Coherent light generators – Particular component circuitry – Power supply
Reexamination Certificate
1999-09-08
2001-09-18
Font, Frank G. (Department: 2877)
Coherent light generators
Particular component circuitry
Power supply
C372S038020, C363S047000, C327S551000, C327S554000, C323S355000
Reexamination Certificate
active
06292501
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to laser diodes, and more particularly to a power supply that generates a drive current for the laser diode having lower amplitude modulation.
BACKGROUND OF THE INVENTION
It has been proposed to use a switching power supply to convert alternating current (AC) wall power to a direct current (DC) drive current for operating DC devices such as laser diodes. The problem with switching power supplies is that they tend to generate drive currents with significant amplitude modulations (current fluctuations) therein. This is a problem for many devices, especially laser diodes, because the drive current amplitude modulations are coupled into the laser diode optical output beam due to the fact that the amplitude of the laser diode output beam is approximately proportional to the laser diode drive current. Many laser diode applications are extremely sensitive to amplitude modulations in the laser diode output beam.
A typical prior art switching power supply is illustrated in
FIG. 1
, which includes a transformer T, diodes D, inductors L and a capacitor C. The current through the laser diode is represented by I(t)=I,
o
+i(t), where i(t) is the relatively small alternating component (A.C.) of the current. The A.C. component of the diode current can be decreased by increasing the output of the LC network (i.e. increasing L and C), but this solution has a limited noise reduction effect and is undesirable because it would require increased size and lower bandwidth. Therefore, many power supply manufactures are using linear power supplies for applications sensitive to drive current modulations. These linear power supplies are much larger and more expensive than switching power supplies.
There is a need for a switching power supply that has minimal output current fluctuations, especially for laser diode applications that require minimal optical beam power fluctuations, but without increasing the size or slowing the bandwidth of the switching power supply.
SUMMARY OF THE INVENTION
The present invention solves the aforementioned problems by providing an integrator circuit to the switching power supply circuit to cancel out a significant portion of the AC noise generated by the switching power supply.
In one aspect of the present invention, an integrator circuit, for filtering an electrical signal passing through an inductor having first and second terminals, includes a first resistor, an amplifier, a second resistor and a first capacitor. The first resistor has first and second terminals, where the first terminal is connected to the first terminal of the inductor. The amplifier has first and second input terminals and an output terminal, where the first input terminal is connected to the second terminal of the first resistor, and the second input terminal is connected to the second terminal of the inductor.
The second resistor has a first terminal connected to the output terminal of the amplifier, and a second terminal connected to the second terminal of the inductor. The first capacitor has a first terminal connected to the first input terminal of the amplifier, and a second terminal connected to the output terminal of the amplifier.
In another aspect of the present invention, a power supply includes a voltage source, an inductor with first and second terminals, the first terminal is connected to the voltage source, and an integrator circuit connected in series with the inductor. The integrator circuit includes a first resistor, an amplifier, a second resistor, and a first capacitor. The first resistor has first and second terminals, the first terminal being connected to the first terminal of the inductor. The amplifier has first and second input terminals and an output terminal, where the first input terminal is connected to the second terminal of the first resistor, and the second input terminal is connected to the second terminal of the inductor. The second resistor has a first terminal connected to the output terminal of the amplifier, and a second terminal connected to the second terminal of the inductor. The first capacitor has a first terminal connected to the first input terminal of the amplifier, and a second terminal connected to the output terminal of the amplifier.
In yet another aspect of the present invention, a laser diode system comprises a voltage source, an inductor having first and second terminals, where the first terminal is connected to the voltage source, an integrator circuit connected in series with the inductor, and a laser diode. The integrator circuit includes a first resistor, an amplifier, a second resistor, and a first capacitor. The first resistor has first and second terminals, the first terminal being connected to the first terminal of the inductor. The amplifier has first and second input terminals and an output terminal, where the first input terminal is connected to the second terminal of the first resistor, and the second input terminal is connected to the second terminal of the inductor. The second resistor has a first terminal connected to the output terminal of the amplifier, and a second terminal connected to the second terminal of the inductor. The first capacitor has a first terminal connected to the first input terminal of the amplifier, and a second terminal connected to the output terminal of the amplifier. The laser diode has a first terminal connected to the second terminal of the inductor, and a second terminal connected to the voltage source, for producing an optical output.
In still yet another aspect of the present invention, a power supply for operating an electrical device having an input and an output terminal, includes a voltage source, an inductor having a first terminal connected to the voltage source and a second terminal connected to the input terminal of the electrical device, and an integrator circuit connected in series with the inductor, and a shunt circuit connected between the input and output terminals of the electrical device. The integrator circuit includes a first resistor having first and second terminals, an amplifier having first and second input terminals and an output terminal, and a first capacitor having first and second terminals. The first terminal of the first resistor is connected to the first terminal of the inductor. The first input terminal of the amplifier is connected to the second terminal of the first resistor, and the second input terminal is connected to the second terminal of the inductor. The first terminal of the first capacitor is connected to the first input terminal of the amplifier. The shunt circuit includes a second resistor and a first transistor. The first terminal of the second resistor is connected to the input terminal of the electrical device. The first transistor has a base terminal connected to the output terminal of the amplifier, a collector terminal connected to the second terminal of the second resistor, and an emitter terminal connected to the output terminal of the electrical device.
In still yet one more aspect of the present invention, a power supply for operating an electrical device having an input and an output terminal includes a voltage source for supplying an operating current, an inductor having a first terminal connected to the voltage source and a second terminal connected to the input terminal of the electrical device so that the operating current flows through the electrical device, and an integrator circuit connected in parallel with the inductor for removing amplitude fluctuations from the operating current. The integrator circuit includes a first resistor having first and second terminals, an amplifier having first and second input terminals and an output terminal, a first capacitor having first and second terminals, and one of a second resistor and a shunt circuit. The first terminal of the first resistor is connected to the first terminal of the inductor. The first input terminal of the amplifiers connected to the second terminal of the first resistor, and the second input terminal of the amplifier i
Coherent Inc.
Font Frank G.
Rodriguez Armando
Stillman & Pollock LLP
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