Laser driver with plural feedback loops

Claim 2

A laser driver circuit comprising a laser constructed as a diode, and a field-effect transistor (FET) for applying current to the laser; current feedback means serially connected with said laser and said FET for signaling an amount of current flow in said laser; optical feedback means optically coupled to said laser for signaling an amount of radiation emitted by said laser; and combining means for combining an input digital command signal with a signal of said current feedback means and with a signal of said optical feedback means to provide a drive signal for activating said FET to apply the current to said laser.

Claim 3

A laser driver circuit comprising a laser constructed as a diode, and a field-effect transistor (FET) for applying current to the laser; current feedback means serially connected with said laser and said FET for signaling an amount of current flow in said laser; optical feedback means optically coupled to said laser for signaling an amount of radiation emitted by said laser; combining means for combining an input digital command signal with a signal of said current feedback means and with a signal of said optical feedback means to provide a drive signal for activating said FET to apply the current to said laser; and wherein said optical feedback means operates with a response time, and said current feedback means operates with a response time many times faster than the response time of said optical feedback means.

Claim 4

A laser driver circuit comprising a laser constructed as a diode, and a field-effect transistor (FET) for applying current to the laser; current feedback means serially connected with said laser and said FET for signaling an amount of current flow in said laser; optical feedback means optically coupled to said laser for signaling an amount of radiation emitted by said laser; combining means for combining an input digital command signal with a signal of said current feedback means and with a signal of said optical feedback means to provide a drive signal for activating said FET to apply the current to said laser; and wherein said optical feedback means operates with a response time, and said current feedback means operates with a response time many times faster than the response time of said optical feedback means.

Claim 5

A laser driver circuit comprising a laser constructed as a diode, and a field-effect transistor (FET) for applying current to the laser; current feedback means serially connected with said laser and said FET for signaling an amount of current flow in said laser; optical feedback means optically coupled to said laser for signaling an amount of radiation emitted by said laser; combining means for combining an input digital command signal with a signal of said current feedback means and with a signal of said optical feedback means to provide a drive signal for activating said FET to apply the current to said laser; and wherein said combining means comprises an input section for receiving the digital command signal and the signal of said of said optical feedback means; and a driver section coupled to an output terminal of said input section and to an output terminal of said current feedback means, each of said input and said driver sections comprising a current source and a differential amplifier powered by said current source, the differential amplifier having two branches; wherein, in said input section, the optical feedback signal activates said current source, the digital command signal is applied to a first branch of said differential amplifier, a second branch of said differential amplifier connects with the output terminal of said input section, and the drive signal for activating said FET is provided by the second branch of said differential amplifier; and wherein, in said driver section, the output terminal of said input section connects with a first branch of said differential amplifier, and said current feedback signal is applied to a second branch of said differential amplifier.

Claim 6

A laser driver circuit comprising a laser constructed as a diode, and a field-effect transistor (FET) for applying current to the laser; current feedback means serially connected with said laser and said FET for signaling an amount of current flow in said laser; optical feedback means optically coupled to said laser for signaling an amount of radiation emitted by said laser; combining means for combining an input digital command signal with a signal of said current feedback means and with a signal of said optical feedback means to provide a drive signal for activating said FET to apply the current to said laser; and wherein said combining means comprises an input section for receiving the digital command signal and the signal of said of said optical feedback means; and a driver section coupled to an output terminal of said input section and to an output terminal of said current feedback means, each of said input and said driver sections comprising a current source and a differential amplifier powered by said current source, the differential amplifier having two branches; wherein, in said input section, the optical feedback signal activates said current source, the digital command signal is applied to a first branch of said differential amplifier, a second branch of said differential amplifier connects with the output terminal of said input section, and the drive signal for activating said FET is provided by the second branch of said differential amplifier; and wherein, in said driver section, the output terminal of said input section connects with a first branch of said differential amplifier, and said current feedback signal is applied to a second branch of said differential amplifier.

Claim 7

A circuit according to claim 3 wherein the differential amplifier of said driver section comprises a current mirror circuit.

Claim 8

A circuit according to claim 3 wherein said combining means further comprises a threshold section coupled to the second branch of the differential amplifier of said input section for establishing a threshold signal level in said drive signal outputted by the second branch of the differential amplifier of said driver section.

Claim 9

A circuit according to claim 3 wherein said optical feedback means comprises a photodetector of the radiation emitted by said laser, means for digitally filtering a signal outputted by said photodetector to provide a filtered photodetector signal, and means for converting said filtered photodetector signal to an analog-formatted signal which serves as the feedback signal of said optical feedback means; and said current feedback means comprises a feedback resistor serially connected with said laser and said FET, and a resistive voltage divider connecting between said feedback resistor and said combining means for providing said feedback signal of said current feedback means.

Claim 10

A circuit according to claim 3 wherein said input section operates in a switching mode in response to said input digital command signal, and said driver section operates in a linear mode.

Claim 11

A circuit according to claim 7 wherein said laser is operative as a part of a laser printer providing for a scanning of the radiation emitted by said laser across a printing medium; and said optical feedback means outputs its feedback signal in synchronism with operation of the laser printer.

Claim 12

A circuit according to claim 8 wherein said combining means further comprises a threshold section coupled to the second branch of the differential amplifier of said input section for establishing a threshold signal level in said drive signal outputted by the second branch of the differential amplifier of said driver section.

Claim 17

A method according to claim 11 wherein said input circuit includes a differential amplifier operating in a switching mode, and wherein said method further comprises a step of energizing said differential amplifier with current from a current source; and regulating current of the current source by said optical feedback signal.

Claim 20

A laser driver circuit comprising a laser constructed as a diode, and a field-effect transistor (FET) for applying current to the laser; current feedback means serially connected with said laser and said FET for signaling an amount of current flow in said laser; optical feedback means optically coupled to said laser for signaling an amount of radiation emitted by said laser; and combining means for combining an input digital command signal with a signal of said current feedback means and with a signal of said optical feedback means to provide a drive signal for activating said FET to apply the current to said laser; wherein said combining means comprises a first differential amplifier circuit and a second differential amplifier circuit each of which has a plurality of input terminals and an output terminal, the output terminal of said first differential amplifier circuit being coupled to an input terminal of said second different amplifier circuit, the digital command signal and the optical feedback signal and the current feedback signal constituting a set of three input signals to said combining means, two of said three input signals being applied to input terminals of said first differential amplifier circuit and a third of said three input signals being applied to an input terminal of said second differential amplifier circuit, said drive signal appearing at the output terminal of said second differential amplifier circuit.

Claim 21

A laser driver circuit comprising a laser constructed as a diode, and a field-effect transistor (FET) for applying current to the laser; current feedback means serially connected with said laser and said FET for signaling an amount of current flow in said laser; optical feedback means optically coupled to said laser for signaling an amount of radiation emitted by said laser; and combining means for combining an input digital command signal with a signal of said current feedback means and with a signal of said optical feedback means to provide a drive signal for activating said FET to apply the current to said laser; wherein said combining means comprises a first differential amplifier circuit and a second differential amplifier circuit each of which has a plurality of input terminals and an output terminal, the output terminal of said first differential amplifier circuit being coupled to an input terminal of said second different amplifier circuit, the digital command signal and the optical feedback signal and the current feedback signal constituting a set of three input signals to said combining means, two of said three input signals being applied to input terminals of said first differential amplifier circuit and a third of said three input signals being applied to an input terminal of said second differential amplifier circuit, said drive signal appearing at the output terminal of said second differential amplifier circuit.

Claim 22

A laser driver circuit comprising a laser constructed as a diode, and a field-effect transistor (FET) for applying current to the laser; current feedback means serially connected with said laser and said FET for signaling an amount of current flow in said laser; optical feedback means optically coupled to said laser for signaling an amount of radiation emitted by said laser; and combining means for combining an input digital command signal with a signal of said current feedback means and with a signal of said optical feedback means to provide a drive signal for activating said FET to apply the current to said laser; wherein said combining means comprises a first combining circuit operating in a switching mode and a second combining circuit operating in a linear mode, the digital command signal and the optical feedback signal and the current feedback signal constituting a set of three input signals to said combining means, two of said set of three input signals being applied to input terminals of said first combining circuit, an output signal of said first combining circuit and a third of said set of three input signals being applied to said second combining circuit, said drive signal appearing at an output terminal of said second combining circuit.

Claim 23

A laser driver circuit comprising a laser constructed as a diode, and a field-effect transistor (FET) for applying current to the laser; current feedback means serially connected with said laser and said FET for signaling an amount of current flow in said laser; optical feedback means optically coupled to said laser for signaling an amount of radiation emitted by said laser; and combining means for combining an input digital command signal with a signal of said current feedback means and with a signal of said optical feedback means to provide a drive signal for activating said FET to apply the current to said laser; wherein said combining means comprises a first combining circuit operating in a switching mode and a second combining circuit operating in a linear mode, the digital command signal and the optical feedback signal and the current feedback signal constituting a set of three input signals to said combining means, two of said set of three input signals being applied to input terminals of said first combining circuit, an output signal of said first combining circuit and a third of said set of three input signals being applied to said second combining circuit, said drive signal appearing at an output terminal of said second combining circuit.

Claim 24

A laser driver circuit according to claim 15 wherein the digital command signal and the optical feedback signal are applied to said first combining circuit.