JPH10190138A - Driving circuit for optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower the voltage of a driving circuit for an optical device, such as the semiconductor laser, optical switch, etc., and to reduce the power consumption of the circuit. SOLUTION: A driving circuit for optical device is provided with transistors Q1-Qn which are respectively connected in series with a plurality of optical devices P1-Pn, a resistor RE, switch circuits S1-Sn for turning on the transistors Q1Qn by using control signals, and an operation amplifier OPA which forms a constant-current circuit by inputting the voltage across both ends of the resistor RE to its (-) terminal and a reference voltage Vr to its (+) terminal and applying its output voltage across the bases of the transistors through the switch circuits S1-Sn between power terminals. Since the transistors Q1-Qn which are respectively connected in series with the optical devices P1-Pn are constituted in one stage, the voltage of the driving circuit can be lowered and the power consumption of the circuit can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a driving circuit for an optical device such as a semiconductor laser or an optical switch. An optical device including an electro-optic effect device, a thermo-optic effect device, an optical switch device for switching an optical signal or modulating an intensity by using a liquid crystal, or an optical device including a light source device such as a semiconductor laser or a light-emitting diode is becoming smaller. Drive voltages have been reduced. Accordingly, there is a demand for lower voltage and lower power consumption of drive circuits.

[0002]

2. Description of the Related Art FIG. 7 is an explanatory view of a conventional driving circuit, wherein P1 to Pn are optical devices, Q1 to Qn are transistors connected corresponding to the optical devices P1 to Pn, and Q0 is a control for forming a constant current circuit. Transistor, _RE is a resistor, OP
A operational amplifier, Vr is the reference voltage, V _C, V _E is the power supply voltage, I1 to indicate the drive current. The optical device P
1 to Pn show the case of an optical switch that selects an input optical signal and uses it as an output optical signal.

The collectors of the transistors Q1 to Qn are connected to the driving terminals of the optical devices P1 to Pn, a control signal is applied to the base, the emitters are connected in common, and the collectors are connected to the collector of the control transistor Q0. Transistor Q
0 of emitter connected to resistor R _E, and configured to apply the output voltage of the operational amplifier OPA base, the operational amplifier OPA compares the terminal voltage and the reference voltage of the resistor R _E, to the difference By applying a corresponding output voltage to the base of the control transistor Q0, a constant current circuit including the control transistor Q0 is formed.

Accordingly, when any one of the control signals is input to, for example, the base of the transistor Q2, the transistor Q2 is turned on, and the constant current flowing through the constant current circuit formed by the control transistor Q0 and the operational amplifier OPA is obtained. The supplied current is supplied to the optical device P2 via the transistor Q2, and when the optical device P2 is turned on, an optical signal is output via the optical device P2. That is, any one of the optical devices P1 to Pn can be selected and turned on by the control signal.

[0005]

The drive circuit of the prior art is
Optical devices P1 to Pn, transistors Q1 to Qn,
A control transistor Q0, a series circuit of a resistor R _E,
Since the power supply voltages V _C and V _E are applied and the transistors Q1 to Qn and the control transistor Q0 are in a two-stage series configuration, a voltage between the collector and the emitter of at least two transistors is required. become. Therefore,
There is also a limit to the reduction in voltage and power consumption. An object of the present invention is to achieve low voltage and low power consumption with a single-stage transistor structure.

[0006]

According to the present invention, there is provided a drive for an optical device of the present invention.
The driving circuit consists of (1) a plurality of optical devices between
Transistors Q1-Qn and a resistor R connected in series
_EAnd the transistors Q1 to Qn are turned on by the control signal.
Switch circuits S1 to Sn and a resistor R _EBoth ends of
Of the ON state by comparing the voltage of
Back to the transistor through the
And an operational amplifier OPA. That is, the optical device
The transistors Q1 to Qn connected to the column have a one-stage configuration.
Therefore, lower voltage and lower power consumption can be achieved.
You.

(2) Transistors and resistors respectively connected in series with a plurality of optical devices between power supply terminals, control transistors and resistors connected between power supply terminals, and both ends of the resistor connected to the control transistor An operational amplifier that compares a voltage with a reference voltage and feeds back to the control transistor to form a constant current circuit; and a switch circuit that applies an output voltage of the operational amplifier to a base of the transistor according to a control signal. I have. That is, the transistor connected in series to the optical device has a one-stage configuration, and the output voltage of the operational amplifier of the constant current circuit including the control transistor and the operational amplifier is fed back to the transistor via the switch circuit according to the control signal. , A plurality of optical devices can be driven simultaneously.

(3) The switch circuit includes a first diode connected between the base of the transistor and an input terminal of the control signal so that the control signal is applied in a reverse bias state, and an output of the operational amplifier. A second diode is provided between the terminal and the base of the transistor, the first diode being in a forward-biased state when the first diode is in a reverse-biased state by a control signal, and applying the output voltage of the operational amplifier to the base of the transistor. be able to.

(4) The switch circuit applies a complementary field-effect transistor QP, which applies a control signal to one of the gates of the other through the inverter INV.
It can be configured by QN parallel connection.

[0010]

FIG. 1 is an explanatory view of a first embodiment of the present invention, wherein P1 to Pn are optical devices, and Q1 to Qn.
The transistor, R1~Rn, R _E is resistance, S1~Sn
Represents a switch circuit, OPA represents an operational amplifier, Vr represents a reference voltage, V _C and _VE represent a power supply voltage, and V _B represents a bias voltage.

The switch circuits S1 to Sn include, for example, a p-channel field effect transistor QP as shown below.
And an n-channel field effect transistor QN and a complementary field effect transistor are connected in parallel, and a control signal cnt
Can be applied to one gate as it is, and to the other gate via an inverter INV.

Also, transistors Q1 to Qn corresponding to the optical devices P1 to Pn, resistors R1 to Rn, and a switch circuit S1
, Sn, a common resistor R _E, and an operational amplifier OPA.
1 to Pn, and a common resistor R
_E , the output terminal of the operational amplifier OPA is connected to the base via the switch circuits S1 to Sn, and the resistor R
1 to Rn, and a resistor R is connected to the negative terminal of the operational amplifier OPA.
The voltage at both ends of _E is input, the reference voltage Vr is input to the + terminal, and the output voltage corresponding to the difference is applied to the base of the transistor via the switch circuit turned on by the control signal. Things.

[0013] Thus, the optical device P1 to Pn, and the transistor Q1 to Qn, the resistor power supply voltage V _C to the series circuit of the R _E, V _E is applied, the switch circuit S1~Sn of complementary field effect transistor QP , QN, the control signal cnt is input to one of the switch circuits, the switch circuit is turned on, the output voltage of the operational amplifier OPA is applied to the base of the transistor, and the transistor is turned on. State.

For example, when the switch circuit S2 is turned on by a control signal, the output voltage of the operational amplifier OPA is applied to the base of the transistor Q2,
2 is turned on, and the transistor Q is connected to the optical device P2.
Current flows through the 2 and resistor R _E. The voltage across the resistor R _E which is proportional to this current, and a reference voltage Vr inputted to the operational amplifier OPA, since the output voltage corresponding to the difference, so that the output voltage becomes zero, transistor Q2 The current flowing through is controlled.

[0015] That is, a switch circuit turned on by the control signal cnt, a transistor switch circuit is connected to the base became this on, the resistance R _E, by an operational amplifier OPA, constitute a constant current circuit A voltage follower type voltage-current converter is formed. in this case,
If the open gain of the operational amplifier OPA is sufficiently large and the input impedance is sufficiently high,-
Is because so that the same potential Vr and + terminal occurs terminal, a constant current _{I = (Vr-V E)} / R E is supplied to the optical device.

[0016] Also with respect to resistance R1~Rn connected to the base of transistor Q1 to Qn, the potential V _B terminal connected to a _{common, V B = Vr + V th} ( where, V _th = transistor threshold Q1 to Qn) By setting it near, the transistors Q1 to Qn can be driven at high speed, and the optical devices P1 to Pn can be driven at high speed. When all the transistors Q1 to Qn are turned off for power down or the like, V _B ≒ V _E can be satisfied.

As described above, the optical devices P1 to Pn can be driven by the one-stage transistors Q1 to Qn, and the voltage and power consumption are reduced as compared with the conventional two-stage configuration. Becomes possible. In this embodiment, a configuration is adopted in which any one of the plurality of optical devices P1 to Pn is selected and driven.
May be divided into a plurality of groups, and the above-described drive circuits may be provided for each group, so that one optical device is selectively driven for each group, and a plurality of optical devices can be simultaneously driven as a whole.

When the switch circuits S1 to Sn are constituted by complementary field-effect transistors QP and QN, the on-state due to the variation in the voltage value of the control signal cnt is smaller than that when the switch circuits S1 to Sn are constituted by a single field-effect transistor. Resistance variations can be reduced, and the optical devices P1 to P
The selection driving of n can be stabilized.

FIG. 2 is an explanatory view of a second embodiment of the present invention. The same reference numerals as in FIG.
1n is a first diode, D21 to D2n are second diodes, PV1 to PVn are voltage-driven optical devices, RP
1 to RPn indicate resistors for current / voltage conversion.

This embodiment shows a case where the switch circuits S1 to Sn in FIG. 1 are constituted by first diodes D11 to D1n and second diodes D21 to D2n, and the bases of transistors Q1 to Qn are shown. And resistors R1 to
The voltage V _B is applied through Rn, and connecting the first diode D11～D1n, between the base of the transistor Q1~Qn in polarity control signal is applied in a reverse bias state and the input terminal of the control signal And the second diode D21
The ～Q2n, when the first diode D11~D1n reverse bias state, and the base of the polarity transistor Q1~Qn the voltage across the common resistor R _E is fed back to the base of the transistor via the operational amplifier OPA Operational amplifier O
Connect between PA output terminal.

[0021] without the control signal is input, the first diode D11~D1n becomes forward biased by a voltage V _B through a resistor R1 to Rn, the transistor Q1
To Qn are turned off. Also for example, when the control signal to the first diode D12 is applied to a reverse bias state, a voltage V _B is applied through a resistor R2 to the base of the transistor Q2, the transistor Q2 is turned on, and the diode D22 is in a forward bias state. Then, the operational amplifier OPA - the terminal, the voltage across the resistor R _E is input from the input to the reference voltage Vr to the positive terminal, the output voltage corresponding to the difference between these second diode D21~D2n Since the output voltage of the operational amplifier OPA is fed back to the base of the transistor Q2 via the diode D22 in a reverse bias state,
_{= (Vr-V E) /} R voltage of the voltage follower type which constant current flows in the _E - current converter is formed.

Since a constant current I flows through the resistor RP2, a constant voltage is applied to the voltage-driven optical device PV2 to drive it. Therefore, all the optical devices PV1 to PVn such as voltage-driven optical switches can be turned off or any one of them can be turned on. In this case, by setting the control signal to have an amplitude value centered on the vicinity of the reference voltage Vr, high-speed driving can be performed. Also when including the case to all off the transistor Q1~Qn for such power-down would the low level of the control signal may be substantially the same potential as the voltage V _E.

FIG. 3 is an explanatory view of a third embodiment of the present invention. The same reference numerals as in FIG. 1 denote the same parts, Q0 is a control transistor, S0 is a control switch circuit, and R0,
R _{E0 to} R _En are resistors.

In this embodiment, the optical devices P1 to Pn
Transistors Q1 to Q2 whose collectors are connected to the drive terminals of
The resistors R _{E1 to} R _En are respectively connected to the emitters of n, the voltage across the resistor R _E0 connected to the emitter of the control transistor Q0 is input to the minus terminal of the operational amplifier OPA, and the reference voltage Vr is input to the plus terminal. The operational amplifier OPA is connected to the base of the control transistor Q0 via the control switch S0.
And the output voltage of the switch S
This is configured to be added to the bases of the transistors Q1 to Qn via 1 to Sn.

Therefore, by turning on the control switch S0, a voltage follower type voltage-current converter including the transistor Q0, the resistor R _E0 and the operational amplifier OPA transistor is formed. A constant current corresponding to Vr flows. in this case,
The control switch S0 can be omitted, and the control transistor Q0 can be kept on at all times.

By setting R0 = R1 = R2... = Rn to make the resistance relatively high, and by setting R _E0 = R _E1 = R _E2 ... = R _En to control the switch circuits S1 to Sn. When the plurality of switches are simultaneously turned on, the transistors Q1 to Qn corresponding to the switch circuits S1 to Sn in the on state are turned on, and the plurality of optical devices P1 to Pn can be simultaneously driven by the same current.

In this embodiment, the optical device P
1 to Pn can be driven by one-stage transistors Q1 to Qn, so that lower voltage and lower power consumption can be achieved as compared with the conventional two-stage transistor. Although the first and second embodiments show a case where any one of the transistors is turned on, in the third embodiment, a plurality of transistors are turned on at the same time.
A plurality of optical devices can be driven by supplying the same current.

FIG. 4 is an explanatory view of a fourth embodiment of the present invention, wherein the same reference numerals as in FIG.
1n is a first diode, D20 to D2n are second diodes, and show a case where the switch circuits S0 to Sn in FIG. 3 are constituted by first and second diodes.

The base of the transistor Q0～Qn, by connecting a resistor R0~Rn a structure for applying a voltage V _B, and the first diode D11～D1n, based input terminal of transistor Q1~Qn control signal And the control signal is connected with a polarity that causes a reverse bias. The second diodes D21 to D2n are connected between the output terminal of the operational amplifier OPA and the bases of the transistors Q1 to Qn when the first diodes D11 to D1n are in a reverse bias state.
Connect with a polarity that becomes a forward bias by _B.

Accordingly, the control transistor Q0 is in a state where the base current flows through the resistor R0, and is always on, and the voltage across the resistor _RE0 and the reference voltage V
r is input to the operational amplifier OPA and is fed back to the base of the control transistor Q0 via the second diode D20. Therefore, as in the case described above, the voltage follower type voltage-current converter is used. Thus, a constant current flows through the control transistor Q0.

When no control signal is applied to the first diodes D11 to D1n, all the transistors are in a forward bias state, and the transistors Q1 to Qn are turned off. When the control signal is, for example, the first diodes D11 and D12
Applied in a reverse bias condition of the second diode D
21, D22 is forward biased via the resistor R1, R2 by voltage V _B, the output voltage of the operational amplifier OPA at this time, the base voltage of the transistor Q1, Q2 becomes a predetermined value, the transistors Q1, Q2 is turned on At the same time, control is performed so that a constant current flows. That is, turning on a plurality of transistors simultaneously,
A plurality of optical devices can be driven simultaneously.

FIG. 5 is an explanatory diagram of applied voltages according to the embodiment of the present invention. FIG. 5 (A) shows an example in which transistors Q1 to Qn corresponding to an optical device are controlled by control signals to drive the optical device. in each embodiment, the voltage V _E and the potential of the ground G, showing a case in which the voltage V _B and the reference voltage Vr and the same potential, high-speed operation becomes possible. Er indicates a reference voltage power supply.

FIG. 5B shows the voltage V _E and the voltage V _B
Is set to the potential of the ground G, and the transistors Q1 to
This is a case including a state in which all Qn are turned off. In addition,
Although the voltage V _C is not shown in (A) and (B), the voltage V _C is applied as a potential with respect to the voltage V _E via an optical device.

FIG. 6 is an explanatory diagram of an application example of the optical signal device according to the embodiment of the present invention, where V _C , V _E , V _B , and Vr indicate voltages in each of the above embodiments. (A) shows a case where the semiconductor lasers LD1 to LDn having the emission wavelengths λ1 to λn are used as an optical device. Therefore, a control signal (not shown)
, The semiconductor lasers LD1 to LDn selected can be driven by a drive circuit to generate an optical signal of a desired wavelength.

FIG. 6B shows optical switches PS1-P.
This shows a case where Sn is an optical device, and the optical switches PS1 to PSn selected by a control signal (not shown) can be turned on to output an input optical signal. In addition, an optical amplifier or an optical modulator can be used as the optical device.

The present invention is not limited to the above embodiments, but can be variously modified.
For example, transistors Q1 to Qn connected to an optical device
Can be a field effect transistor. Further, it is easy to form an integrated circuit including the operational amplifier OPA.

[0037]

As described above, according to the present invention, the driving terminal of the optical device P1~Pn connects the transistor Q1~Qn and resistor R _E, via a switch circuit S1~Sn which is turned on by a control signal the output voltage of the operational amplifier OPA is connected to apply to the base of the transistor Q1~Qn Te, a voltage with a reference voltage Vr across the resistor R _E is input to the operational amplifier OPA, the output voltage, the control signal Is fed back to the base of the transistor through the switch circuit which is turned on by the switch to form a voltage follower type voltage-current converter, thereby supplying and driving a constant current to the optical devices P1 to Pn selected by the control signal. The transistors Q1 to Q1 are connected to the optical devices P1 to Pn.
Since the driving circuit has a one-stage configuration using Qn, there is an advantage that low voltage and low power consumption can be achieved.

A voltage follower type voltage-to-current converter is formed by the control transistor, the resistor, and the operational amplifier, and the output voltage of the operational amplifier is connected to the bases of the transistors Q1 to Qn connected to the optical devices P1 to Pn. In addition, by using a configuration that is applied via a switch circuit that is turned on by a control signal, a plurality of optical devices can be simultaneously driven with a constant current. Also in this case, the optical devices P1 to Pn have a one-stage drive circuit composed of the transistors Q1 to Qn, so that the voltage can be reduced and the power consumption can be reduced as compared with the conventional example. .

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a second embodiment of the present invention.

FIG. 3 is an explanatory diagram of a third embodiment of the present invention.

FIG. 4 is an explanatory diagram of a fourth embodiment of the present invention.

FIG. 5 is an explanatory diagram of an applied voltage according to the embodiment of the present invention.

FIG. 6 is an explanatory diagram of an application example of the optical signal device according to the embodiment of the present invention.

FIG. 7 is an explanatory diagram of a conventional driving circuit.

[Explanation of symbols]

P1~Pn optical device Q1~Qn transistor OPA operational amplifier S1~Sn switch circuit R _E, R1 to Rn resistance

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Satoshi Kuroyanagi 4-1-1 Kamikadanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Tetsuya Nishi 4-1-1 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture No. 1 Inside Fujitsu Ltd. No. Japan Telegraph and Telephone Corporation

Claims (4)

[Claims] 1. A transistor and a resistor respectively connected in series with a plurality of optical devices between power supply terminals, a switch circuit for turning on the transistor by a control signal, and comparing a voltage across the resistor with a reference voltage. Feedback to the transistor through the switch circuit in the ON state,
An optical device driving circuit, comprising: an operational amplifier constituting a constant current circuit. 2. A transistor and a resistor respectively connected in series with a plurality of optical devices between power supply terminals, a control transistor and a resistor connected between power supply terminals, and a voltage across the resistor connected to the control transistor. An operational amplifier that compares the reference voltage with the reference voltage and feeds back to the control transistor to form a constant current circuit; and a switch circuit that applies the output voltage of the operational amplifier to the base of the transistor according to a control signal. A drive circuit for an optical device, comprising: 3. A switch circuit comprising: a first diode connected between a base of the transistor and an input terminal of the control signal so that the control signal is applied in a reverse bias state; Between the output terminal of the first transistor and the base of the transistor, the first diode being in a forward bias state when the control signal is in a reverse bias state, and applying the output voltage of the operational amplifier to the base of the transistor. 3. A driving circuit for an optical device according to claim 1, wherein the driving circuit comprises a diode. 4. The switch circuit according to claim 1, wherein one side of the control signal is applied as it is, and the other side of the switch circuit is connected in parallel to complementary field effect transistors that apply the gates to respective gates via an inverter. 3. A drive circuit for an optical device according to item 2.