The Design Of A Low Input Voltage And Low Noise Voltage Regulator

With the development of semiconductor technology, the power supplied into a system is diminished, which will deteriorate the performance of analog circuits, or even fail it. In mix signal circuits, digital circuits operate at a lower voltage and analog circuits at a higher one, so as to meet the requirement of power dissipation and performance. Besides, a stable voltage is required by analog circuits because of its sensitiveness to noise. And in different applications, the voltages needed are varied, which can't provide directly by the mainstream batteries. Therefore it is necessary to convert voltage into a lower-ripple one.First, from the view of noise and efficiency, various boost circuits are analyzed, concluded that the combination structure of charge pump and low dropout regulator is the best method to obtain a low ripple and high quantity voltage. Next, the proposed combination structures are analyzed in detail, whose advantages and disadvantages are compared. Finally, employing the equivalent electricity quantity approach, the steady state output voltage expression of charge pump is derived. The equivalent control circuit of charge pump is developed, from which it is derived that the method of regulating output voltage employing pulse frequency modulation, pulse width modulation and conduct resistance control is actually the regulating method of adopting resistances in serial and needs to consume energy. As it has an excellent dynamic transient response, the low dropout regulator can regulate the change of output caused by a break of the input or the load in a short time, resulted in a high efficiency and a low ripple output voltage if it follows charge pump.To meet the requirements best, the regulator designed can output different voltages according to the different control signals. The decoder determines the optimum conversion ratio to improve the efficiency of system from the relation between the input and output voltage. It is the basis of computing the size of switch transistors to derive the model of the power dissipation and efficiency of charge pump. At the same time, how to eliminate the noise is also considered at the process of circuits design. A serial of digital and analog circuits are designed, which are combined to simulate the performance of the system. The results show that the system designed meets the design objective basically.