JP2002354054A - Duty compensating communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve duty of output voltage signals. SOLUTION: A first differential amplifier 102 is configured so that its gain becomes 1. Voltage of an inputted voltage signal is detected substantially and correctly, and mid-level voltage corresponding to the detected voltage is fed back. The feedback circuit configuration is also simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to communication technology, and more particularly to a communication system which receives an external input signal of an optical signal, converts the external input signal into an electric signal having a rectangular waveform, and outputs the signal. The present invention relates to a duty compensation communication system.

[0002]

2. Description of the Related Art In the technical field of optical communication, for example, general-purpose optical interface units and high performance, low power consumption and low cost of photodiode (hereinafter referred to as PD) modules are desired. For example, there is a PD module with a wide dynamic range amplifier and a built-in amplifier.

[0003] As this conventional PD module, for example, a light receiving device disclosed in a document: (Transactions of the Institute of Electronics, Information and Communication Engineers 1995, B-1165) is known. FIG. 2 is a block diagram conceptually showing a configuration example of the conventional light receiving device. The configuration of this conventional light receiving device includes a light detecting unit or current output unit 40 that outputs a current according to the amount of light received by an optical signal, a variable transimpedance preamplifier 42 that outputs a voltage according to an input current level, and ,
In order to match the dynamic range of the input level, the first and second differential amplifiers 5 connected sequentially are used.
2, 54. Furthermore, this light receiving device includes
A DC feedback circuit 66 is provided for controlling the waveforms of the voltage signals output from the differential amplifiers 52 and 54, that is, for performing duty compensation of the rectangular voltage output waveform.

In this light receiving device, first, a current output unit 40 having a light receiving element senses an input of an optical signal as an external input, and outputs a current signal corresponding to the input level of the optical signal to a variable transimpedance type preamplifier. 42. This variable transimpedance type preamplifier 42
Converts an input current signal into a voltage signal. And
This output voltage signal is input to one input terminal 52a of the first differential amplifier 52. The differential amplifier 52 amplifies and outputs the input voltage signal. On the other hand, the output voltage signal from the variable transimpedance type preamplifier 42 is supplied to the first differential amplifier 52 by the DC feedback circuit 66.
Is fed back to the other input terminal 52b. With such a DC feedback type configuration, the DC feedback voltage input to the first differential amplifier 52 is adjusted or set so as to be at the center of the amplitude of the output rectangular wave output voltage signal. With these configurations and operations, the first
Of the output voltage waveform of the differential amplifier 52, that is, the duty of the output voltage signal. Then, the duty-compensated output voltage is amplified by the second differential amplifier 54 to a desired voltage signal.

[0005]

SUMMARY OF THE INVENTION Conventional DC feedback circuit 6
6 is a third differential amplifier 56 having two input terminals 56a and 56b connected to one and the other input terminals of the first differential amplifier 52, that is, the first and second input terminals 52a and 52b, respectively. Having. Further, the first and second peak detectors 58 and 60 connected to the two output terminals 56c and 56d of the third differential amplifier, respectively.
And an extraction terminal connected to the respective output terminals of the first and second peak detectors 58 and 60 to extract and output an intermediate value of the voltage, that is, an intermediate voltage between the H level and the L level, as intermediate voltage data. And a portion 62. Further, the circuit 66 is connected to the first and second peak detectors 58 and 60 and supplies an amplifier 70 that supplies a DC voltage.
That is, it has an operational amplifier. And this circuit 66
Has a variable capacitor 64. The capacity of the variable capacitor 64 is controlled to a capacity according to the intermediate voltage data from the extraction unit. And this variable capacitor 64
Acts to control the DC voltage obtained based on the voltage from the amplifier 70 and feed it back to the input terminals 52b and 56b.

However, in the above-described conventional light receiving device, empirically, the first differential amplifier 52 and the third differential amplifier 56 are connected to the first node 50 of the output line of the variable impedance amplifier 42. Therefore, the direct current feedback circuit itself as a feedback circuit has a complicated configuration, and a problem occurs in the feedback followability.

In some cases, an input offset voltage is generated between two input voltage signals of the first differential amplifier 52, that is, both voltages of a non-inverting input and an inverting input.
When this input offset voltage is generated, the output voltage signal is gain-multiplied with its center shifted in amplitude due to the input offset voltage. Therefore, it has been difficult for the conventional light receiving device to accurately compensate for the duty.

In addition, since the gain of the third differential amplifier 56, that is, the amplification factor is larger than 1, the first and second
The peak detectors 58 and 60 perform peak detection on the monitor voltage signal of the amplified voltage signal. For this reason, the extraction unit 62 cannot accurately extract the intermediate voltage of each voltage value, and an error occurs in the capacitance control of the variable capacitor due to this. Appears as an error when returning. This is also a factor that deteriorates the duty ratio of the output voltage signal.

[0009]

In order to solve these problems, a duty compensation communication system according to the present invention comprises: a current output section for converting an optical signal input from the outside into a current signal and outputting the current signal; A preamplifier connected to the current output section for converting the current signal into a voltage signal; and a second input terminal connected to the preamplifier, for amplifying the voltage signal, and amplifying the amplified voltage signal. And a second differential amplifier, which is connected to the subsequent stage of the first differential amplifier, amplifies the amplified voltage signal to a desired voltage signal, and outputs the amplified voltage signal. And first and second output terminals of the first differential amplifier, respectively connected to the first and second output terminals of the first differential amplifier and to the first input terminal. Input the positive-phase and negative-phase monitor voltage signals from the And converting the monitor voltage signal of the opposite phase into a voltage of an intermediate level of each monitor voltage signal, using the intermediate level voltage as a control voltage signal, and using the control voltage signal as a first input of the first differential amplifier. In a duty compensation communication system having a duty compensation feedback circuit for outputting to a terminal, the gain of the first differential amplifier is set to 1.

In this duty compensation feedback circuit, the input voltage signal is not amplified by setting the gain of the first differential amplifier to 1. For this reason, the peak detection unit in the duty compensation feedback circuit performs peak detection on the voltage signal that has not been amplified. Therefore,
Peak detection can be performed accurately.

Further, since the feedback circuit is not complicated, the followability is improved.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. It should be noted that the drawings are only schematically shown to the extent that the present invention can be understood, and accordingly, the configurations, connection relations, signal flows, numerical conditions, arrangement positions, dimensions and shapes of the respective components are illustrated in the drawings. It is not limited.

The duty compensation communication system according to the present invention converts an optical signal input from the outside into a rectangular voltage signal, and further converts the rectangular voltage signal into a voltage signal having a desired magnitude. This is applied to a light-receiving device that outputs to

To facilitate understanding of the present invention, first, the configuration and operation of the light receiving device will be described.

<Structure of Light Receiving Device> FIG. 1 shows this light receiving device 100. The light receiving device 100 includes a current generating unit, that is, a photodiode 30, a preamplifier, that is, a variable transimpedance preamplifier 32, and first and second differential amplifiers 102 and 104. This photodiode 30 is connected to a variable transimpedance type preamplifier 32. Further, the variable transimpedance type preamplifier 32 is connected to the second input terminal 100b of the first differential amplifier 102, and the first and second output terminals 102a and 102b of the first differential amplifier 102. Are connected to the input terminals 104a and 104b of the second differential amplifier 104. The output terminal of the second differential amplifier 104 is connected to the outside as output terminals 100c and 100d of the light receiving device.

A first input terminal of the first differential amplifier 102 is connected to the outside (here, an output terminal of the duty compensation feedback circuit 110, that is, a fourth node 178) as an input terminal 100a of the light receiving device. ing. Then, the gain of the first differential amplifier 102 is set to 1.

Here, as the photodiode 30, a light receiving element such as a pin photodiode (pin-PD) or an avalanche photodiode (APD) made of germanium, silicon, and ternary (for example, InGaAs) is used. Although the case where an optical signal is received is shown here,
When an electric signal or the like is received, a radio frequency tuning receiver, an acoustic receiver, a full-wave receiver, a synchro receiver, a telegraph receiver, a coordinate data receiver, or the like may be used in addition to the wireless receiver.

<Operation of Light Receiving Device> The current output section, that is, the photodiode 30, receives an optical signal, and generates and outputs a current signal corresponding to the input optical signal level. The variable transimpedance preamplifier 32 converts this current signal into a voltage signal corresponding to the current signal, and outputs this voltage signal. Then, the first differential amplifier 102
Obtains a control voltage signal (described later) by the action of a duty compensation feedback circuit. Also, the first differential amplifier 1
02 amplifies the voltage difference between the aforementioned voltage signal and the control voltage signal. Then, the amplified voltage difference is output to the second differential amplifier 104 as a positive-phase voltage signal and a negative-phase voltage signal. Next, the second differential amplifier 104 amplifies the positive-phase voltage signal and the negative-phase voltage signal into desired voltage signals.
Then, the positive-phase voltage signal and the negative-phase voltage signal amplified to the desired voltage signal are output to the outside.

Next, the configuration and operation of the duty compensation feedback circuit 110 will be described with reference to FIG.

<Configuration of Duty Compensation Feedback Circuit> FIG. 1 shows the configuration of the light receiving device 100 and the duty compensation feedback circuit 110 described above. Focusing on the configuration relationship between the light receiving device 100 and the duty compensation feedback circuit 110, the duty compensation feedback circuit 110 uses the first (first stage) as a supplied voltage signal, that is, a monitor voltage signal.
The positive-phase output (terminal) 102a and the negative-phase output (terminal) 102b of the differential amplifier 102 are adopted. That is, a connection point (first node) 106 between the terminals 102 a and 104 a as an input of the duty compensation feedback circuit 110 and a terminal 1
A connection point (second node) 108 of 02b and 104b is connected. Then, the output terminal of the duty compensation circuit 110, that is, the fourth node 178, is connected to the first input terminal 100a of the first differential amplifier 102.

Here, the duty compensation feedback circuit 11
0 will be described. The duty compensation feedback circuit 110 includes first and second peak detectors 152 and 154.
It has. Then, the first node 106 and the first peak detection unit 152 to which the first monitor signal voltage is input are connected. Similarly, the second peak detection unit 1 to which the second node 108 and the second monitor signal voltage are input
54 are connected. Each of the first and second peak detectors 152 and 154 is connected to an extractor 156 to which the first and second voltage values are input. In addition, each of the first and second peak detection units 152 and 154 and the extraction unit 156 are connected to the voltage control unit 158 to which the above-described first and second monitor signal voltages are input.
The output terminal of the voltage control unit 158 is connected to the fourth node 178 to supply the control voltage signal to the light receiving device 100.
It is connected to the.

<Operation of Duty Compensation Circuit> A first monitor voltage signal (a voltage signal: a positive-phase signal) is supplied from a first node 106 to a first peak detection unit 152, and the voltage value at that time is converted to a first peak detection value. It outputs to the extraction unit 156 as a voltage value of 1. A second monitor voltage signal (a voltage signal and a voltage signal having a phase opposite to that of the first monitor signal voltage) is supplied from the second node 108 to the second peak detection unit 154, and the voltage value at that time is similarly determined. As a second voltage value to the extraction unit 156. Then, the extracting unit 156 measures the voltage difference between the respective voltages based on the input first and second voltage values, that is, extracts the intermediate voltage between the respective voltage values substantially accurately. , And outputs the extraction result, that is, the intermediate voltage data, to voltage control section 158. Further, the voltage control unit 158 determines, based on the intermediate voltage data,
The first and second monitor voltage signals are controlled so that the voltage value becomes a voltage at an intermediate level between these voltage values. The intermediate-level voltage obtained by this control, that is, a control voltage signal is output from fourth node 178 to the outside.

In this embodiment, a case is shown in which voltage control section 158 is constituted by amplifier 172 and variable capacitor 174.

The first peak detecting section 152 includes an amplifier 17
2 non-inverting input terminals 172a. The second peak detector 154 is connected to the inverting input terminal 1 of the amplifier 172.
72b. The output terminal 172 of this amplifier
c is connected to the third node 176. Further, the variable capacitor 174 is connected between the third node 176 and the ground, and the variable capacitor 1
74 is connected to the extraction unit 156. In addition, the third node 176 is connected to the fourth node 178.

With this configuration, the amplifier, that is, the operational amplifier 172, outputs a DC voltage obtained based on the voltage difference between the input first and second monitor voltage signals to its output terminal 172c.

Then, according to the extraction result of the extraction unit 156,
The capacitance of the variable capacitor 174 changes, and as a result, the DC feedback voltage, that is, the control voltage signal is maintained at the center, that is, the intermediate voltage level between the voltage values of the input first and second monitor voltage signals.

Further, the difference between the operation of the present invention and the conventional operation will be described with reference to a timing chart in order to facilitate understanding.

<Operation of First Differential Amplifier Inside Light-Receiving Apparatus According to Prior Art and the Present Invention> FIG. 3 shows the relationship between the time and voltage signals at the input and output of the first differential amplifier 102 according to the present invention. 6 is a timing chart showing a relationship.

FIG. 4 is a timing chart showing the relationship between the time and the voltage signal at the input and output of the conventional differential amplifier 52 shown in FIG. 3 and 4, time is taken on the horizontal axis, and the time when the input voltage signal and the control voltage signal after DC feedback first become equal voltage is t0, and the time when the next voltage becomes equal is t1. It is sequentially defined as tn (n is a positive integer). 3 and 4, the time at which the voltage becomes equal in the time range from t0 to t2 is graduated. In addition, the vertical axis indicates a voltage (arbitrary unit) and indicates a range from GND, that is, 0 V to a voltage Vcc represented by a positive real number. The duty ratio is (t1-t0) / (t2-t) in FIGS.
0).

First, referring to FIG. 2 and FIG.
The input and output of the differential amplifier 52 will be described. The input voltage waveform, that is, the input voltage signal is input to the first input terminal 52a of the first differential amplifier via the first node 50. The input voltage signal at this time is shown by a rectangular waveform (a) in the upper part of FIG. Also, the feedback voltage from the DC feedback circuit 66, that is, the voltage signal is the second signal of the first differential amplifier.
Is input to the input terminal 52b. The control voltage signal input at this time is shown by a horizontal line (b) in the upper part of FIG.

Here, the characteristic of the differential amplifier is to amplify the voltage difference between two input terminals of the differential amplifier, that is, to multiply the gain by a gain. The output of the differential amplifier is two voltage signals of a positive phase and a negative phase.

To facilitate understanding of this operation, time t
The relationship between the input and the output will be described sequentially from 0 to time t1, and further from time t1 to time t2.

As shown in FIG. 4, from time t0 to time t1, a (rectangular waveform) input voltage signal (a) is a control voltage signal obtained from the second node 80 (see FIG. 2), that is, a DC feedback circuit 66. The positive-phase output voltage signal (d) is at the H level and the negative-phase output voltage signal (e) is at the L level.
Output as a level.

From time t1 to time t2, the rectangular waveform voltage signal (a) is the voltage signal after the DC feedback at the second node 80, that is, the DC feedback voltage applied from the DC feedback circuit 66. Since the voltage is lower than (b), the positive-phase output voltage signal (d) goes low and the negative-phase output voltage signal (e) goes high. Thereafter, this cycle is repeated.

The output signal of the first differential amplifier 52 is the intermediate level (c1) of the input voltage signal (that is, the center of the amplitude of the input voltage signal, (H level-L level) / 2) and the control voltage. Depending on the voltage difference with the signal. Therefore, the duty ratio of the output signal and the amplitude of the voltage change according to the voltage difference.

That is, in the configuration of the conventional light receiving device shown in FIG. 2, when an offset voltage, ie, an internal voltage error occurs at the time of signal input to the first differential amplifier 52, an intermediate level of the input voltage signal, ie, the voltage signal When a voltage difference occurs between the center (c1) of the amplitude of the signal and the input feedback voltage (b) (see FIG. 4), the input voltage signal is directly converted to the first and second differential amplifiers 52 by the difference in the voltage difference. , 54. Therefore, the duty of the positive-phase and negative-phase output voltage signals deteriorates.

On the other hand, according to the duty compensation communication system of the present invention, the operation is as follows, as is clear from the characteristics of the duty compensation feedback circuit shown in FIG.
The first differential amplifier 102 amplifies the difference between the input voltage signal (a) (see FIG. 1) and the DC feedback voltage from the duty compensation feedback circuit 110, that is, the control voltage signal (b). The voltage control unit 158 controls the control voltage signal (b) so as to be at an intermediate level (c1) between these two input voltage signals (a and b). This control voltage signal (b) substantially exactly matches the intermediate level (c1) of both input voltage signals. Therefore, the deterioration of the duty ratio of the positive-phase and negative-phase output voltage signals is reduced.

Further, by setting the gain of the first differential amplifier 102 of the duty compensation communication system of the present invention to 1, the first and second peak detectors 152 and 154 can monitor the unamplified monitor voltage signal. Use Therefore, the voltage value can be detected substantially more accurately. As a result, the deterioration of the duty ratio of the positive-phase and negative-phase output voltage signals of the differential amplifier 102 is reduced.

The duty compensation communication system operates as described above, so that the input duty ratio of 50% is reduced to about 70% in the conventional method.
However, in the present invention, the result is improved to about 55%.

In this embodiment, the case where the second differential amplifier 104 is constituted by one (one stage) is shown. However, in order to finally obtain a desired voltage signal, the second differential amplifier 104 may be an n-stage (n is a positive integer) differential amplifier.

[0041]

As is clear from the above description, according to the duty compensation communication system of the present invention, even if an offset voltage is generated in the first differential amplifier, it can be controlled by controlling the control voltage signal to the outside. The duty ratio of the output voltage signal can be improved.

Since the gain of the first differential amplifier is 1, the monitor signal voltage is not amplified. Therefore, peak detection can be performed accurately. Therefore, the duty ratio of the output voltage signal can be improved by controlling the control voltage signal substantially accurately.

Also, since it is not a complicated feedback circuit configuration,
Followability is improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a duty compensation communication system of the present invention.

FIG. 2 is a circuit diagram schematically showing an internal configuration of a conventional light receiving device.

FIG. 3 is a timing chart of the present invention.

FIG. 4 is a timing chart of the related art.

[Explanation of symbols]

30: Photodiode 32: Variable transimpedance type preamplifier 40: Current output unit 42: Variable transimpedance type preamplifier 50: First node 52: First differential amplifier 52a: First differential amplifier First input terminal 52b: second input terminal of first differential amplifier 54: second differential amplifier 56: third differential amplifier 56a: first input terminal 56b of third differential amplifier : Second input terminal 56c of the third differential amplifier 56c: first output terminal 56d of the third differential amplifier 56d: second output terminal of the third differential amplifier 58: first peak detector 60 : Second peak detection unit 62: extraction unit 64: variable capacitor 66: DC feedback circuit 70: amplifier 100: light receiving device 100a: first input terminal of the light receiving device (first differential amplifier) 100b: light receiving device ( No. 1st differential amplifier) second input terminal 100c: first output terminal of the light receiving device (second differential amplifier) 100d: second output terminal of the light receiving device (second differential amplifier) 102: First differential amplifier 102a: First output terminal of first differential amplifier 102b: Second output terminal of first differential amplifier 104: Second differential amplifier 104a: Second differential amplifier First input terminal 104b: second input terminal of the second differential amplifier 106: first node 108: second node 110: duty compensation feedback circuit 152: first peak detector 154: second 156: Extraction unit 158: Voltage control unit 172: Amplifier 172a: Non-inverting input terminal 172b: Inverting input terminal 172c: Output terminal 174: Variable capacitor 176: Third node 178: Fourth node

Claims (2)

[Claims] A current output unit that converts an optical signal input from outside into a current signal and outputs the current signal; a preamplifier connected to the current output unit and converts the current signal into a voltage signal; A second input terminal connected to the operational amplifier, a first differential amplifier for amplifying the voltage signal and outputting an amplified voltage signal, and a first differential amplifier connected to a subsequent stage of the first differential amplifier; Amplifying the applied voltage signal to a desired voltage signal and outputting the amplified voltage signal
And a first and a second output terminals of the first differential amplifier, respectively, which are connected to first and second output terminals of the first differential amplifier and to a first input terminal, respectively. The positive-phase and negative-phase monitor voltage signals are input from the output terminals, respectively, and the positive-phase and negative-phase monitor voltage signals are converted into intermediate-level voltages of the respective monitor voltage signals. And a duty-compensation feedback circuit that outputs the control voltage signal to a first input terminal of the first differential amplifier as a signal, wherein the gain of the first differential amplifier is 1. A duty compensation communication system, comprising: 2. The duty compensation communication system according to claim 1, wherein the second differential amplifier has n stages (n is a positive integer).