May 1, 2013Introduction toAnalog Ultra Low Power (AULP)designTuvia LiranNano Retina Ltd.May 2013
May 1, 2013Definition of Ultra Low PowerA design methodology that enablesimplementing VLSI products with powerconsumption ...
May 1, 2013Outline• Applications of ULP• Low voltage operation• Power sources• MOS operation at sub-threshold range• Chall...
May 1, 2013Applications of low-voltage AULP• Medical devices (implantable; wearable)• Remote controllers• Wireless sensors...
May 1, 2013Why low voltage?• For digital circuits:– Reduced dynamic power (P=C*V2*f)– Reduced electric fields in scaled de...
May 1, 2013Power sources• Batteries (size, duration)• Energy harvesting• Remote power transferBio-RetinaImplantRetinaIRlas...
May 1, 2013MOS operation ranges• Operating in sub-threshold (weakinversion)• Voltages are scaled to nUT (32 mV for n =1.2 ...
May 1, 2013Challenges in low voltage AULP• Limited dynamic range• Large process variance and mis-match• Non-linear (logari...
May 1, 2013AULP design techniques• System level:– Avoiding DC-DC up-converter– Optimized partitioning to digital/analog/DT...
May 1, 2013Device modeling for weak inversion• BSIM (Berkley):– Parameters have physical meaning– Most widely used– Poor a...
May 1, 2013Low voltage current mirrors - examples
May 1, 2013Bulk driven amplifiers• Enables amplifyinglow/negative signals• Lower gain and GBW• Requires isolated well• Hig...
May 1, 2013Example of sub-threshold low voltagecircuit – ULP amplifierPresented by E. VittozAmplifier withcontrolled offse...
May 1, 2013Static high value resistors• Often require >GΩ resistors• Alternative implementations:– Polysilicon inverse dir...
May 1, 2013Discrete Time Analog (DTA) circuits• Switched capacitor filters• Chopped amplifiers• ULP ADC• ULP DAC
May 1, 2013Switched capacitor filters• Enables very low BW when frequency is low• Disturbed by charge injection (αCm/Cs)• ...
May 1, 2013Chopped Amplifier• Cancels offset almost completely• Relevant for differential amplifiers only• Ø1 – direct | Ø...
May 1, 2013ADC - Figure of MeritPower=FoM*Fs*2ENOB [There are other definitions]World record: 4.4fJM. van Elzakker, E. van...
May 1, 2013ULP DAC architecture• R-2R architecture is an alternative architecture• Ratioed MOS transistors operating at we...
May 1, 2013Summary• ULP is enabler to many applications• ULP design is challenging but doable• Operation at low supply vol...
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TRACK E: Introduction to Analog Ultra Low Power (AULP) design/ Tuvia Liran

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TRACK E: Introduction to Analog Ultra Low Power (AULP) design/ Tuvia Liran

  1. 1. May 1, 2013Introduction toAnalog Ultra Low Power (AULP)designTuvia LiranNano Retina Ltd.May 2013
  2. 2. May 1, 2013Definition of Ultra Low PowerA design methodology that enablesimplementing VLSI products with powerconsumption in the sub microwatt range• Comment: Some applications provide very low powerconsumption by activation during short period of time, but itis not ULP• How it is achieved:– Very low voltage - <1 OOM– Sub-threshold operation – 2-5 OOM– Micro-architecture
  3. 3. May 1, 2013Outline• Applications of ULP• Low voltage operation• Power sources• MOS operation at sub-threshold range• Challenges of ULP design:– Architecture– Device modeling• Analog circuits operating at ULP• Discrete Time Analog (DTA) circuits• ULP data converters• Summary
  4. 4. May 1, 2013Applications of low-voltage AULP• Medical devices (implantable; wearable)• Remote controllers• Wireless sensors• Watches
  5. 5. May 1, 2013Why low voltage?• For digital circuits:– Reduced dynamic power (P=C*V2*f)– Reduced electric fields in scaled devices• For analog circuits:– Typically requires higher power for same BW– Low BW applications can operate with low voltage– Integration of low power digital + RFMedical devices often require very low frequency
  6. 6. May 1, 2013Power sources• Batteries (size, duration)• Energy harvesting• Remote power transferBio-RetinaImplantRetinaIRlaserbeam12534Optical power transfer(Nano Retina)Electromagnetic power transfer(Second Sight)Examples of implementations of artificial retina
  7. 7. May 1, 2013MOS operation ranges• Operating in sub-threshold (weakinversion)• Voltages are scaled to nUT (32 mV for n =1.2 )• ∆Id/∆Vgs = 70 80mV/decade• Weak inversion expression:TTGsDsatnUVVII 0expC37atmV7.26 TqkTUTPower consumption in the nW range force the operation in sub-threshold
  8. 8. May 1, 2013Challenges in low voltage AULP• Limited dynamic range• Large process variance and mis-match• Non-linear (logarithmic) Id/Vgs• Modeling of devices• Noises (flicker; coupling; substrate)• Limited bandwidth• Charge injection in SC circuits
  9. 9. May 1, 2013AULP design techniques• System level:– Avoiding DC-DC up-converter– Optimized partitioning to digital/analog/DTA• Circuit level:– Operation at moderate/weak inversion– Optimal Vt (low Vt devices; Vsb<0)– Use bulk driven MOS transistors– Avoiding stacking of transistorsDTA = Discrete Time Analog
  10. 10. May 1, 2013Device modeling for weak inversion• BSIM (Berkley):– Parameters have physical meaning– Most widely used– Poor accuracy in moderate inversion(non-monotonic)• EKV (EPFL):– Charge based models– Only 18 parameters. Simpler to generate– Works well in strong & weak inversion• PSP (ASU & Philips):– Approved as “next industry standard” by“compact modeling council”– Based upon looking at surface potential
  11. 11. May 1, 2013Low voltage current mirrors - examples
  12. 12. May 1, 2013Bulk driven amplifiers• Enables amplifyinglow/negative signals• Lower gain and GBW• Requires isolated well• Higher noise
  13. 13. May 1, 2013Example of sub-threshold low voltagecircuit – ULP amplifierPresented by E. VittozAmplifier withcontrolled offsetAmplifier withextendeddynamic range
  14. 14. May 1, 2013Static high value resistors• Often require >GΩ resistors• Alternative implementations:– Polysilicon inverse direction diodes– PMOS inverse direction sub-threshold– Switched resistor• Both options have poor accuracy & matching• Switched resistor is disturbed by charge injection
  15. 15. May 1, 2013Discrete Time Analog (DTA) circuits• Switched capacitor filters• Chopped amplifiers• ULP ADC• ULP DAC
  16. 16. May 1, 2013Switched capacitor filters• Enables very low BW when frequency is low• Disturbed by charge injection (αCm/Cs)• Differential or CMOS implementations reduces thecharge injection significantlyNMOS CMOSDifferential
  17. 17. May 1, 2013Chopped Amplifier• Cancels offset almost completely• Relevant for differential amplifiers only• Ø1 – direct | Ø2 – inverted inputs and outputs• Vos is modulated at phase frequency and filtered byLPF
  18. 18. May 1, 2013ADC - Figure of MeritPower=FoM*Fs*2ENOB [There are other definitions]World record: 4.4fJM. van Elzakker, E. van Tuijl, P. Geraedts, D. Schinkel, E. Klumperink, and B. Nauta, “A 1.9μW 4.4fJ/Conversion-step 10b 1MS/scharge-redistribution ADC,” Proc. of IEEE Solid-State Circ. Conf. (ISSCC), San Francisco, California, pp. 244–245, Feb., 2008.µW10> Power=-10; ENOB=Msps1Fs=fJ;10: FOM=1ExamplenW10> Power=-10; ENOB=Ksps1Fs=fJ;10: FOM=2Example
  19. 19. May 1, 2013ULP DAC architecture• R-2R architecture is an alternative architecture• Ratioed MOS transistors operating at weak inversionact as linear resistive devices• Device matching degrades INL/DNL
  20. 20. May 1, 2013Summary• ULP is enabler to many applications• ULP design is challenging but doable• Operation at low supply voltage is doable• ULP is processed with standard CMOS process flows

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