JPH11196053A - Optical receiving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To dispense with a large scale AGC circuit, to reduce and simplify the scale of an optical receiving circuit, and to reduce its power consumption by using an amplitude limited amplifying circuit that consists of a simple differential amplifying circuit. SOLUTION: An amplitude limited amplification circuit 3 operates in a linear amplifying region, when an optical input level of an APD 1 is low, and the bias voltage of the APD 1 is automatically controlled so that the reference voltage is equal to the peak value by a feedback loop which consists of a peal value detection circuit 5 and a voltage control circuit 6. The output amplitude of an equalizing amplification/circuit 4 becomes constant in the operating range of the feedback loop, and the S/N ratio is determined by the electrical noise produced by a preamplifying circuit 2, the circuit 3 and the circuit 4 and the shot noises of the APD 1. When an optical input level of the APD 1 becomes large, the output amplitude of the circuit 4 is increased and the multiplication factor of the ADP 1 and also the shot noises become small respectively. The electrical noises are kept at constant levels, regardless of the output amplitude of the circuit 4, and accordingly the S/N ratio is high.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical receiving circuit,
In particular, the present invention relates to an optical receiving circuit using an APD as an optical conversion element.

[0002]

2. Description of the Related Art A conventional optical receiving circuit using an APD is shown in FIG.
Shown in FIG. 3A is a block diagram illustrating a main configuration of the optical receiving circuit, and FIG. 3B is a circuit diagram illustrating an example of an AGC circuit included in the optical receiving circuit.

[0003] An optical receiving circuit using a conventional APD shown in FIG. 3A includes an APD 1, a preamplifier circuit 2, an AGC
(Automatic Gain Control) circuit 7, equalizing amplifier circuit 4, peak value detecting circuit 5, and A
It is composed of a GC control circuit 8 and a voltage control circuit 6, and controls a multiplication factor of the APD 1 and a gain of the AGC circuit 7 according to a light receiving level, thereby outputting a signal of a constant amplitude. The amplification factor of the APD 1 is controlled by the bias voltage of the APD.

The AGC circuit is excellent in high frequency characteristics and has a simple configuration, and is easy to control the gain. Therefore, as shown in FIG. 3B, a circuit in which transistors TR are vertically stacked is used. TR3, TR4 and TR2 and TR
5 and TR6 are connected in series, respectively, so that a high power supply voltage is required.

[0005] Further, an optical receiving circuit having a wide dynamic range using a limit amplifier circuit instead of the AGC circuit has been proposed.
For example, it has been proposed in JP-A-62-15909. This optical receiver circuit includes a preamplifier circuit for converting a photoelectrically converted current into a voltage, a limit amplifier circuit including a differential amplifier circuit, a preamplifier circuit for controlling an offset of the limit amplifier circuit, and a limit amplifier circuit. And an offset detection circuit for controlling the offset control circuit. The amplitude is limited with respect to the center value of the output amplitude of the preamplifier circuit from the minimum light reception level to the maximum light reception level. It outputs a signal.

The limit amplifier circuit limits the signal with respect to the center value of the output amplitude of the preamplifier circuit. Therefore, when the output signal of the preamplifier circuit has the same light emission and non-light emission noises, , PIN-PD (PIN type Photo Di)
mode) is effective when used as a light receiving element.

[0007]

In an optical receiving circuit using a conventional AGC circuit, when the light receiving dynamic range is to be increased, the configuration of the AGC circuit is multi-tiered, so that the circuit scale is increased and the power consumption is increased.

When an AGC circuit in which transistors are stacked vertically as shown in FIG. 2B is used as the AGC circuit, the dynamic range of light reception cannot be increased particularly when the power supply voltage is small because the input dynamic range of the AGC circuit cannot be increased. Becomes smaller.

In an optical receiving circuit using a conventional limit amplifier circuit, when an APD is used as a light receiving element, an output signal having a small signal-to-noise ratio is obtained in the vicinity of a minimum light receiving level. The reason is that in the output signal of the preamplifier circuit, the APD shot noise is superimposed on the noise at the time of light emission,
This is because, when the amplitude is limited with respect to the signal amplitude center value, noise at the time of light emission increases, and as a result, the signal-to-noise ratio of the output signal decreases.

When an APD is used as a light receiving element,
Since the amplitude of the output signal is limited even near the minimum light receiving level, it is difficult to control the bias voltage of the APD.

An object of the present invention is to provide an optical receiving circuit capable of increasing the dynamic range of light reception, reducing the size and simplification of the circuit scale, and reducing power consumption.

[0012]

An optical receiving circuit according to the present invention comprises:
An optical signal amplifier for voltage-converting the current signal photoelectrically converted by the photoelectric conversion element, limiting the amplitude when the voltage-converted voltage level is equal to or higher than a predetermined level, equalizing and amplifying, and the optical signal amplifier; And a feedback controller for detecting the peak of the output voltage, comparing the output voltage with a preset reference value, extracting a difference, and controlling the output current signal of the photoelectric conversion element.

A photoelectric conversion element for photoelectrically converting an optical signal to output a current signal; a preamplifier for converting the current signal into a voltage to output a voltage signal; and an output voltage of the preamplifier. Amplifying the signal, and when the voltage level of the amplified output voltage signal is equal to or higher than a predetermined level, an amplitude limiting amplifier circuit that limits the amplitude of the output voltage signal and outputs the resultant signal.
An equalizing amplifier circuit for equalizing and amplifying the output voltage signal of the amplitude limiting amplifier circuit; a peak value detecting circuit for detecting a peak value of the amplitude of the equalized and amplified voltage signal; and a peak detected by the peak value detecting circuit. A voltage control circuit that compares the value with a preset reference value, extracts a difference, generates a control signal corresponding to the difference, and controls an output current signal of the photoelectric conversion element.

Further, the photoelectric conversion element may be an APD (Av
characterized in that it is an Alanche Photo Diode.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a main configuration of an optical receiving circuit according to the present invention. FIG. 2 is a diagram showing an output signal waveform of the optical receiving circuit of the present invention, and FIG.
FIG. 4B is a diagram illustrating an output signal waveform when the optical input level of the APD is small, FIG. 4B is a diagram illustrating an output signal waveform when the optical input level of the APD is large and close to the lower limit of the operation region, and FIG. FIG. 7 is a diagram illustrating an output signal waveform when the operation of the APD is below the lower limit of the operation region, and FIG. 7D is a diagram illustrating an output signal waveform when the operation of the amplitude limiting amplifier is in the amplitude limitation region.

The outline of the operation of the present invention is as follows. When the light input level of the APD 1 is small, the amplitude limiting amplifier circuit 3 operates in the linear amplification region, and the feedback loop composed of the peak value detection circuit 5 and the voltage control circuit 6 , The bias voltage of the APD 1 is automatically controlled so that the peak value becomes equal to the reference voltage. In the range in which the feedback loop operates, the output amplitude of the equalizing amplifier circuit 4 is constant, and the signal-to-noise ratio is generated by the preamplifier circuit 2, the amplitude limiting amplifier circuit 3, and the equalizing amplifier circuit 4, respectively. It is determined from electrical noise and APD shot noise.

When the light input level of the APD 1 increases,
The output amplitude of the equalizing amplifier circuit 4 increases. At this time AP
The multiplication factor of D1 is small, and the shot noise is small. Also,
The electrical noise is constant regardless of the output amplitude. Therefore,
The signal to noise ratio is large.

When the optical input level of the APD further increases, the amplitude limiting amplifier 3 operates in the amplitude limiting region, and the output amplitude of the equalizing amplifier 4 becomes constant. At this time, since the noise is removed by the amplitude limiting amplifier circuit 3, the signal-to-noise ratio is large.

Next, the operation of the present invention will be described in detail with reference to FIGS. The optical receiving circuit shown in FIG.
An APD 1 that photoelectrically converts an optical signal and outputs a current signal;
A preamplifier circuit 2 for current-to-voltage conversion of a current signal output from the APD 1 to output a voltage signal; and a preamplifier circuit 2
Amplifies the voltage signal output by the amplifier, outputs an amplitude-limited voltage signal when the amplified voltage signal is equal to or higher than a predetermined level, and equalizes and amplifies the voltage signal output by the amplitude-limited amplifier circuit 3. Equalization amplifier circuit 4 and peak value detection circuit 5 for detecting the peak value of the amplitude of the equalized and amplified signal
And a voltage control circuit 6 for comparing the detection voltage output from the peak detection circuit 5 with the value of the reference voltage source to extract a difference and controlling the bias voltage of the APD 1.

When the light input level to the APD 1 is small, the amplitude limiting amplifier circuit 3 operates in the linear amplification region, and the feedback loop composed of the peak value detection circuit 5 and the voltage control circuit 6 causes the reference voltage and the peak value to be reduced. AP so that
The bias voltage of D1 is automatically controlled.

The range in which the feedback loop operates (APD)
2 (A), the amplitude of the output voltage signal of the equalizing amplifier circuit 4 is constant, and the signal-to-noise ratio of the output voltage signal is The amplifier circuit 2, the amplitude limiting amplifier circuit 3, and the equalizing amplifier circuit 4 are determined based on the electrical noise and the shot noise of the APD 1, respectively.

When the amplitude limiting amplifier 3 is operating in the linear amplification region, the preamplifier 2 and the amplitude limiting amplifier 3
Since the gain of the equalizing amplifier circuit 4 is constant, when the optical input level is small, a feedback loop operates so that the multiplication factor of the APD 1 increases, and the amplitude of the output voltage signal of the equalizing amplifier circuit 4 becomes constant. Become.

As the light input level increases, the APD1
And the shot noise is reduced. Accordingly, when the operating area of the APD reaches an optical input level at which the lower limit is reached, shot noise is reduced, and the signal-to-noise ratio of the output voltage signal of the equalizing amplifier circuit 4 is increased as shown in FIG.

When the light input level further increases, the operating area of the APD becomes the lower limit, and the multiplication factor of the APD 1 is fixed to a small value. Since the optical input level is large and the doubling rate is fixed, the amplitude of the input current from the APD 1 to the preamplifier circuit 2 increases, and the amplitude of the output voltage signal of the equalization amplifier circuit 4 becomes as shown in FIG. growing.

Also, since the multiplication factor of the APD 1 is fixed to a small value, shot noise noise is small, and
When the multiplication factor is fixed, the signal-to-noise ratio increases as the light receiving level increases. Therefore, although the amplitude of the output voltage signal increases, the signal-to-noise ratio increases as compared with FIG. 2B.

When the light input level to the APD 1 further increases, the amplitude limiting amplifier 3 operates in the amplitude limiting region, and the amplitude of the output voltage signal of the equalizing amplifier 4 becomes constant. At this time, since the noise is removed by the amplitude limitation, the signal-to-noise ratio of the output voltage signal of the equalizing amplifier circuit 4 is large. When the amplitude of the output voltage signal of the equalizing amplifier circuit 4 is limited, as shown in FIG. 2D, the output voltage signal is a noise-free output voltage signal, and the signal-to-noise ratio is sufficiently large.

[0027]

As described above, according to the present invention, by using an amplitude limiting amplifier circuit which can be constituted by a simple differential amplifier circuit, there is no need to use an AGC circuit having a large circuit size as in the prior art. Can be reduced and simplified,
Further, power consumption can be reduced.

Further, by using an amplitude limiting amplifier circuit which can be constituted by a simple differential amplifier circuit, the dynamic range due to the restriction of the power supply voltage is not narrowed unlike the conventional AGC circuit, and the light receiving dynamic range is increased. . In particular, when the power supply voltage is small, the effect is great.

Further, an output signal having a large signal-to-noise ratio can be obtained as compared with the case where a conventional limit amplifier circuit is used.
When the optical input is small, the shot noise of the APD is superposed but linearly amplified, so that the signal-to-noise ratio of the output signal is large.

Further, since the bias voltage of the APD can be controlled by the feedback loop, it is easy to control the bias voltage of the APD.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a main configuration of an optical receiving circuit according to the present invention.

FIGS. 2A and 2B are diagrams showing output signal waveforms of the optical receiving circuit of the present invention, wherein FIG. 2A is a diagram showing an output signal waveform when the optical input level of the APD is small, and FIG. It is a figure which shows the output signal waveform when a level is large and is near the lower limit of an operation area, (C) is a figure which shows the output signal waveform when it exceeds the lower limit of the operation area of APD, (D) is an amplitude limit FIG. 7 is a diagram illustrating an output signal waveform when the operation of the amplifier is in an amplitude limiting region.

FIG. 3 is a diagram showing an optical receiving circuit using a conventional APD, where (A) is a block diagram showing a main configuration of the optical receiving circuit;
FIG. 3B is a diagram showing details of the AGC circuit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 APD 2 preamplifier circuit 3 amplitude limiting circuit 4 equalizing amplifier circuit 5 peak detection circuit 6 voltage control circuit 7 AGC circuit 8 AGC control circuit

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H03G 3/30

Claims (3)

[Claims] An optical signal amplifier for voltage-converting a current signal photoelectrically converted by a photoelectric conversion element, limiting an amplitude when a voltage level of the voltage-converted voltage is equal to or higher than a predetermined level, and equalizing and amplifying; An optical receiving circuit, comprising: a feedback control unit that detects a peak of an output voltage of the optical signal amplifying unit, compares the output voltage with a preset reference value, extracts a difference, and controls an output current signal of the photoelectric conversion element. . 2. A photoelectric conversion element for photoelectrically converting an optical signal to output a current signal, a preamplifier circuit for current-to-voltage conversion of the current signal to output a voltage signal, and an output voltage of the preamplifier circuit. Amplifying the signal, when the voltage level of the amplified output voltage signal is equal to or higher than a predetermined level, an amplitude limiting amplifier circuit that limits the amplitude of the output voltage signal and outputs the output voltage signal, and an output voltage signal of the amplitude limiting amplifier circuit. An equalizing amplifier circuit for equalizing and amplifying, a peak value detecting circuit for detecting a peak value of the amplitude of the equalized and amplified voltage signal, and comparing the peak value detected by the peak value detecting circuit with a preset reference value. A voltage control circuit for extracting a difference, generating a control signal corresponding to the difference, and controlling an output current signal of the photoelectric conversion element. 3. The method according to claim 1, wherein the photoelectric conversion element is an APD (Aval
3. The optical receiving circuit according to claim 1, wherein the optical receiving circuit is an anchor photo diode.