Analysis and Design of CMOS Analog Building Blocks Márcio Cherem Schneider Universidade Federal de Santa Catarina NAMITEC Colloquium Campinas - 2010 Analysis and design of CMOS analog building blocks EMICRO II - Bahia Analysis and Design of CMOS Analog Building Blocks EMICRO II - Bahia EMICRO II - Bahia 1
Analysis and design of CMOS analog building blocks Contents The intrinsic gain stage The source-coupled pair The two-transistor current mirror A self-biased current source NAMITEC Colloquium Campinas - 2010 Analysis and design of CMOS analog building blocks EMICRO II - Bahia Analysis and Design of CMOS Analog Building Blocks EMICRO II - Bahia 2
Analysis and design of CMOS analog building blocks Summary of main design equations Technology parameters Forward and reverse currents Size- and bias-related transistor parameters UICM 0.35 um CMOS technology Saturation voltage Saturation NAMITEC Colloquium Campinas - 2010 Analysis and design of CMOS analog building blocks EMICRO II - Bahia Analysis and Design of CMOS Analog Building Blocks EMICRO II - Bahia
THE INTRINSIC GAIN STAGE - 1 VDD VI M1 + IB CL ID IL M2 Vmax Vmin maximum output swing VDSsat1 VDSsat2 VDD vo vi VTH vo=vi Av M1,M2 in saturation vi VDD Class A amplifier: SR->SR+. ~3 if |AV0|dB From UICM we find the dc voltage VTH at the input: Low-frequency gain versus inversion level NAMITEC Colloquium Campinas - 2010 Analysis and design of CMOS analog building blocks EMICRO II - Bahia Analysis and Design of CMOS Analog Building Blocks EMICRO II - Bahia
Voltage gain vs frequency THE INTRINSIC GAIN STAGE - 2 VDD VI M + IB CL ID IL V-I converter (transconductor) followed by an I-V converter (output impedance) |AV|dB u b -20 dB/dec |AV0| CL go gmvg vi + vg vo VO Voltage gain vs frequency is the transconductance is the output impedance NAMITEC Colloquium Campinas - 2010 Analysis and design of CMOS analog building blocks EMICRO II - Bahia Analysis and Design of CMOS Analog Building Blocks EMICRO II - Bahia
Analysis and design of CMOS analog building blocks THE INTRINSIC GAIN STAGE - 3 VDD VI M1 + IB CL ID IL CL go gmvg vi + vg vo VO ECF Sizing and biasing: W, L, IB Power-area tradeoff How long can L be? CIN and transit time are both proportional to L2 (for constant W/L)! NAMITEC Colloquium Campinas - 2010 Analysis and design of CMOS analog building blocks EMICRO II - Bahia Analysis and Design of CMOS Analog Building Blocks EMICRO II - Bahia
Noise current generator Input-referred noise model THE INTRINSIC GAIN STAGE - 4 VO VDD VI M1 + IB CL ID IL MOST noise model Thermal 1/f Bias-dependent factor Corner frequency 1/2 (WI) 2/3 (SI) Noise current generator Input-referred noise model Noiseless MOST - + 0.35 um CMOS technology NAMITEC Colloquium Campinas - 2010 Analysis and design of CMOS analog building blocks EMICRO II - Bahia Analysis and Design of CMOS Analog Building Blocks EMICRO II - Bahia
Analysis and design of CMOS analog building blocks THE SOURCE-COUPLED PAIR -1 VSS IT + vG1 - M1 M2 I1 I2 vG2 First order analysis: Ideal current source M1 & M2 in saturation I1 & I2 independent of drain voltage; Normalization 8 4 12 -4 -8 -12 1 it=1000 100 10 <1 I1/IT I2/IT NAMITEC Colloquium Campinas - 2010 Analysis and design of CMOS analog building blocks EMICRO II - Bahia Analysis and Design of CMOS Analog Building Blocks EMICRO II - Bahia
Analysis and design of CMOS analog building blocks THE SOURCE-COUPLED PAIR - 2 VSS IT + vG1 - M1 M2 I1 I2 vG2 Offset voltage VOS = VG =VG2- VG1 such that ID= I2- I1=0 Simple model ir =0 (sat) The differential input voltage at the input required for ID =0 is NAMITEC Colloquium Campinas - 2010 Analysis and design of CMOS analog building blocks EMICRO II - Bahia Analysis and Design of CMOS Analog Building Blocks EMICRO II - Bahia
Analysis and design of CMOS analog building blocks THE SOURCE-COUPLED PAIR - 3 VSS IT + vG1 - M1 M2 I1 I2 vG2 Uncorrelated VT & IS Pelgrom’s model (I) (II) Notes: 0.35 um CMOS technology (I) is dominant over (II) for NAMITEC Colloquium Campinas - 2010 Analysis and design of CMOS analog building blocks 10 EMICRO II - Bahia Analysis and Design of CMOS Analog Building Blocks EMICRO II - Bahia
THE TWO-TRANSISTOR CURRENT MIRROR - 1 VDD ii + vG - io vo M1 M2 1:1 iD vD locus vD=vG vG vo iD1 iD2 M1: iv converter M2: vi converter Basic principle VG1=VG2; VS1=VS2; vout>VDsat ioii Error due to difference in VD’s Error due to mismatch NAMITEC Colloquium Campinas - 2010 Analysis and design of CMOS analog building blocks EMICRO II - Bahia Analysis and Design of CMOS Analog Building Blocks EMICRO II - Bahia
Analysis and design of CMOS analog building blocks THE TWO-TRANSISTOR CURRENT MIRROR - 2 ii io M1 M2 VDD ac analysis ii + v - io C1 C2 1:A Noise analysis Uncorrelated noise sources iin io M1 M2 i1 i2 1:A The effect of M1 on noise is A times greater than that of M2 NAMITEC Colloquium Campinas - 2010 Analysis and design of CMOS analog building blocks EMICRO II - Bahia Analysis and Design of CMOS Analog Building Blocks EMICRO II - Bahia
Analysis and design of CMOS analog building blocks CURRENT MIRROR: GAIN SCHEMES Gain-of-two current mirrors VDD II IO 1:2 W/L Gain=A Gain=1/(NM) VDD ii io==Aii ...... ii io==ii/(NM) ...... . N M VDD II IO 1/2:1 W/L VDD ii io==ii/A ...... Gain= 1/A NAMITEC Colloquium Campinas - 2010 Analysis and design of CMOS analog building blocks EMICRO II - Bahia Analysis and Design of CMOS Analog Building Blocks EMICRO II - Bahia
A SELF-BIASED CURRENT SOURCE – 1 SELF-CASCODE MOSFET (SCM) Sat. Triode Applying UICM to both M1 & M2 The self-biased current source we have designed is based on the self-cascode MOSFET shown in the slide and the self-biased circuit shown in the previous slide. In our design, we have chosen N=1 through a unity-gain current mirror. VX is a PTAT voltage generated by means of a second self-cascode MOSFET biased in weak inversion. VX is copied to the source of M2 through a voltage following current mirror. The family of curves represents the variation of VX in terms of the inversion level of M2 for several values of . This factor accounts for the relative sizes of M1 and M2 and the current mirror gain. From the curves one can see that, for a given pair (, VX), the inversion level is poorly defined if M2 operates in weak inversion .In other words, the sensitivity of the inversion level to VX is extremely high in weak inversion. In our particular design example, we have chosen the nominal values of VX and to be around 60 mV and 3.4 resulting in if2=3 and if1=10.2. The resulting gate-to-source voltage across M1 is around the threshold voltage plus 70 mV. NAMITEC Colloquium Campinas - 2010 Analysis and design of CMOS analog building blocks Analysis and Design of CMOS Analog Building Blocks EMICRO II - Bahia EMICRO II - Bahia 14
V-I CHARACTERISTICS OF THE SCM A SELF-BIASED CURRENT SOURCE – 2 V-I CHARACTERISTICS OF THE SCM Sat. Triode I2=NIx In WI: NAMITEC Colloquium Campinas - 2010 Analysis and design of CMOS analog building blocks EMICRO II - Bahia Analysis and Design of CMOS Analog Building Blocks EMICRO II - Bahia
VOLTAGE FOLLOWING (NMOS) CURRENT MIRROR (PMOS)1 A SELF-BIASED CURRENT SOURCE – 3 VOLTAGE FOLLOWING (NMOS) CURRENT MIRROR (PMOS)1 When both M8 & M9 operate in WI: 1 B. Gilbert, AICSP vol. 38, pp. 83-101, Feb. 2004 NAMITEC Colloquium Campinas - 2010 Analysis and design of CMOS analog building blocks EMICRO II - Bahia Analysis and Design of CMOS Analog Building Blocks EMICRO II - Bahia
A self-biased current source Vx VFCM A self-biased current source NAMITEC Colloquium Campinas - 2010 Analysis and design of CMOS analog building blocks EMICRO II - Bahia Analysis and Design of CMOS Analog Building Blocks EMICRO II - Bahia
Analysis and design of CMOS analog building blocks Output current: Iref=10 nA ISHn-channel100 nA, ISHp-channel40 nA A SBCS – 5: DESIGN =1 Let us choose M1 &M2 in MI: if2 = 10 S2= S1, N = 1 =10 nA VFCM M3 &M4 in WI: if3(4) <<1 Let us choose if3=0.187 NAMITEC Colloquium Campinas - 2010 Analysis and design of CMOS analog building blocks EMICRO II - Bahia Analysis and Design of CMOS Analog Building Blocks EMICRO II - Bahia
Analysis and design of CMOS analog building blocks A SBCS – 6: DESIGN Summary VFCM =1 =10 nA S if ir M1 0.01 10 M2 30 M3 1.13 0.187 M4 M8, M8(a) 1 0. 1 M9, M9(a) MP (all) 2.5 0.1 NAMITEC Colloquium Campinas - 2010 Analysis and design of CMOS analog building blocks EMICRO II - Bahia Analysis and Design of CMOS Analog Building Blocks EMICRO II - Bahia
A SBCS – 7 : IOUT vs. VDD AT CONSTANT T NAMITEC Colloquium Campinas - 2010 Analysis and design of CMOS analog building blocks EMICRO II - Bahia Analysis and Design of CMOS Analog Building Blocks EMICRO II - Bahia
Analysis and design of CMOS analog building blocks NAMITEC Colloquium Campinas - 2010 Analysis and design of CMOS analog building blocks EMICRO II - Bahia Analysis and Design of CMOS Analog Building Blocks EMICRO II - Bahia