JP4620509B2 - Optical receiver - Google Patents

Description

  The present invention relates to an optical receiver that receives an optical signal transmitted from an optical transmitter through an optical fiber cable, for example, in an apartment house or a general subscriber's house in a CATV system.

  Conventionally, in a CATV system, an optical fiber cable is generally used for a trunk line connected to a head end device, and the optical fiber cable and a system subscriber are connected by a coaxial cable. That is, a signal is transmitted by a high-speed optical fiber cable on the trunk line, and a signal is transmitted by a coaxial cable between the trunk line and the system subscriber's house.

  However, in recent years, CATV systems have been used to transmit terrestrial digital TV broadcasts in addition to analog TV broadcasts and satellite broadcasts, and also to transmit information such as the Internet, which requires large capacity and high speed transmission. The number of subscribers who use the high-speed transmission function is increasing. For this reason, recently, a system using an FTTF (Fiber to the Home) system in which an optical fiber cable is drawn into an individual subscriber's house and all transmission lines are completely converted into optical fibers has been considered. (For example, refer to Patent Document 1).

  FIG. 8 shows an example in which the optical signal output from the optical transmitter 11 is transmitted to the optical receiver 13 through the optical fiber cable 12 in the system using the FTTH system as described above. The optical transmitter 11 converts an input electrical signal into an optical signal and transmits the optical signal to the optical receiver 13 through the optical fiber cable 12. The optical receiver 13 converts the input optical signal into an electrical signal, adjusts the signal to a constant level by an automatic gain adjustment circuit (AGC circuit), and outputs the signal.

In this case, if the input level of the optical signal input to the optical receiver 13 is too low, the TV image may be disturbed or not displayed due to noise, and if the input level of the optical signal is too high, the TV image may be disturbed or not displayed. That is, the optical receiver 13 has an appropriate range of the optical input level. When an optical signal is input within an appropriate range, the optical receiver 13 converts the optical signal into an electrical signal, and outputs the electrical signal at a constant level by a gain adjustment amplifier circuit.
US Pat. No. 5,841,563

  As described above, the optical receiver 13 converts the optical signal sent by the optical fiber cable 12 into an electrical signal, and outputs it at a constant level by the automatic gain adjustment circuit. Operates in conjunction with the input level. The appropriate range of the input level of the optical signal varies depending on the level increase / decrease of the electric signal (TV signal) input to the optical transmitter 11. For example, when the level of the electric signal input to the optical transmitter 11 is increased, the optical input level on the optical receiver 13 side is decreased, and the appropriate range of the optical input level moves in the lower level direction.

  Usually, after determining the input level of the electrical signal of the optical transmitter 11, the optical input level of the optical receiver 13 is determined, and an automatic gain adjustment circuit specialized for this optical input level or lighting for displaying an appropriate optical input level. A circuit is determined. Therefore, when the input level of the electrical signal to the optical transmitter 11 is changed later, the optical receiver 13 specialized for the predetermined optical input level cannot be used as it is, and a new appropriate optical input level range is set. It must be replaced with another suitable optical receiver.

  As described above, since the conventional optical receiver 13 cannot cope with the movement of the appropriate optical input level range when the input level of the electrical signal to the optical transmitter 11 is changed, it is suitable for a new appropriate optical input level range. There is a problem that the installation cost becomes very expensive because it must be replaced with another one.

  The present invention has been made to solve the above-described problems. Even when the input level of an electric signal to the optical transmitter is changed, the present invention can be easily adapted to a new appropriate optical input level range and can reduce the installation cost. An object is to provide an optical receiver.

According to a first aspect of the present invention , a plurality of optical signal input levels to an optical transmitter are set according to an operation mode, and an appropriate input level range corresponding to each of the plurality of electric signal input levels to the optical transmitter is different. In the machine
A photoelectric conversion element that converts an optical input signal input to the optical receiver into an electrical signal, a resistance element for electrical signal extraction connected in series to the photoelectric conversion element, and a high-frequency component generated at both ends of the resistance element First signal extracting means for extracting the signal, second signal extracting means for extracting the received light voltage of the photoelectric conversion element generated as a DC voltage at both ends of the resistance element, and the high-frequency component extracted by the first signal extracting means A gain adjusting amplifier circuit that adjusts and outputs the level of the signal, a signal level detecting means for detecting the level of the received light voltage of the photoelectric conversion element extracted by the second signal extracting means, and a signal of the signal level detecting means detection level is more set corresponding to the proper input level range of the optical receiver, the electrical signal input level of the signal detection level set plurality of the said optical transmitter A detection level switching means for switching a plurality of stages to a value corresponding to the value, sets the signal output level of the gain adjustment amplifier circuit to a certain appropriate level in accordance with the signal level detected by said signal level detecting means Gain adjusting means.

According to a second invention , in the optical receiver according to the first invention, a plurality of light emitting elements for displaying an input state of an optical input signal to the optical receiver, and a signal level detected by the signal level detecting means are And a light emitting element driving means for driving the plurality of light emitting elements so as to indicate whether or not each signal detection level switched by the detection level switching means is within an appropriate input level range .

  According to the present invention, there is provided signal level detection means for detecting the level of the electric signal converted by the photoelectric conversion element, and level setting means for switching and setting the signal detection level of the signal level detection means in a plurality of stages. It is possible to cope with multiple operation levels, and when the operation level is changed while the system is in operation, there is no need to replace the optical receiver with a new one. It becomes possible to reduce the number of receiver models.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic system configuration diagram when the present invention is implemented in a CATV system. In FIG. 1, reference numeral 20 denotes a head-end device, for example, a TV receiving antenna 21 that receives TV broadcast radio waves in the VHF band and UHF band, and satellites such as BS (Broadcasting Satellite) and CS (Communications Satellite). A satellite broadcast receiving antenna 22 for receiving broadcasts is provided. The signal received by the TV receiving antenna 21 and the signal received by the satellite broadcasting receiving antenna 22 and converted into an intermediate frequency signal (IF) by a converter (not shown) are input to the retransmission head end 23. The The retransmission head end 23 converts the TV broadcast signal received by the TV receiving antenna 21 into a predetermined frequency in the CATV frequency band of 70 to 770 MHz, and also converts the TV broadcast signal by the converter of the satellite broadcast receiving antenna 22. The satellite broadcast signal converted into the intermediate frequency signal (IF) is converted into a predetermined frequency in a band of 1000 to 2610 MHz, for example, and output.

  The TV signal output from the retransmission head end 23 is input to the optical transmitter 24 at a signal level set in advance according to the operation mode. The optical transmitter 24 converts a TV signal (electric signal) output from the retransmission head end 23 into an optical signal having a wavelength of 1.55 μm, for example, and inputs the optical signal to a WDM (Wavelength Division Multiplexing) multiplexer 25.

  The head end device 20 is provided with an optical transmission terminal 26. The optical transmission terminal 26 is connected between the WDM multiplexer 25 and an external optical network 27. For example, the optical transmission terminal 26 uses a wavelength of 1.49 [mu] m for the downstream signal and 1.31 [mu] m for the upstream signal. To do.

  The WDM multiplexer 25 includes a 1.55 μm optical signal (video signal) from the optical transmitter 24 and 1.49 μm (downstream) and 1.31 μm (upstream) optical signals (communication) used by the optical transmission terminal 26. Signal) is wavelength division multiplexed and output to the optical fiber cable 31. The optical fiber cable 31 is laid between the head end device 20 and the subscriber's home 40, and is branched into a plurality by a splitter 32 provided in the middle thereof.

  The optical fiber cable 31 is connected to the termination box 41 in the subscriber's home 40. The termination box 41 is connected to a WDM filter 42 provided in the subscriber's home 40. The WDM filter 42 selects a 1.49 μm optical signal (downlink signal for communication) from among the multiplexed signals transmitted by the optical fiber cable 31 and inputs the selected signal to the communication optical terminal 43. The output 1.31 μm optical signal (uplink signal for communication) is selected and output to the optical fiber cable 31. The WDM filter 42 selects a 1.55 μm TV signal from among the multiplexed signals transmitted by the optical fiber cable 31 and inputs the selected TV signal to an optical receiver (V-ONU: Video Optical Network Unit) 45.

  A terminal device such as a personal computer (PC) 44 is connected to the communication optical terminal 43. The communication optical terminal 43 converts a downstream optical signal input from the optical fiber cable 31 via the WDM filter 42 into an electrical signal, inputs the electrical signal to the personal computer 44, and outputs an upstream signal output from the personal computer 44. The electrical signal is converted into an optical signal and output to the optical fiber cable 31 via the WDM filter 42. The personal computer 44 uses the downstream signal (1.49 μm optical signal) and the upstream signal (1.31 μm optical signal) transmitted by the optical fiber cable 31, for example, to perform communication via the Internet.

A TV receiver 46 is connected to the optical receiver 45. The TV receiver 46 has a reception function for analog TV broadcast, digital TV broadcast, satellite broadcast, and the like. The optical receiver 45 has a reception function of an optical wavelength of 1.55 μm, for example, and receives received optical signals at frequencies of 70 to 770 MHz for CATV and 1000 to 2610 MHz for CS / BS-IF (satellite broadcasting), for example. A function of converting into an electrical signal of a band is provided, and the converted electrical signal is amplified and output to the TV receiver 46. The optical receiver 45 has a function of switching the appropriate optical input level range with a switch in accordance with the operation level, and details thereof will be described later.

FIG. 2 is a basic circuit configuration diagram of the optical receiver 45. In FIG. 2, 51 is a photoelectric conversion element using a photodiode, for example, which is connected to the output end of the WDM filter 42 via an optical fiber, and converts the optical signal selected by the WDM filter 42 into an electrical signal. In the photoelectric conversion element 51, the power supply voltage Vcc is supplied to the cathode, and the anode is grounded via the resistor 52. Since a reverse bias voltage is applied to the photoelectric conversion element 51 by the power supply voltage Vcc, when an optical signal is input, a current flows according to the strength of the photoelectric conversion element 51 and a voltage V ₀ is generated across the resistor 52. . The voltage V ₀ generated in the resistor 52 is composed of a direct current component and a high frequency component. The voltage V ₀ generated across the resistor 52 is input to the photoelectric control circuit 54 and also to the gain adjustment amplifier circuit 56.

The photoelectric control circuit 54 is provided with a changeover switch 55 for switching the operation level according to the operation level. The photoelectric control circuit 54 detects the DC voltage of the voltage V ₀ generated at both ends of the resistor 52 at the operation level set by the changeover switch 55, that is, the received light voltage (DC component) in the photoelectric conversion element 51, and the operation level. Is output to the gain adjustment amplifier circuit 56.

  The photoelectric control circuit 54 is connected to light emitting elements for detecting the level of the optical input signal, for example, light emitting diodes LED1 and LED2. The light-emitting diode LED1 is for informing the over-input state of the optical signal to the photoelectric conversion element 51, and the light-emitting diode LED2 is for informing the state that the optical signal to the photoelectric conversion element 51 is input at an appropriate level or higher. Is.

The gain adjustment amplification circuit 56 is an amplification circuit that extracts and amplifies a high-frequency component of the voltage V ₀ generated at both ends of the resistor 52. The gain adjustment amplification circuit 56 adjusts the gain according to a control signal supplied from the photoelectric control circuit 54, and always maintains a constant level. The signal is output. The output signal of the gain adjustment amplification circuit 56 is sent from the signal output terminal 57 to the TV receiver 46.

  As described above, the optical receiver 45 switches the change-over switch 55 of the photoelectric control circuit 54 in accordance with the operation state of the optical transmitter 24 provided in the head end device 20 of FIG. Even when the operation mode is changed, the gain adjustment amplification circuit 56 is configured to always output a high-frequency signal at a constant level.

  FIG. 3 shows a setting example when the optical receiver 45 is made to correspond to two patterns of operation levels. In this example, it is assumed that the electric signal input level to the optical transmitter 24 is 70 dBμV (operation 1) and 80 dBμV (operation 2). The optical receiver 45 switches between operation 1 and operation 2 by the changeover switch 55 according to the electric signal input level to the optical transmitter 24.

  When the optical receiver 45 is switched to operation 1 by the changeover switch 55, the appropriate optical input level range is “−5 to 0 dBm”, and the electrical signal output level of the gain adjustment amplification circuit 56 is “80 dBμV”.

  When the optical receiver 45 is switched to operation 2 by the changeover switch 55, the appropriate optical input level range is “−8 to −3 dBm”, and the electric signal output level of the gain adjustment amplification circuit 56 at that time is “80 dBμV”. Is.

  As described above, even when the operation level of the optical transmitter 24, that is, the electric signal input level to the optical transmitter 24 is changed, the operation of the optical receiver 45 is switched by the changeover switch 55, whereby the gain adjustment amplification circuit The 56 electric signal output levels can be kept constant. For example, when the operation level of the system is set to “operation 1” and the electric signal input level to the optical transmitter 24 is “70 dBμV”, the appropriate optical input level range to the optical receiver 45 is “−5 to 0 dBmW”. It has become. In this case, the electric signal output level of the gain adjustment amplification circuit 56 is “80 dBμV”.

  When the operation level of the optical transmitter 24 is set to “operation 2” and the electric signal input level to the optical transmitter 24 is set to “80 dBμV” in the above state, the optical input level range to the optical receiver 45 is lower. Moving. At this time, when the operation level of the optical receiver 45 is switched to “operation 2” by the changeover switch 55, the appropriate optical input level range to the optical receiver 45 becomes “−8 to −3 dBm” and the light to the optical receiver 45 is lighted. Even when the input level is lowered, the electric signal output level of the gain adjustment amplification circuit 56 can be kept at “80 dBμV” which is the same as “operation 1”.

  As described above, since the optical receiver 45 can cope with a plurality of operation levels by switching the changeover switch 55, there is no need to newly replace the optical receiver 45 when changing the operation level during operation of the system. This can be done by simply switching 55, and the installation cost can be reduced. Further, by making the optical receiver 45 compatible with a plurality of operation levels by the changeover switch 55, the number of models can be reduced when manufacturing the optical receiver 45.

FIG. 4 is a detailed circuit configuration diagram of the optical receiver 45.
In FIG. 4, a photoelectric conversion element 51 converts an optical signal (TV signal) sent from the WDM filter 42 through an optical fiber as described above into an electrical signal, and a power supply voltage Vcc is supplied to the cathode. The anode is grounded via a resistor 52. Since a reverse bias voltage is applied to the photoelectric conversion element 51 by the power supply voltage Vcc, when an optical signal is input, a current flows according to the intensity of the optical signal, and a voltage V ₀ is generated across the resistor 52. To do. The voltage V ₀ generated in the resistor 52 is composed of a direct current component and a high frequency component as described above.

The high frequency component of the voltage V ₀ generated in the resistor 52 is input to the signal amplifier (high frequency amplifier) 62 through the coupling capacitor 61. The high frequency signal (TV signal) amplified by the signal amplifier 62 is output from the signal output terminal 57 via the attenuator 63 and sent to the TV receiver 46 shown in FIG. The above-described coupling capacitor 61, signal amplifier 62, and attenuator 63 constitute the gain adjustment amplification circuit 56 shown in FIG. 2, and the attenuation amount of the attenuator 63 is automatically attenuated by a control signal given from a computing unit 71 described later in detail. Controlled.

The DC voltage V _0d in the voltage V ₀ generated at the resistor 52 is input to the buffer amplifier 66 via the choke coil 58 provided in the photoelectric control circuit 54. The input terminal of the buffer amplifier 66 is grounded via a capacitor 59. That is, the voltage V ₀ generated in the resistor 52 is blocked from high frequency components by the choke coil 58 and the capacitor 59, and the DC fluctuation component of the voltage V ₀ is input to the buffer amplifier 66. The buffer amplifier 66 is a DC amplifier circuit that outputs the input DC voltage V _{0d as it is} with the same value, and its output signal is input to the common terminal of the changeover switch 55. The changeover switch 55 has a high and low changeover terminal, and resistors 67 and 68 are provided in series between the high changeover terminal and the ground. The low changeover terminal is connected to the common connection point of the resistors 67 and 68. Is connected. The resistors 67 and 68 are set to the same value, for example.

The voltage generated at the common connection point of the resistors 67 and 68 is input to the buffer amplifier 70. The buffer amplifier 70 is a DC amplifying circuit that outputs the input DC voltage as it is with the same value as the buffer amplifier 66, and has the function of preventing the influence between the circuits and transmitting only the voltage. Yes. The output voltage V _0d ′ of the buffer amplifier 70 is input to one input terminal of the calculator 71 and also input to one input terminal of the first voltage comparator 72 and the second voltage comparator 73.

_A reference voltage V _A obtained by dividing the power supply voltage Vcc with resistors 74 and 75 is input to the other input terminal of the calculator 71. The computing unit 71 controls the attenuation amount of the attenuator 63 based on the output voltage. When the DC voltage V _0d ′ larger than the reference voltage V _A is input from the buffer amplifier 70, it is output from the signal amplifier 62. The attenuator 63 is controlled so as to be attenuated by [1 / (V _0d ′ ÷ V _A )] times with respect to the signal voltage.

Further, the reference voltage V _A obtained by dividing by the resistors 74 and 75 is input to the other input terminal of the second voltage comparator 73. Further, the first voltage comparator 72, a reference voltage _{V B} which is obtained by dividing the power supply voltage Vcc by the resistors 76 and 77 are input. The light emitting diodes LED1 and LED2 are driven by the output signals of the first voltage comparators 72 and 73.

The first voltage comparator 72 turns on the light emitting diode LED1 and a large voltage is input from the buffer amplifier 70 than the reference voltage V _B, the second voltage comparator 73 is greater than the reference voltage V _A When input from the buffer amplifier 70, the light emitting diode LED2 is turned on.

  FIG. 5 shows the correspondence between the lighting state of the light emitting diodes LED1 and LED2 and the input state of the optical signal. That is, when both the light emitting diodes LED1 and LED2 are turned off, it indicates that the optical signal is insufficiently input. Further, when the light emitting diode LED1 is turned off and the light emitting diode LED2 is turned on, it indicates that the optical signal is a proper input. When both the light-emitting diodes LED1 and LED2 are lit, it indicates that the optical signal is excessively input.

Next, the operation of the optical receiver 45 shown in FIG. 4 will be described.
As shown in FIG. 1, when an optical signal (multiplexed signal) output from the headend device 20 is sent to the subscriber's home 40 via the optical fiber cable 31, the WDM provided in the subscriber's home 40. The filter 42 selects a TV signal from the received optical signals and inputs the selected TV signal to the optical receiver 45.

When an optical signal is input from the WDM filter 42, the optical receiver 45 converts the optical signal into an electrical signal by the photoelectric conversion element 51 as shown in FIG. That is, since a reverse bias voltage is applied to the photoelectric conversion element 51 by the power supply voltage Vcc, when an optical signal is input, a current corresponding to the intensity of the optical signal is generated, and this current flows through the resistor 52 to generate a direct current. A voltage V ₀ including a component and a high frequency component is generated. The high-frequency component of the voltage V ₀ is extracted through the coupling capacitor 61, amplified by the signal amplifier 62, adjusted to a predetermined level signal by the attenuator 63, and sent to the TV receiver 46 (see FIG. 1). .

The voltage V ₀ generated by the resistor 52 is blocked from high frequency components by the choke coil 58 and the capacitor 59, and the DC voltage V _0d is input to the changeover switch 55 via the buffer amplifier 66. When the changeover switch 55 is switched to the Low side, the DC voltage V _0d output from the buffer amplifier 66 is input to the buffer amplifier 70 as it is, and is output from the buffer amplifier 70 as the DC voltage V _0d ′. Therefore, in this case, V _0d = V _0d ′.

When the changeover switch 55 is switched to the High side, the DC voltage V _0d output from the buffer amplifier 66 is divided by half by the resistors 67 and 68 and input to the buffer amplifier 70. The buffer amplifier 70 outputs the DC voltage V _0d ′. Therefore, in this case, V _0d / 2 = V _0d ′.

The direct-current voltage V _0d ′ output from the buffer amplifier 70 is input to the first voltage comparator 72, and is compared with the reference voltage V _B obtained by dividing the power supply voltage Vcc by the resistors 76 and 77, thereby the light emitting diode LED1. Drive. Further, the DC voltage V _0d ′ output from the buffer amplifier 70 is input to the second voltage comparator 73, and is compared with the reference voltage V _A obtained by dividing the power supply voltage Vcc by the resistors 74 and 75, thereby producing a light emitting diode. LED2 is driven.

FIG. 6 shows an example of lighting of the light emitting diodes LED1 and LED2 when the changeover switch 55 is Low and High when the reference voltage V _{A is set} to 1 volt and the reference voltage V _B is set to 2 volts. Note that the DC voltage V _0d in the voltage V ₀ generated in the resistor 52 by the change of the optical signal input to the photoelectric conversion element 51 is 0.5 volts, 1.5 volts, 2.5 volts, 4.5 volts. To change.

First, the lighting operation of the light emitting diodes LED1 and LED2 in a state where the changeover switch 55 is switched to the low side will be described. In the state where the changeover switch 55 is switched to the low side, the DC voltage V _0d in the voltage V ₀ generated in the resistor 52 and the voltage V _0d ′ output from the buffer amplifier 70 have the same value. Therefore, when the DC voltage V _0d in the voltage V ₀ generated in the resistor 52 changes to 0.5, 1.5, 2.5, and 4.5 volts, the DC voltage V _0d output from the buffer amplifier 70 is changed. ′ Similarly changes to 0.5, 1.5, 2.5, and 4.5 volts.

When the output voltage V _0d ′ of the buffer amplifier 70 is 0.5 volts, it is lower than the reference voltage V _B (2 volts) and the reference voltage V _A (1 volt), so the first voltage comparators 72 and 73 are activated. The light emitting diodes LED1 and LED2 are both turned off, indicating that the light input level is insufficient.

Further, when the output voltage V _0d ′ of the buffer amplifier 70 is 1.5 volts, the second voltage comparator 73 is lower than the reference voltage V _B (2 volts) and higher than the reference voltage V _A (1 volt). Is activated and the light emitting diode LED2 is turned on. That is, the light-emitting diode LED1 is turned off and the light-emitting diode LED2 is turned on, indicating that the light input level is in the proper range.

Further, when the output voltage V _0d ′ of the buffer amplifier 70 is 2.5 volts, it becomes higher than the reference voltage V _B (2 volts) and the reference voltage V _A (1 volt). Is activated and both the light emitting diodes LED1 and LED2 are lit, indicating that the light input level is over input.

Further, when the output voltage V _0d ′ of the buffer amplifier 70 is 4.5 volts, it is similarly higher than the reference voltage V _B (2 volts) and the reference voltage V _A (1 volt), so the first voltage comparator 72 and 73 are activated, and both the light emitting diodes LED1 and LED2 are lit, indicating that the light input level is over input.
When the changeover switch 55 is switched to the low side as described above, the appropriate range of the DC voltage V _0d in the input voltage V ₀ is 1 to 2 volts.

Next, the lighting operation of the light emitting diodes LED1 and LED2 in a state where the changeover switch 55 is switched to the high side will be described. When switching the changeover switch 55 to the High side, the DC voltage V _0d in voltage V ₀ generated in the resistor 52 is selected by the choke coil 58 and a capacitor 59, is input to the changeover switch 55 via the buffer amplifier 66, resistors 67, The voltage is divided by half at 68. The _divided DC voltage V _0d / 2 is input to the buffer amplifier 70 and output as a DC voltage V _0d ′. Therefore, when the DC voltage V _0d in the voltage V ₀ generated in the resistor 52 changes to 0.5, 1.5, 2.5, and 4.5 volts, the buffer amplifier 70 supplies 0.25 volts, 0 DC voltage V _0d ′ of .75 volts, 1.25 volts, and 2.25 volts is output.

When the output voltage V _0d ′ of the buffer amplifier 70 is 0.25 volts and 0.75 volts, the first voltage comparator 72 is lower than the reference voltage V _B (2 volts) and the reference voltage V _A (1 volt). 73 do not operate, and both the light emitting diodes LED1 and LED2 are turned off, indicating that the light input level is insufficient.

When the output voltage V _0d ′ of the buffer amplifier 70 is 1.25 volts, it is lower than the reference voltage V _B (2 volts) and higher than the reference voltage V _A (1 volt). Is activated and the light emitting diode LED2 is turned on. That is, the light-emitting diode LED1 is turned off and the light-emitting diode LED2 is turned on, indicating that the light input level is in the proper range.

Further, when the output voltage V _0d ′ from the buffer amplifier 70 is 2.5 volts, it becomes higher than the reference voltage V _B (2 volts) and the reference voltage V _A (1 volt). Is activated and both the light emitting diodes LED1 and LED2 are lit, indicating that the light input level is over input.
When the changeover switch 55 is switched to the high side as described above, the appropriate range of the DC voltage V _0d in the input voltage V ₀ is 2 to 4 volts.

The output voltage V _0d ′ of the buffer amplifier 70 is input to the calculator 71. The calculator 71 'compares the large DC voltage _{V 0d} than the reference voltage _{V A'} output voltage _{V 0d} of the reference voltage _{V A} and the buffer amplifier 70 when the input is output from the signal amplifier 62 The attenuator 63 is controlled to attenuate [1 / (V _0d ′ ÷ V _A )] times the signal voltage. That is, the arithmetic unit 71 adjusts the level of the output signal of the signal amplifier 62 by controlling the attenuator 63, and always keeps the level of the high-frequency signal output from the signal output terminal 57 constant.

  FIG. 7 shows an example of the level of the signal output from the signal output terminal 57, that is, the relationship between the optical input voltage and the signal output level when the electrical input level to the optical transmitter 24 is constant. By switching the changeover switch 55 between Low and High, a signal of a constant level is output within each appropriate range. In this case, FIG. 7 shows a state in which a signal at a higher level is output when the changeover switch 55 is switched to High than when it is Low. Therefore, the level of the electric signal output from the signal output terminal 57 is always kept constant.

  In the above embodiment, the optical receiver 45 is shown as having a receiving frequency band of 70 to 770 MHz for CATV and 1000 to 2610 MHz for CS / BS-IF (satellite broadcasting). Even a device having only a frequency band of 70 to 770 MHz can be implemented in the same manner as in the above embodiment.

In the above embodiment, the operation level is switched to two stages by the changeover switch 55. However, the operation level may be switched to more stages.
In the above embodiment, the operation level is switched by the changeover switch 55. However, the operation level may be changed by using a variable resistor instead of the changeover switch 55. When the operation level is switched and set using a variable resistor, the optical input level or the like is measured using a measuring device. Moreover, as a measuring device, the optical input level can be measured by voltage conversion (conversion from mW to dBm) using a simple tester.

  Moreover, although the case where the optical receiver according to the present invention is used in the CATV system has been described in the above embodiment, it can also be used in, for example, a collective housing system. That is, the present invention can be implemented in an optical signal transmission system that transmits an optical signal output from an optical transmitter to an optical receiver through an optical fiber cable.

  Further, the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying constituent elements without departing from the scope of the invention in the implementation stage.

1 is a schematic configuration diagram of a CATV system according to an embodiment of the present invention. It is a figure which shows the basic composition of the optical receiver in the embodiment. It is a figure which shows the example of switching setting of the operation level of the optical receiver in the embodiment. It is a circuit diagram which shows the detailed structural example of the optical receiver in the embodiment. In the optical receiver which concerns on the embodiment, it is a figure which shows the correspondence of the lighting state of a light emitting diode, and the input state of an optical signal. In the optical receiver which concerns on the embodiment, it is a figure which shows the example of lighting operation of the light emitting diode with respect to switching of a changeover switch and an optical signal input. In the optical receiver which concerns on the embodiment, it is a figure which shows the relationship between the optical input voltage and signal output level when the electric input level to an optical transmitter is constant. It is a figure which shows the example in the case of transmitting the optical signal output from an optical transmitter to an optical receiver with an optical fiber cable in the system using the conventional FTTH system.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Optical transmitter, 12 ... Optical fiber cable, 13 ... Optical receiver, 20 ... Head end apparatus, 21 ... TV receiving antenna, 22 ... Satellite broadcast receiving antenna, 23 ... Retransmission head end, 24 ... Optical transmitter 25 ... WDM multiplexer, 26 ... optical transmission terminal, 27 ... optical network, 31 ... optical fiber cable, 32 ... splitter, 40 ... subscriber's home, 41 ... termination box, 42 ... WDM filter, 43 ... optical for communication Terminal 44, personal computer, 45 optical receiver, 46 TV receiver, 51 photoelectric conversion element, 52 resistance, 54 photoelectric control circuit, 55 switch, 56 gain adjustment amplifier circuit, 57 signal Output terminal 58 ... Choke coil 59 ... Capacitor 61 ... Coupling capacitor 62 ... Signal amplifier 63 ... Attenuator 66,70 ... Ffaanpu, 67, 68 ... resistors, 71 ... calculator, 72 ... first voltage comparator, 73 ... second voltage comparator, 74-77 ... resistance, LED1, LED2 ... light-emitting diode.

Claims (2)

In the optical receiver in which a plurality of electrical signal input levels to the optical transmitter are set according to the operation mode, and the appropriate input level range is different corresponding to each of the electrical signal input levels to the plurality of optical transmitters,
A photoelectric conversion element that converts an optical input signal input to the optical receiver into an electrical signal, a resistance element for electrical signal extraction connected in series to the photoelectric conversion element, and a high-frequency component generated at both ends of the resistance element First signal extracting means for extracting the signal, second signal extracting means for extracting the received light voltage of the photoelectric conversion element generated as a DC voltage at both ends of the resistance element, and the high-frequency component extracted by the first signal extracting means A gain adjusting amplifier circuit that adjusts and outputs the level of the signal, a signal level detecting means for detecting the level of the received light voltage of the photoelectric conversion element extracted by the second signal extracting means, and a signal of the signal level detecting means detection level is more set corresponding to the proper input level range of the optical receiver, the electrical signal input level of the signal detection level set plurality of the said optical transmitter A detection level switching means for switching a plurality of stages to a value corresponding to the value, sets the signal output level of the gain adjustment amplifier circuit to a certain appropriate level in accordance with the signal level detected by said signal level detecting means An optical receiver comprising gain adjusting means. A plurality of light emitting elements for displaying an input state of an optical input signal to the optical receiver, and an appropriate input level at each signal detection level in which the signal level detected by the signal level detection means is switched by the detection level switching means The optical receiver according to claim 1, further comprising: a light emitting element driving unit that drives the plurality of light emitting elements so as to indicate whether the range is reached.

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