JP2674544B2 - Optical receiving circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiver circuit used for high-speed optical communication, and more particularly to an optical receiver circuit capable of converting a photocurrent obtained by a light receiving element into a stable voltage signal.

[0002]

2. Description of the Related Art In an optical receiver provided on the receiving side of high-speed optical communication, a photocurrent is generated by a light receiving element based on a received optical signal, and this photocurrent is converted into a voltage signal (voltage amplitude signal).
Is converted to. In this case, a circuit configuration is often adopted in which a photocurrent is amplified by a preamplifier and the amplified output signal is further amplified by an amplifier circuit. Moreover, in order to integrate these preamplifiers and amplifier circuits, the amplifier circuit is particularly used. In most cases, a differential amplifier circuit suitable for integration is adopted.

However, although the preamplifier has a single output, the differential amplifier circuit requires a differential input, as is well known. Therefore, the other input to which the preamplifier of the differential amplifier circuit is not connected is input. It is necessary to apply an appropriate offset voltage and perform offset compensation to make the offset voltage at the output of the differential amplifier circuit zero.

Therefore, for example, Japanese Patent Laid-Open No. 62-13940.
An offset compensating circuit as shown in FIG. 4 is proposed in Japanese Patent Laid-Open No. In the figure, the output of the light receiving element 11 is amplified by the preamplifier 12 and connected to one input terminal of the differential amplifier circuit 13. Further, an offset detector 14 for detecting an offset voltage by detecting the difference in DC component of the differential output of the differential amplifier circuit 13 is provided, and the control circuit 15 controls the differential amplifier circuit based on the detected offset voltage. The voltage generated by the reference voltage generating circuit 16 for inputting the voltage to the other input terminal is controlled. As a result, the differential amplifier circuit 13
The offset voltage of the differential output becomes zero, and offset compensation is performed.

[0005]

In such a conventional circuit configuration for offset compensation, the offset detector 1 is used.
4. Since the control circuit 15 and the reference voltage generation circuit 16 are required, there is a problem that the circuit configuration becomes complicated. Also,
Since feedback control is performed in the offset compensation, there is a problem that unless the time constant of the control circuit 15 is properly set, the offset compensation operation becomes unstable and oscillation may occur.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical receiving circuit which simplifies the circuit structure and ensures stable operation.

[0007]

An optical receiving circuit according to the present invention comprises:
As shown in FIG. 1A, one end of the light receiving element 1 is connected to one input end of the differential amplifier circuit 5 via the first preamplifier 2, and the other end of the light receiving element 1 is connected to the current mirror circuit 3. The current mirror circuit 3 is connected to the reference current terminal, and the output terminal of the current mirror circuit 3 is connected to the other input terminal of the differential amplifier circuit 5 via the second preamplifier 4.

In this case, the light-receiving element 1 has the bias voltage connection side terminal connected to the reference current terminal of the current mirror circuit 3. The first and second preamplifiers 2 and 4 are composed of the same circuit, and their gains are designed to be equal. Further, it is preferable that the current mirror circuit 3 is composed of a Wilson mirror.

[0009]

The photocurrent generated in the light receiving element 1 is input to the one input terminal of the differential amplifier circuit 5 as the output signal V1 such as a voltage signal by the first preamplifier 2 as shown in FIG. 1 (b). It Further, by connecting the current mirror circuit 3 to the light receiving element 1, the average current Ip flowing through the light receiving element 1 is used as the reference current of the current mirror circuit 3, and the current Ip 'having the same value is output to its output terminal. This current Ip 'is
By inputting to the other input end of the differential amplifier circuit 5 as the output signal V2 such as a voltage signal by the preamplifier 4, the output signal V2 becomes an average value of the output signal V1, and the output signal of the differential amplifier circuit 5 becomes The offset voltage is eliminated and offset compensation is performed.

[0010]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a circuit diagram of the first embodiment of the present invention. The light receiving element 1 is arranged so as to face an optical communication path (not shown), and is composed of a photodiode or the like that receives a transmitted optical signal and generates a photocurrent. One end of the light receiving element 1 is connected to the first preamplifier 2 and is configured to output the photocurrent generated in the light receiving element 1 as a voltage signal. The output of the first preamplifier 2 is connected so as to be input to one input terminal of the differential amplifier circuit 5.

On the other hand, the other end of the light receiving element 1 is connected to the reference current side terminal of the current mirror circuit 3. This current mirror circuit 3 is a known circuit composed of a pair of PNP transistors Q1 and Q2 whose bases are commonly connected. The collector of one transistor Q1 serves as a reference current side terminal and is connected to this reference current side terminal. A current having the same value as the current that flows is configured to flow to the collector of the other transistor Q2.

The collector of the other transistor Q2 is connected to a second preamplifier 4 having the same structure as the first preamplifier 2 for offset compensation, and the output of the second preamplifier 4 is differentially amplified. It is connected so as to be input to the other input end of the circuit 5. The differential amplifier circuit 5 has a pair of NPN transistors Q3 and Q4 whose emitters are commonly connected to a constant current source I and whose collectors are connected to loads R1 and R2 to serve as differential output terminals.
The base ends of the transistors Q3 and Q4 are respectively configured as the input ends.

According to this light receiving circuit, when a photocurrent is generated in the light receiving element 1 which receives an optical signal,
As shown in (b), this photocurrent is converted into a voltage signal V1 by the first preamplifier 2 and input to one input terminal of the differential amplifier circuit 5. At this time, the average current Ip of the generated photocurrent flows through the bias supply side terminal of the light receiving element 1, that is, the side connected to the current mirror circuit 3, and this average current Ip is used as a reference current in the current mirror circuit. 3 to the transistor Q1.

Therefore, in the current mirror circuit 3, a current Ip 'having the same current value as the reference current Ip flows in the transistor Q2, and this current Ip' is input to the second preamplifier 4 and output as the voltage signal V2. It Therefore, since the gains of the first and second preamplifiers 2 and 4 are the same, the voltage signal V2 has the same voltage as the average value (DC component) of the voltage signal V1 output from the first preamplifier 2. . Then, the voltage signal V2 is applied to the differential amplifier circuit 5
Since the input voltage is input to the other input terminal, the offset voltage at the output of the differential amplifier circuit 5 disappears and offset compensation is performed.

Therefore, the circuit of this embodiment does not require the conventional offset detector, control circuit and reference voltage generating circuit, but instead has the second preamplifier 4 having the same configuration as the first preamplifier 2. Only the current mirror circuit 3 needs to be provided, and the preamplifiers 2 and 4 and the current mirror circuit 3 have a small number of circuit constituent elements and thus have a simple circuit structure. It becomes possible to simplify.

Further, in the circuit of this embodiment, since the offset compensation is not performed by the feedback control based on the output of the differential amplifier circuit 5, the adjustment for setting the time constant appropriately becomes unnecessary, and the oscillation or the like occurs. A stable signal conversion operation can be achieved.

When the characteristics of the optical receiver of this embodiment were tested, the 2.4 Gb / s optical receiver realized a reduction in power consumption and a dynamic range of 30 dB in input optical power.

FIG. 3 is a circuit diagram of the second embodiment of the present invention. The same parts as those in FIG. 2 are denoted by the same reference numerals.
In the second embodiment, as the current mirror circuit 3A,
A Wilson mirror that can operate with high precision is applied. Wilson Miller is one of the PNP transistors Q5 and Q6 having a common base, which is a transistor Q5.
In addition to the collector of, the emitter of PNP transistor Q7
The collector is connected and its base is connected to the collector of the other transistor Q6.

The bias supply side terminal of the light receiving element 1 is connected to the collector of the transistor Q6, and the second preamplifier 4 is connected to the collector of the transistor Q7.
Therefore, the average current Ip generated in the light receiving element 1 is passed through the Wilson mirror as a reference current, and at this time, the base current of the transistors Q5 and Q6 is compensated by the transistor Q7, so that the collector of the transistor Q7 can be accurately adjusted. The current Ip 'of the same value will flow. Therefore, even if the value of the current Ip is very small, the current Ip 'that follows it flows.

The current Ip 'is input to the second preamplifier, and the voltage signal V2 based on the current Ip' is input to the other input terminal of the differential amplifier circuit, whereby the average of the output V1 of the second preamplifier is obtained. The voltage is input, and the offset compensation is executed as in the first embodiment.

With respect to the characteristics of the optical receiver of the second embodiment, the same test as that of the first embodiment was carried out, and it was found that the dynamic range was 5d more than that of the first embodiment.
B Improved.

In the present invention, it is possible to use a current mirror circuit having a structure other than the current mirror circuit used in each of the above embodiments. In addition, by integrating the preamplifier and the differential amplifier circuit in each of the above embodiments into one integrated circuit, and further configuring the current mirror circuit as an integrated circuit with them, it is possible to realize the integration of the optical receiving circuit. Needless to say.

[0023]

As described above, according to the present invention, the optical signal
A light-receiving element that receives light and generates a photocurrent between the two terminals,
It is connected to one terminal of this light receiving element
A first that amplifies the output current signal and converts it into a voltage amplitude signal
The preamplifier and the reference current input terminal to the other side of the light receiving element
Current mirror circuit to which the terminal of is connected and the input terminal
Is connected to the output current terminal of the current mirror circuit
Output voltage from the current mirror circuit.
Second preamplifier for conversion to signal and one input terminal is
Connected to the output of the first preamplifier, the other input terminal
Is a differential amplifier connected to the output of the second preamplifier.
Since it is composed of a width circuit , a voltage signal based on a current of the same value as the average current flowing through the light receiving element is input to the other input terminal of the differential amplifier circuit, which causes the output of the differential amplifier circuit to be input. Offset voltage is eliminated and offset compensation is performed.

Therefore, the offset detector, the control circuit, and the reference voltage generating circuit in the conventional circuit are unnecessary, and only the second preamplifier and the current mirror circuit need to be provided instead, and the preamplifier and the current mirror circuit have a circuit configuration. Since the number of elements is small and the circuit configuration is simple, it is possible to greatly simplify the circuit configuration as a whole of the optical receiving circuit.

Further, since the offset compensation is not performed by the feedback control based on the output of the differential amplifier circuit, the adjustment for setting the time constant appropriately becomes unnecessary, and the stable signal conversion operation can be performed without causing the oscillation. Becomes

The light receiving element is composed of a photodiode,
Since the bias voltage connection terminal is connected to the reference current terminal of the current mirror circuit, an optical signal is generated from one end of the photodiode and the output signal of the first preamplifier is input to the differential amplifier circuit, At the other end of the photodiode, an average current flows as a reference current of the current mirror circuit, and this average current is input to the differential amplifier circuit as an average output signal by the second preamplifier to perform offset compensation.

Since the first and second preamplifiers are composed of the same circuit and their gains are set to be equal, the output signal for offset compensation is the average signal of the output signals of the light receiving elements, and highly accurate offset compensation is executed. To be done.

Since the current mirror circuit is composed of a Wilson mirror, it is possible to output the current of the same value with high precision even for a minute reference current, and highly accurate offset compensation is executed.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing a basic configuration of an optical receiving circuit of the present invention and a signal waveform diagram thereof.

FIG. 2 is a circuit diagram of a first embodiment of an optical receiving circuit according to the present invention.

FIG. 3 is a circuit diagram of a second embodiment of the optical receiving circuit of the present invention.

FIG. 4 is a circuit diagram of an example of a conventional optical receiving circuit.

[Explanation of symbols]

 1 light receiving element 2 first preamplifier 3 current mirror circuit 4 second preamplifier 5 differential amplifier circuit

Claims (5)

(57) [Claims] 1. A light receiving element for receiving an optical signal to generate a photocurrent between two terminals, and an output current signal of the light receiving element which is connected to one terminal of the light receiving element and amplifies an output current signal of the light receiving element.
First preamplifier for converting to width signal and reference current input terminal
A current mirror circuit whose input terminal is connected to the other terminal of the light receiving element, and an input terminal of the current mirror circuit.
Connected to the output current terminal from the current mirror circuit
Second preamplifier for converting the output current of the first preamplifier into a voltage amplitude signal, and one input terminal connected to the output of the first preamplifier.
And the other input terminal is the output of the second preamplifier
And a differential amplifier circuit connected to the optical receiver circuit. 2. The light receiving circuit according to claim 1, wherein the light receiving element is composed of a photodiode, and a bias voltage connection terminal thereof is connected to a reference current terminal of the current mirror circuit. 3. The optical receiving circuit according to claim 1, wherein the first and second preamplifiers are composed of the same circuit, and their gains are set to be equal. 4. The optical receiving circuit according to claim 1, wherein the current mirror circuit is a Wilson mirror. 5. The optical receiving circuit according to claim 1, wherein the first and second preamplifiers, the differential amplifier circuit, and the current mirror circuit are configured by one integrated circuit.