1. DC/DC Converter with Transparent Electronics for application on Photovoltaic Panels Romano Torres 19th July 2013 1 Supervisor: Vitor Grade Tavares Second Supervisor: Pedro Miguel Cândido Barquinha Second Supervisor: Pydi Ganga Bahubalindruni Master of Electrical and Computers Engineering

2. Outline Motivation Objectives a-IGZO TFTs DC/DC Converter Amplifier Regulator Fabrication Conclusions Future Work 2

3. Motivation To construct circuits on flexible substracts, such as plastic, glass: – Possible to embody in photovoltaic panels. Low cost fabrication at room temperature. 3

4. Objectives Design of a boost DC/DC converter using transparent electronics in order to have an increased and stable voltage level with direct current. – Vout > 1.5*Vin; – Efficiency >= 40% Fabrication of the circuit in CENIMAT/UNL. 4

5. a-IGZO TFTs High parasitic resistance; P-type transistors with low performance; Threshold voltage shift. 5 Staggered bottom-gate TFT structure Problems:

6. Voltage Boosting Stage – DC/DC converter 6 Indutors are avoided due to their low performance in transparent technology; Capacitor is used to save charge in electric field; Vdd < Vout < 2*Vdd

7. Voltage Boosting Stage - out of phase clock signals 7 Lower variation of Vout level.

8. 2 Voltage Boosting Stages in Cascade 8 To increase the voltage level twice; Parasitic effects reduce the efficiency; 4 TFTs of 320 μm in parallel for each diode- connection are used; Vdd < Vout << 3*Vdd

9. Separation between Boosting Stages 9 Allow a stable voltage level at node E; Avoid clock feedthrough in TFT1 and TFT2.

10. 3 Boosting Stages in Cascade 10 Proposed DC/DC converter includes 3 Voltage Boosting Stages; Settling time is increased.

11. Bootstrapping Stage – Proposed DC/DC converter 11 Bootstrapping stage is used to reduce the settling time of the circuit; Power consumption is negligble; Small capacitors and transistors can be used.

12. Comparison with previous DC/DC converters in the same technology 12 DC/DC converter from other authorsProposed DC/DC converter

13. DC/DC Converter - Simulation 13 Output voltage With Load I_load = 162 μA Vout=16.37 V Without Load Vout=35.5 V Bootstrapping Cross-connected

14. Efficiency The supplied current of each voltage source is measured (I_in=167 μA); The currents multiplied by the supplied voltage (Vin=10V) are added, resulting in the input power; With the same current for each voltage source, efficiency is: The current supplied in bootstrapping stage is very low (I_bs=0.12μA); The efficiency is: 39.93% 14

15. 3 Voltage Boosting Stages - Simulation 15 Voltage levels for each stage

16. DC/DC converter - Layout 16 5793.55 μm 3068.55 μm

17. 10 DC/DC converters in parallel - The equivalent resistance of 10 converters in parallel is lower than with only one converter. 17 Output voltage

18. Final circuit with regulation 18 Circuit specifications: Vdd = 10 V R1 and R2 >> RL Objectives: Vout ≃ 20 V 50% lower ΔV Advantage: More stable voltage level even with load variation.

19. Proposed Amplifier – Block diagram 19

20. Amplifier 20

21. Differential Stage 21

22. Positive Feedback Stage 22

23. Source-Follower Stages 23

24. Common-Source Stages 24

25. Phase Compensation -In order to have higher phase margin. 25

26. Gain and Phase Response 26 Gain: 36.7dB Phase Margin: 83.79 °

27. Proposed Amplifier - Layout 27 2383.8 μm 2450 μm

28. Regulator 28 Voltage levels Vout = 17.65 V The voltage variation with the load decreased 80%.

29. Final Circuit - Layout 29 18709.55 μm 14557.1 μm

30. Fabrication 30 DC/DC converter with bootstrapping and 2 boosting stages

31. Conclusions DC/DC converter: – Wide transistors reduce parasitic resistance; – Bootstrapping stage decreases settling time; – 10 converters in parallel reduce the parasitic resistance and allow more voltage boosting stages, increasing the output voltage level. Amplifier: – Good phase margin was achieved; – Voltage gain is enough for the regulation; Regulator: – 80% lower fluctuation of the voltage level with load variations. 31

32. Improve the design of the amplifier to increase the gain; PWM regulation with duty-cycle variation. Future Work 32

33. The End Thank you! 33