Development of Low-Power High-Accuracy Ultrafast-Transient-Response Low-Dropout Regulators for Battery-Powered Applications

As battery-powered devices such as mobile electronics and implantable biomedical devices become increasingly important, the embedded power-management units nowadays are required to be highly accurate, fast responding and also energy conserving. Low-dropout regulators (LDOs) are excellent candidates and have been widely used due to their characteristics in high accuracy, low noise, fast transient and structurally simple when compared to other types of dc-dc converters. However, when sudden voltage variations can be reduced by using a larger output capacitor, at the same time the response time of the LDO will deteriorate. In this thesis, techniques are presented and analyzed to improve LDO transient responses while the usage of a large output capacitor is retained.;A low-power LDO with multiple small-gain stages implemented in 90-nm technology is first introduced. The proposed channel-resistance-insensitive small-gain stages provide loop gain enhancements without introducing low-frequency poles before the unity-gain frequency (UGF). As a result, both the loop-gain and loop-bandwidth of the LDO are improved, so that the accuracy and response speed of voltage regulation are significantly enhanced. As no on-chip compensation capacitor is required, the active chip area of the LDO is only 72.5 microm x 37.8 microm. Experimental results show that the LDO is capable of providing an output of 0.9 V with maximum output current of 50 mA from a 1-V supply. The LDO has a quiescent current of 9.3 microA, and has significantly improvement in line and load transient responses as well as performance in power-supply rejection ratio (PSRR).;The second proposed design is a wide-loop-bandwidth LDO in 0.18-microm technology. A dominant-pole substitution (DPS) technique is introduced, analyzed and applied to a LDO to generate a low-frequency zero using current feed-forward and current multiplication to cancel the dominant pole, while a higher-frequency pole substitutes in and becomes the new dominant pole. The loop-bandwidth of proposed LDO therefore can be greatly extended while a large output capacitor can still be used. The resultant DPS-LDO benefits from both fast response time from the wide loop-bandwidth and large charge reservoir from the output capacitor, thus has significant enhancement in transient performances. The proposed DPS-LDO is fabricated and is shown to be capable of delivering 100 mA at 1.0-V output from a 1.2-V supply, with current efficiency of 99.86%. Experimental results show that dynamic performances, including transient responses and PSRR are significantly enhanced.