconductance and the load capacitance, not on the output resistance

Analysis and Design of Analog Integrated Circuits UQSTC Bode diagram: Gain Av,BW and GBW Amplitude of the gain IAv It BW -20 dB/decade Avo=9mTDs GBW= 9m GBW 1 2πCL Phase of the gain φ(Av)f Avo 00 φ(Av)=.45o -90° at BW GBW is the product of Avo and the BW.At BW itself,the phase shift is-45. 2019/9/3 UESTC-Luo Ping 8

Analysis and Design of Analog Integrated Circuits 2019/9/3 UESTC – Luo Ping 8 Bode diagram: Amplitude of the gain Phase of the gain GBW is the product of AV0 and the BW. At BW itself, the phase shift is -45 °

Analysis and Design of Analog Integrated Circuits UOSTC Single-transistor amplifier Exercise GBW=100 MHz for CL=3 pF GBW= 9m 2元CL Techno.:K'n≈50AW2 Lmin=0.5μm gm=2mS Ips L?W? GBW.CL2 Ips FOM,Figure of Merit,.质量因素 's-'=0.2V 2Ips 8m=Vas-VI 三W/L=200 1-"2(s=02am1 L≈4×Lmin=2um 21 →W=400um 台W1L=200 2019/9/3 UESTC-Luo Ping 9

Analysis and Design of Analog Integrated Circuits 2019/9/3 UESTC – Luo Ping 9 2 m g mS  0.2 V V V GS T     W L/ 200 min L L m    4 2   W m 400 2 ( ) 0.2 2 n ox D GS T W C I v V mA L       W L/ 200 2 DS m GS T I g V V   FOM Figure of Merit , ,质量因素

Analysis and Design of Analog Integrated Circuits Gain,Bandwidth and Gain-bandwidth No load capacitance, But a large input Avo=9m'Ds capacitance Ces Vout BW= 2n RsCGS Cos GBW= 、11 2n CGS Rs Rs WCox VGs-VT W?L?VGs-VT? BW is simple given by the RC product at the input. For high-frequency performance,it is not sufficient however to make fr large. The channel length does not seem to play a role,both W and Ves-V must be made small! 2019/9/3 UESTC-Luo Ping 10

Analysis and Design of Analog Integrated Circuits 2019/9/3 UESTC – Luo Ping 10 No load capacitance, But a large input capacitance CGS BW is simple given by the RC product at the input. For high-frequency performance, it is not sufficient however to make fT large. The channel length does not seem to play a role, both W and VGS-VT must be made small!