current source & bias circuits
DESCRIPTION
CSE598A/EE597G Spring 2006. Current Source & Bias Circuits. Insoo Kim, Kyusun Choi Mixed Signal CHIP Design Lab. Department of Computer Science & Engineering The Pennsylvania State University. Introduction. Required Features of Current Source High Rout Wide Operation Range - PowerPoint PPT PresentationTRANSCRIPT
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Current Source & Bias Circuits Current Source & Bias Circuits
Insoo Kim, Kyusun ChoiMixed Signal CHIP Design Lab.Department of Computer Science & EngineeringThe Pennsylvania State University
CSE598A/EE597G Spring 2006
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04/22/23 Insoo Kim
IntroductionIntroduction Required Features of Current Source
High Rout Wide Operation Range Constant Current Source Low PVT (Process, Voltage, Temperature) Sensitivity
Required Features of Bias Circuit Low Rout Low PVT Sensitivity
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Current SourceCurrent Source
• Basic Current Source• Wilson Current Mirror• Cascode Current Mirror
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04/22/23 Insoo Kim
Ideal vs. Actual Current SourceIdeal vs. Actual Current Source
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Simple NMOS Current SourceSimple NMOS Current Source
What’s the bad feature of this?
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Cascode Current SourceCascode Current Source
What’s the bad feature of this?
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Basic Current MirrorBasic Current Mirror
What’s the bad feature of this?
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Wilson Current MirrorWilson Current Mirror
What’s the drawback of this circuit?
2
1
2
1
)/()/(LWLWI
ggII refm
mrefout
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Cascode Current MirrorCascode Current Mirror
But, it still has limited output swing problem.
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Wide Swing Cascode Current MirrorWide Swing Cascode Current Mirror
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Bias CircuitsBias Circuits
• Self Bias Circuits• PTAT Bias Circuits• Band gap Reference
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Power Supply Dependency of Current SourcePower Supply Dependency of Current Source
Consideration Factors - VDD
- Channel Length Modulation
- Transistor Mismatch
How do we generate Iref independent of the supply voltage?
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Self Biasing CircuitSelf Biasing Circuit
What’s the advantage of these circuits?
What’s the problem of these circuits?
What’s role of Rs?
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Improved Self Biasing CircuitImproved Self Biasing Circuit
Improved Circuit eliminating Body Effect
Improved Circuit with Start-up Circuit
* This Circuit is practical only if
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A Simple Temperature Compensation ConceptA Simple Temperature Compensation Concept
M1(Vgs)
M1(Ids)
0℃90℃
ZTC (Zero Temperature Coefficient)
Negative TC Positive TC
Self Bias Circuit
VDD VDD
v vr0
M1
R11. R1 is a conductor which has positive TC 2. M1 has negative TC below ZTC point (Semiconductor)3. If we control Vr0 below ZTC point, Vr0 become less sensitive to temperature due to opposite TC of M1 and R1
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Case Study (I) – Self Bias Circuit in DRAMCase Study (I) – Self Bias Circuit in DRAM
ⓐ ⓑ
starter
For Temp. Compensation pmos diode
ⓑ
ⓐ
vref
Vext
What’s the drawback of these circuits?
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Case Study (II) – Self Bias Circuit in DRAMCase Study (II) – Self Bias Circuit in DRAM
ⓐ
Voltage Buffer
starter For Temp. Compensation
ⓐvr1
Why does this circuit need the voltage buffer?
Why are PMOS current mirrors stacked in the reference bias circuit?
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VBE Referenced CMOS Self-bias CircuitVBE Referenced CMOS Self-bias Circuit
How do we fabricate BJT in CMOS Process Technology? * Temperature Sensitivity ~ - 4000 ppm/C
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Realization of pnp BJT in CMOS TechnologyRealization of pnp BJT in CMOS Technology
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Vth Referenced CMOS Self-Bias CircuitVth Referenced CMOS Self-Bias Circuit
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Thermal Voltage Referenced CMOS Self-Bias CircuitThermal Voltage Referenced CMOS Self-Bias Circuit
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Thermal Voltage Referenced CMOS Self-Bias CircuitThermal Voltage Referenced CMOS Self-Bias Circuit
* Temp. Sensitivity ~ +3300 ppm/C
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CMOS Band gap ReferenceCMOS Band gap Reference
What’s the problem?
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(cont’d) CMOS Band gap Reference(cont’d) CMOS Band gap Reference
Actual Implementation of CMOS Band Gap Reference
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Actual Implementation of CMOS Band gap ReferenceActual Implementation of CMOS Band gap Reference
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Design Lab. – Self Bias Circuit with Temp. CompensationDesign Lab. – Self Bias Circuit with Temp. Compensation
(a) Basic Schematic (b) actual implementation
Schematics
* AMIS 0.5um Tech
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Design Lab. – Self Bias Circuit with Temp. CompensationDesign Lab. – Self Bias Circuit with Temp. Compensation
Simulation Results
VDDVr0b
Vr0 (a)
Vr0 (b)
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04/22/23 Insoo Kim
Design Lab. – Self Bias Circuit with Temp. CompensationDesign Lab. – Self Bias Circuit with Temp. Compensation
Simulation Results – Temp. Compensation
Vr0 Current
(b)
(a)
(b)
(a)
90C25C
-10C -10C
25C90C
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Design Lab. – Self Bias Circuit with Temp. CompensationDesign Lab. – Self Bias Circuit with Temp. Compensation
Zero Temperature Coefficient Point
0.82V
90C
25C
-10C
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ReferencesReferences Joongho Choi, “CMOS analog IC Design,” IDEC Lecture
Note, Mar. 1999. B. Razavi, “Design of Analog CMOS Integrated Circuits,”
McGraw-Hill, 2001. Hongjun Park, “CMOS Analog Integrated Circuits
Design,” Sigma Press, 1999.