Laser driving circuit

Claim 2

A laser driving circuit for controlling electrical current flowing through a laser diode in accordance with an intensity of a laser beam emitted by said laser diode, said laser driving circuit comprising: means for receiving a plurality of predetermined signals; means for supplying electrical current to said laser diode; and means for gradually shifting an amplitude of said electrical current supplied by said supplying means to a predetermined destination value a predetermined period of time after all of said plurality of predetermined signals have been received by said receiving means.

Claim 3

The laser driving circuit according to claim 1, wherein said shifting means comprises detection means for detecting whether all of said plurality of signals have been received.

Claim 4

The laser driving circuit according to claim 2, wherein said detection means comprises an AND gate circuit.

Claim 5

The laser driving circuit of claim 1, wherein said amplitude of said electrical current increases to said predetermined destination value without exceeding said predetermined destination value.

Claim 6

The laser driving circuit of claim 1, said shifting means further comprising means for reducing said amplitude of said electrical current to a value lower than said destination value when at least one of said plurality of predetermined signals is not received by said receiving means.

Claim 7

The laser driving circuit according to claim 5, wherein said shifting means maintains said amplitude of said electrical current at said lower value for a predetermined period of time even if all of said plurality of predetermined signals have been received by said receiving means.

Claim 8

The laser driving device according to claim 5, wherein said shifting means gradually shifts said amplitude of said electrical current from said lower value to said predetermined destination value.

Claim 9

The laser driving circuit of claim 1, wherein said means for gradually shifting comprises a delay circuit that delays said shifting of said amplitude of said electrical current.

Claim 10

The laser driving circuit of claim 8, wherein said delay circuit has a response speed slower than a response speed of said supplying means.

Claim 11

The laser driving circuit of claim 8, wherein said shifting means stepwisely changes said amplitude of said electrical current in accordance with said voltage outputted by said delay circuit.

Claim 12

The laser driving circuit of claim 8, wherein said delay circuit comprises a resistor and a capacitor that form an RC circuit that operates to gradually lower said amplitude of said electrical current to said predetermined destination value in accordance with a time constant value of said RC circuit.

Claim 13

The laser driving circuit of claim 8, wherein said shifting means comprises a transistor located between said electrical current supplying means and said delay circuit, said transistor controlling said electrical current supplying means in such a manner that said electrical current supplying means increases said amplitude of said electrical current to said predetermined destination value as an output voltage of said delay circuit decreases.

Claim 14

A laser driving circuit for controlling a laser diode to emit a laser beam, comprising: means for supplying an electrical current to said laser diode; means for detecting an intensity of said laser beam emitted by said laser diode; a circuit for controlling an amplitude of said electrical current to said laser diode in accordance with said detected intensity of said laser beam so that said amplitude of said electrical current reaches a predetermined destination value; means for determining whether said electrical current is supplied to said laser driving circuit and for determining whether an instruction signal instructing a turning ON of said laser diode is inputted to said laser driving circuit; and means for gradually shifting said amplitude of said electrical current to said predetermined destination value a predetermined period of time after both said electrical current and said instruction signal are inputted to said laser driving circuit.

Claim 15

A laser driving circuit for controlling a laser diode to emit a laser beam, comprising: means for supplying an electrical current to said laser diode; means for detecting an intensity of said laser beam emitted by said laser diode; a circuit for controlling an amplitude of said electrical current to said laser diode in accordance with said detected intensity of said laser beam so that said amplitude of said electrical current reaches a predetermined destination value; means for determining whether said electrical current is supplied to said laser driving circuit and for determining whether an instruction signal instructing a turning ON of said laser diode is inputted to said laser driving circuit; and means for gradually shifting said amplitude of said electrical current to said predetermined destination value a predetermined period of time after both said electrical current and said instruction signal are inputted to said laser driving circuit.

Claim 16

A laser driving circuit according to claim 13, wherein said shifting means maintains said amplitude of said electrical current at a value lower than said predetermined destination value for a predetermined period even if both said electrical current and said instruction signal have been inputted to said laser driving circuit.

Claim 17

The laser driving circuit of claim 13, wherein said amplitude of said electrical current flow increases to said predetermined destination value without exceeding said predetermined destination value.

Claim 18

The laser driving circuit of claim 13, said shifting means further comprising means for reducing said amplitude of said electrical current to a value lower than said predetermined destination value when said instruction signal is not input to said laser driving circuit.

Claim 19

The laser driving circuit according to claim 16, wherein said shifting means gradually shifts said amplitude of said electrical current from said lower value to said predetermined destination value.

Claim 20

The laser driving circuit of claim 13, wherein said means for gradually shifting comprises means for delaying said shifting of said amplitude of said electrical current.

Claim 21

The laser driving circuit of claim 18, wherein said delaying means has a response speed slower than a response speed of said supplying means.

Claim 22

The laser driving circuit of claim 19, wherein said shifting means stepwisely changes said amplitude of said electrical current in accordance with said voltage outputted by said delaying means.

Claim 23

The laser driving circuit of claim 18, wherein said delaying means comprises a resistor and a capacitor that form an RC circuit that operates to gradually lower said amplitude of said electrical current to said predetermined destination value in accordance with a time constant value of said RC circuit.

Claim 24

A laser driving circuit for controlling a laser diode to emit a laser beam, said laser driving circuit comprising: a variable current source for supplying an electrical current to said laser diode, said variable current source having a control terminal, an amplitude of said electrical current being varied in accordance with a voltage applied to said control terminal; a photodiode for generating an electrical current in accordance with an intensity of said laser beam emitted by said laser diode; an inverse peak hold circuit having an input terminal and an output terminal, said input terminal being connected in series with said photodiode, said output terminal being connected with said control terminal of said variable current source; a pull down resistor connected to said input terminal of said inverse peak hold circuit; means for receiving a plurality of predetermined signals; and means for shifting said voltage applied to said control terminal to cause said amplitude of said electrical current to gradually increase to a predetermined destination value a predetermined period of time after all of said plurality of predetermined signals have been received by said receiving means.

Claim 25

A laser driving circuit for controlling a laser diode to emit a laser beam, said laser driving circuit comprising: a variable current source for supplying an electrical current to said laser diode, said variable current source having a control terminal, an amplitude of said electrical current being varied in accordance with a voltage applied to said control terminal; a photodiode for generating an electrical current in accordance with an intensity of said laser beam emitted by said laser diode; an inverse peak hold circuit having an input terminal and an output terminal, said input terminal being connected in series with said photodiode, said output terminal being connected with said control terminal of said variable current source; a pull down resistor connected to said input terminal of said inverse peak hold circuit; means for receiving a plurality of predetermined signals; and means for shifting said voltage applied to said control terminal to cause said amplitude of said electrical current to gradually increase to a predetermined destination value a predetermined period of time after all of said plurality of predetermined signals have been received by said receiving means.

Claim 26

The laser driving circuit according to claim 22, wherein said shifting means keeps said voltage applied to said control terminal to said predetermined destination value for a predetermined period even if all of said plurality of predetermined signals have been received by said receiving means.

Claim 27

The laser driving circuit of claim 22, wherein said amplitude of said predetermined destination value increases to said predetermined destination value without exceeding said predetermined destination value.

Claim 28

The laser driving circuit of claim 22, said shifting means further comprising means for lowering said amplitude of said electrical current to a value lower than said predetermined destination value when at least one of said predetermined signals is not inputted to said laser driving circuit.

Claim 29

The laser driving circuit of claim 22, wherein said means for shifting comprises means for delaying said shifting of said amplitude of said electrical current.

Claim 30

The laser driving circuit of claim 26, wherein said shifting means stepwisely changes said amplitude of said electrical current in accordance with said voltage outputted by said delaying means.

Claim 31

The laser driving circuit of claim 26, wherein said delaying means comprises a resistor and a capacitor that from an RC circuit that operates to said amplitude of said electrical current to said predetermined destination value in accordance with a time constant value of said RC circuit.

Claim 32

A laser driving circuit for controlling an electrical current flowing through a laser diode in accordance with an intensity of a laser beam emitted by said laser diode, said laser driving circuit comprising: a receiver that receives a plurality of control signals; a variable current source that supplies electrical current to said laser diode; and a controller that controls said variable current source to start supplying said electrical current to said laser diode a predetermined period of time after said control signals are received by said receiver, such that an amplitude of said electrical current is gradually increased to a destination value.

Claim 33

A laser driving circuit for controlling an electrical current flowing through a laser diode in accordance with an intensity of a laser beam emitted by said laser diode, said laser driving circuit comprising: a receiver that receives a plurality of control signals; a variable current source that supplies electrical current to said laser diode; and a controller that controls said variable current source to start supplying said electrical current to said laser diode a predetermined period of time after said control signals are received by said receiver, such that an amplitude of said electrical current is gradually increased to a destination value.

Claim 34

The laser driving circuit of claim 29, further comprising means for determining whether all of said plurality of control signals are received by said receiver.

Claim 35

The laser driving circuit of claim 29, wherein said controller increases said amplitude of said electrical current to said destination value without exceeding said destination value.

Claim 36

The laser driving circuit of claim 29, said controller further comprising means for lowering said amplitude of said electrical current to a value lower than said destination value when at least one of said plurality of control signals is not received by said receiver.

Claim 37

A laser driving circuit, comprising: a receiver that receives a control signal; and a controller that controls an electrical current supplied to a laser diode, said controller gradually increasing an amplitude of said electrical current supplied to said laser diode to a predetermined destination value a predetermined period of time after said control signal is received by said receiver means.

Claim 38

A laser driving circuit, comprising: a receiver that receives a control signal; and a controller that controls an electrical current supplied to a laser diode, said controller gradually increasing an amplitude of said electrical current supplied to said laser diode to a predetermined destination value a predetermined period of time after said control signal is received by said receiver means.