1 DCIS’03, Ciudad Real, November 2003 Measuring Power and Energy of CMOS Circuits: A Comparative Analysis J. Rius, A. Peidro, S. Manich, R. Rodriguez Departament d’Enginyeria Electrònica Universitat Politècnica de Catalunya E. Boemo Escuela Politécnica Superior Universidad Autónoma de Madrid

2 DCIS’03, Ciudad Real, November 2003 Motivation Power and energy consumption are critical issues in circuit design estimation However, measurement is still mandatory: –Validation of design specifications –Testing Ammeter measurements are not always the best solution !!

3 DCIS’03, Ciudad Real, November 2003 Average value i DD (t) I DD = i DD (t) dt lim T T   T 0 P = V DD I DD E = V DD I DD T Conventional ammeter measurements Easy experimental setup Stable reading if T W << T Direct reading Accuracy Small disturbance (R MEAS << 0.1 W) Integration time Drawback: it does not allow determining the power or energy in short (ns,  s) periods of time

4 DCIS’03, Ciudad Real, November 2003 C-based measurement method Cautions: Protection diodes Floating node “Intelligent” switch... T VV

5 DCIS’03, Ciudad Real, November 2003 Experimental set-up Measuring board Standard cell 8x8 bits Guild multiplier Experiments test if it is possible to obtain: the same results as ammeter in loops consumption of a single operation Multiplier board

6 DCIS’03, Ciudad Real, November 2003 Standard cell circuit used in the measurements DATA IN CK CS1 CS2 CS4 CS8 CS15 CK DATA OUT granularity = 15 granularity = 8 granularity = 4 granularity = 2  = 1

7 DCIS’03, Ciudad Real, November 2003 CK Multiplier V DD, VVDD, GND Jumpers V DD, VVDD Resistors Multiplier and measuring boards Logic Analyzer connections Measuring board Multiplier board

8 DCIS’03, Ciudad Real, November 2003 Clock tree consumption vs. granularity  V 15 V1V1 V2V2 V4V4 V8V8 Clock frequency = 200 KHz Granularity

9 DCIS’03, Ciudad Real, November 2003 Drop voltages of four sets of 50 multiplications Clock frequency = 1 MHz, granularity = 15

10 DCIS’03, Ciudad Real, November 2003 Set 1Set 2 Set 7 V1V1 V2V2 V7V7 Seven successive sets of 10 multiplications Clock frequency = 200 KHz, granularity = 15

11 DCIS’03, Ciudad Real, November 2003 Five consecutive multipications Clock frequency = 100 KHz, granularity = 15 V1V1 V2V2 V3V3 V4V4 V5V5 LSB of result

12 DCIS’03, Ciudad Real, November 2003 Consumption of 50 sets of 5 multiplications Clock frequency = 100 KHz, granularity = 15

13 DCIS’03, Ciudad Real, November 2003 Comparison for clock tree power between ammeter and C- based method A: ammeter C: C-based

14 DCIS’03, Ciudad Real, November 2003 Datapath power vs. Clock frequency circles: ammeter, squares: C-based measurements Granularity = 15

15 DCIS’03, Ciudad Real, November 2003 Conclusions Ammeter measurement is the best method if only average i DD is needed C-based measurement is a suitable method to know consumption in short sequences of input patterns or instructions C-based method allows to know the consumption of a single transition C-based measurements give the same results as ammeter measurements with repetitive sequences.