DE3233177A1 - Optically coupled rectifier element - Google Patents

Abstract

A series-connected photodiode arrangement (2) which is formed in a monolithic semiconductor chip is optically coupled to a light source constructed outside the chip, e.g. an LED (12), with the formation of an optically coupled rectifier element of high output voltage. The LED (12) is arranged adjacent to the diodes (24) but electrically isolated therefrom, and leads (26, 28) connected to the output of the diode arrangement (22) proceed from the chip and can be connected to an external load (33), so that the optically coupled rectifier element can be used in various new spheres of application. <IMAGE>

Description

OPTICALLY COUPLED DIRECTORATE

The invention relates generally to semiconductor devices, in particular an improved optically coupled directional guide.

When light hits the surface of a photodiode, the generates Diode a photoelectric voltage proportional to it at its pn junction. Photodiodes were i.a. proposed for use as an optically coupled directional guide; a Such a directional guide is used for the optical instead of the electrical coupling of two Circuits with electrical isolation of the two circuits from each other. According to z. U.S. Patents 4,160,308, 4,056,719, 4,114,177, 4,124,860, 4,112,308, 4,040 078 and 4 122 479, an optically coupled directional guide typically comprises a light emitting one Element, e.g. B. an LED, as well as a photodiode or some other light-sensitive Semiconductor device. Both known optically coupled directional ladders according to the cited patents, both the Light source and light sensor housed. Typical light sensors used in the known optically coupled directional conductors are used, for. B. a Phototransistor, a photo darlington circuit and a photodiode.

The photo transistor or the photo darlington pair both work so that the light hitting them turns the device on so that it conducts electricity will. The driving force for this current is an external voltage supply. the Photodiode can be operated in reverse direction, whereby the input light the diode residual current increased to a significant level. The driving force for this current is again an external power supply.

The photodiode can also be operated in the forward direction, with the ring input light generates a forward bias voltage by photoelectric means, which results in a generated current and voltage. With this photoelectric Arrangement, no external power supply is required. The effect of light alone is sufficient for self-actuation of the forward-biased diode.

For certain applications in electronic circuits the light-generated electricity is of interest, while at <ierer # application m # '# g 1 the light-generated voltage is of primary circuit interest. A The fundamental disadvantage, however, is that a single photodiode only takes approx. 0.5V can produce what for typical circuit requirements, at which approx. 5.0 V are required, is completely inadequate.

A photodiode array can be used as a component of an optical relay that works in the same way as a mechanical relay, i.e. a Exercises switching function based on an input or control signal. An optical one Relay of this type is disclosed in US Pat. No. 4,227,098, an LED being optically with a photodiode array is coupled, the output of which is internal and without external Access is connected to the gate of a MOSFET. In doing so, the photodiode array generates a voltage due to the incident radiation emanating from the LED, so that as a result of the internal connection with the gate of the FET, the latter becomes live.

The from a photodiode in a photodiode array is due to incident The amount of light-electrical current produced by light radiation is related to the Intensitac of the light energy hitting the photodiodes. The intensity of the the light received by the individual diodes of the arrangement changes in turn depending on the position of the diode in relation to the light source. In a multiple diode arrangement determines the diode that receives the least amount of incident light, the output stream of the gas office arrangement. As the furthest away from the light source The diode receives the least amount of radiation, is due to the conventional superimposed and side-by-side arrangement of the LED in relation to the photodiodes the size of the photodiode arrangement, those with a single source of radiation to produce a desired level of photocurrent can be used, essentially limited.

In general, photodiodes have been known for many years, but theirs Coupling, their limited current and voltage output, and other factors have hitherto been the case the possible applications for an advantageous use of the photodiodes are limited.

The object of the invention is to provide an optically coupled Director who can be used for functions not previously suspected; should a photodiode array can be specified, which at a certain intensity of the emitted light radiation generate an increased voltage and an increased current can; furthermore, in the case of the optically coupled directional guide, between an input and an output electrical isolation can be achieved, and an output voltage should be achieved which is a linear function of the current applied to the input, within a range of several V or more; furthermore should the optically Coupled directional conductors can generate a voltage that corresponds to the ambient temperature is proportional; furthermore, a photodiode array is to be specified which generates a capacitance at an external output which is a function of a light input signal is; in addition, the photodiode array should have a higher luminous flux level at a can generate a certain intensity of the emitted light radiation.

According to the invention, an optically coupled device is used to solve this problem Directional guide provided with a photodiode array residing in a common substrate is arranged, on which there is an LED. According to one aspect of the invention the light receiving part is not a single one photosensitive Diode, but a monolithic chip that contains a number of photodiodes connected in series contains in an arrangement. In contrast to the prior art, the Output of the diode array connected leads led out of the chip, so that the output of the arrangement can be connected to an external consumer, This results in previously unimaginable application possibilities for the arrangement result.

According to a further aspect of the invention, the series-connected Photodiode array arranged in the chip so that it surrounds the LED, the LED on a central area of the substrate in which the photodiodes are formed, is located close to the photodiodes but electrically isolated with respect to them; this is an optimal current diffraction from the photodiode array at a certain LED Uihd achieved a certain LED current magnitude.

The photodiode arrangement can be explained together with the LED in FIG Ways to be used to generate an output that is electrical from the input isolated and linearly related to the input current applied to the LED stands. Further possible uses of the new optically coupled directional guide arise in the form of a device that generates an output voltage that is too the ambient temperature is related, as well as a semiconductor capacitor whose Value is directly related to the input current applied to the LED. at Another possible application can be the output voltage or the output current the photodiode array to the control terminal of a switching unit, for. B. a FET or a silicon controlled one Rectifier, are applied, which is switched so that high-speed operation can be achieved.

The invention is explained in more detail, for example, with the aid of the drawing. 1 shows a schematic diagram of an optically coupled directional guide with the features of the invention; Fig. 2 is a plan view of the photodiode array and the light-emitting diode of the optically coupled directional conductor according to FIG. 1; Fig. 3 a Sectional view 3-3 of FIG. 2; and FIG. 4 is a schematic circuit diagram of the optical coupled directional conductor and the photodiode array according to the invention, wherein the Output of the arrangement is connected to a switching FET.

Referring to Fig. 1, the optically coupled directional guide according to the invention comprises an LED 12, which has a cathode 14 and an anode 16, which has two inputs 18 and 20 are connected. One of a plurality of series-connected photodiodes 24, which are formed in a monolithic silicon chip 25, existing arrangement 22 is connected between two electrodes 26 and 28 and optically with the LED 12 coupled and receives light radiation 29 generated by the LED due to a to the Inputs 18 and 20 applied input current is generated. The electrode 26 is with the anode of a photodiode at one end of the assembly and the electrode 28 connected to the cathode of a photodiode at the other end of the array.

The chip 25 and the LED 12 are arranged in a common housing 27. Outside the housing 27, two external output connections 30 and 32 are provided. The external connections are - in contrast to the completely internal connections to the diode arrangement of the device according to the aforementioned US-PS 4 227 098 - connected to electrodes 26 and 28, respectively, which are in chip 25 and the housing 27 are included. This arrangement of the output connections outside of the chip and the photodiode array makes it possible that of the photodiode array generated signal processed outside the chip and thus for one or more previously not suspected applications can be used, and also enables the connection of the output of the arrangement to a Verbraucb-r 33, z. B. a tension or current-sensitive device according to FIG. 1 between the two external Output terminals 30 and 32 can be switched.

In operation, applying a sufficiently large current causes between the inputs 18 and 20 that the LED 12 emits radiation 29, which on the photodiode array 22 hits. The series-connected photodiode arrangement generates due to this radiation 22 a voltage at electrodes 26 and 28, which is the sum of the individual voltages (typically 0.5 V) generated in each photodiode 24. The resulting Output voltage thus generated between electrodes 26 and 28 is a multiple of the number of photodiodes in the arrangement 22 and is independent of any external power supply. This output voltage is at the Output connections 30 and 32 and thus removable from the consumer 33.

In the known optically coupled directional guide according to the initially the patents referenced, the LED is typically on the side or above of the photodiodes positioned so that a large part of the emitted by the LED Light does not reach the photodiodes due to the reflection.

Furthermore, the photodiodes furthest away from the LED receive the least light, and the photocurrent generated by the photodiode array, the is applied to the circuit or control component is thus limited.

In one embodiment of the specified optically coupled Directional conductor, an increased photocurrent is generated due to the photodiode arrangement the arrangement of the LED in relation to the photodiode arrangement 22. Here are according to the FIGS. 2 and 3 show the photodiodes 24 in a common polycrystalline silicon substrate 34 is formed, and the LED 12 is positioned in the middle of the diode array, so that the photodiodes surround the LED. The individual diodes of the arrangement are over connecting conductor tracks 36 connected in series, the conductor tracks each having the The cathode of a photodiode connects to the anode of the following photodiode in the arrangement. 3, each photodiode 24 of the array is in one formed in substrate 34 Well or trough 38 is formed. Each photodiode is opposite to substrate 34 and the remaining photodiodes of the arrangement isolated by a layer or pocket 40 of silicon dioxide surrounding each well 38 and to the surface of the substrate runs.

Referring to Figure 3, the LED 12 is electrically on an aluminum film 42 conductive epoxy 44 secured. The aluminum film 42 is over a central portion attached to the surface of the substrate and is separate from the substrate and this opposite insulated by an oxide film 46 overlying part of the adjacent surrounding photodiodes 24 and the upper portions of the insulating oxide film 40 of these diodes. The input leads 18 and 20 to the LED t2 are with the surface of the LED or the aluminum film 42 and thus with the connections connected to the LED. The two photodiodes according to FIG. 3 also include a central one n + region 48, which is surrounded by a p - region 50, which is a pn photo junction forms with the n-conductive material of the trough 38. The LED 12 is above one inactive tub in which no photoelectric response takes place.

Due to the placement of the LED 12 with respect to the photodiode array 22 according to FIGS. 2 and 3, an increased amount of the photodiodes of the activated LED received emitted light, so that compared with the conventional Arrangement of the LED and the photodiodes an increase in the light-generated electricity (Isc) results, which is generated by the arrangement with a certain amount of LED current. There are at least two reasons for this.

First, it has been found that most of the light is from an LED emitted light usually emanates from the edges or side surfaces of the LED and is not directed downwards. Therefore, the arrangement of the LED and of the photodiodes according to FIGS. 2 and 3, the light-emitting edges or surfaces of the LED in optical proximity to the photodiodes, and only a very small one Amount of light is lost through reflection.

Second, the spacing becomes greater than the conventional arrangement between the LED and the most distant photodiode of the array is reduced, so that assuming that all conditions remain constant, from the on The most distant photodiode generates a higher photocurrent. With the LED photodiode arrangement Experiments carried out according to FIGS. 2 and 3 have shown that compared to one Side-by-side arrangement with the same LED and with the same LED activation cycle about four times as much photocurrent is generated.

As already mentioned, the optically coupled directional guide shows of the invention by connecting external leads 30 and 32 to the output electrodes 26 or 28 additional advantageous and previously unrealized properties in In contrast to the known arrangement, in which the access to the output of the diode arrangement to an external measuring device on the one hand was hardly practicable and otherwise was probably not considered either.

A new area of application for the optically coupled directional guide is based on the finding that the photodiode array has an output voltage generated at the electrodes 26 and 28 and thus at the external leads 30 and 32, which is directly linearly proportional to the input current applied to LED 12, and within a significant range of input currents, typically between 10 and 50 mA. Attempts with a 16-diode arrangement in Series connection have shown that over an output range between 1.0 V and 5.0 V a linearity between the input current and the output voltage of 0.1% can be achieved. The voltage range within which this linearity can be easily expanded by adding more on the chip Series-connected photodiodes are formed. Furthermore, in addition to the direct Linearity to the input current of the output circuit also compared to the input circuit electrically isolated. An advantageous application for such a visual coupled directional conductor for which a known input current value is a precisely predictable one Output voltage generated, and also input and output electrical are isolated, results as an input circuit to an isolation amplifier circuit.

Another new application for the FotodXode and LED array according to the invention, which is due to the external connection of the supply lines of the Diouen arrangement results, is as a semiconductor capacitor, which on the external leads 30 and 32 is obtained. The value of the capacitance CT for N identical series-connected Diodes each with a capacitance value C is: CT C cT = C / N.

It has been found that when the series-connected photodiode array is irradiated according to the invention by an LED the capacitance of the photodiode array changes significantly as a function of LED lighting, which in turn changes the input current applied to the LED is proportional. With the optically coupled Tests carried out by directional guides resulted in a change in the value applied to the LED Input current from 15 mA to 65 mA in a capacity on the external supply lines 30 and 32, which was less than 10% of its starting value, i.e. i.e., the capacity at the diode output changed from 150 pF to 10 pF. In other words it was due to a 4: change in the input current to the LED and a change in the input voltage of approx. 1 V applied to the LED achieves a 15: 1 capacity range.

A correspondingly arranged LED enables this application in connection with the diode arrangement explained, the fine-tuning of the capacitance within a wide range of values, and further has the added benefit of electrical isolation between input and output achieved. The total capacity range, which is achievable can be achieved by adding more series-connected photodiodes can be increased. Such an optically isolated one having four connections Semiconductor capacitor device with a capacitance tuning range of 15: 1 or larger can be used advantageously in many ways, e.g. B. in a television channel selector, the channel selection by changing the light output of an LED as a result of a change the input current and then directing the LED output to the photodiode array can be done.

Another field of application of the photodiode array according to the invention results as a precision temperature sensor, being the essentially constant temperature coefficient of the voltage drop in the forward direction at pn transition of a photodiode within a temperature range between -50 0C and 150 0C is used within a current interval. A typical temperature coefficient a single photodiode within this temperature range is approx -2.0 mV / OC. In the case of a series-connected multiple photodiode arrangement with 16 series-connected For photodiodes, the voltage-temperature coefficient would be 16 times this value or -32.0 mV / OC.

For example, a voltmeter or a voltage-sensitive circuit provides connected as a consumer 33 between the external leads 30 and 32 and in 0C or the like.

is calibrated, an accurate and direct temperature display.

E.g. a photodiode array of 50 diodes connected in series produces corresponding to each other by means of the dielectric silicon dioxide insulation of the manner explained with reference to FIGS. 2 and 3, one Change of 0.1 V per Oc when the arrangement is at a constant forward current level is biased in the forward direction. It should be noted that with this temperature sensor no LED needs to be used; if this is the case, changes the light generated voltage also with the temperature.

Another possible application for the optically coupled directional guide or the photodiode array according to the invention is shown in Fig. 4, wherein the Output voltage of the photodiode arrangement at the electrode 26 and the lead 30 to the input of a switching element in the form of a Field effect transistor or FET 52 is connected. The source and drain electrodes of FET 52 are in turn connected to output electrodes 54 and 56, respectively. The FET is preferred 52 an enhancement n-channel FET. A depletion FET 58 or resistor can be in the manner shown as a resistance element to the output of the photodiode array and connected in parallel to the gate of FET 52.

In operation, by applying a sufficiently high current between the inputs 18 and 20 causes the LED 12 to emit radiation 30 which is directed to the Photodiode array 22 impinges. Generated due to this incident radiation the series-connected photodiode arrangement 22 applies a voltage to the electrodes 26 and 28, which corresponds to the sum of the voltage generated in each photodiode. the The voltage thus generated between electrodes 26 and 28 is passed through the external leads 30 and 32 are applied to the gate and source of FET 52 so that between Source and drain of the FET power conduction takes place when the gate voltage is one has a sufficiently high level. In the absence of current flow between the inputs 18 and 20 no radiation is generated by the LED, so that at the diode arrangement 22 no voltage is generated. As a result, the FET 52 is rendered non-conductive, and the impedance appearing at its outputs 54 and 56 is high. The FET or Resistor 58, connected in parallel with the gate of FET 52, serves as a discharge path for the gate of the control FET 52 so that the control transistor is turned off very quickly is when the LED 12 no longer generates radiation, i.e. when at the inputs 18 and 20 no more current is applied and the photodiode array as a result none Control voltage at the gate of the FET 52 generated more.

Thus, it can be seen that the present invention provides an improved optically coupled directional conductor with high output voltage is created, the due to the new arrangement of the external leads connected to the output of the diode array are coupled, the use of the arrangement as an optically coupled driver for a FET switch or a silicon controlled rectifier, a temperature sensor, enables a linear voltage-current isolator and a photo-changeable capacitor.

The optically coupled directional guide according to the invention thus has the new properties discussed above and summarized below: 1. Output voltages well above 5.0 V can be achieved.

2. There will be an extremely linear relationship between output voltage and input (LED) current with less than 0.1% linearity deviation.

3. It is a much higher temperature sensitivity due to the multiple effect of the temperature coefficient per diode, multiplied by the Number of diodes in the series connection, achieved. This effect can serve that To modulate the output voltage of the optically coupled directional conductor, or the series-connected If there is no LED input, the photodiode array can be externally switched to a forward mode are driven and have a temperature coefficient of the same size.

4. The capacitance of the diode array is against changes in the Highly sensitive input (LED) light. So by changing the input or LED current has a strong modulation of the output capacitance, which opens up many possible uses as a semiconductor capacitor, e.g. B. in RF channel selector circuits, eryeben.

It goes without saying that the possible uses explained above the photodiode arrangement is not a restriction.

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Claims (13)

P a t e n t a n s p r ü c h e Optically coupled directional guide, g e k e n n n z e i c h n e t d u r c h - one input (18, 20), - one with the input connected light source (12) which can be activated by a signal applied to the input - a semiconductor substrate (25) adjoining the light source (12), - a series-connected photodiode array (22) formed in the substrate (25), and - Two output electrodes connected to the output of the photodiode arrangement (22) (26, 28, 30, 32) which extend outward from the substrate (25) for connection to a voltage sensitive device (33) so that the output electrodes (26, 28, 30, 32) occurring voltage to the signal applied to the input in Relationship stands. 2. Optically coupled directional conductor according to claim 1, characterized in that that the light source is an LED (12) which is placed on a central area of the substrate (25) is arranged and surrounded by the photodiodes (24). 3. Optically coupled directional guide according to claim 2, characterized by - a first insulation (40) which electrically separates the photodiodes (24) from one another insulates, and - a second insulation (46) that separates the LED (12) from the substrate (34) and the photodiodes (24) electrically isolated. 4. Optically coupled directional guide according to claim 3, characterized in that - That each photodiode (24) is formed in one in the surface of the substrate (34) Trough (38) is shaped, - that the first insulation is a plurality of oxide films (40) which surround each well (38) and extend to the surface of the substrate (34), and - that the second insulation is an oxide layer (46) which is between the LED (12) and the surface of the substrate (34) is arranged and extends over a part at least one of the plurality of oxide films (40) extends. 5. Optically coupled directional guide according to claim 1, characterized by a switching device (52) with one of the output electrodes (26, 28, 30, 32) connected control element. 6. Semiconductor temperature sensor with a substrate made of semiconductor material, marked by a plurality of series-connected ones formed in the substrate (34) Photodiodes (24), - two electrically connected to the output of the photodiode arrangement (22) Electrodes (26, 28) extending outwardly from the substrate (34), and - one Voltmeter, calibrated in temperature units, attached to the outer electrodes (26, 28) is electrically connected. 7. Temperature sensor according to claim 6, characterized by an in optical proximity of the photodiodes (24) arranged LED (12). 8. Semiconductor capacitor with a substrate, characterized by - A plurality of series-connected photodiodes formed in the substrate (34) (24) and - two electrically connected to the output of the photodiode array (22) Electrodes (26, 28), which run outside of the substrate (34), so that the capacitance between the electrodes is proportional to the light emitted by the light source (12) is. 9. Semiconductor capacitor according to claim 8, characterized in that that the light source is an LED (12) in a central area of the substrate (34) is arranged and surrounded by the photodiodes (24). 10. Semiconductor capacitor according to Claim 9, characterized by - a first insulation (40) which electrically isolates the photodiodes (24) from one another, and - a second insulation (46) which separates the LED (12) from the substrate (34) and electrically isolating the photodiodes (24). 11. Semiconductor capacitor according to claim 9, characterized in that - That each photodiode (24) is formed in one in the surface of the substrate (34) Trough (38) is shaped, - that the first insulation is a plurality of oxide films (40) which enclose each well (38) and extend to the surface of the substrate (34), and - that the second insulation is an oxide layer (46) which is between the LED (12) and the surface of the substrate (34) lies and extends over a part at least one of the plurality of oxide films (40) extends. 12. Optically coupled semiconductor directional guide with a substrate of semiconductor material, characterized by - an arrangement (22) in the substrate (34) molded series-connected photodiodes (24), - one on or near the substrate (34) arranged LED (12), which is surrounded by the photodiodes (24) and these are optical is adjacent, - a first insulation (40), which the photodiodes (24) electrically insulated from each other, and - a second insulation (46) that opposes the LED (12) to the Electrically isolated substrate (34) and the photodiodes (24). 13. Optically coupled semiconductor directional conductor according to claim 12, characterized characterized in that each photodiode (24) is in one in the surface of the substrate (34) formed trough (38) is formed, - that the first insulation a plurality Oxide films (40) surrounding each well (38) and to the surface of the substrate (34) run, and - that the second insulation is an oxide layer (46) between the LED (12) and the surface of the substrate (34) lies and extends over a part at least one of the plurality of oxide films (40) extends.