1. Field
This disclosure relates generally to semiconductors, and more specifically, to charge pump circuits.
2. Related Art
Lower power consumption continues to have importance in data electronic systems, due, for example, to widespread use of electronics that are powered by batteries or low voltage sources. Power conservation is not only particularly important for portable electronic devices, but is also important for applications such as automotive and medical electronics which are also powered from a battery.
Charge pump circuits are typically used to increase voltage levels in applications where the power supply voltage is not high enough for a particular need. There are many varying forms of charge pump circuits. Generally, known charge pump circuits consume a significant amount of power, particularly during the start-up portion of operation. Charge pump circuits transfer charge to a capacitor and then boost the stored voltage by coupling an input voltage to the capacitor to increase the stored voltage by an amount equal to the input voltage. This leads to large transients seen by the power supplies which are not optimal to a low power system. Some known charge pump circuits try to change the ramp rate of the boosted output voltage to avoid problems in the load circuits such as high current surges which may damage circuitry. However, such circuits do not change the power consumption. In some applications, a pull-down transistor is used to control a voltage ramp rate. In such applications, the pull-down transistor increases the amount of energy that is required for the charge pump. Other known charge pumps control a voltage ramp-up rate by changing the charge pump clock frequency. However, by changing the clock frequency, the performance of the circuit can be degraded and the output impedance of the charge pump increased. Such circuits generally have large power consumption.
Another problem associated with some charge pumps occurs when the boosted voltage increases at a high ramp rate and stresses the output capability of a high output impedance power supply. These circuit conditions impose a very high demand on a system power supply source as the high impedance and sudden increase in voltage results in the system power supply sourcing a very large amount of current. As a result, a brown-out condition may result within the system so that the power supply is not able to adequately power other system circuitry.