FR2767994A1 - RECEIVER OF OPTICAL DATA EXCHANGED BETWEEN ELECTRONIC DEVICES - Google Patents

Abstract

The invention relates to an optical data receiver, and relates to a receiver which comprises a photodetector (1) which generates electrical pulses representative of light pulses which it receives, an intensifier circuit (4) for selectively increasing the duration. in time of the electrical pulses so that the boosted signals have a minimum predetermined duration, a pulse amplitude shift circuit (5) which creates a detection threshold based on the amplitude of electrical signals received from the photodetector (1 ), and a comparator (6) coupled to the pulse booster and pulse amplitude offset circuits (4) (5) and for creating a pulse when the boosted signals have an amplitude greater than the detection threshold. optical data exchange.

Description

The present invention relates to receivers for optical communications

  data and, in particular but not exclusively, receivers for communications

  data optics that work by pulse detection

  sions of light that represent digital data. Data can be communicated in the form of light pulses between an optical transmitter and an optical receiver. Data communication in this way provides a means of electrically isolating devices associated with a data transmitter and a receiver

of data.

  It is often necessary that a commercial electronic device produced by one manufacturer can be replaced by a device produced by another manufacturer. However,

  when data is communicated in the form of an impulse

  light ions, there may be a large variation in the duration and intensity of the light pulses produced by devices from different manufacturers. In addition, other factors can cause a significant variation in the duration and intensity of the light pulses to be detected by an optical receiver. The detection of pulses with a significant variation in width over time and intensity by an optical receiver with minimization of the complexity and cost of the optical receiver

poses a technical problem.

  The technical problem of pulse detection

  which show a significant variation in the

  time and intensity is resolved by a

  optical receiver according to the invention.

  Thus, the invention relates to an optical data receiver which comprises a photodetector which creates signals

  in the form of electrical pulses representative of

  light ions received by the photodetector, a pulse booster circuit coupled to the photodetector and intended to receive the signals in the form of electrical pulses and to selectively increase the duration over time of the electrical pulses so that the signals in the form of electrical pulses thus reinforced have a predetermined minimum length over time, a pulse amplitude offset circuit which creates a detection threshold based on the amplitude of several signals in the form of electrical pulses received from the photodetector and of a threshold predetermined offset, and a comparator coupled by a first input to the pulse booster circuit and by a second input to the pulse amplitude offset circuit and intended to create a pulse forming an output signal when the reinforced signals have a amplitude above the detection threshold. Some light pulses detected by a photodetector may have a much shorter duration than other pulses. A pulse booster can be used to increase the duration over time of these short duration pulses detected by the photodetector so that signals in the form of electrical pulses representative of the detected light pulses have

  a minimum predetermined length. In addition, the impulses

  light ions can present a significant variation in energy and therefore in intensity. The amplitude of these pulses can also vary. However, this variation takes place in the relatively long term because the amplitude of the pulses does not change during a large number of pulses. Consequently, a peak amplitude shift circuit can be used to create a threshold as a function of the average amplitude of the pulses detected by the photodetector. The change of scale of this average amplitude by a shift factor, according to a predefined level, allows the creation of a pulse detection threshold. The transmission of the elongated pulses and of the threshold to the first and to the second input of a comparator allows the optical receiver to include a means for creating pulses of data representative of the optical data without the need to use a circuit.

  relatively fast and therefore expensive comparator.

  The term "light" used in this specification refers to light from both visible and invisible spectra. The optical receiver may further include a fast recovery amplifier which is connected between the photodetector, the pulse lengthening device and the pulse amplitude shift circuit and can amplify the signals as electrical pulses

  from the photodetector. The amplifier to restore

  It can also recover quickly from a state of saturation caused by pulses.

  relatively high amplitude received from the photodetector.

  The invention also relates, in another aspect, to a method of detecting optical data pulses and of creating signals representative of these data pulses, comprising the following steps: the creation of signal pulses representative of pulses of optical data detected by an optical detector, the selective increase in the duration of the signal pulses so that each signal pulse has a predetermined minimum length over time,

  the formation of the mean of the amplitude of the pulses

  sions of the detected signals for the formation of an average amplitude, the shift of the average amplitude for the creation of a detection threshold corresponding to the pulses of the signals to be detected and the comparison of the threshold with the amplitude of pulses of the signals elongated, and the creation of an output signal representative of the

  data pulses detected based on comparison

  right. Other characteristics and advantages of the invention

  will emerge better from the description which follows

  of embodiments, made with reference to the appended drawings in which: FIG. 1 is a block diagram of a circuit for receiving optical data; FIG. 2 is a diagram of a circuit for producing a first part of the optical reception circuit of FIG. 1; and FIG. 3 is a diagram of a circuit of the second part of the optical reception circuit represented on the

figure 1.

  Infrared data association (IrDA) receiver and detector systems have become a de facto standard for data communication using optical pulses. Communication according to this standard is carried out by sending and receiving infrared pulses. The October 1995 version 1.1 of the IrDA series infrared physical layer binding specification specifies that a

  infrared pulse receiver must detect these pulses

  sions with a width between 1.4 and 20 ps and an intensity between 4 and 500,000 pW / cm2. These values correspond to data frequencies of up to 9.6 kbps. Such optical receivers must also be insensitive to stray radiation which can be received by the detector. A receiver of such infrared pulses

  must be able to create well-defined impulses representing

  tatives of each of the infrared pulses of the radiation received by the optical receiver, without variation with the width or intensity of the pulses in the ranges

mentioned above.

  An optical receiver which is intended to receive the infrared pulses according to the aforementioned specification is shown in FIG. 1. The arrangement of the block diagram of FIG. 1 corresponds to an efficient and inexpensive means of detecting the infrared pulses with operation requiring voltage. which can be as low as 3 V. Such a circuit can also work with greater energy savings than the

known optical receiver.

  In FIG. 1, a photodetector 1 is intended to receive light pulses transmitted by the line

  2, communicating with a suitable communication device

  indication such as an optical fiber. An amplifier 3 with rapid recovery is connected to the photodetector 1. An input of a pulse booster circuit 4 and a pulse amplitude shift member are connected to an output of the amplifier 3. The respective outputs of the circuits booster 4 and offset 5 are connected to a first and a second input of a comparator 6. The comparator 6 is intended to drive a conductor of

exit 8.

  In operation, pulses of infrared light are received by the photodetector 1 which creates signals in the form of electrical pulses in the conductor 10, with a duration in time and an intensity which represent the infrared pulses received. The electrical signals are transmitted by the conductor 10 to the amplifier 3. In general, the amplifier 3 provides

  amplification of signals in the form of electric pulses

  triques representative of the infrared pulses received from the photodetector 1. However, the amplifier 3 is further intended to amplify the signals of the electrical pulses with a large dynamic range. This result is obtained by incorporating, in amplifier 3 with rapid recovery, a recovery device after reception of an electrical signal pulse which has a sufficient amplitude to drive the amplifier in a state of

  saturation. Amplifier 3 can recover quickly

  ment after saturation so that a next pulse can be amplified and transmitted to the booster circuit 3 and to the

shift circuit 5.

  The amplified electrical pulses representative of the infrared light pulses are produced by the photodetector 1 and transmitted to the booster circuit 4 and to the offset circuit 5 by a conductor 10. The booster circuit 4 selectively increases the width over time of each pulse so that all the pulses presented at the output of the booster circuit have a predetermined minimum width over time. The booster circuit 4 can therefore work as an integrator with a short time constant which integrates the pulses received.

  of amplifier 3. The offset circuit 5 of amplifiers

  pulse studies also works on signals from

  electrical pulses representative of the infrared pulses

  red detected by the photodetector 1. This offset circuit 5 determines an average amplitude of several electrical pulses received. The number of pulses chosen to determine the average amplitude can be adjusted according to the operating conditions of the optical receiver and gives a relatively long-term average of the amplitude of the pulses received. The average amplitude then undergoes a change of scale by a predetermined factor so that a reference or detection threshold is created and can be used for the determination of the fact that a pulse has been detected. This detection threshold is presented at the output of the circuit 5 for shifting the average of the pulses in the form of a threshold which reaches a second input of the comparator 6. The detection threshold is therefore a function of the long-term time of the number of pulses received. A threshold transmitted to the second input of comparator 6 is therefore representative of a pulse detection decision point. Comparator 6 receives at a first input the output signal from the booster circuit 4. Consequently, if the booster circuit 4 communicates a pulse having a predetermined minimum width over time and an amplitude greater than the threshold, comparator 6 is intended to create an output pulse by the conductor 8 which has a predetermined width and amplitude which are sufficient for controlling a next stage of the electrical appliance. An assembly comprising the booster circuit 4 combined with the circuit 5 which forms the average amplitude of pulses cooperates so that fast and low amplitude pulses have a probability of detection practically identical to that of longer and larger pulses amplitude. The result of this greater probability of detection is that a less sensitive and therefore less expensive comparator 6 can be used for detecting the pulses. In addition, the optical receiver can work with components which have a relatively longer response time, so that the energy saving is considerable. Figures 2 and 3 show in circuit form an embodiment of the present invention, the parts which also appear in Figure 1 having the same numerical references. In FIG. 2, the photodetector 1 is represented as comprising a photodiode D1 and a resistor R1. Photodiode D1 is intended to work in photovoltaic mode in which it is coupled in alternating current to an amplifier and is intended to have a parallel resistance or of low value. This arrangement gives a short response time and insensitivity in practice to daylight or other radiation, without the current consumed in steady state being significant. Figure 2 also shows amplifier 3 to

  rapid response which is connected to photodetector 1.

  The amplifier 3 is formed by five transistors T1, T2, T3, T4, T5 which are intended to ensure a rapid amplification of the pulses detected by the photodetector 1 and to transmit a representation of the optical pulses in the form of electrical pulses to a conductor 20. The collectors of the transistors T1, T2, T3, T4 are connected to a positive supply voltage Vcc by resistors R2, R3, R4, R5 while the collector of the transistor T5 is connected directly to the supply Vcc. The transistors T2, T3 and T3 have emitters connected to ground via resistors R6, R7 and R8. Other resistors R9, R10 and R11 and capacitors C1, C2, C3, C4 and C5 are intended to ensure the polarization and the

  signal coupling in the amplifier 3.

  FIG. 3 represents a diagram of a compressed circuit

  nant the pulse booster circuit 4, the pulse amplitude offset circuit 5 and the comparator 6. The booster circuit 4 is shown as comprising a transistor T6 whose collector is connected to the positive supply rail Vcc and whose l he transmitter is connected by resistors R12, R13 and a capacitor C9 to a GND ground rail. The emitter of transistor T6 is coupled by capacitor C10 and resistor R14 to a negative input of a comparator 22 which forms comparator 6. The pulse amplitude shift circuit is represented as comprising a transistor T7 whose collector is connected to the positive supply rail Vcc and the transmitter is connected by a resistor R15 and a capacitor C6 to ground. The base of transistor T7 and the base of transistor T6 are connected to terminal 24 which, during use, is connected to a terminal of conductor 20 and is intended

  to receive the electrical impulses from the amplifier

  ficitor 3. A bias circuit for the booster circuit and the offset circuit 26 is shown as comprising a transistor T8 whose emitter is connected to the ground rail GND by a resistor R16 and whose collector is connected by a resistor R17 to terminal 24. A positive input of comparator 22 is connected to an output of the offset circuit 5, in the middle between the resistor R15 and the capacitor C16, by a resistor R18. Resistors R19 and R20 form in combination with the resistor R21 a set of polarization of

  the operational amplifier 22 which forms the comparator 6.

  Coupling capacitors C7, C8, Cll are also part of the circuit of FIG. 3. The comparator 22 is intended to create an output pulse of defined amplitude and width over defined time which appears at a terminal of

exit 28.

  The invention can be modified in various ways.

  For example, it can be used for the detection of any form of light pulses representative of

  data to be communicated and can also be applied to the detection

  tion of data transmitted by other types of radiation

  electromagnetic, for example signals in microwave

  quences. It is understood that the invention has only been described and shown as a preferred example and that

  may bring any technical equivalence in its elements

  constitutive elements without departing from its framework.

Claims (5)

  1. Optical data receiver, characterized in that it comprises a photodetector (1) which creates signals   in the form of electrical pulses representative of   light ions received by the photodetector (1), a   pulse booster circuit (4) coupled to the photodetector   tor (1) and intended to receive the signals in the form of electrical pulses and to selectively increase the duration in time of the electrical pulses so that the signals in the form of electrical pulses thus reinforced have a predetermined minimum length in time, a pulse amplitude offset circuit (5) which creates a detection threshold based on the amplitude of several signals in the form of electrical pulses received from the photodetector   (1) and a predetermined offset threshold, and a comparison   tor (6) coupled by a first input to the pulse booster circuit (4) and by a second input to the pulse amplitude offset circuit (5) and intended to create a pulse forming an output signal when the signals reinforced have an amplitude above the threshold detection.   2. Receiver according to claim 1, characterized in   which it further comprises an amplifier (3) with feedback   bliss connected between the photodetector (1), the pulse booster circuit (4) and the pulse amplitude offset circuit (5) and intended to amplify the signals   in the form of electrical pulses from the photo- detector (1).   3. Receiver according to claim 2, characterized in   that the amplifier (3) is an amplifier to restore   fast recovery intended to recover quickly from a condition   saturation caused by pulses of relative amplitude   tively high received from the photodetector (1).   4. Receiver according to any one of the claims   previous, characterized in that the photodetector (1)   works in photovoltaic mode and thus gives a reduction-   notable current consumption in the standby state.   5. A method of detecting optical data pulses and creating signals representative of these data pulses, characterized in that it comprises the following steps: the creation of signal pulses representative of optical data pulses detected by an optical detector, selectively increasing the duration of the signal pulses so that each signal pulse has a predetermined minimum length over time,   the formation of the mean of the amplitude of the pulses   sions of the detected signals for the formation of an average amplitude, the shift of the average amplitude for the creation of a detection threshold corresponding to the pulses of the signals to be detected and the comparison of the threshold with the amplitude of pulses of the signals elongated, and the creation of an output signal representative of the   data pulses detected based on comparison right.