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Master of Electrical and Computers Engineering DC/DC Converter with Transparent Electronics for application on Photovoltaic Panels Supervisor: Vitor Grade Tavares Second Supervisor: Pedro Miguel Cândido Barquinha Second Supervisor: Pydi Ganga Bahubalindruni Romano Torres 19th July 2013 1 Outline • • • • • • • • • Motivation Objectives a-IGZO TFTs DC/DC Converter Amplifier Regulator Fabrication Conclusions Future Work 2 Motivation • To construct circuits on flexible substracts, such as plastic, glass: – Possible to embody in photovoltaic panels. • Low cost fabrication at room temperature. 3 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 a-IGZO TFTs Problems: • High parasitic resistance; • P-type transistors with low performance; • Threshold voltage shift. Staggered bottom-gate TFT structure 5 Voltage Boosting Stage – DC/DC converter • Indutors are avoided due to their low performance in transparent technology; • Capacitor is used to save charge in electric field; • Vdd < Vout < 2*Vdd 6 Voltage Boosting Stage - out of phase clock signals Lower variation of Vout level. 7 2 Voltage Boosting Stages in Cascade • To increase the voltage level twice; • Parasitic effects reduce the efficiency; • 4 TFTs of 320 μm in parallel for each diodeconnection are used; • Vdd < Vout << 3*Vdd 8 Separation between Boosting Stages • Allow a stable voltage level at node E; • Avoid clock feedthrough in TFT1 and TFT2. 9 3 Boosting Stages in Cascade • Proposed DC/DC converter includes 3 Voltage Boosting Stages; • Settling time is increased. 10 Bootstrapping Stage – Proposed DC/DC converter • Bootstrapping stage is used to reduce the settling time of the circuit; • Power consumption is negligble; • Small capacitors and transistors can be used. 11 Comparison with previous DC/DC converters in the same technology DC/DC converter from other authors Proposed DC/DC converter 12 DC/DC Converter - Simulation Output voltage Bootstrapping Cross-connected With Load Without Load I_load = 162 μA Vout=16.37 V Vout=35.5 V 13 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 3 Voltage Boosting Stages - Simulation Voltage levels for each stage 15 DC/DC converter - Layout 3068.55 μm 5793.55 μm 16 10 DC/DC converters in parallel - The equivalent resistance of 10 converters in parallel is lower than with only one converter. Output voltage 17 Final circuit with regulation 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. 18 Proposed Amplifier – Block diagram 19 Amplifier 20 Differential Stage 21 Positive Feedback Stage 22 Source-Follower Stages 23 Common-Source Stages 24 Phase Compensation -In order to have higher phase margin. 25 Gain and Phase Response Gain: 36.7dB Phase Margin: 83.79° 26 Proposed Amplifier - Layout 2383.8 μm 2450 μm 27 Regulator Voltage levels Vout = 17.65 V The voltage variation with the load decreased 80%. 28 Final Circuit - Layout 14557.1 μm 18709.55 μm 29 Fabrication DC/DC converter with bootstrapping and 2 boosting stages 30 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 Future Work • Improve the design of the amplifier to increase the gain; • PWM regulation with duty-cycle variation. 32 The End Thank you! 33