Circuit for providing a constant current

Abstract

Two substantially identical currents (I , I ) are subtracted from each other, while being generated by elements ( ) in such a way that noise in the current value of said two currents (I , I ) is determined by shot noise. The differential current, determined only by shot noise, is supplied to a capacitor ( ). A second current (I ) is used to charge a second capacitor ( ). It is periodically determined whether the value of a voltage across the first capacitor ( ) is within or outside a range bounded by the (negative and positive values of the) voltage of the second capacitor ( ) which has been charged over the same period of time. The currents (I , I ) are set in dependence on the result of the comparison. The signal to set the currents (I , I ) also serves as control signal for an element ( ) connected as a constant current source. The setting signal and thus the constant current (I ) delivered by the element ( ) connected as a current source is to a high degree independent of the temperature sensitivity of different components of the circuit and is determined essentially solely by the ratio of values of similar components ( ) of the circuit. By choosing components whose ratio appears in a value of the constant current (I ) delivered by the circuit and which have the same temperature dependence, it is achieved that the temperature dependence disappears completely or substantially completely from the constant current (I ) delivered by the circuit.