The present invention relates to improvement in charge pump circuits for producing a voltage output that can double or triple the supply voltage.
Capacitor based voltage doubling and voltage inverting circuits are widely known and used in electronics systems where power consumption is relatively low and a variety of different voltage levels are required for operation. Typically, a single unipolar voltage supply of, for example, five volts can be used to generate a range of different voltages between minus five and plus ten volts. This is the most desirable when these voltage doubling/inverting circuits, known as charge pumping circuits, can be locally sited on specific boards near specific IC""s which rely on them.
Typically, a charge pump circuit first applies a charging voltage across a capacitor and then connects the capacitor between the power supply and the node to be pumped. This procedure is repeated at a high enough rate and with a large enough capacitor to generate a pumped voltage that can supply a desired load current.
In order for the pumped voltage to supply large current without suffering undesired voltage droop, it is necessary to switch at a high rate and to use low resistance switches. This typically causes the nodes connected to the pump capacitor to have high slew rates. The high slew rates radiate RF energy and causes undesired noise spikes in neighboring circuits.
The present invention describes a charge pump or voltage doubler that generates low RF switching noise. The present invention utilizes a current source gate drive technique to generate the control signals in such a way as to limit the slew rate of the capacitor nodes without reducing the on resistance of their FET drivers.