Circuit arrangement and method for receiving optical signals

Abstract

In order to further develop a circuit arrangement (CR; CR′) for receiving optical signals (SI) from at least one optical guide (GU), said circuit arrangement (CR; CR′) comprising: at least one light-receiving component (PD) for converting the optical signals (SI) into electrical current signals (I.sub.PD), at least one transimpedance amplifier (TA), being provided with the electrical current signals (I.sub.PD) from the light-receiving component (PD), at least one automatic gain controller (AG) for controlling the gain or transimpedance (R) of the transimpedance amplifier (TA), at least one integrator (IN) in a feedback path (FP), said integrator (IN) generating a control signal (V.sub.int), at least one voltage-controlled current source (CS), being provided with the control signal (V.sub.int) from the integrator (IN), at least one limiter (LI) acting as a comparator and generating in its output a logic level for positive or negative voltages in its input,
and a corresponding method in such a way that a multilevel optical link can be provided, at least one second transimpedance amplifier (TA2) arranged in parallel to the transimpedance amplifier (TA), and at least one automatic offset controller (AO) for setting the voltage (V.sub.offset) for the second transimpedance amplifier (TA2)
are proposed.

Claims

1. A circuit arrangement for receiving optical signals from at least one optical guide, said circuit arrangement comprising: at least one light-receiving component for converting the optical signals into electrical current signals, at least one transimpedance amplifier, being provided with the electrical current signals from the at least one light-receiving component, at least one automatic gain controller for controlling a gain or transimpedance of the at least one transimpedance amplifier, at least one integrator in a feedback path, said at least one integrator generating a control signal, at least one voltage-controlled current source, being provided with the control signal from the at least one integrator, at least one limiter acting as a comparator and generating in its output a logic level for positive or negative voltages in its input, at least one second transimpedance amplifier arranged in parallel to the at least one transimpedance amplifier, and at least one automatic offset controller for setting a voltage for the at least one second transimpedance amplifier, wherein a short is arranged between an output node of a first stage of the at least one transimpedance amplifier and an output node of a first stage of the at least one second transimpedance amplifier.

2. The circuit arrangement according to claim 1, further comprising at least one second limiter coupled to only the at least one second transimpedance amplifier and to the at least one automatic offset controller.

3. The circuit arrangement according to claim 1, wherein the at least one second transimpedance amplifier is a copy of the at least one transimpedance amplifier, or is a scaled version of the at least one transimpedance amplifier.

4. The circuit arrangement according to claim 1, wherein the at least one automatic gain controller sets the same gain or same transimpedance for both the at least one transimpedance amplifier and the at least one second transimpedance amplifier by sensing an amplitude of an output of the at least one transimpedance amplifier.

5. The circuit arrangement according to claim 4, wherein the amplitude of the output of the at least one transimpedance amplifier is provided to an input of the at least one automatic offset controller.

6. The circuit arrangement according to claim 4, further comprising at least one peak detector circuit for sensing the amplitude of the output of the at least one transimpedance amplifier.

7. The circuit arrangement according to claim 6, wherein the amplitude of the output of the at least one transimpedance amplifier is provided to an input of the at least one automatic offset controller.

8. The circuit arrangement according to claim 6, wherein the at least one peak detector circuit is part of the automatic gain control or is shared between the at least one automatic gain controller and the at least one automatic offset controller.

9. The circuit arrangement according to claim 8, wherein the amplitude of the output of the at least one transimpedance amplifier is provided to an input of the at least one automatic offset controller.

10. The circuit arrangement according to claim 1, wherein the at least one transimpedance amplifier is at least one multi-stage amplifier.

11. The circuit arrangement according to claim 1, wherein the at least one second transimpedance amplifier is at least one multi-stage amplifier.

12. The circuit arrangement according to claim 1, wherein the at least one light-receiving component is at least one photodetector.

13. The circuit arrangement according to claim 1, wherein the at least one optical guide is at least one fibre.

14. The circuit arrangement according to claim 1, wherein an end of the at least one optical guide, which is not coupled to only the at least one light-receiving component, is coupled to only at least one light-emitting component, which is preceded by at least one driver, wherein the at least one driver and the at least one light-receiving component are for converting electrical data logic levels into the optical signals.

15. Use of at least one circuit arrangement according to claim 1 for optical transmission of data signals and of status signals comprising: optically transmitting the data signals, and optically transmitting the status signals.

16. A circuit arrangement for receiving optical signals from at least one optical guide, said circuit arrangement comprising: at least one light-receiving component for converting the optical signals into electrical current signals, at least one transimpedance amplifier, being provided with the electrical current signals from the at least one light-receiving component, at least one automatic gain controller for controlling a gain or transimpedance of the at least one transimpedance amplifier, at least one integrator in a feedback path, said at least one integrator generating a control signal, at least one voltage-controlled current source, being provided with the control signal from the at least one integrator, at least one limiter acting as a comparator and generating in its output a logic level for positive or negative voltages in its input, at least one second transimpedance amplifier arranged in parallel to the at least one transimpedance amplifier, and at least one automatic offset controller for setting a voltage for the at least one second transimpedance amplifier, wherein the at least one second transimpedance amplifier is at least one multi-stage amplifier, and wherein a short is arranged between an output node of a first stage of the at least one transimpedance amplifier and an output node of a first stage of the at least one second transimpedance amplifier.

17. A method for receiving optical signals from at least one optical guide, comprising the steps of: converting the optical signals into electrical current signals by means of at least one light-receiving component; providing the electrical current signals from the at least one light-receiving component to at least one transimpedance amplifier; controlling a gain or transimpedance of the at least one transimpedance amplifier by means of at least one automatic gain controller; generating a control signal by means of at least one integrator in a feedback path; providing the control signal from the at least one integrator to at least one voltage-controlled current source; generating in an output of at least one limiter a logic level for positive or negative voltages in its input; and setting a voltage for at least one second transimpedance amplifier by means of at least one automatic offset controller, said at least one second transimpedance amplifier being arranged in parallel to the at least one transimpedance amplifier, wherein a short is arranged between an output node of a first stage of the at least one transimpedance amplifier and an output node of a first stage of the at least one second transimpedance amplifier.

18. The method according to claim 17, wherein the gain or transimpedance of the at least one transimpedance amplifier is controlled in order to keep an amplitude of an output of the at least one transimpedance amplifier to a desired level for different levels of the electrical current signals.

19. The method according to claim 18, wherein the desired level is a constant level.

20. A method for receiving optical signals from at least one optical guide, comprising the steps of: converting the optical signals into electrical current signals by means of at least one light-receiving component; providing the electrical current signals from the at least one light-receiving component to at least one transimpedance amplifier; controlling a gain or transimpedance of the at least one transimpedance amplifier by means of at least one automatic gain controller; generating a control signal by means of at least one integrator in a feedback path; providing the control signal from the at least one integrator to at least one voltage-controlled current source; generating in an output of at least one limiter a logic level for positive or negative voltages in its input; and setting a voltage for at least one second transimpedance amplifier by means of at least one automatic offset controller, said at least one second transimpedance amplifier being arranged in parallel to the at least one transimpedance amplifier, wherein the at least one second transimpedance amplifier is at least one multi-stage amplifier, and wherein a short is arranged between an output node of a first stage of the at least one transimpedance amplifier and an output node of a first stage of the at least one second transimpedance amplifier.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) As has already been discussed hereinbefore, there are various possibilities for embodying and further developing the teaching of the present invention in an advantageous manner. For this purpose, on the one hand reference is made to the explanations above and to the dependent claims, and on the other hand further embodiments, features and advantages of the present invention are explained in greater detail hereinafter, inter alia by way of the exemplary embodiments illustrated by FIG. 3 to FIG. 5.

(2) It is shown in:

(3) FIG. 1 in a schematic diagram an example of a circuit arrangement according to the prior art operating according to the method of the prior art;

(4) FIG. 2 in a comparative diagram an example of the prior art signalling of the circuit arrangement of FIG. 1;

(5) FIG. 3 in a schematic diagram a first exemplary embodiment of a circuit arrangement according to the present invention operating according to the method of the present invention;

(6) FIG. 4 in a comparative diagram an exemplary embodiment of the signalling of the circuit arrangement of FIG. 3; and

(7) FIG. 5 in a schematic diagram a second exemplary embodiment of a circuit arrangement according to the present invention operating according to the method of the present invention.

(8) Like or similar embodiments, elements or features are provided with identical reference numerals in FIG. 1 to FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

(9) In order to avoid unnecessary repetitions, the following explanations regarding the embodiments, features and advantages of the present invention—unless specified otherwise—relate both to the first exemplary embodiment of a circuit arrangement CR shown in FIG. 3, FIG. 4 and to the second exemplary embodiment of a circuit arrangement CR′ shown in FIG. 5.

(10) A typical optical communication system (cf. FIG. 1: typical optical link; FIG. 2: typical optical link signalling) has been explained above in the chapter “Background of the present invention”. In order to avoid unnecessary repetitions, these explanations in the chapter “Background of the present invention” are incorporated by reference in the present chapter “Best mode of embodying the present invention” with regard to the present invention; in particular, the explanations in the chapter “Background of the present invention” with regard to FIG. 1 are incorporated by reference in the present chapter “Best mode of embodying the present invention” with regard to FIG. 3 and/or to FIG. 5, and the explanations in the chapter “Background of the present invention” with regard to FIG. 2 are incorporated by reference in the present chapter “Best mode of embodying the present invention” with regard to FIG. 4.

(11) According to the present invention and compared to the typical optical link as shown in FIG. 1, a signal V.sub.in-status-digital is inputted on the transmitter side. V.sub.in-status-digital is a slow signal comprising short pulses widely spaced-in-time. The transition rate of V.sub.in-status-digital is significantly low compared to the transition rate of V.sub.in-data-digital.

(12) V.sub.in-status-digital, together with the high speed signal V.sub.in-data-digital, modulates the transmitted optical signal as shown in the signal listing in FIG. 4 (=optical link signalling according to a preferred embodiment of the present invention). The optical power P.sub.2 is chosen to be higher than P.sub.1, such that the received currents I.sub.2 and I.sub.1 fulfill the relation I.sub.2≧2*I.sub.1.

(13) The second transimpedance amplifier TA2 can be a copy of the transimpedance amplifier TA, or the second transimpedance amplifier TA2 can be an exactly scaled version of the transimpedance amplifier TA. The automatic gain control block AG sets the same gain or same transimpedance R for both the transimpedance amplifier TA and the second transimpedance amplifier TA2 by sensing only the V.sub.out-data-analog amplitude with of a peak detector circuit, which can be part of the automatic gain control AG or can be shared between the automatic gain control AG and an automatic offset control AO.

(14) The automatic offset control AO sets the voltage V.sub.offset for the second transimpedance amplifier TA2; for example, V.sub.offset can be R*(I.sub.1−I.sub.0)/2. The value of V.sub.offset is independent of I.sub.2, and the information about its value is extracted only from V.sub.out-data-analog. For example, V.sub.offset=R*(I.sub.1−I.sub.0)/2 is achieved by setting V.sub.offset double the amplitude.

(15) Again the amplitude V.sub.out-data-analog can be measured with a peak detector circuit. The peak detector circuit can be part of the automatic offset control AO or can be shared between the automatic offset control AO and the automatic gain control AG. To close the feed-back loop for the V.sub.offset control, V.sub.out-status-analog is used as the feedback signal for the automatic offset control block AO because the V.sub.out-status-analog average value is −V.sub.offset. The averaging circuit is part of the automatic offset control block AO.

(16) As to the link operation, during an initial phase, only the high speed V.sub.in-data-digital signal is transmitted. The V.sub.in-status-digital signal is kept low during this phase. Also, during this initial phase, the automatic gain control AG and the automatic offset control AO outputs settle to their final value. The time constant of these two loops is significantly lower than the time distance between the two consecutive pulses on the V.sub.in-status-digital signal.

(17) Only after this first initial phase the V.sub.in-status-digital signal can be transmitted. When the V.sub.in-status-digital signal is low, the V.sub.out-data-digital signal follows the V.sub.in-data-digital signal. When the V.sub.in-status-digital signal is high, the optical power transmitted is always P.sub.2, independently of the value of the V.sub.in-data-digital signal. As a consequence, V.sub.out-data-digital will be high independently of the value of V.sub.in-data-digital. The V.sub.out-status-digital, as desired, goes high as well.

(18) As to an improvement of the signal-to-noise ratio on the receiver side, in case and the second transimpedance amplifier TA2 are multistage amplifiers, in order to improve the signal-to-noise ratio, a short between the output nodes of the first stage of the first transimpedance amplifier TA and of the first stage of the second transimpedance amplifier TA2 can be provided, as depicted in FIG. 5.

(19) Such shorting does not have any effect on the desired signal. Only the total noise power drops compared to a non-shorted version. Hence an improvement of the signal-to-noise ratio can be achieved in the receiver.

(20) By means of the above-proposed arrangement as well as method, the slow speed signal can be reliably transmitted by sharing the same physical optical link and using multilevel signalling.

LIST OF REFERENCE NUMERALS

(21) AG automatic gain controller or automatic transimpedance controller AO automatic offset controller CR circuit arrangement (=first embodiment; cf. FIG. 3) CR′ circuit arrangement (=second embodiment; cf. FIG. 5) CS current source, in particular voltage-controlled current source DR driver FP feedback path GND reference potential, in particular earth potential or ground potential or zero potential GU optical guide, in particular fibre IN integrator I.sub.DC input of current source CS I.sub.in-main input of transimpedance amplifier TA I.sub.in-rep input of second transimpedance amplifier TA2 I.sub.PD electrical current signal LD light-emitting component, in particular laser diode LI limiter, in particular first limiter LI2 second limiter PD light-receiving component, in particular photodetector, for example photodiode R gain of transimpedance amplifier TA or transimpedance of transimpedance amplifier TA SH short SI optical signal TA transimpedance amplifier, in particular first transimpedance amplifier TA2 second transimpedance amplifier V.sub.in-data-digital input, in particular data input, of driver DR V.sub.in-status-digital input, in particular status input, of driver DR V.sub.int control signal or output of integrator IN V.sub.offset voltage for second transimpedance amplifier TA2 V.sub.out-data-analog output of transimpedance amplifier TA V.sub.out-data-digital output of limiter LI V.sub.out-status-analog output of second transimpedance amplifier TA2 V.sub.out-status-digital output of second limiter LI2 1S first stage of transimpedance amplifier TA 1S2 first stage of second transimpedance amplifier TA2 2S further or second stage of transimpedance amplifier TA 2S2 further or second stage of second transimpedance amplifier TA2

(22) While this invention has been described as having a preferred design, it is understood that it is capable of further modifications, and uses and/or adaptations of the invention and following in general the principle of the invention and including such departures from the present disclosure as come within the known or customary practice in the art to which the invention pertains, and as may be applied to the central features hereinbefore set forth, and fall within the scope of the invention.