Method and Apparatus for a Floating Current Source

摘要

As taught herein, a floating current source outputs a load biasing current from a source terminal into an external load which may have a variable resistance, and sinks the load biasing current from the load into a sink terminal. Advantageously, the floating current source includes a single-transistor current sink having a bias control that sets the magnitude of the load biasing current desired, and further includes a single-transistor current source that self-biases from the float voltage developed on the external load to an operating point at which the single-transistor current source sources the desired magnitude of load biasing current. One or more AC shunts within the self-biasing network prevent any AC fluctuations present or impressed on the source terminal of the floating current source from changing the operating point of the single-transistor current source, thereby imparting a high effective impedance to the single-transistor current source.

主权项

1. A floating current source configured to source a load biasing current through a load having first and second terminals coupled to source and sink terminals of the floating current source, respectively, said floating current source comprising:
a first transistor having a first terminal operative as a first transistor biasing input, a second terminal coupled to a reference ground, and a third terminal coupled to the second terminal of the load and operative as the sink terminal; a first biasing network coupled to the first transistor biasing input and configured to generate a first transistor biasing signal that sets a magnitude of the load biasing current; a second transistor having a first terminal operative as a second transistor biasing input, a second terminal coupled to a voltage supply for drawing the load biasing current, and a third terminal coupled to the first terminal of the load and operative as the source terminal; and a second biasing network coupling the second transistor biasing input to the source terminal so as to automatically adjust the float voltage so that the magnitude of the load biasing current sourced from the voltage supply matches the magnitude set by the first biasing network; wherein the second biasing network includes an AC shunt that prevents AC fluctuations at the first terminal of the load from affecting the load biasing current.