Current mirror source circuitry

Claim 1

A current source circuit comprising: (a) a pair of current sources; (b) a current mirror circuit comprising a plurality of transistors having a common base electrode, such plurality of transistors including a master transistor and at least one slave transistor, emitter electrodes thereof being electrically connected to a voltage source; (c) differential amplifier means comprising a pair of transistors having emitter electrodes connected to a first one of the pair of current sources, a first one of the pair of transistors having a base electrode coupled to a collector electrode of the master transistor and to a second one of the pair of current sources and a collector electrode coupled to the voltage source, and a second one of the pair of transistors having a collector electrode connected to the common base electrode, for producing a current flow through the collector electrode of at least one slave transistor substantially proportional to the current flow through the collector electrode of the master transistor; (d) wherein the differential amplifier means includes a diode connected transistor coupled between the collector electrode of the second one of the pair of transistors of the differential amplifier means and the voltage source and wherein the first one of the pair of current sources produces a mirror current MI where I is the current produced by the first one of the pair of current sources and M is at least equal to (n(1+hfe min )+X+1)/hfe min where n is the ratio of the emitter current density of the diode connected transistor to the current density of the master transistor, X is the ratio of the total collector current of the slave transistor to the collector current of the master transistor and hfe min is the minimum current gain of the plurality of transistors of the current mirror circuit.