Patent ID: 7075348

Claim:
A differential charge pump, comprising: a first current source, used to provide a first current according to an adjusting signal; a second current source, used to provide a second current; a first switching device, wherein a first terminal of the first switching device is coupled with the first current source, and a conducting state of the first switching device is based on presence of a pump-up signal for conducting; a second switching device, wherein a terminal of the second switching device is coupled with another terminal of the first switching device at a first node, and another terminal of the second switching device is coupled with the second current source, in which a conducting state of the second switching device is based on presence of a pump-down signal for conducting; a first phase inverting switching device, wherein one terminal of the first phase inverting switching device is coupled with the first current source and a conducting state of the first phase inverting switching device is inverse to the first switching device; a second phase inverting switching device, wherein one terminal of the second phase inverting switching device is coupled with the first phase inverting switching device at a second node, and another terminal of the second phase inverting switching device is coupled with the second current source, in which a conducting state of the second phase inverting switching device is inverse to the second switching device; a common mode feedback device, used to receive a reference voltage, a voltage of the first node, and a voltage of the second node, and to export the adjusting signal accordingly; a first capacitor, one terminal of the first capacitor being coupled to the first node, and the other terminal of the first capacitor being coupled to a ground voltage; and a second capacitor, one terminal of the second capacitor being coupled to the second node, and the other terminal of the second capacitor being coupled to the ground voltage, wherein output of the differential charge pump is taken between the first node and the second node, wherein a common mode voltage is an average of the voltage of the first node and the voltage of the second node, and wherein when the pump-up signal and the pump-down signal are present at the same time, the first switching device and the second switching device are both conducting and the adjusting signal is exported by the common mode feedback device, and when the pump-up signal and the pump-down signal are absent at the same time, the first phase inverting switching device and the second phase inverting switching device are conducting and the adjusting signal is also exported by the common mode feedback device, such that no matter what combination of pump-up signal and pump-down signal occurs, adjustment of the first current source is always performed, the first and second current sources are not floating, and the occurrence of a shift in the common mode voltage is prevented.