Fast Transient Output-Capacitorless Low-Dropout Voltage Regulator

• Main Authors: Chun-HsunWu, 吳俊勳
• Other Authors: Le-Ren Chang-Chien
• Format: Others
• Language: en_US
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/69608068930430767157

博士 === 國立成功大學 === 電機工程學系碩博士班 === 100 === With the versatile developing trend of the portable electronic devices, the role of on-chip power converters is becoming more and more important for the integrated circuits (ICs). This dissertation first introduces three types of commonly used on-chip power converters. Following that, the topic focuses on the low-dropout voltage regulator (LDO) due to its generality and significance in the IC power supply. LDO’s basic working principle, small signal model, as well as load transient response are comprehensively illustrated. Major issues of the recent researches including the low supply voltage, low quiescent current, fast load transient response and output-capacitorless structure are discussed. Specifically, influence of the quiescent current of the OPA on LDO’s load transient and reference tracking is then reviewed in detail. To achieve fast transient but keep quiescent current as low as possible for improving the power efficiency, this dissertation proposes two dynamic bias approaches to enhance the transient response of the LDO. The first proposed circuit is called transient quiescent current booster (TQCB). Embedding a TQCB within the OPA of a LDO, theoretical analysis and test results have shown its effectiveness in the fast transient performance. However, this design does not reach the optimal power efficiency because the TQCB circuit always consumes a branch current either the LDO is working in standby or active mode. To design a faster transient response and more power-efficient LDO, a full quiescent current enhancement (FQCE) circuit which possesses the automatic shut-off function is proposed afterward. Testing results show that the voltage spike is reduced about 62% compared with the LDO without the proposed circuit in response to 50mA/300ns load change. Under such a load change, the voltage recovery time of the LDO is less than 0.5μs and the stability is guaranteed. In addition to the load transient response, the other important feature that the FQCE circuit can do is to facilitate the reference tracking speed. Reference tracking is generally required in the bio-implantable medical devices to achieve dynamic voltage and frequency scaling (DVFS) for saving more power. The key factor for optimizing the reference tracking is determined by the quiescent current Iq as well. Therefore, the FQCE circuit is also suitable to the reference tracking issue. With the FQCE circuit, a fast transient output-capaciotrless LDO working at low supply voltage with high power efficiency could be easily implemented in various IC power applications.