JP3324520B2 - Gain control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a loop for controlling the gain of an equalizing amplifier stage in an optical receiver, in which a band-limiting, band-eliminating, or band-pass filter is inserted to prevent unnecessary signals (interference waves) from the outside. ), And to a gain control circuit for preventing a malfunction of the gain control loop due to this.

[0002]

2. Description of the Related Art In recent years, there has been an increase in demand for mobile phones and the like which generate electromagnetic waves, and there has been an increasing number of cases where optical communication devices are installed near wireless transmission stations or the like which handle large power.

[0003] Unlike a wireless communication device, an optical transceiver for optical communication needs to amplify a signal in a wide band from a low frequency region close to DC to a high frequency band near a transmission bit rate due to characteristics of a data signal.

In the case of a radio receiver, even when an unnecessary signal appears in the vicinity, if the frequency is not exactly the same, the influence of cross modulation or the like can be avoided by narrowing the band of the intermediate frequency amplifier or improving the selectivity. be able to.

[0005]

[SUMMARY OF THE INVENTION] However, in the case of the optical receiver, it is necessary bandwidth of the amplifier or the like is wideband,
It is difficult to remove unnecessary signals using a filter or the like.

Unnecessary signals are mixed with the equalized amplified signal itself, and it is impossible to completely remove the deterioration of the reception sensitivity and the like due to this. However, a malfunction of the gain control loop changes the optimum point of discrimination and reproduction, and the reception sensitivity is reduced. Deterioration can be prevented.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and prevents a gain control loop from being disturbed by the influence of an external unnecessary signal (interfering wave) to prevent reception sensitivity from deteriorating. It is an object of the present invention to provide a gain control circuit that can optimize signal amplitude by constant gain control and thereby optimize reception sensitivity as an optical receiver.

[0008]

According to a first aspect of the present invention, there is provided:
The gist of the invention described above is that a light receiving element for photoelectrically converting a signal light modulated by a data signal, a plurality of equalizing amplifiers provided in an optical receiver for amplifying the output of the light receiving element, some of the amplified signal and a clock extraction circuit for generating a clock signal, a regenerator circuit for reproducing a data signal from the equalized amplified signal based on the clock signal, originally equalized amplified signal Unnecessary signal from outside
The frequency corresponding to the unnecessary signal component when the signal is added
By removing the band, the main cause of unwanted external signals is
Characteristics of the gain control loop
A signal filter to prevent the door, detects the output signal strength of the signal filter, level detection controlling the gain of the signal filter of the output signal strength the equalizing amplifier based on the detected value of
And it can only containing the identification given to the reproducing circuit equalizing amplification
Equalization increase so that the amplitude of the
Said signal filter so that each of the breadths can be amplified
Is detected by the level detection circuit.
The gain of each of the equalizing amplifiers so that the value is constant
In the gain control circuit.
The gist of the invention described in claim 2 of the present invention is that
2. The gain control circuit according to claim 1 , wherein the level detector has a function of controlling the amplitude of the equalized and amplified signal input to the identification reproduction circuit to be constant.
Exists. Further, the essentials of the invention described in claim 3 of the present invention are as follows.
2. The advantage of claim 1 , wherein the clock recovery circuit is configured to generate a clock signal from an equalized amplified signal branched from between the stages of the plurality of equalization amplifiers.
In the control circuit. Further, according to claim 4 of the present invention.
The gist of the invention is that the signal filter is configured to detect the level
2. A gain control circuit according to claim 1, wherein said filter is a band-elimination filter provided at a stage preceding said filter, and has a center frequency matched with a frequency of an unnecessary signal such as an interference wave.
I do. The gist of the invention described in claim 5 of the present invention
2. The gain control circuit according to claim 1 , wherein said signal filter is a plurality of band-pass filters.
I do. The gist of the invention described in claim 6 of the present invention
Is a light receiving element that photoelectrically converts a signal light modulated by a data signal, a plurality of equalizing amplifiers provided in an optical receiver for amplifying the output of the light receiving element, and a part of the equalized and amplified signal. a clock extraction circuit for generating a clock signal, a regenerator circuit for reproducing a data signal from the equalized amplified signal based on the clock signal, the equalizing amplification
Unnecessary signal added to the original signal to the original signal
In such a case, the frequency band corresponding to the unnecessary signal component is removed.
The gain control loop is mainly due to unnecessary signals from the outside.
A signal filter to prevent the-loop characteristics malfunctioning is degraded, the acceleration circuit output signal from the signal filter is input, to detect an unnecessary signal from outside, the test
An output corresponding to the intensity of the unwanted signal out and a receiving circuit for input to said acceleration circuit, unwanted external signals the light
When the signal enters the receiver, the unnecessary signal is
Signal is detected and according to the strength of the detected unnecessary signal.
A detection output is generated, and the output of the equalization amplifier is
At the same time as the gain decreases, the output from the receiving circuit
In order to increase the gain of each of the equalizing amplifiers.
The reverse control voltage is applied to the adjustment circuit, and the equalization is performed.
The identification is performed without changing the gain of each of the amplifiers.
The amplitude of the equalized and amplified signal input to the regeneration circuit is constant
The gain control circuit is characterized in that
Further, the gist of the invention described in claim 7 of the present invention, the <br/> signal filter is a band elimination filter, it has to match the center frequency and the frequency of the unwanted signal interference waves and the like
7. The gain control circuit according to claim 6, wherein
Further, the gist of the invention described in claim 8 of the present invention, the <br/> signal filter is a plurality of bandpass filters
A gain control circuit according to claim 6 characterized by the above-mentioned.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a gain control circuit according to Embodiment 1 of the present invention. FIG. 2 is a block diagram of a gain control circuit according to Embodiment 3 of the present invention. FIG. 3 is a waveform diagram showing a spectrum of the equalized amplified signal according to the first embodiment. FIG.
3 is a waveform chart according to Embodiment 1. FIG. FIG. 5 is a waveform chart according to the second embodiment. FIG. 6 shows the second embodiment.
FIG.

(Embodiment 1) In FIG. 1, 101 is a light receiving element, 102 and 103 are equalizing amplifiers, 104 is an identification reproducing circuit, 105 is a clock reproducing circuit, 106 is a signal filter, and 107 is a level detector. Is shown.

The signal light modulated by the data signal is
Photo-electric conversion is performed by the light receiving element 101. The output is output from the equalization amplifiers 102 and 103 to the discrimination reproduction circuit 1 in the subsequent stage.
04 Ru is amplified to an amplitude necessary to identify.

Further, the equalized amplified signal is branched from between the stages of the equalizing amplifiers 102 and 103 and guided to the clock recovery circuit 105. The clock recovery circuit 105 generates a clock signal from the equalized amplified signal.

The identification reproduction circuit 104 performs identification reproduction of the equalized amplified signal using the generated clock signal. The amplitude of the equalized amplified signal provided to the identification reproducing circuit 104 has an optimum value.

That is, the equalizing amplifiers 102 and 103 must amplify so as to always have this amplitude. Therefore, the output amplitude is detected by the level detector 107, and the gains of the equalizing amplifiers 102 and 103 are varied so that this value becomes constant.

When an unnecessary signal (interference wave) is added from the outside to the original signal to the equalized amplified signal, the signal filter 106
The frequency band corresponding to the unnecessary signal component is removed. As a result, it is possible to prevent the gain control loop from malfunctioning due to unnecessary signals from the outside and deteriorating the characteristics.

Next, the operation of the gain control circuit shown in FIG. 1 will be described. Since the principle of the internal operation of the optical receiver is as described above, the following description focuses on the equalized amplified signal.

FIG. 3 shows the spectrum of the equalized amplified signal. F0 in the figure indicates the frequency of the transmitted bit rate. In this figure, an unnecessary signal (interference wave) is already on the equalized amplified signal, but usually there is no such interference wave.

In recent years, when the demand for portable telephones, PHSs and the like has increased, and there are nearby high-power transmitting stations such as broadcasting stations and wireless relay stations, unnecessary signals (interfering waves) as shown in FIG. 3 are added. It is highly possible that

[0019] Now, when the unnecessary signal is in no state, Les
The bell detector 107 regards the level of the signal as the maximum value, and controls the gains of the equalizing amplifiers 102 and 103 such that the level becomes a certain fixed value. In this case, the signal amplitude to the identification and reproduction circuit 104 is optimal, and the receiving sensitivity is also maximum.

Here, assuming that an unnecessary signal (interfering wave) is added to the equalized signal, the level detector 107 detects that the maximum value of the equalized amplified signal is. In such a case, since the gain control is performed so that the level of the signal becomes a predetermined value, the amplitude of the actual equalized amplified signal becomes small, and the receiving sensitivity is deteriorated. .

As can be seen in FIG.
6 is provided before the level detector 107. At this time, the signal filter 106 serves as a band elimination filter, and its center frequency is made to coincide with the frequency of the unnecessary signal (interference wave).

FIG. 4 shows the spectrum of the equalized amplified signal after passing through the signal filter 106. As can be seen from FIG. 4, the spectrum of the unnecessary signal (interference wave) portion has been removed. As a result, the level detector 107 detects the level of the signal as the maximum value, normal gain control is performed, and it is possible to avoid deterioration of the reception sensitivity.

As described above, according to the present embodiment, the signal amplitude input to the discrimination and reproduction circuit is optimized by the constant gain control, and this operation optimizes the receiving sensitivity as the optical receiver.

Further, it is possible to prevent the gain control loop from being disturbed by the influence of an unnecessary signal (interfering wave) from the outside. This can prevent reception sensitivity from deteriorating.

Therefore, stable gain control can be performed even under a strong electric field near a radio transmission station. Furthermore, malfunctions due to electromagnetic waves emitted by mobile phones and the like, which have been increasing in recent years, can be prevented.

(Embodiment 2) In this embodiment, the signal filter 106 shown in FIG.
Is a plurality of band-pass filters. FIG. 5 shows the spectrum of the equalized amplified signal output from the pass band filter.
Shown in

As shown in FIG. 5, a filter having three passbands is provided here. Of course, any number of filters may be used, but it is necessary to avoid only the frequency of the unnecessary signal (interference wave). When the outputs of these filters are detected by the level detector 107, the level indicated by is the maximum value. If gain control is performed based on this, the input amplitude to the discrimination / reproduction circuit 104 can be kept optimal, and the influence of external unnecessary signals (interference waves) can be prevented.

Further, as shown in FIG. 6, there is no problem with one filter as long as the frequency of the unnecessary signal (interference wave) is avoided. In this case, since there is only one filter, it is advantageous in terms of cost.

Third Embodiment FIG. 2 shows a third embodiment. In FIG. 2, 201
Is a light receiving element, 202 and 203 are equalizing amplifiers, 204 is an identification reproducing circuit, 205 is a clock reproducing circuit, 206 is a level detector, 207 is an unnecessary signal (interference wave) receiving circuit, 20
Numeral 8 denotes an adding / subtracting circuit.

In this configuration, a receiving circuit 207 for detecting an external unnecessary signal (interference wave) is provided. Here, if a certain unnecessary signal (interference wave) is applied to the optical receiver, the unnecessary signal (interference wave) is simultaneously detected by the receiving circuit 207, and a detection output is generated according to the intensity.

The gain control of the optical receiver causes an erroneous operation due to this effect, and the gain of the equalizing amplifiers 202 and 203 decreases, and at the same time, the gain of the equalizing amplifiers 202 and 203 increases by the output from the receiving circuit 207. The opposite control voltage is provided to the adjustment circuit 208. As a result, the amplitude of the equalized amplified signal input to the identification reproducing circuit 204 is kept constant without changing the gains of the equalizing amplifiers 202 and 203 .

In the case of the third embodiment, the receiving circuit 20
7 is the same as that of the equalizing amplifiers 202 and 203 , so that any unnecessary signal (interference wave) of any frequency within the band can be used.
The effect can be removed.

[0033]

As described above, according to the gain control circuit of the present invention, the following effects can be obtained. By the constant gain control, the signal amplitude input to the discrimination reproduction circuit is optimized.
This operation optimizes the receiving sensitivity as an optical receiver. It is possible to prevent the gain control loop from being disturbed by the influence of an unnecessary signal (interference wave) from the outside. In addition, it is possible to prevent reception sensitivity deterioration. Stable gain control can be performed even under a strong electric field near a wireless transmitting station. It is possible to prevent malfunctions due to electromagnetic waves emitted from mobile phones and the like, which have been increasing in recent years.

[Brief description of the drawings]

FIG. 1 is a block diagram of a gain control circuit according to Embodiment 1 of the present invention.

FIG. 2 is a block diagram of a gain control circuit according to Embodiment 3 of the present invention.

FIG. 3 is a waveform chart showing a spectrum of an equalized amplified signal according to Embodiment 1 of the present invention.

FIG. 4 is a waveform chart according to the first embodiment of the present invention.

FIG. 5 is a waveform chart according to the second embodiment of the present invention.

FIG. 6 is a waveform chart according to the second embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 101 light receiving element 102 , 103 equalizing amplifier 104 identification reproduction circuit 105 clock reproduction circuit 106 signal filter 107 level detector 201 light reception element 202 , 203 equalization amplifier 204 identification reproduction circuit 205 clock reproduction circuit 206 level detector 207 reception circuit 208 adjustment circuit

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H03G 1/00-3/34 H04B 7/005

Claims (8)

(57) [Claims] A light receiving element for photoelectrically converting a signal light modulated by a data signal; a plurality of equalizing amplifiers provided in an optical receiver for amplifying an output of the light receiving element; A clock extraction circuit that generates a clock signal from a unit, an identification reproduction circuit that reproduces a data signal from the equalized and amplified signal based on the clock signal, and the like.
Unnecessary signals are added from the outside to the original signal to the amplified signal.
Frequency band corresponding to the unnecessary signal component
Gains mainly due to external unwanted signals.
Prevents control loops from malfunctioning and deteriorating characteristics.
And immediately signal filter, it detects the output signal strength of the signal filter, viewed contains a level detector to control the gain of the equalizing amplifier based on the detected value of the output signal strength of the signal filter, the identification reproducing circuit Of the equalized and amplified signal
Each of the equalizing amplifiers so that the width always becomes the optimum value.
Output signal strength of the signal filter so that
Is detected by the level detection circuit, and this value becomes constant.
To vary the gain of each of the equalizing amplifiers
A gain control circuit, characterized in that : 2. The level detector according to claim 1, wherein the level detector has a function of controlling the amplitude of the equalized and amplified signal input to the identification reproduction circuit to be constant.
A gain control circuit as described. 3. The clock recovery circuit according to claim 1, wherein the clock recovery circuit is configured to generate a clock signal from an equalized amplification signal branched from between the stages of the plurality of equalization amplifiers.
A gain control circuit as described. 4. The signal filter is a band elimination filter provided in a stage preceding the level detector , and has a center frequency matched with a frequency of an unnecessary signal such as an interference wave. The gain control circuit according to claim 1, wherein 5. The gain control circuit according to claim 1, wherein said signal filter is a plurality of band-pass filters. 6. A light receiving element for photoelectrically converting the modulated signal light by a data signal, a plurality of equalizing amplifier for amplifying the output of the receiving <br/> optical element provided in the optical receiver, the equalization A clock extraction circuit that generates a clock signal from a part of the amplified signal, and an identification reproduction circuit that reproduces a data signal from the equalized and amplified signal based on the clock signal,
Unnecessary signals from the outside are added to the original signal in the equalized and amplified signal.
Frequency band corresponding to the unnecessary signal component
By removing the signal, it is useful mainly due to external unnecessary signals.
That the control loop will malfunction and degrade the characteristics.
A signal filter to prevent the acceleration circuit output signal from the signal filter is input, detects the unwanted signal from the outside, and a receiving circuit for receiving an output corresponding to the intensity of the unwanted signal the detected said acceleration circuit With unnecessary external signals
Signal is applied to the optical receiver by the receiving circuit
The unnecessary signal is detected, and the strength of the detected unnecessary signal is
The detection output is generated according to the degree,
At the same time as the gain of the
These outputs increase the respective gains of the equalizing amplifier.
The opposite control voltage is applied to the adjusting circuit.
Therefore, the gain of each of the equalizing amplifiers does not change.
And the equalized and amplified signal input to the discrimination reproduction circuit.
Characterized in that the amplitude of the gain control circuit is kept constant . 7. The gain control circuit according to claim 6, wherein said signal filter is a band elimination filter, and a center frequency thereof is made coincident with a frequency of an unnecessary signal such as an interference wave. 8. The gain control circuit according to claim 6, wherein said signal filter is a plurality of band-pass filters.