Negative Capacitance and its Applications in Parasitic Capacitance Cancellation
The negative capacitance can be used to cancel positive parasitic capacitance. CPES has investigated the methods to generate negative capacitance. Generally, the first method to generate negative capacitance is using mutual capacitance concept and the other four methods are using mutual inductance and an extra capacitor to generate negative capacitance. For mutual capacitance case, any two conductors can be treated as one capacitor. And any two capacitors have mutual capacitance. The mutual capacitance can be expressed using the capacitance among the four conductors of two capacitors. As long as the certain condition is met, the mutual capacitance can be canceled. If the winding capacitance of the inductor is considered as mutual capacitance, then the mutual capacitance concept can be utilized to cancel winding capacitance. Negative capacitance can also be generated using coupled inductor windings and a small capacitor. Depending on the coupling polarities and connected points of the capacitor, the generated negative capacitance can be on the input side, output side or top side of the network. When it is on the top side, negative capacitance can be used to cancel winding capacitance. When it is in the input or output side, it can be used to cancel CM parasitic capacitance so as to greatly reduce CM noise.