w3,4: operational amplifier design
DESCRIPTION
Fall 2005 EE/CSE 596 Individual Study. W3,4: Operational Amplifier Design. Insoo Kim, Jaehyun Lim, Kyungtae Kang Mixed Signal CHIP Design Lab. Department of Computer Science & Engineering The Pennsylvania State University. 2 Stage OP Amp Design. 2 Stage OP Amp. Frequency Compensation. - PowerPoint PPT PresentationTRANSCRIPT
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W3,4: Operational Amplifier W3,4: Operational Amplifier
Design Design
Insoo Kim, Jaehyun Lim, Kyungtae KangMixed Signal CHIP Design Lab.Department of Computer Science & EngineeringThe Pennsylvania State University
Fall 2005 EE/CSE 596 Individual Study
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2 Stage OP Amp Design2 Stage OP Amp Design
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Insoo KimSep. 28th, 2005
2 Stage OP Amp2 Stage OP Amp
Frequency Compensation
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Insoo KimSep. 28th, 2005
[Reminder] Common Mode[Reminder] Common Mode
Common Mode Gain
Common Mode Rejection Ratio
Common Mode Input Voltage RangeVSS+VTN1+VDSAT5+VDSAT1 < VIC < VDD–|VDSAT3|–|VTP3|+| VTN1|
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Insoo KimSep. 28th, 2005
2 Stage OP Amp Design 2 Stage OP Amp Design
Design Process Model Parameter Extraction (1/6)
kn : 55.84 uA/V2 - kp : 23.51 uA/V2 n : 0.025 - p : 0.055 Vthn : 0.776 V - Vthp : 0.858 V
Assign Current from Power Consumption Spec. (2/6) Power Consumption : 2 mW Total Current : 0.4 mA @ 5V VDD Input Pair : 0.2 mA Second Stage : 0.2 mA
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Insoo KimSep. 28th, 2005
2 Stage OP Amp Design2 Stage OP Amp Design Design Process
Determine minimum channel length (3/6) Determine channel width (4/6)
Determine W1,2 from voltage gain spec.
Determine W5 & Bias Voltage from power consumption & CM min.
Determine W3,4 from CM max.
Determine Bias Level of Current Source Tr. (5/6)
Considering CM min value and the transistor size Check other specifications (6/6)
Repeat step 4 to 6
ICDSAT1DSAT5TN1SS V VVVV
|V ||V|–|V|–V V TN1TP3DSAT3DDIC
)||(2
)||(
42
422,1
ooD
oomv
rrIL
W
rrgA
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Insoo KimSep. 28th, 2005
A Calculation ExampleA Calculation Example
Calculated Gain= 3000 (70dB)
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Insoo KimSep. 28th, 2005
Simulation ResultsSimulation Results
Gain: 59dB
BW: 1.15 GHz
This OP Amp is unstable!
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Insoo KimSep. 28th, 2005
[Reminder] Feedback & Stability[Reminder] Feedback & Stability
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Insoo KimSep. 28th, 2005
Before Frequency CompensationBefore Frequency Compensation
A unit gain buffer characteristic without frequency compensation
+
-
VinVout
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Insoo KimSep. 28th, 2005
Frequency AnalysisFrequency Analysis
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Insoo KimSep. 28th, 2005
(cont’d) Frequency Analysis(cont’d) Frequency Analysis
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Insoo KimSep. 28th, 2005
Positive Zero & Pole-Zero CancellationPositive Zero & Pole-Zero Cancellation
Feed Forward
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Insoo KimSep. 28th, 2005
Positive Zero & Pole-Zero CancellationPositive Zero & Pole-Zero Cancellation
Pole-Zero Cancellation
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Insoo KimSep. 28th, 2005
An Example of Frequency CompensationAn Example of Frequency Compensation
Poles moved!
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Insoo KimSep. 28th, 2005
After Frequency CompensationAfter Frequency Compensation
A unit gain buffer characteristic with frequency compensation
+
-
VinVout
Frequency compensated OP Amp
Frequency Compensation must be considered in designing OP Amps
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Folded Cascode Op AmpFolded Cascode Op Amp
Basic Folded Cascode
Design of Single Ended Folded Cascode
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Insoo KimSep. 28th, 2005
Cascode StageCascode Stage Small Signal Analysis
Rout
)||(
)||(
1
1
Doutmv
inmDoutout
RRgA
VgRRV
]1)([
]1)[(
2212
22221
mbmoo
oombmoout
ggrr
rrggrR
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Insoo KimSep. 28th, 2005
Folded Cascode StageFolded Cascode Stage
Schematic
Advantages Wider Operating Range than telescopic cascode stage Easy to set Common Mode Voltage
Disadvantages Limited Output swing Large Voltage Headroom Large Power Consumption
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Insoo KimSep. 28th, 2005
Single Ended Folded Cascode Op AmpSingle Ended Folded Cascode Op Amp
Circuit Configuration
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Insoo KimSep. 28th, 2005
(cont’d) Single Ended Folded Cascode Op Amp(cont’d) Single Ended Folded Cascode Op Amp Gm
2idv
2idv
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Insoo KimSep. 28th, 2005
(cont’d) Single Ended Folded Cascode Op Amp(cont’d) Single Ended Folded Cascode Op Amp Rout
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Insoo KimSep. 28th, 2005
(cont’d) Single Ended Folded Cascode Op Amp(cont’d) Single Ended Folded Cascode Op Amp
Design Process (1/3) Model Parameter Extraction
kn : 55.84 uA/V2 - kp : 23.51 uA/V2 n : 0.025 - p : 0.055 Vthn : 0.776 V - Vthp : 0.858 V
Assign Current from Power Consumption Spec. Total Current : 0.375 mA Input pair : 0.125 mA Current mirror : 0.25 mA
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Insoo KimSep. 28th, 2005
(cont’d) Single Ended Folded Cascode Op Amp(cont’d) Single Ended Folded Cascode Op Amp
Design Process (2/3) Determine W3 from CM_min, CM_max Spec.
CM_min
CM_max
Determine W4~W7 and Bias2 from Vout_max Spec. Vout_max : Determine VB2 Assign Vdsat of M4,5 and M6,7 from Vout_max Spec
Eg) Vout_max=4V Vdsat of M4,5= 0.6V, Vdsat of M6,7 = 0.4V Calculate W4~7 to satisfy Vdsat & Ids of M4~7
Determine W8~W11 from Vout_min Spec. Assign Vdsat of M8~M11 from Vout_min Spec.
Eg) Vout_min=0.8V Vdsat of M8~11 = 0.4V Calculate W8~11 to satisfy Vdsat and Ids of M8~11
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Insoo KimSep. 28th, 2005
(cont’d) Single Ended Folded Cascode Op Amp(cont’d) Single Ended Folded Cascode Op Amp
Design Process (3/3) Determine W1,2 from Gain Spec.
Calculate Rout_tot
Calculate Required Gm value to satisfy Gain Spec. Gain = Gm*Rout
Calculate W1,2 from Gm Check other Spec. and Repeat the design process to optimize
transistors size Slew Rate CM_min Check required CMRR, PSRR Check and Modify Bias Voltage to optimize transistor size.
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Insoo KimSep. 28th, 2005
(cont’d) Single Ended Folded Cascode Op Amp(cont’d) Single Ended Folded Cascode Op Amp
Frequency Analysis
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Insoo KimSep. 28th, 2005
39.75
39.75
39.75
39.75
89.7
53.1
89.7
53.1
68.168.1
3.54V
1.0V
80.25
3.14V
(cont’d) Single Ended Folded Cascode Op Amp(cont’d) Single Ended Folded Cascode Op Amp
Design Example
Calculated Gain= 3000 (70dB)
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Insoo KimSep. 28th, 2005
(cont’d) Single Ended Folded Cascode Op Amp(cont’d) Single Ended Folded Cascode Op Amp
Simulation Result
Gain: 68dB
BW: 170MHz
Loading: 2pF
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Insoo KimSep. 28th, 2005
Folded Cascode Op Amp with CMFBFolded Cascode Op Amp with CMFB
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Insoo KimSep. 28th, 2005
Slew Rate Enhanced Folded Cascode Op AmpSlew Rate Enhanced Folded Cascode Op Amp
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Insoo KimSep. 28th, 2005
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.