RESEARCH

  • Power management integrated circuits (power management ICs or PMICs or PMU as unit) are integrated circuits for power management. Although PMIC refers to a wide range of chips (or modules in system-on-a-chip devices), most include several DC/DC converters or their control part. A PMIC is often included in battery-operated devices such as mobile phones and portable media players to decrease the amount of space required. Power management ICs are solid state devices that control the flow and direction of electrical power. Many electrical devices have multiple internal voltages (e.g., 5 V, 3.3 V, 1.8 V, etc.) and sources of external power (e.g., wall outlet, battery, etc.), meaning that the power design of the device has multiple requirements for operation. A PMIC can refer to any chip that is an individual power related function, but generally refer to ICs that incorporate more than one function such as different power conversions and power controls such as voltage supervision and undervoltage protection. By incorporating these functions into one IC, a number of improvements to the overall design can be made such as better conversion efficiency, smaller solution size, and better heat dissipation. A PMIC may include battery management, voltage regulation, and charging functions. It may include a DC to DC converter to allow dynamic voltage scaling. Some models are known to feature up to 95% power conversion efficiency. Some models integrate with dynamic frequency scaling in a combination known as DVFS (dynamic voltage and frequency scaling). Some models feature a low-dropout regulator (LDO), and a real-time clock (RTC) co-operating with a backup battery.

  •  Research Example 1

I. A Design of The DC-DC boost Converter using DTMOS switch with ESD Protection Devices

Leakage current control method in DTMOS

DTMOS and CMOS threshold voltage comparison

Overall block diagram of DC-DC boost converter

  • Recently, the importance for power management IC(PMIC) is emphasized as battery-powered portable electronics such as smart phone are commonly used. In addition, research and development on high efficiency is essential to maximize the use of portable device that are preferred various functions than in the past. PMIC for high efficiency usually change drastically from Linear regulator to Switching regulator. But the switching regulator have disadvantage of low efficiency compared with linear regulator at light load conditions. Therefore, this paper is presented the using of switching regulator at heavy load conditions. All power supply device of Mobile appliance must be made stable and various DC output voltage of high effectiveness from a unstable DC input power supply. For that reason, it is used do a power supply of Switched Mode Power Supply(SMPS) method instead of a power supply of conventional linear method. Therefore, in this paper, DC-DC converter for power supplies are designed using DT-CMOS which is low on-resistance than CMOS.

II. PWM (Pulse Width Modulation) Design

DT-CMOS switch reduces the output ripple and the conduction loss.

Boost Converter simulation at output voltage 12V

Boost converter using DTMOS and CMOS switch Efficiency change with load current

  • The DC-DC converter converts the voltage to drive electronic products such as MP3s, PDAs, and laptops using a power supply voltage such as a battery or a rectified DC voltage. In other words, it plays a role in providing a specific voltage required for driving the device.The output voltage of the DC-DC converter changes due to a change in circuit characteristics or malfunction of the feedback system that occurs when the DC-DC converter is manufactured. When the voltage is higher than the maximum allowable voltage of the device and circuit, the corresponding electronic component or semiconductor device is destroyed.

III. Results and Discussion

Simulation result of PFM mode

 Simulation result of switch's input

Simulation result of DC-DC converter’s output

  • The PFM Mode DC-DC converter that has low on-resistance switching elements are designed by using the DT-CMOS. High effectiveness for miniaturization and many long hours use is becoming a key issue in the DC-DC converter that is applied to portable terminal. Therefore, the proposed DC-DC converter heightened efficiency using the DT-CMOS instead of conventional CMOS and shortened size of a inductor that dominate the biggest area in the DC-DC converter using a switching frequency of 1.2MHz. The performance of the DC-DC converter is a 3.3V input voltage, a 1.4V output voltage, maximum output current 100mA, a 1.2MHz switching frequency, maximum efficiency of 95%(inductor, capacitor ESR of 100mΩ ).

  •  Research Example 2

I. A Design of Low-dropout Regulator with Adaptive Threshold Voltage Technique

Body Effect in PMOSFET

Body bias Technique

The Characteristics of body bias variation Ibs - Vbs Characteristics

  • A Low-area Low Drop-out (LDO) regulator using the body biasing technique is presented. The body biasing technique can decrease the threshold voltage and increase the drain current. The technique is applied to the error amplifier, voltage buffer and pass transistor in the proposed LDO regulator to reduce chip size and provide the proposed LDO regulator with the same performance as the conventional LDO regulator. A pass transistor using the technique can reduce its size by 5.5% at 100mA load condition. The proposed current mirror in the error amplifier and voltage buffer has about 61% smaller area at coterminous performance. The proposed LDO regulator showed about 26% smaller area, not including the bias blocks, while it showed coterminous performance and characteristics

II. The Propoesed LDO Regulator

The Characteristics of body bias variation VDS - VBS Characteristics

The Characteristic of temperature variation

Schematic of the proposed LDO rugulator

  • The most critical aspect of an LDO regulator design is the choice of the pass transistor. It affects virtually every critical performance metric of a regulator including dropout, stability and regulation. Furthermore, with the pass transistor consuming upwards of 50% of the die space, the commercial practicality of an LDO regulator depends largely on the pass transistor's current drive per die area. In order to drive a large load and achieve low drop out, the pass transistor should have a large aspect ratio. However, a large pass transistor has a large gate capacitance and causes system instability and slow transient responses.

III. Results and Discussion

Frequency responses under full-load and no-load

The Proposed current mirror Output impedance

The Proposed current mirror Schematic

  • LDO regulator using the body biasing technique was proposed. The technique was applied to the error amplifier, voltage buffer and pass transistor to reduce chip size and maintain the same performance as conventional LDO regulator. The pass transistor occupied 5.5% smaller area than the conventional pass transistor, which was not applied with the body biasing technique, at same dropout voltage. The current mirrors in the LDO control blocks such as the error amplifier and voltage buffer occupied approximately 61% smaller areas than conventional current mirrors, showing coterminous performance  and characteristics.

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