Active filter for electromagnetic interference (EMI) reduction using a single connection point and a negative impedance converter with cross-coupled transistors

A single-connection-point active filter comprising:

• a bi-directional connection point to a noisy line having a noisy current;
• a connection capacitor connected from the bi-directional connection point to a first node;
• a trans-impedance circuit having the first node as an input, the trans-impedance circuit generating a first current in response to the first node;
• a transfer impedance connected to the first output node, the transfer impedance converting the first current generated by the trans-impedance circuit to an output voltage of the first output node;
• wherein a voltage of the first node causes the transfer impedance to inject a compensation voltage back through the connection capacitor and into the noisy line at the bi-directional connection point;
• wherein the compensation voltage compensates the noisy line for changes in the noisy current.

An active noise filter comprising:

• a connection capacitor coupled between a connection point on a current-carrying line and a first node, wherein changes in current carried by the current-carrying line generates a sense current through the connection capacitor to the first node;
• a gain control unit, connected to the first node to receive the sense current from the connection capacitor, for generating a transfer current in response to the sense current;
• a transfer impedance that receives the transfer current generated by the gain control unit, the transfer impedance converting the transfer current into a transfer voltage;
• wherein the transfer voltage on the transfer impedance induces an injected voltage across the connection capacitor to compensate the current-carrying line,
• whereby Electro-Magnetic Interference (EMI) generated by the current-carrying line is reduced by the active noise filter.