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Philips Research University of Twente, Faculty of Electrical Engineering A 1-V 15 mW High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl A 1-V 15mW High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl Contents • • • • • • Introduction Circuit fundamentals Design strategy Implementation Specifications Conclusions A 1-V 15mW High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl Introduction Why need integrated CMOS temperature indicator? – enable thermal protection (shutdown,clock frequency lowering etc.) – use in integrated measurement or control devices A 1-V 15mW High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl Introduction Why design switch and not a linear temperature dependent output? – Thermal protection only requires threshold temperature detection (125 °C) – Multiple threshold values together form a digital temperature indicator A 1-V 15mW High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl Design goals • • • • • • Standard 0.18 mm CMOS process Low voltage, Low power, Small area High accuracy Portable Switch temperature of 125 °C Extendable: adjustable switch temperature multiple switch temperatures high accuracy over large T range A 1-V 15mW High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl Circuit Fundamentals Use bandgap principle: V Vgap,0 = IPTAT k*R T V Vptat A T R V Vbe (1) (n) T A 1-V 15mW High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl Circuit Fundamentals Detect crossing of Vptat with Vbe V = Vbe = IPTAT T Binary out A R1 V R2 (1) (n) Vptat T A 1-V 15mW High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl Design strategy Identify accuracy limitations: – Bipolar transistor Vbe spread – Resistor matching & spread – Offset and noise of MOST devices Establish quantitative relation for optimal MOST area distribution A 1-V 15mW High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl Design strategy Io Io = Io = Vo2 Vo1 Binary out A R1 R2 (1) 2V comp (n) R V2o 2 V2o1 2 1 R1 2 2 R R 2 2 2 1 R2 I o 2 ln( n) A 1-V 15mW High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl Design strategy Assume: 2 VGS Av WL , 2 ID AI WL Find equivalent offset (or flicker noise): 2 tot X3 X1 X2 Area1 Area2 Area3 Minimal total given fixed Areatotal when: X3 X1 X2 2 2 2 Area1 Area2 Area3 A 1-V 15mW High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl Implementation Implementation goals: – High amplifier gain; speed may be low. – High supply and substrate noise rejection. Implementation limitations: – Low supply voltage cascoding difficult. – Folded cascodes not desirable A 1-V 15mW High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl Implementation = = IPTAT Binary out A R1 R2 (1) (n) A 1-V 15mW High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl Implementation Vdd Iout Vin- A Vin+ Iout Positive feedback; high gain, small bandwidth A 1-V 15mW High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl Implementation Strong points: – Robust circuit, easy to port – Small flicker noise & offset straightforward use of large transistors instead of using complex dynamic offset cancellation techniques. – No cascoding or shielding low supply voltage – All matched transistors have matched conditions at threshold temperature A 1-V 15mW High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl Implementation Weak point: – Nested inner loop stability analysis not straightforward A 1-V 15mW High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl Chip photograph Diode Resistors connected BJTs Transconductance amplifier Comparator 190 mm A 1-V 15mW High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl 150 mm Specifications This work Other work Supply voltage 1.0-1.8 V 2.2-5.5 V Supply current 16mA 25mA DC Technology CMOS 0.18 mm CMOS 2 mm Area 0.03 mm2 1.5 mm2 Inaccuracy (3) 1.1C 1C Calibration No Yes DC supply sensitivity 0.05C/V 0.1C/V Switch temperature 128.5C - Hysteresis 1.2C - A 1-V 15mW High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl Conclusions • Efficient & Robust Design strategy • Very low power circuit – can decrease further with duty-cycle mode • Good performance without calibration – 3 intra-batch deviation of only 1.1 C • Design is well-suited for multiple thresholds extension A 1-V 15mW High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl A 1-V 15mW High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl Philips Research University of Twente, Faculty of Electrical Engineering A 1-V 15 mW High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl A 1-V 15mW High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl Philips Research University of Twente, Faculty of Electrical Engineering A 1-V 15 mW High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl A 1-V 15mW High-Precision Temperature Switch D. Schinkel, R.P. de Boer, A.J. Annema and A.J.M. van Tuijl