Design Of A Negative Voltage Output LDO Based On Bipolar Process

With the decrease of circuit working voltage, the circuit is becoming more and more sensitive to noise. The line regulator is widely used in noise-sensitive device because it can serve as a low noise and low ripple power supply.A low-dropout-voltage negative output line regulator based on bipolar process is presented in this thesis. The device is capable of supplying-200 mA of output current with the output voltage of-5V. By using a structure of merged reference voltage source and error amplifier, the whole circuit is simplied. The quiescent current is relatively low under no load condition. The device offers a BYP pin, with the addition of an external capacitor, the output noise can be reduced and the transiscent response can be enhanced.The device incorporates several protection features such as current limit protection,thermal protection and safe operating protection. First the thesis introduces the operational principle and major performance parameters of the LDO, then lists the possible noise in the circuit and some methods to decrease the output noise. On this basis, the circuit design of this thesis is presented and each module of the circuit is analysed. After that, the thesis discusses the system stability and presents the frequency compensation circuit.Based on the bipolar process of research institute of CETC and the CADENCE simulation software, the design is validated. The major simulation includes the temperature performance of the voltage reference and output voltage, the noise of the output, the transistent response and the protection functions. According to the simulation result, the quiescent current can be as low as 40 μA under no load condition;with the addition of a 0.01 μF capacitor, the output noise can reach 25μV_RMS and the output voltage overshoot is also decreased.