Design Of A Low Dropout Regulator For Micro-Machined Accelerometer

Based on full comprehension of the current situation and development trend oflow dropout regulator, this paper analyzes the operating principle and performanceparameters of LDO, then core modules of LDO and the whole circuit are designedand simulated.Firstly, this paper designs and simulates the core modules of LDO, which areerror amplifier, reference voltage source, power device and auxiliary circuit. Theerror amplifier adopts two stage structure, the first stage is a folded cascadedifferential amplifier and the second stage uses a current feedback amplifier toimprove the transient response. Error amplifier largely decides noise characteristicsof the system, so chopper-stabilizing technique is employed in this design and itsignificantly reduces the system noise. Reference voltage source plays a definitiverole in deciding the temperature coefficient of the system. Traditional referencevoltage source has a large temperature coefficient, therefore this paper uses forth-order curvature compensation technique to lower temperature coefficient. PMOSwith low dropout voltage and minor quiescent current is chosen as power device. Inaddition this paper designs relative auxiliary circuit for better system operation. Itincludes overheat protection circuit which employs temperature sampling transistorwith hysteresis temperature of10℃, over-current protection circuit which samplescurrent by current mirror, FTO can increase turning on speed through fast chargingthe output capacitance. Simulation of every independent module is done after thedesign and the results indicate that every module achieves expected object.Additionally, this paper does designs for frequency compensation. The systemadopts pole zero tracking method and the method enhances the stability of the system.Finally, performance simulation of the whole LDO is done in0.5μm CMOS process.Noise factor is22.375nV/Hz1/2, linear adjustment rate is1.611mV/V, load regulationis0.90mV/mA, PSRR is58dB@10kHz, so the transient performance is well,stability of the system is good, the system satisfies indexes of micro accelerometer.