Predistortion equalizing circuit

DETAILED DESCRIPTION Another object of this invention is to provide a new and improved predistortion equalizer that utilizes the similarity of a semiconductor diode V-I characteristic and the optical power/current characteristic of a light emitting diode.
Still another object of this invention is to provide a new and improved predistortion equalizer which utilizes the similarity of a semiconductor diode V-I characteristic and the optical power/current characteristic of a light emitting diode wherein both curves have more radical curvature at low current and less curvature (more linearity) at high current.
Yet another object of this invention is to provide a new and improved predistortion equalizer that can be easily operated and economically coupled to linearize a light emitting diode through the adjustment of two controls at a low cost and relatively simple circuitry.
In accordance with one aspect of the invention, a predistortion equalizing circuit for cancellation of second order distortion that is caused by a serially connected light emitting diode includes a pair of complementary transistors.
Each transistor has a collector, a base, and an emitter.
Means are provided for coupling an input signal to the bases of the two transistors.
First impedance means couple the collector of the NPN transistor to a source of positive potential.
Second impedance means couple the collector of the PNP transistor to a source of negative potential.
Third impedance means couple the emitter of the NPN transistor to a source of negative potential, and fourth impedance means couple the emitter of the PNP transistor to a source of positive potential.
Means are provided for coupling the collectors to the light emitting diode.
Emitter resistance means for the equalizing circuit include a serially connected first variable resistance and semiconductor diode coupled as a dynamic emitter load resistance across the emitters and a point of reference potential.
A second variable resistance couples one electrode of the semiconductor diode to a voltage source of such polarity as to cause current to flow through such semiconductor diode