JP2001313614A - System for driving light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light emitting element driving system capable of performing miniaturization, cost reduction and low power consumption by making a transmitting part simple when an electrical transmission system has been changed to an optical transmission system. SOLUTION: In this light emitting element driving system, the cathode terminal of an semiconductor light emitting element 106 is directly connected or the cathode terminal side of the element 106 is connected to the output terminal of a transmission IC 101 having a current drawing type outputting part, a resistance is also serially connected to the element 106, and the element 106 is driven.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving a light emitting element of an optical transmitter in an optical transmission system, an optical transmitter using the same, and an optical wiring using the same.

[0002]

2. Description of the Related Art With the spread of liquid crystal displays, digital interfaces between displays and computers (hereinafter referred to as digital monitor interfaces) have been developed. Compared to the analog interface, improvement in display quality, extension of transmission line length, and reduction in system cost are expected.

[0003] PanelLink is a transmission system for a digital monitor interface developed by Si1icon Image.
The company has developed its own transmitting and receiving ICs.
An image data signal and a control signal from a graphics controller of a computer are converted into a transmission signal of three channels (hereinafter, referred to as ch) by an encoding circuit of a transmission IC. The decoding circuit of the receiving IC converts these three-channel transmission signals into an image data signal and a control signal, and inputs them to the display. The clock signal from the graphics controller is used in the encoding circuit of the transmitting IC and the decoding circuit of the receiving IC. Therefore, the transmitter and receiver are 3ch
(Image data signal, control) +1 channel (clock) are connected by a total of four transmission lines.

FIG. 4 shows a configuration diagram of a PanelLink transmission system. In FIG. 4, 101 is a transmitting IC, 102 and 103 are output transistors, 104 is a constant current source, 401 is a receiving IC, 402 is a differential amplifier, 403 and 404 are terminating resistors, and 405 to 408 are transmission twins. The score, 409, is a twinax cable. Note that only one channel is described to avoid complication of the figure.

[0005] The twinax core is formed by shielding the twisted pair wire and the drain wire with aluminum foil or the like. A twinax cable is obtained by bundling a plurality of twinax cores and further shielding them. Twinax cables are used in high-speed transmission systems because of their stable impedance and low electromagnetic induction noise. Pa
nelLink uses twinax cables with four twinax cores.

However, with PanelLink, the transmission speed per channel is several hundred Mbps or more, so that long-distance transmission with a twinax cable is difficult. For this reason, a product called LightPipe, which uses an optical fiber for the transmission path, has been released.

FIG. 5 shows the configuration of the transmitting section. In FIG.
501 is an optical transmission module. 4ch electric signal to 4ch
Into an optical signal. An LD (Laser Diode) drive circuit 502, an LD 503, and a transmission unit coupling system 504 are provided for each channel. The LD drive circuit 502 is an AC coupled ECL (Emitter Coupled Logi
c) A logic interface is provided, and one of the differential outputs of the PanelLink transmission IC 101 is input. Each channel has individual optical connectors 505 to 508, and individual optical fiber cables 509 to 512 are connected. Note that only one channel is described here to avoid complication of the figure.

[0008]

In the above example, PanelL
The output of the transmission IC 101 of the ink is input to the optical transmission module 501 as a logic signal, and is converted into an optical signal. Since the optical transmission module includes a logic interface and an LD drive circuit, changing from an electric transmission system to an optical transmission system increases components and power consumption. Also, 4
Since it is for ch, the size of the optical transmission module itself is not small.

An object of the present invention is to provide a light emitting element driving system which can simplify a transmitting unit when an electric transmission system such as Pane1Link is changed to an optical transmission system, and which can be reduced in size, cost and power consumption. It is an object of the present invention to provide an optical transmitter and an optical wiring using the same.

[0010]

According to the present invention, there is provided a light emitting device driving system according to the present invention, wherein a cathode terminal of a semiconductor light emitting device is directly connected to an output terminal of a transmission IC having a current draw type output section. The light-emitting element is driven. This eliminates the need for using an optical transmission module having a complicated configuration, and allows the transmission unit to be simplified, downsized, reduced in cost, and reduced in power consumption. According to the present invention, matching of the output voltage level of the transmission IC, the voltage applied to the anode of the semiconductor light emitting device, and the voltage-current characteristics of the semiconductor light emitting device can be achieved by selecting an appropriate semiconductor light emitting device and a connection form thereof. Thus, a simple driving method as described above is realized.

Further, the light emitting device driving method of the present invention for achieving the above-mentioned object is a transmitting device having a current draw type output section.
C. connecting the cathode terminal of the semiconductor light emitting device to the output terminal via a resistor to drive the semiconductor light emitting device, or connecting the semiconductor light emitting device to the output terminal of a transmission IC having a current draw type output unit. Or the cathode terminal of the semiconductor light emitting device is directly connected, and a resistor is connected to the anode terminal of the semiconductor light emitting device to drive the semiconductor light emitting device. As a result, with respect to the output voltage level of the transmission IC,
The range of selection of usable semiconductor light emitting devices is expanded.

In the above configuration, a Zener diode may be connected between an anode and a cathode of the semiconductor light emitting device or between terminals of a series circuit of the semiconductor light emitting device and a resistor. Thereby, the destruction of the semiconductor light emitting element due to static electricity and surge can be prevented.

As the semiconductor light emitting element, a semiconductor laser (edge emitting LD, VCSEL (Vertical Cavity Surface)
Emitting Laser). As a result, an optical transmitter or the like using this driving method can be reduced in size and performance. Light emitting diodes (LEDs) can also be used.

In a transmission system having two or more channels, a light-emitting element driving system in which each semiconductor light-emitting element is connected to the output terminal of each transmission IC as described above may be employed.
This makes it possible to reduce the size, cost, and power consumption of the parallel optical transmission system, particularly the transmission unit of the digital monitor interface.

According to another aspect of the present invention, there is provided an optical transmitter for performing optical transmission using the above-described light emitting element driving method. This makes it possible to reduce the size, cost, and power consumption of the transmission unit of the optical transmitter.

In the optical wiring of the present invention, which achieves the above object, an input / output signal is connected by an electrical connector, and in an optical wiring using an optical fiber as a transmission line, a driving method of a semiconductor light emitting element of an optical transmission unit is used. It is characterized by using the above light emitting element driving method. As a result, it is possible to reduce the size, cost, and power consumption of the transmission unit of the optical wiring, which has the advantages of the electrical connector and the optical fiber cable.

[0017]

According to the present invention, a logic interface,
The optical transmitter can be configured without using the optical transmission module including the LD drive circuit, and the configuration of the optical transmitter is simplified.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a first embodiment of a light emitting element driving circuit according to the present invention. In FIG. 1, 101 is a PanelLink transmission IC, 102 and 103 are output transistors thereof, 104 is a constant current source, 105 is an optical transmitter side connector of an active optical wiring described later, 106 is a light emitting element LD, and 107 is a Zener diode , 108 are termination resistors. 102 to 108 constitute a component of one channel. Since PanelLink has 4 channels, there are four channels 102 to 108, but only one channel is shown in FIG. 1 to avoid complexity.

The output section of the transmission IC 101 is of a current draw type, and the load (usually a transmission line and a terminating resistor) includes a power supply and a transmission I
Connected between the outputs of C101.

The output transistors 102 and 103 have PanalLin
The differential signal generated by the encoding circuit in the k transmission IC is input, and one is turned on and the other is turned off. The current of the constant current source 104 flows through the load (LD 106 or terminating resistor 108) connected to the output transistor in the ON state.

The Zener diode 107 is mounted for protecting the LD 106. In this embodiment, the transistors 102 and 103 for driving the LD are placed outside the optical transmission unit connector 105. Therefore, when the Zener diode 107 is not provided, and when the transmitter connector 105 of the active optical wiring is not connected to the connector of the device (or circuit board), the LD 106
The anode and the cathode are open. Due to static electricity or surge when connecting / disconnecting the connector, LD106
May be broken. By attaching the Zener diode 107, this can be prevented. An appropriate Zener voltage is about 3V.

FIG. 2 is a schematic diagram of an active optical wiring.
The active optical wiring referred to here is one in which a light emitting / receiving element and associated circuits are incorporated in connectors at both ends of an optical fiber cable. Equipment (or circuit board side)
Is electrically connected to the connector in the same manner as a normal electric cable. It has the advantages of an electrical connector (easy to handle) and the advantages of an optical fiber cable (low loss, light weight, small diameter, high noise resistance, no ground potential difference problem).

In FIG. 2, reference numeral 105 denotes a transmitter connector, and reference numeral 106 denotes L
D, 201 is a transmission unit optical coupling system, 202 is a transmission unit electrical connection pin,
Reference numeral 203 denotes a receiving unit connector, 204 denotes a photodiode (also called PD), 205 denotes a receiving circuit, 206 denotes a receiving unit optical coupling system, 207 denotes a receiving unit electrical connection pin, and 208 denotes an optical fiber cable. The description of the Zener diode 107 for LD protection is omitted.

The transmitter connector 105 includes an LD 106, a transmitter optical coupling system 201, and a transmitter electrical connection pin 202. The transmission unit electrical connection pins 202 include a power supply pin and a GND pin in addition to a transmission signal pin. The transmission unit optical coupling system 201 is an LD 106
Is coupled to the optical fiber cable 208. This includes a method using a lens, a method in which one end of an LD and an optical fiber cable are closely opposed and fixed on one substrate, and the like. Since PanalLink has four channels, there are four transmission signal pins, and the LD 106 and the transmission unit optical coupling system 201 use one for each of four channels or a four-channel array. As the optical fiber cable 208, a bundle of four optical fibers called a ribbon fiber bundled is used.

The receiving unit connector 203 includes a PD 204 and a receiving circuit.
205, a receiving unit optical coupling system 206, and a receiving unit electrical connection pin 207 are provided inside. The receiving unit electrical connection pin 207 includes a power supply pin and a GND pin in addition to the transmission signal pin. The PD 204 is used in a reverse-biased state, and a current flows when an optical signal is incident. The receiving circuit 205 includes a preamplifier, a postamplifier, a comparator, a logic interface, and the like. This converts the current signal of PD204 into a voltage signal,
Amplify and output a logic-level voltage signal. The receiver optical coupling system 206 converts the light from the optical fiber cable 208 into a PD20.
Join to 4. Since PanalLink has 4 channels, there are four transmission signal pins, and the PD 204, the receiving unit optical coupling system 206, and the receiving circuit 205 use ones each for 4 channels or a 4 channel array.

In this embodiment, as shown in FIG.
LD10 between the output transistor of the ink transmission IC 101 and the power supply
Connect 6 directly. This corresponds to the output voltage level of the transmitting IC 101, the voltage V _CC2 applied to the anode of the LD 106, and L
This is made possible by matching the voltage-current characteristics of D106.

Hereinafter, an example of the matching will be described. In order to simplify the estimation, the current-voltage characteristics of the _LD 106 are expressed by the voltage drop (hereinafter referred to as V _LD ) when a forward voltage is applied to the pn junction and the element resistance R _LD above the _LD 106 of V _LD. Model as follows. Current is 0 to V _{L D} for the voltage, then the slope
_Suppose it increases at 1 / R _LD .

The output voltage level of the PanelLink transmission IC 101 is 3.3 V at the "H" (high) level and 2.8 V at the "L" (low) level. The _LD 106 has a V _LD of 1.5 V (wavelength 8
50nm band), R _LD is 80Ω VCSEL (Vertical Cavity Su
rface Emitting Lasers) and the voltage V _CC2 applied to the anode is set to 5.0 V, the L at each voltage level
The approximate value of the driving current of D106 is as follows.

I _H = (5.O-3.3-1.5) /80=2.5 mA I _L = (5.O-2.8-1.5) /80=8.8 mA If the threshold current of the LD 106 is about 2 mA, It is possible to drive with this drive circuit.

Since I _H <I _L , when the electrical signal is converted into an optical signal, the digital signal “H” and “L” are inverted, so that the output transistor 103 connected to the LD 106 has a differential output. Negative logic side of. In FIG. 1, it is assumed that this is the case.

In this embodiment, since the LD 106 is directly driven by the output transistor of the transmission IC 101 of PanelLink, no extra electric circuit is required. The configuration can be simplified, power consumption can be reduced, and cost can be reduced. Further, by using active optical wiring, it is possible to realize long-distance transmission and reduction of electromagnetic induction noise, which are features of optical transmission, while maintaining the same usability as a conventional electric cable. Further, the protection zener diode 107 can prevent the LD from being destroyed due to static electricity and surge, thereby improving the reliability of the optical wiring.

(Second Embodiment) Hereinafter, a second embodiment of the present invention will be described with reference to the drawings.

FIG. 3 is a diagram showing a second embodiment of the light emitting element drive circuit according to the present invention. The difference from FIG. 1 showing the light emitting element drive circuit of the first embodiment is that the cathode of the LD 106 is connected to a resistor 301.
To the output transistor via the

In this embodiment, a 1.3 μm band edge emitting type LD is used as the LD 106. V _LD is 0.95V, R _LD is several Ω
Degree. Assuming that the resistance of the resistor 301 is 50-R _LD and V _CC2 is 5.0 V, the drive current value of the LD 106 at each logic level is as follows.

I _H = (5.0-3.3-0.95) / 50 = 15 mA I _L = (5.0-2.8-0.95) / 50 = 25 mA If the threshold current of the LD 106 is about 13 mA, this drive circuit It is possible to drive.

In this embodiment, since the resistance value of the resistor 301 can be used for setting the drive current in addition to V _CC2 , the range of selection of a semiconductor light emitting device such as an LD is widened.

(Other Embodiments) In the above embodiment, the LD
Although V _CC2 connecting the anodes is set to 5 V, other values may be used depending on the characteristics of the semiconductor light emitting device such as an LD used. The above V _LD , R _LD , and threshold current of the _LD are merely examples, and an LD having other characteristics can be used as long as operation is not hindered.

Although the transmission IC of PanelLink has been described as a specific example, the present invention can be applied to a transmission IC in which the output unit is of a current draw type.

Although the LD is used as the semiconductor light emitting element, another semiconductor light emitting element such as an LED can be used. Although the Zener voltage of the Zener diode is set to 3 V, it is possible to use a voltage that does not hinder the operation.

As a countermeasure against the logical inversion of the digital signal in the driving circuit, the method of connecting the LD to the transistor on the negative logic side of the differential output of the transmission IC has been described. However, the logical inversion is performed in the logic interface of the receiving circuit. It is also possible.

Further, in the second embodiment, the resistor 301 is connected to the cathode side of the LD 106, but may be connected to the anode side. Also, Zener diode 107
Can be directly connected (not via the resistor 301) between the terminals of the LD 106.

[0043]

As described above, according to the present invention,
The electric transmission system can be changed to an optical fiber transmission system without using a complicated optical transmission module. Since the number of newly added components is reduced, downsizing, cost reduction, and low power consumption can be achieved. It is especially effective for PanelLink optical fiber specifications.

[Brief description of the drawings]

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

FIG. 2 is a schematic diagram of an active optical wiring according to the present invention.

FIG. 3 is a diagram showing a second embodiment of the light emitting element drive circuit according to the present invention.

FIG. 4 is a digital monitor interface PanelL.
FIG. 2 is a configuration diagram of an ink transmission system.

FIG. 5 is a configuration diagram of a conventional example of a transmission unit of the PanelLink optical transmission system.

[Explanation of symbols]

 101 Transmission IC 102, 103 Output transistor 104 Constant current source 105 Active optical wiring transmitter connector 106 LD 107 Zener diode 108 Terminating resistor 201 Transmitter optical coupling system 202 Transmitter electrical connection pin 203 Active optical wiring receiver connector 204 PD 205 Reception Circuit 206 Receiver optical coupling system 207 Receiver electrical connection pin 208 Optical fiber cable 301 Resistor 401 Conventional receiver IC 402 Differential amplifier 403, 404 Conventional terminal resistor 405-408 Twinax core 409 Twinax cable 501 Conventional example Optical transmission module 502 Conventional LD drive circuit 503 Conventional LD 504 Conventional optical coupling system 505-508 Optical connector 509-512 Optical fiber cable

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H01S 5/042 610 H04N 7/22

Claims (10)

[Claims] 1. A transmission IC having a current draw type output unit.
A cathode terminal of the semiconductor light emitting device is directly connected to the output terminal of the light emitting device to drive the semiconductor light emitting device. 2. A transmission IC having a current draw type output unit.
A cathode terminal of the semiconductor light emitting device is connected to the output terminal of the semiconductor light emitting device via a resistor, and the semiconductor light emitting device is driven. 3. A transmission IC having a current draw type output unit.
The cathode terminal of the semiconductor light emitting device is directly connected to the output terminal of, the resistor is connected to the anode terminal of the semiconductor light emitting device,
A light-emitting element driving method comprising driving the semiconductor light-emitting element. 4. A semiconductor light emitting device comprising:
4. The light emitting device driving method according to claim 1, wherein a Zener diode is connected between terminals of a series circuit of the semiconductor light emitting device and the resistor. 5. The semiconductor light emitting device according to claim 1, wherein a semiconductor laser or a light emitting diode (LED) is used.
The light-emitting element driving method according to any one of the above. 6. A light-emitting element driving method in which the light-emitting element driving method according to claim 1 is applied to a transmission system having two or more channels. 7. An optical transmitter which performs optical transmission by using the light emitting element driving method according to claim 1. 8. An electric connector for connecting input / output signals.
7. An optical wiring using an optical fiber as a transmission path, wherein a driving method of a semiconductor light emitting element of an optical transmission unit is used.
An optical wiring using the light-emitting element driving method according to any one of the above. 9. A transmission IC having a current draw type output unit.
A light emitting element driving circuit used by being connected to the output terminal of the semiconductor light emitting element, wherein the cathode terminal of the semiconductor light emitting element is directly connected to the output terminal to drive the semiconductor light emitting element. Light emitting element driving circuit. 10. A transmission I having a current draw type output.
C is a light emitting element drive circuit used by being connected to the output terminal of C, wherein the cathode terminal side of the semiconductor light emitting element is connected to the output terminal, and a resistor is connected in series with the semiconductor light emitting element. A light-emitting element driving circuit, which is configured to be driven.