In the past few years, industry has been paying more attention on the size, efficiency and reliability of the power converters in portable electronic equipment. Highly-efficient low-voltage low-power switch-mode DC-DC converters are mandatory in these devices to regulate the supply voltage for maximizing the run-time of the systems. According to the semiconductor roadmap from Semiconductor Industry Association, the supply voltages of digital circuits have to be reduced to 0.9-l.2V by the year 2005. Moreover, the current-mode control is well-known to have faster response than the voltage-mode control, but requires more advanced circuit structures and is difficult to implement in low supply voltages. The design of low-voltage current-mode switch-mode DC-DC converters, therefore, become...[ Read more ]

In the past few years, industry has been paying more attention on the size, efficiency and reliability of the power converters in portable electronic equipment. Highly-efficient low-voltage low-power switch-mode DC-DC converters are mandatory in these devices to regulate the supply voltage for maximizing the run-time of the systems. According to the semiconductor roadmap from Semiconductor Industry Association, the supply voltages of digital circuits have to be reduced to 0.9-l.2V by the year 2005. Moreover, the current-mode control is well-known to have faster response than the voltage-mode control, but requires more advanced circuit structures and is difficult to implement in low supply voltages. The design of low-voltage current-mode switch-mode DC-DC converters, therefore, becomes a very challenging and important research.

This thesis is aimed to develop novel circuit structures for monolithic highly-efficient low-voltage current-mode DC-DC converters targeted for battery-operated handheld devices. Five novel circuitries have been proposed and implemented, including two low-voltage current-sensing circuits for PMOS and NMOS switches, a low-voltage voltage-controlled oscillator, a voltage-to-current generator, as well as a startup circuitry for boost converter. In addition, the detailed studies of the current-mode switch-mode DC-DC converter and the low-voltage circuit designs of the required building blocks are included in this thesis.

The proposed current-mode buck and boost converters have been implemented in AMS 0.6-μm CMOS technology with V_thn≈│V_thp│≈0.85V at room temperature. The proposed buck converter is able to operate at 1.2-V supply with more than 89.6% conversion efficiency and a maximum output current of 125mA, while the proposed boost converter is able to operate at 1-V supply with more than 85% conversion efficiency and a maximum output current of 150mA. The accuracy of the proposed current-sensing circuitry is higher than 93%.