JPH1174567A - Light emitting diode drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To permit higher speed in light transfer of a light emitting diode, by improving not only responsiveness at on-driving of the light emitting diode, but that at off-driving. SOLUTION: A drive circuit comprises a switching circuit B11, connected to a light emitting diode D11, for on/off controlling a drive current supplied to a light emitting diode D11 with a pulse signal of specified frequency inputted, and a voltage-driving type peaking current generating circuit B14 connected to the light emitting diode D11, the drive current is transiently increased in synchronism with on-driving time of the switching circuit B11 with the drive signal inputted, while it is transiently decreased in synchronism with off driving time of the switching circuit B11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode driving circuit, and more particularly, to a light emitting diode driving circuit for driving a light emitting diode for converting a telecommunication signal into an optical signal and transmitting the signal to an optical fiber at a high speed.

[0002]

2. Description of the Related Art In recent years, the development of optical fiber networks has been advanced.
2. Description of the Related Art The technology of an optical fiber link for converting a telecommunication signal into an optical signal and optically transmitting the optical communication signal using an optical fiber as a medium has become widespread. In order to spread the optical transmission, there is a demand for an optical fiber link which can be operated at a low cost and at a high speed. However, in a conventional optical fiber link, a semiconductor laser capable of high-speed response is used for a light emitting element for speeding up. However, since this semiconductor laser is expensive, the response of an optical signal is slower than that of a semiconductor laser. However, as a cheaper light emitting element, there is a need for a technique of using a light emitting diode to increase the response.

For example, as a conventional light emitting diode driving circuit for driving a light emitting diode at high speed, there is known a circuit configuration incorporating a peaking current generating circuit for adding a peaking current when a driving current of the light emitting diode for converting to an optical signal rises. ing.

FIG. 7 is a diagram showing a light emitting diode drive circuit of the first conventional example. In FIG. 7, D21 is a light emitting diode. A21 is a differential amplifier. B21 is a switching circuit including transistors Q21 and Q22 that are differentially configured to control on / off of a drive current supplied to the light emitting diode D21. B22 is a current mirror circuit for generating a constant current for the switching circuit 21 to perform switching driving of the light emitting diode D21, and is composed of transistors Q23 and Q24.

B23 is a differential transistor Q25,
This is a peaking current generating circuit including Q26. B24
Is a constant current source for generating a constant current to be supplied to the peaking current generating circuit B23. The light emitting diode D21 includes a switching circuit B21 and a peaking current generation circuit B2.
3 are connected. Input IN2 of differential amplifier A21
1, input signals Vk and Vl are input to IN22, and outputs Vn and Vm of differential amplifier A21 are connected to switching circuit B
21, while the output Vn is input to the input of the peaking current generation circuit B23 via the capacitor C22.

FIG. 8 is a diagram showing voltage / current waveforms at the time of operation of each circuit of the light emitting diode drive circuit of the first conventional example. In FIG. 8, Vk and Vl are input portions I of the differential amplifier A21.
7 shows voltage waveforms of input signals input to N21 and IN22. Vm and Vn indicate voltage waveforms of output signals output from the differential amplifier A21. Vo indicates a voltage waveform obtained by differentiating the falling edge of the output signal Vn output from the differential amplifier A21 at the “H” level. Vp indicates a reference voltage level for generating peaking current by transistor Q26.

Id22 indicates a current waveform that is turned on / off by the switching circuit B21. Id23 indicates the current waveform of the peaking current generated by the peaking current generation circuit B23 when the switching is on. Id21 indicates a current waveform at the time of switching of the light emitting diode D21.
In the light emitting diode D21, a current in which the switched current of Id22 and the peaking current of Id23 are superimposed flows.

However, in the light emitting diode driving circuit of the prior art example 1, it is necessary to always supply a current to a constant current source for generating a peaking current in addition to the driving current of the light emitting diode. When the peaking current is 30 mA and the peaking current is 30 mA, the current consumption is always 60 mA or more, the current consumption increases, and there is a problem in the power saving of the light emitting diode drive circuit. In order to solve this problem, for example, there is known a circuit configuration of Conventional Example 2 which can obtain a peaking current without using a constant current source only for generating a peaking current.

FIG. 9 is a diagram showing a light emitting diode drive circuit according to a second conventional example. 9, the same components as those in FIG. 7 are denoted by the same reference numerals. D21 is a light emitting diode. A
21 to A23 are differential amplifiers. B21 is a switching circuit that switches the light emitting diode D21 and drives it with a constant current. The light emitting diode D21 is connected to the collector of the transistor Q22 of the switching circuit B21. B22 is a current mirror circuit that supplies a constant current to the switching circuit 21. The switching circuit B21 is connected to the transistor Q of the current mirror circuit B22.
23 collectors.

B25 is a differential amplifier A13 and a capacitor C
21 is a peaking current generator. The peaking current generation circuit B25 is connected to a transistor Q23 constituting the current mirror circuit 22 via a capacitor C21.
Connected to the base. The peaking current generation circuit B25 is formed of a linear IC, and does not consume much current because a constant current source is not provided in the peaking current generation circuit. Since the constant current generated by the current mirror circuit B22 is transiently increased in synchronization with the ON driving of the switching, the current can be effectively increased at the time of the rise of the light emitting diode D21 during the ON driving to perform switching.

FIG. 10 is a diagram showing voltage / current waveforms at the time of operation of each circuit of the light emitting diode drive circuit of the second conventional example.
10, the same signals as those in FIG. 8 are denoted by the same reference numerals. Vk and Vl are the inputs IN21 of the differential amplifier A21,
3 shows a voltage waveform of an input signal input to IN22. V
m and Vn indicate voltage waveforms of output signals output from the differential amplifier A21. Vq indicates the voltage waveform of the output signal output from the differential amplifier A23.

Vr indicates a voltage waveform obtained by differentiating the rise of the output signal Vq with the base level of the transistor Q23 of the current mirror circuit B22. As a result, the constant current of the current mirror circuit B22 increases excessively, so that the output current when the switching by the switching circuit B21 is turned on is transiently increased. Id24 is the light emitting diode D
21 shows a current waveform at the time of switching of No. 21. This allows
A current in which a peaking current is superimposed flows through the light emitting diode D21.

[0013]

However, in the light emitting diode drive circuit of the first or second prior art, the driving current has peaking from the time when the light emitting diode is turned on to the time when the light emitting diode is turned on (at the time of rising). However, since the driving current is only turned off when the light emitting diode is turned on (falling) from on, the light signal does not turn off at high speed. There is a problem that high-speed driving is not performed.
This is because even if the switching drive of the light emitting diode is turned off at high speed, there are carriers remaining inside the light emitting diode, so that it is not turned off at high speed as an optical signal.

The present invention has been made in consideration of the above circumstances. For example, the driving current is excessively increased in synchronization with the ON driving of the light emitting diode, and the driving current is transiently increased in synchronization with the OFF driving. It has a voltage-driven peaking current generation circuit that reduces the number of light-emitting diodes. By forcibly extracting carriers remaining in the light-emitting diode during off-drive, not only the response of the light-emitting diode during on-drive but also the response during off-drive It is an object of the present invention to provide a light emitting diode driving circuit which remarkably improves performance and realizes high speed light transmission of the light emitting diode.

[0015]

According to the present invention, there is provided a switching circuit connected to a light emitting diode for inputting a driving signal and controlling on / off of a driving current supplied to the light emitting diode; A voltage-driven type that receives the drive signal and transiently increases the drive current in synchronization with the on-drive of the switching circuit and transiently decreases the drive current in synchronization with the off-drive of the switching circuit. A light-emitting diode drive circuit comprising a peaking current generation circuit.

In the present invention, a light emitting diode (LED) is used as a light emitting element for converting an electric signal from an information source into an optical signal. The switching circuit is a high-speed switching NPN twin transistor, PNP
It is preferred to be constituted by the twin transistors. It is preferable that the voltage-driven peaking current generating circuit is constituted by a linear IC having a built-in differential amplifier. Also,
The drive signal is a telecommunication signal, which is amplified and shaped by a differential amplifier and input to a switching circuit and a voltage-driven peaking current generation circuit.

According to the present invention, there is provided a voltage driving type peaking current generating circuit which excessively increases the driving current in synchronization with the on driving of the light emitting diode and transiently decreases the driving current in synchronization with the off driving. By forcibly extracting the carriers remaining in the light emitting diode during off driving, not only the response of the light emitting diode during on driving but also the response during off driving is significantly improved, and the light transmission speed of the light emitting diode is increased. Realization.

It is preferable that the peaking current generating circuit is configured to supply a voltage driving signal having the same phase as a driving current to be turned on / off by the switching circuit to the light emitting diode via a capacitor.

According to the above configuration, the peaking current generating circuit supplies the peaking current when the light emitting diode is turned on / off by a simple circuit configuration in which only a DC cut capacitor is added to the differential amplifier, for example. In addition, it is possible to excessively increase the driving current when the light emitting diode is turned on, and to transiently decrease the driving current when the light emitting diode is turned off.

The peaking current generating circuit is a complementary type M
It is preferable that the output unit further include an output unit including an OS transistor.

According to the above configuration, when the peaking current is generated, the output amplitude of the voltage driving signal can be maximized without being aware of the saturation characteristic generated by the bipolar transistor. The responsiveness of the light emitting diode is further improved.

A current mirror circuit for generating a constant current and supplying the current to the switching circuit; and a current mirror circuit connected to the current mirror circuit for receiving the drive signal and synchronizing with the current mirror circuit when the switching circuit is turned on. It is preferable that the configuration further includes a current driving type peaking current generation circuit that outputs a peaking signal for generating a peaking current.

According to the above configuration, the current mirror circuit can generate the peaking current in synchronization with the constant current supplied to the switching circuit and when the switching circuit is turned on, so that the current consumption can be reduced.

The current driving type peaking current generating circuit inputs a voltage driving signal synchronized with a driving current on / off controlled by the switching circuit to a base of a twin transistor constituting the current mirror circuit via a capacitor. It is preferable to configure so that

According to the above configuration, the current driving type peaking current generation circuit generates the peaking current in the current mirror circuit with a simple circuit configuration in which only a DC cut capacitor is added to the differential amplifier, for example. Can be.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings. The present invention is not limited by this.

FIG. 1 is a diagram showing a light emitting diode drive circuit according to Embodiment 1 of the present invention. In FIG. 1, D11 is a light emitting diode (LED) that converts an input signal into an optical signal. A11 to A14 are differential amplifiers for amplifying and shaping input signals, and are configured by linear ICs of bipolar transistors. B11 is a differentially configured transistor Q1
1, a switching circuit composed of Q12. The collector of the transistor Q12 is connected to the cathode of the light emitting diode D11 for switching.

B12 is a current mirror circuit composed of transistors Q13 and Q14 and resistors R12 to R14.
The constant current is connected to the emitter of the switching circuit B11 and supplied to the switching circuit B11. Thereby, the switching circuit B11 is connected to the light emitting diode D11.
Can be controlled on / off and driven with a constant current.

B13 is a differential amplifier A13 and a capacitor C
12 is a driving voltage generating circuit including a current driving type peaking current generating circuit.
And a current mirror circuit B12. It is connected to the base of the transistor Q13 of the current mirror circuit B12, and generates a peaking current when the switching drive of the switching circuit B11 is on (at the time of rising), thereby excessively increasing the constant current. This makes it possible to excessively increase the constant current when the switching drive is turned on, thereby increasing the response of the light emitting diode D11.

B14 is a differential amplifier A14 and a capacitor C
A voltage-driven peaking current generating circuit comprising a resistor 11 and a resistor 11, which is connected to the cathode of the light-emitting diode D11 and the transistor Q12 to supply a reverse bias voltage to the cathode of the light-emitting diode D11 when the switching drive is off (falling). (Peaking voltage) is excessively applied, and the carriers remaining in the light emitting diode D11 are converted to the power supply voltage V.
It is forcibly pulled out to the cc side. This makes it possible to excessively reduce the residual carriers at the time of the switching drive OFF, thereby increasing the response of the light emitting diode D11.

Further, the peaking current generation circuit B14
A peaking voltage is excessively applied at the time of switching driving (at the time of rising), and the driving current of the light emitting diode is forcibly extracted to the peaking current generating circuit B14. This makes it possible to further speed up the response when the light emitting diode D11 is turned on. Therefore, the switching current for switchingly driving the light emitting diode can be excessively increased by the combination of the current driving type peaking current generation circuit and the voltage driving type peaking current generation circuit, so that the responsiveness can be further improved. it can. In this embodiment, the fall of the light output of the light emitting diode was improved from 10 ns to 3 ns.

In this embodiment, the resistor R11 for generating a peaking current and the capacitor C11 are connected between the output of the differential amplifier A14 and the cathode of the light emitting diode D11, but the resistor R11 is added for current limitation. If the withstand current and the withstand voltage of the output section of the differential amplifier A14 are large, the differential amplifier A14 can be constituted only by the capacitor 11.

FIG. 2 is a diagram showing an output section of the voltage-driven peaking current generating circuit of this embodiment. In FIG.
1 are denoted by the same reference numerals. As shown in FIG. 2, the output O of the peaking current generating circuit (differential amplifier A14)
11 is composed of PMOS / NMOS transistors F1 and F2. It can also be constituted by a field effect transistor EFT.

According to the above configuration, when the peaking current is generated, the output amplitude of the voltage driving signal can be maximized without considering the saturation characteristic generated in the bipolar transistor. The responsiveness of the light emitting diode is further improved.

FIG. 3 is a diagram showing voltage / current waveforms during operation of each circuit of the light emitting diode drive circuit of the first embodiment. In FIG. 3, Va and Vb are input portions I of the differential amplifier A11.
9 shows voltage waveforms of input signals input to N11 and IN12. Vc and Vd indicate voltage waveforms of output signals output from the differential amplifier A11. Vi and Vj are differential amplifiers A12
3 shows a voltage waveform of an output signal output from the ASIC. Ve indicates a voltage waveform of an output signal output from the differential amplifier A13.

Vf indicates a voltage waveform of a peaking signal (transient signal) input from the differential amplifier A13 to the base of the transistor Q13 of the current mirror circuit B12. Vh
Indicates a voltage waveform of an output signal output from the differential amplifier A14. Vg indicates a voltage waveform of a switching signal obtained by combining a switching circuit B11 for switching the light emitting diode D11 and a peaking voltage input from the differential amplifier A14 to the cathode of the light emitting diode D11.
Id11 indicates a current waveform for driving the light emitting diode D11. ON / OFF of the switching drive of the light emitting diode D11
When turned off, a peaking current is superimposed.

FIG. 4 is a diagram showing a light emitting diode driving circuit according to a second embodiment of the present invention. 4, the same components as those in FIG. 1 are denoted by the same reference numerals. D11 is a light emitting diode that converts an input signal into an optical signal. A11, A12, and A14 are differential amplifiers that amplify and shape input signals, and are configured by linear ICs of bipolar transistors. B11 is a switching circuit including transistors Q11 and Q12 in a differential configuration. The collector of the transistor Q12 is connected to the cathode of the light emitting diode D11 and is driven for switching.

A constant current source B15 is connected to the switching circuit B11 and is driven by a constant current. As a result, the switching circuit B11 can perform switching driving of the light emitting diode D12 with a constant current.

B14 is a differential amplifier A14 and a capacitor C
A voltage-driven peaking current generating circuit comprising a resistor 11 and a resistor 11, which is connected to the cathode of the light-emitting diode D11 and the transistor Q12 to supply a reverse bias voltage to the cathode of the light-emitting diode D11 when the switching drive is off (falling). (Peaking voltage) is excessively applied, and the carriers remaining in the light emitting diode D11 are converted to the power supply voltage V.
It is forcibly pulled out to the cc side to speed up the response when the switching drive of the light emitting diode is turned off. Further, when the switching drive is turned on (at the time of rising), a peaking voltage is excessively applied to forcibly pull out the driving current of the light emitting diode to the peaking current generating circuit B14.
The response when the switching drive of the light emitting diode is turned on is made faster.

Vg 'is the switching voltage output from the switching circuit B11 and the peaking current generation circuit B1.
4 shows a switching voltage in combination with the peaking voltage output from the reference numeral 4 and is substantially the same as the voltage waveform of Vg shown in FIG. Id12 indicates a switching current for driving the light emitting diode D11, which is almost the same as the current waveform of Id11 shown in FIG.

FIG. 5 is a diagram showing a light emitting diode drive circuit according to Embodiment 3 of the present invention. 5, the same components as those in FIG. 1 are denoted by the same reference numerals. D11 is a light emitting diode that converts an input signal into an optical signal. A11 and A14 are differential amplifiers for amplifying and shaping an input signal, and are constituted by linear ICs of bipolar transistors. B11 is a switching circuit including transistors Q11 and Q12 in a differential configuration, and the collector of the transistor Q12 is connected to the cathode of the light emitting diode D11 to perform switching driving.

B12 is a current mirror circuit composed of transistors Q13 and Q14 and resistors R12 and R13.
It is connected to the switching circuit B11 and is driven by a constant current.
As a result, the switching circuit B11 can perform switching driving of the light emitting diode D12 with a constant current.

B16 is a differentially configured transistor Q
6, Q7, capacitor C12, resistors R15, R16, R
17 is a current driving type peaking current generating circuit composed of 17 elements. BB 17 is a constant current source for generating a constant current to be supplied to the peaking current generating circuit 16. Light emitting diode D2
1 is connected to a switching circuit B21 and a peaking current generating circuit B23.

The input sections IN11 and IN of the differential amplifier A11
12, input signals Va and Vb are input to the differential amplifier A
The outputs Vc and Vd of 11 are input to the switching circuit B11, while the output Vd is input to the input of the peaking current generating circuit B16 via the capacitor C12. As a result, it is possible to increase the on-current for switching driving the light emitting diode D11 excessively, and to speed up the response.

B14 is a differential amplifier A14 and a capacitor C
A voltage-driven peaking current generating circuit comprising a resistor 11 and a resistor 11, which is connected to the cathode of the light-emitting diode D11 and the transistor Q12 to supply a reverse bias voltage to the cathode of the light-emitting diode D11 when the switching drive is off (falling). (Peaking voltage) is excessively applied, and the carriers remaining in the light emitting diode D11 are converted to the power supply voltage V.
It is forcibly pulled out to the cc side. As a result, the off-current for switching driving of the light emitting diode is excessively reduced, and the response can be speeded up.

In the peaking current generation circuit B14, a peaking voltage is excessively applied at the time of switching drive (ON), and the driving current of the light emitting diode is forcibly extracted to the peaking current generation circuit B14 side. Thereby, the response at the time of ON of the switching drive of the light emitting diode can be made faster. Therefore, the on-current for switchingly driving the light emitting diode can be excessively increased by the combination of the voltage driving type peaking current generation circuit B14 and the current driving type peaking current generation circuit B16, thereby further improving the responsiveness. be able to.

FIG. 6 is a diagram showing voltage / current waveforms during operation of each circuit of the light emitting diode drive circuit of the third embodiment. In FIG. 6, Va and b are input portions IN of the differential amplifier A11.
11 shows a voltage waveform of an input signal input to IN12. Vc and Vd indicate voltage waveforms of output signals output from the differential amplifier A11. Vo indicates a voltage waveform obtained by differentiating the falling edge of the output signal Vd output from the differential amplifier A11 by "H" level. Vp indicates a reference voltage level for generating peaking current from transistor Q16.

Id13 indicates a constant current waveform for switching the light emitting diode D11 by the switching circuit B11. Id14 indicates a current waveform of a peaking current when the light emitting diode D11 is switched on by the peaking current generation circuit B16. Id15 indicates the current waveform of the peaking current when the light emitting diode D11 is switched by the peaking current generation circuit B14. Id12 indicates a current waveform at the time of switching of the light emitting diode D11.

In the present invention, the switching circuit and the current mirror circuit are configured using NPN transistors. However, a circuit configuration using PNP transistors may be used. Further, all the circuits of the light emitting diode drive circuit can be constituted by a one-chip linear IC.

[0050]

According to the present invention, the switching voltage is excessively increased in synchronization with the ON driving of the light emitting diode,
A voltage-driven peaking current generation circuit that transiently reduces the switching voltage in synchronization with off-drive is provided.
By forcibly pulling out the carriers remaining in the light emitting diode during the off-drive, not only the response of the light-emitting diode during the on-drive but also the response during the off-drive is significantly improved, and the light transmission speed of the light-emitting diode is increased. I do.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a light emitting diode drive circuit according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an output unit of a voltage-driven peaking current generation circuit according to the present embodiment.

FIG. 3 is a diagram illustrating voltage / current waveforms during operation of each circuit of the light emitting diode drive circuit according to the first embodiment.

FIG. 4 is a diagram illustrating a light emitting diode drive circuit according to a second embodiment of the present invention.

FIG. 5 is a diagram illustrating a light emitting diode drive circuit according to a third embodiment of the present invention.

FIG. 6 is a diagram illustrating voltage / current waveforms during operation of each circuit of the light emitting diode drive circuit according to the third embodiment.

FIG. 7 is a diagram showing a light emitting diode drive circuit of Conventional Example 1.

FIG. 8 is a diagram showing voltage / current waveforms at the time of operation of each circuit of the light emitting diode drive circuit of Conventional Example 1.

FIG. 9 is a diagram showing a light emitting diode drive circuit of Conventional Example 2.

FIG. 10 is a diagram showing voltage / current waveforms during operation of each circuit of the light emitting diode drive circuit of Conventional Example 2.

[Explanation of symbols]

 A11 to A14 Differential amplifier B11 Switching circuit B12 Current mirror circuit B13 Driving voltage generating circuit B14 Voltage driving type peaking current generating circuit B15 Constant current source B16 Current driving type peaking current generating circuit B17 Constant current source C11 to C12 Capacitor D11 Light emission Diode F1, F2 MOS transistor R11-R17 Resistance Q11-Q16 Transistor

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI H04B 10/06

Claims (5)

[Claims] A switching circuit connected to a light emitting diode for inputting a driving signal and controlling on / off of a driving current supplied to the light emitting diode; and a switching circuit connected to the light emitting diode and inputting the driving signal. A voltage-driven peaking current generation circuit that transiently increases the drive current in synchronization with the on-drive of the switching circuit and transiently decreases the drive current in synchronization with the off-drive of the switching circuit. A light-emitting diode drive circuit, characterized in that: 2. The light-emitting diode according to claim 1, wherein the peaking current generating circuit supplies a voltage driving signal having the same phase as a driving current on / off controlled by the switching circuit to the light emitting diode via a capacitor. A light emitting diode drive circuit as described in the above. 3. The light emitting diode driving circuit according to claim 1, wherein said peaking current generating circuit further comprises an output section comprising a complementary MOS transistor. A current mirror circuit for generating a constant current and supplying the current to the switching circuit; and a current mirror connected to the current mirror circuit, receiving the drive signal and synchronizing with the ON state of the switching circuit. 2. The light emitting diode driving circuit according to claim 1, further comprising a current driving type peaking current generating circuit for outputting a peaking signal for causing the circuit to generate a peaking current. 5. The peaking current generating circuit of the current drive type comprises: a base of a twin transistor forming a current mirror circuit via a capacitor with a voltage drive signal synchronized with a drive current on / off controlled by the switching circuit. 5. The light emitting diode drive circuit according to claim 4, wherein the signal is input to the circuit.