Electric lamp and discharge devices: systems – Current and/or voltage regulation
Reexamination Certificate
1998-03-13
2001-06-05
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
C315S309000, C315S149000, C315S158000, C362S800000
Reexamination Certificate
active
06242870
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relate to a light emitting device driving circuit.
In recent years, along with the advances made in optical communications and the advances made in an optical disc device etc., use of light emitting devices has rapidly spread. Looking at the optical communications, for example, an optical repeater is one of the important devices for realizing optical communications. In this optical repeater, a semiconductor laser or other light emitting device is used. This plays the role of converting an input electrical signal to an optical signal.
The light emitting device driving circuit according to the present invention is a driving circuit particularly preferred for driving a light emitting device comprised of a semiconductor laser (laser diode).
2. Description of the Related Art
As will be explained in detail later by using the drawings, when a light emitting device having a threshold current (Ith) or a differential quantum efficiency (&eegr;) which fluctuates according to the temperature is used as the above light emitting device, in the light emitting device driving circuit of the related art, the optical output power (Pout) fluctuates according to the fluctuation of the temperature. For this reason, when such a light emitting device is used in the light emitting device driving circuit of the related art, of course, there is a problem that the range of the operating temperature is limited, so application to a circuit where optimum operation is required in a wide range of temperature is difficult. Conversely, when it is desired to apply the light emitting device driving circuit of the related art to a circuit where optimum operation is required in a wide range of temperature, there arises a problem in that the selection of the light emitting device becomes difficult.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a light emitting device driving circuit capable of, at all times, feeding a constant optical output power Pout over a wide range of temperature even in a case of driving a light emitting device having a threshold current (Ith) and a differential quantum efficiency (&eegr;) which fluctuate according to temperature fluctuations.
To attain the above object, the light emitting device driving circuit of the present invention is provided with a driving transistor for feeding a bias current and a pulse current to a light emitting device having a grounded-cathode, an adjusting resistor for adjusting the pulse current and bias current fed to the light emitting device, and a resistive dividing circuit comprising series-connected dividing resistors for individually setting the pulse current and bias current, wherein the series-connected dividing resistors are constituted by a temperature dependent resistive unit.
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Koyanagi Hisako
Rokugawa Hiroyuki
Fujitsu Limited
Staas & Halsey , LLP
Vo Tuyet T.
Wong Don
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