A −0.5V-input voltage booster circuit for on-chip solar cells in 0.18µm CMOS technology

In this paper, we design and fabricate a voltage booster circuit, aiming at the realization of a monolithic system LSI that utilize on-chip solar cell to eliminate the need for external voltage supply. Since the voltage that can be obtained from an on-chip solar cell is about -0.5V, we need an efficient voltage booster to obtain voltage around +4.0V if we need to program a non-volatile memory on the same chip. First, it is confirmed by circuit simulation that a 10-stage cross-coupled charge pump circuit using 0.18μm process technology can generate +4.0V from -0.5V input. A ring oscillator using current starved inverters with 2R-1T bias circuit is developed, whose frequency is successfully compensated within ±10% for supply voltage ranging between 0.45V and 0.60V. From measurement of the test chip of proposed circuits using Rohm 0.18μm CMOS process technology, it is confirmed that the voltage booster TEG with 2-stage cross-coupled charge pump circuit generates voltage beyond +0.8V from -0.5V input voltage with about 40% efficiency even at a bright environment of 6.1klux illumination. In addition, it is demonstrated that by implementing an on-chip solar cell, the voltage booster, and a standard-cell-based digital circuit in a single chip, an external piezoelectric diaphragm makes a sound only by the power from on-chip solar cell.

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