Current generator circuit and method of providing drive current to a laser diode driver

A method of providing drive current in a laser diode circuit, the method comprising the steps of:

• providing an input current to an input stage of a current mirror, the input current provided to a collector electrode of a first transistor;
• coupling together base electrodes of the first transistor and a second transistor of an output stage of the current mirror, the coupling occurring through a resistive element R1 arranged to cause generation of a voltage drop across the resistive element;
• and
• modulating an output current from the output stage of the current mirror, the output current boosted by the voltage drop across the resistive element to provide the drive current;
• wherein the method further comprises the step of coupling a first emitter resistor R2 and a second emitter resistor R3 to emitter electrodes of the first and second transistors, respectively, the emitter resistors R2 and R3 have resistances relationship of the form:
• R 3 = 1 N ⁢ R 2
• and one of:
• R1=(N+1)R2
• and R 1 R 2 = ( N + 1 ) ⁢ ( 1 + NV T R 2 ⁢ I out )
• where:
• N is an overall gain of the current mirror;
• and
• VT=kT/q, where k is Boltzmann's constant, q is charge and T is the absolute temperature.

A current mirror circuit connectable, in use, to a laser driver circuit, the current mirror circuit comprising a current mirror, said current mirror comprising:

• first and second mirror transistors each having a base electrode and an emitter electrode;
• a resistive element R1 coupled between said base electrodes;
• and
• a first emitter resistor R2 and a second emitter resistor R3 coupled, respectively, to the emitter electrodes of the first and second mirror transistors;
• wherein
• the resistive element is coupled between said base electrodes such that, in use, base leakage current to the first transistor from a current supply causes a voltage drop across the resistive element, wherein the voltage drop acts to boost a voltage through the emitter resistor of the second mirror transistor, thereby to boost, in use, output current provided by the second mirror transistor to the laser driver circuit;
• and
• the emitter resistors R2 and R3 have resistances relationship of the form:
• R 3 = 1 N ⁢ R 2
• and one of:
• R1=(N+1)R2
• and R 1 R 2 = ( N + 1 ) ⁢ ( 1 + NV T R 2 ⁢ I out )
• where:
• N is an overall gain of the current mirror;
• and
• VT=kT/q, where k is Boltzmarm's constant, q is charge and T is the absolute temperature.