JPH09298426A - Optical receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical receiver with less deterioration due to distortion and a wide gain band width. SOLUTION: A resistor 20 connects to an anode terminal of a photo diode 10 and a reverse bias voltage is applied to a cathode terminal. One terminal of a capacitor 30 connects to the anode terminal of the photo diode 10 and the other terminal of the capacitor 30 connects to an input terminal of a preamplifier 40. The preamplifier 40 is made up of a FRET 41 acting like an amplifier element and a negative feedback attenuator 42, which is placed between an output terminal (drain terminal) of the FET 41 and an input terminal (gate terminal), and its attenuation factor is controlled based on a control signal received by a control terminal 40. A frequency characteristic of the preamplifier 40, that is, that of the negative feedback attenuator 42 is selected to cancel a frequency characteristic of the photo diode 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiver used for reception in an optical communication system, and in particular, a wide dynamic range is required in an analog communication system such as CATV in which a wide frequency band is used. The present invention relates to an optical receiver.

[0002]

2. Description of the Related Art Conventionally, a photodiode has been widely used as a light receiving element in an optical receiver in an optical communication system. FIG. 10 is a block diagram of a conventional optical receiver. As shown in this figure, the photodiode 1 and the load resistor 2 are connected in series, and a bias voltage is applied to the photodiode 1. At this time, when light is incident on the photodiode 1, the photodiode 1
Outputs a current signal according to the amount of incident light. The current signal passes through the capacitor 3, the preamplifier 4, the variable attenuator 5, and the main amplifier 6 in this order, is amplified, and is output as a voltage signal. Further, the output signal of the main amplifier 6 is input to the AGC circuit 7, and the AGC circuit 7 controls the attenuation rate of the variable attenuator 5 based on the level of the voltage signal output from the main amplifier 6, The voltage signal output from 6 is maintained substantially constant.

FIG. 11 is a block diagram of a preamplifier in a conventional optical receiver. In the preamplifier 4, a resistor R and a capacitor C as negative feedback are connected in series between the input and output terminals of an FET (Field Effect Transistor) as an amplification element. The amplification factor of the preamplifier 4 is determined by the resistance value of the resistor R and the capacitance of the capacitor C.

[0004]

However, in the above-mentioned conventional example, when the amount of light received by the photodiode 1 is large, the output of the preamplifier 4 becomes excessive and the distortion characteristic deteriorates. Although it is possible to use a power amplifier with small distortion as the preamplifier 4,
With this, deterioration of the noise figure NF and increase of power consumption cannot be avoided.

It is also conceivable to suppress deterioration of distortion by using variable resistance means for the negative feedback of the preamplifier 4 and controlling the resistance value of the resistance means according to the amount of received light. However, in this case, there is a problem that the gain band becomes narrow due to the junction capacitance of the photodiode 1 when the resistance value is increased.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an optical receiving apparatus with less distortion deterioration and a wider gain band.

[0007]

An optical receiving device according to the present invention comprises: (1) a light receiving element that outputs a light receiving signal according to the amount of received light; and (2) the frequency characteristics of the light receiving element are substantially canceled. And a preamplifier for amplifying the received light signal and outputting the amplified signal, which is provided with a negative feedback attenuator for making the frequency characteristic of the output substantially flat. According to the present invention, the frequency characteristic of the photodiode is canceled by the frequency characteristic of the preamplifier, and the frequency characteristic of the entire optical receiving device becomes substantially flat.

In the optical receiver according to the present invention,
The negative feedback attenuator may have an attenuation rate set based on the first control signal. In this case, the attenuation factor of the negative feedback attenuator, that is, the amplification factor of the preamplifier is controlled by the first control signal to suppress the CNR deterioration of the preamplifier when the amount of received light is small, and the distortion deterioration of the preamplifier when the amount of received light is large. Is suppressed.

Further, the optical receiving device according to the present invention outputs the first control signal based on the level of the signal output from the preamplifier to control the attenuation factor of the negative feedback attenuator, and outputs from the preamplifier. A to keep the signal level approximately constant
A GC circuit may be further provided.

Further, in the optical receiver according to the present invention, (1) the attenuation factor is set based on the second control signal, and the signal output from the preamplifier is attenuated according to the attenuation factor and output. An attenuator, (2) a main amplifier that amplifies and outputs the signal output from the variable attenuator, and (3) the first and second based on the level of the signal output from the main amplifier.
And an AGC circuit that outputs the respective control signals to control the attenuation rate of each of the negative feedback attenuator and the variable attenuator to maintain the level of the signal output from the main amplifier substantially constant. .

Further, in this case, the AGC circuit mainly controls the attenuation factor of the variable attenuator when the light amount received by the light receiving element is small, and mainly the amplification factor of the preamplifier when the light amount received by the light receiving element is large. To control
Both CNR deterioration and distortion deterioration of the preamplifier can be suppressed more efficiently.

The negative feedback attenuator comprises at least one PIN.
A bridged T-type configuration including a diode or a π-type configuration including at least one PIN diode may be used. In any case, the frequency characteristic of the entire optical receiving device is made substantially flat, and the attenuation rate is controlled by the control signal.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

(First Embodiment) First, the first embodiment will be described. FIG. 1 is a configuration diagram of an optical receiving device according to the first embodiment. In the optical receiving device according to the present embodiment, the resistor 20 is connected to the anode terminal of the photodiode 10.
And a reverse bias voltage is applied to the cathode terminal. The anode terminal of the photodiode 10 is also connected to one terminal of the capacitor 30, and the other terminal of the capacitor 30 is connected to the input terminal of the preamplifier 40.

The preamplifier 40 comprises a FET 41 as an amplifying element and a negative feedback attenuator 42. FET41
The source terminal is grounded and the gate terminal is capacitor 3
It is connected to the 0 terminal to become the input terminal 40a, and the drain terminal becomes the output terminal 40b. The negative feedback attenuator 42 is F
It is arranged between the drain terminal and the gate terminal of the ET 41, and its attenuation rate is controlled based on the control signal input to the control terminal 40c.

Next, a specific circuit configuration of the negative feedback attenuator 42 will be described. FIG. 2 is a circuit configuration diagram of the variable attenuator of the preamplifier of the optical receiver according to the present embodiment. This is a bridge T-type variable attenuator, and the attenuation rate is variably set according to the level of the control signal input to the control terminal 40c.

In this negative feedback attenuator 42, the control terminal 40
The voltage applied between the anode terminal and the cathode terminal of the PIN diode D11 varies depending on the level of the control signal input to c, and the resistance value of the PIN diode D11 varies depending on the applied voltage. Therefore, the level of the control signal input to the control terminal 40c is
11 and the potential of the PIN diode D11 divided by the ratio of the sum of the resistance values of the PIN diode D11 and the resistance value of the resistor R14 and appearing at the position A (connection point between the PIN diode D11 and the resistor R14) in the figure is the control signal. Changes in a non-linear relationship with changes in the level of.

The cathode terminal of the PIN diode D12, the resistor R13 and the resistor R14 are connected in series, and a bias voltage is applied to the anode terminal of the PIN diode D12 by the DC power source E1. Therefore, if the potential at position A changes, the PIN diode D
The voltage applied to 12 changes and PIN diode D1
The resistance value of 2 changes, and thereby the potential of the position B (the connection point between the PIN diode D12 and the resistor R13) also changes. As described above, the potentials of the position A and the position B are different according to the level of the control signal applied to the control terminal 40c, and thus the attenuation rate is set.

Further, the capacitor C14 is connected to the position B, and the other terminal of the capacitor C14 is grounded, whereby the attenuation factor of the negative feedback attenuator 42 has a frequency characteristic. Furthermore, the preamplifier 40 also has frequency characteristics.

FIG. 3 is a diagram showing a calculation example of the frequency characteristic of the attenuation rate of this variable attenuator. This figure shows a conventional variable attenuator (without the capacitor C14 in FIG. 2).
An example of calculating the frequency characteristics of the attenuation rate of is also shown. This figure shows that the larger the absolute value of the numerical value on the vertical axis, the larger the attenuation rate. Therefore, the larger the value of the level Vc of the control signal applied to the control terminal 40c, the smaller the attenuation rate. Further, the attenuation rate of the conventional variable attenuator is flat without frequency dependence, whereas the attenuation rate of the variable attenuator according to the present invention is frequency dependent, and the higher the frequency, the larger the attenuation rate.

FIG. 4 is a diagram showing a calculation example of the frequency characteristic of the amplification factor of the preamplifier using this variable attenuator. This figure also shows a calculation example of the frequency characteristic of the amplification factor of the conventional preamplifier. As shown in this figure, the control terminal 40c
The larger the value of the level Vc of the control signal applied to, the smaller the amplification factor. Further, the amplification factor of the conventional type preamplifier has no frequency dependence and is flat, whereas the amplification factor of the preamplifier according to the present invention depends on frequency, and the higher the frequency, the larger the amplification factor.

When the output current of the photodiode 10 is amplified by the preamplifier 40 having such a frequency characteristic, this photodiode 10 also has a frequency characteristic, so that the frequency characteristic of the optical receiving device as a whole is that of the photodiode 10. The frequency characteristic and the frequency characteristic of the preamplifier 40 are integrated.

FIG. 5 is a diagram showing an example of calculating the frequency characteristic of the amplification factor of the optical receiving apparatus using this preamplifier. This figure also shows an example of calculating the frequency characteristic of the amplification factor of the conventional optical receiver. As shown in this figure, the control terminal 40c
The larger the value of the level Vc of the control signal applied to, the smaller the amplification factor. Further, whereas the conventional optical receiver has a large frequency dependency of the amplification factor, the optical receiver of the present invention has a small frequency dependency of the amplification factor.

The frequency characteristic can be explained as follows. That is, the photodiode 10
In general, the higher the frequency is, the smaller the output current signal level is, whereas the preamplifier 40 of the optical receiving apparatus according to the present invention has the higher amplification rate as the frequency is higher. The current signal output from the photodiode 10 is
If amplified by this preamplifier 40, the photodiode 1
Since the frequency characteristic of 0 is canceled out, the frequency characteristic of the entire optical receiving apparatus approaches a flat characteristic.

The specific circuit configuration of the negative feedback attenuator 42 is as follows.
The circuit configuration is not limited to that shown in FIG. 2, and other circuit configurations may be used. FIG. 6 is another circuit configuration diagram of the variable attenuator of the preamplifier of the optical receiving device according to the present embodiment. This is a π-type variable attenuator in which the attenuation rate is variably set according to the level of the control signal input to the control terminal 40c.

In this variable attenuator, the voltage applied between the anode terminal and the cathode terminal of each of PIN diodes D21 and D22 differs according to the level of the control signal input to control terminal 40c, and PIN diode D21 The resistance values of D22 and D22 differ depending on the applied voltage. Therefore, the level of the control signal input to the control terminal 40c is the same as that of the resistors R21 and PIN.
The potential that is divided by the ratio of the sum of the resistance values of the diode D21 and the resistance value of the resistor R24 and appears at the position A (the connection point between the PIN diode D21 and the resistor R24) in the figure is the level change of the control signal. Changes in a non-linear relationship to. Similarly, the level of the control signal input to the control terminal 40c is the same as that of the resistor R21 and the PIN diode D22.
Is divided by the ratio of the resistance value of the resistor R25 to the resistance value of the resistor R25, and the potential appearing at the position B (the connection point between the PIN diode D22 and the resistor R25) in the figure corresponds to the level change of the control signal. Changes in a non-linear relationship.

Further, the resistor R26, the resistor R22 and the PI
The N diode D23 and the resistor R24 are connected in series, and similarly, the resistor R26, the resistor R23, and the PI.
The N diode D24 and the resistor R25 are connected in series, and the bias voltage is applied to the other terminal of the resistor R26 by the DC power supply E2. Therefore, position A
When the potentials of the B diode and the position B change, the voltages applied to the PIN diodes D23 and D24 change, and the resistance values of the PIN diodes D23 and D24 change, which causes the position C (resistor R2
2 also changes the potential of the connection point of the resistor R23). As described above, the potentials at the positions A, B, and C are different according to the level of the control signal applied to the control terminal 40c, and the attenuation rate is set accordingly.

Further, at a position D which is a connection point of the resistor R21 and the PIN diodes D21 and D22,
The capacitor C25 is connected, and the other terminal of the capacitor C25 is grounded, so that the attenuation factor of the negative feedback attenuator 42 has a frequency characteristic.
Furthermore, the preamplifier 40 also has frequency characteristics.

The frequency characteristic of the attenuation factor of the negative feedback attenuator 42 having the circuit configuration as shown in FIG. 6 is also attenuated as the control signal applied to the control terminal 40c is larger, like the characteristic shown in FIG. The smaller the rate and the higher the frequency, the larger the attenuation rate. Further, the frequency characteristics of the amplification factor of the preamplifier 40 using the negative feedback attenuator 42 and the frequency characteristics of the amplification factor of the optical receiving device using the preamplifier 40 are also the frequency characteristics shown in FIGS. 4 and 5, respectively. Is the same as.

The circuit configuration of the negative feedback attenuator 42 is not limited to those shown in FIGS. 2 and 6, but any configuration is possible, and the point is that the frequency characteristics as shown in FIG. That is, the frequency characteristic of the amplification factor of the entire optical receiving device is made substantially flat.

In the optical receiving apparatus having the above-mentioned structure according to the present embodiment, when the amount of light received by the photodiode 10 is small and the signal level input to the preamplifier 40 is small, the signal is input to the control terminal 40c of the preamplifier 40. The level of the control signal is reduced, the attenuation factor of the negative feedback attenuator 42 is increased, and the amplification factor of the preamplifier 40 is increased. Thereby, CNR deterioration can be suppressed.
Conversely, when the amount of light received by the photodiode 10 is large and the signal level input to the preamplifier 40 is large, the level of the control signal input to the control terminal 40c of the preamplifier 40 is increased to increase the attenuation rate of the negative feedback attenuator 42. To reduce the amplification factor of the preamplifier 40. Thereby, distortion deterioration can be suppressed. The output of the preamplifier 40 has a substantially flat frequency characteristic regardless of the amplification factor of the preamplifier 40, that is, regardless of the amount of light received by the photodiode 10.

(Second Embodiment) Next, a second embodiment will be described. FIG. 7 is a configuration diagram of the optical receiving device according to the second embodiment. The optical receiving apparatus according to the present embodiment is the optical receiving apparatus according to the first embodiment to which an AGC circuit for maintaining the preamplifier output level within a certain range is added.

The preamplifier 40 in this embodiment is the same as the preamplifier described in the first embodiment. The control terminal 40c of the preamplifier 40 has an AGC
A control signal is applied by the circuit 70. The AGC circuit 70 inputs the output signal of the preamplifier 40, monitors the output signal level thereof, and outputs a control signal so as to control the amplification factor of the preamplifier 40 so that the output signal level of the preamplifier 40 falls within a certain range. To do.

That is, when the AGC circuit 70 determines that the output signal level of the preamplifier 40 is lower than the predetermined range, it reduces the value of the control signal, thereby increasing the amplification factor of the preamplifier 40 and vice versa. , Preamplifier 40
When it is determined that the output signal level of 1 is higher than the predetermined range, the value of the control signal is increased, and thereby the amplification factor of the preamplifier 40 is decreased. Thus, by setting the amplification factor of the preamplifier 40 based on the level of the output signal of the preamplifier 40, the level of the output signal of the preamplifier 40 is maintained within a substantially constant range. Also in this embodiment, the frequency characteristic of the output of the preamplifier 40 is substantially flat regardless of the amplification factor of the preamplifier 40. The fixed range in which the level of the output signal of the preamplifier 40 should be maintained is determined in consideration of CNR deterioration and distortion deterioration.

(Third Embodiment) Next, a third embodiment will be described. FIG. 8 is a configuration diagram of an optical receiving device according to the third embodiment. The optical receiver according to the present embodiment further includes a variable attenuator and a main amplifier connected to the optical receiver according to the first embodiment, and an AGC circuit that maintains the output level of the main amplifier within a certain range. It has been added.

The preamplifier 40 in this embodiment is the same as the preamplifier described in the first embodiment. The control terminal 40c of the preamplifier 40 has an AGC
A control signal is applied by the circuit 80. The output signal of the preamplifier 40 is attenuated by the variable attenuator 50 and further amplified by the main amplifier 60. Here, the variable attenuator 50 has its attenuation rate set by a control signal input to the control terminal 50c. The variable attenuator 50, unlike the negative feedback attenuator 42 in the preamplifier 40, preferably has a substantially flat frequency characteristic. The main amplifier 60 has a constant amplification factor, and this output becomes the output of the optical receiver. The AGC circuit 80 inputs the output signal of the main amplifier 60, monitors the level thereof, and controls the amplification factor of the preamplifier 40 and the attenuation factor of the variable attenuator 50 so that the output signal level of the main amplifier 60 falls within a certain range. Therefore, each control signal is output.

This optical receiver operates as follows.
FIG. 9 is a diagram qualitatively showing the characteristics of the overall amplification factors of the preamplifier 40 and the variable attenuator 50 with respect to the amount of light received by the photodiode 10. As shown in this figure,
The larger the amount of light received by the photodiode 10, the smaller the overall amplification factor of the preamplifier 40 and the variable attenuator 50, whereby the output level of the entire optical receiving device is maintained within a certain range.

However, when the amount of light received by the photodiode 10 is relatively small (range A in the figure), the attenuation rate of the variable attenuator 50 is mainly controlled, and the amount of light received by the photodiode 10 is relatively large. At this time (range B in the figure), the amplification factor of the preamplifier 40 is mainly controlled. That is, when the amount of light received by the photodiode 10 is relatively small, that is,
When the distortion of the preamplifier 40 is relatively small, the multiplication factor of the preamplifier 40 is kept constant at a large value, and the attenuation rate of the variable attenuator 50 is increased as the amount of received light increases. On the other hand, when the amount of light received by the photodiode 10 is relatively large,
The larger the amount of received light, the smaller the multiplication factor of the preamplifier 40, the distortion of the preamplifier 40 is suppressed, and the attenuation rate of the variable attenuator 50 is made constant. By doing so, distortion deterioration of the preamplifier 40 can be suppressed, and good distortion characteristics, flatness of frequency characteristics, and CNR characteristics can be realized over a wide dynamic range.

[0039]

As described above in detail, according to the present invention, the received light signal output from the light receiving element according to the amount of received light is substantially canceled out in the frequency characteristic of the light receiving element, and the frequency characteristic of the output is obtained. Since the amplification is performed by the preamplifier including the negative feedback attenuator that makes the frequency substantially flat, the frequency characteristic of the photodiode is canceled by the frequency characteristic of the preamplifier, and the frequency characteristic of the entire optical receiving device becomes substantially flat.

Further, the attenuation factor of the negative feedback attenuator can be set by the control signal, and the AGC circuit is provided to output the control signal based on the level of the signal output from the preamplifier to reduce the negative feedback attenuation. The attenuation rate of the negative feedback attenuator, that is, the amplification rate of the preamplifier is controlled by the first control signal by controlling the attenuation rate of the preamplifier and maintaining the level of the signal output from the preamplifier substantially constant. CNR deterioration of the preamplifier is suppressed when
When the amount of received light is large, distortion deterioration of the preamplifier is suppressed, and a substantially flat frequency characteristic is obtained as the entire optical receiver.

The signal output from the preamplifier is
The signal is output via the variable attenuator and the main amplifier, and the AGC circuit controls the attenuation factors of the negative feedback attenuator and the variable attenuator based on the level of the signal output from the main amplifier, and outputs from the main amplifier. CNR of the preamplifier by maintaining the level of the
Both deterioration and distortion deterioration are suppressed, and a substantially flat frequency characteristic is obtained as the entire optical receiver.

In particular, the AGC circuit mainly controls the attenuation factor of the variable attenuator when the light amount received by the light receiving element is small, and mainly controls the amplification factor of the preamplifier when the light amount received by the light receiving element is large. , Preamp C
Both NR deterioration and distortion deterioration are suppressed more efficiently.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical receiving device according to a first embodiment.

FIG. 2 is a circuit configuration diagram of a negative feedback attenuator of a preamplifier of the optical receiving device according to the first embodiment.

FIG. 3 is a diagram showing a frequency characteristic of an attenuation factor of a negative feedback attenuator.

FIG. 4 is a diagram showing a frequency characteristic of an amplification factor of a preamplifier.

FIG. 5 is a diagram showing a frequency characteristic of an amplification factor of the optical receiving device.

FIG. 6 is another circuit configuration diagram of the negative feedback attenuator of the preamplifier of the optical receiving device according to the first embodiment.

FIG. 7 is a configuration diagram of an optical receiving device according to a second embodiment.

FIG. 8 is a configuration diagram of an optical receiving device according to a third embodiment.

FIG. 9 is a diagram qualitatively showing the characteristics of the overall amplification factors of the preamplifier and the variable attenuator with respect to the amount of light received by the photodiode in the third embodiment.

FIG. 10 is a block diagram of a conventional optical receiver.

FIG. 11 is a configuration diagram of a preamplifier in a conventional optical receiver.

[Explanation of symbols]

10 ... Photodiode, 20 ... Resistor, 30 ... Capacitor, 40 ... Preamplifier, 41 ... FET, 42 ... Negative feedback attenuator, 50 ... Variable attenuator, 60 ... Main amplifier, 7
0,80 ... AGC circuit.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H04B 10/26 10/14 10/04 10/06

Claims (7)

[Claims] 1. A light-receiving element that outputs a light-receiving signal according to the amount of received light, and a negative feedback attenuator that substantially cancels the frequency characteristic of the light-receiving element to make the frequency characteristic of the output substantially flat. An optical receiving device comprising: a preamplifier that amplifies and outputs a signal. 2. The optical receiving device according to claim 1, wherein the negative feedback attenuator has an attenuation rate set based on a first control signal. 3. The level of the signal output from the preamplifier is controlled by outputting the first control signal based on the level of the signal output from the preamplifier to control the attenuation factor of the negative feedback attenuator. 3. The optical receiving device according to claim 2, further comprising an AGC circuit that maintains a constant value. 4. A variable attenuator having an attenuation rate set on the basis of a second control signal, attenuating the signal output from the preamplifier according to the attenuation rate, and outputting the variable attenuator. A main amplifier that amplifies and outputs the signal, and the negative feedback attenuator and the variable attenuator that respectively output the first and second control signals based on the level of the signal output from the main amplifier. The optical receiver according to claim 2, further comprising: an AGC circuit that controls the respective attenuation rates and maintains the level of the signal output from the main amplifier substantially constant. 5. The AGC circuit mainly controls the attenuation factor of the variable attenuator when the light amount received by the light receiving element is small, and mainly the amplification factor of the preamplifier when the light amount received by the light receiving element is large. 5. The optical receiving device according to claim 4, wherein 6. The optical receiver according to claim 1, wherein the negative feedback attenuator has a bridging T-type configuration including at least one PIN diode. 7. The optical receiving apparatus according to claim 1, wherein the negative feedback attenuator has a π-type configuration including at least one PIN diode.