JPH05122158A - Photoelectric converter - Google Patents

Abstract

PURPOSE:To cancel a noise by executing the current/voltage conversion of a signal obtained by the current/voltage conversion of a signal outputted from a photodetecting photoelectric conversion element and a signal outputted from a shielded photoelectric conversion element, comparing and amplifying both the signals. CONSTITUTION:An optical signal is received by a 1st photoelectric conversion element 1 and an output from the element is converted by a 1st current/voltage conversion circuit 2. On the other hand, an output from a shielded 2nd photoelectric conversion element 5 having the same structure as the element 1 is converted by a 2nd current/voltage conversion circuit 6 having the same structure as the circuit 2. Outputs from both the circuits 2, 6 are inputted to a differential amplifier circuit 11 and compared and amplified to cancel a noise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric conversion device for transmitting data by optical signals.

[0002]

2. Description of the Related Art FIG. 3 shows a circuit example of a conventional photoelectric conversion device. In the figure, 1 is a first photoelectric conversion element that receives a transmitted optical signal and converts it into an electric signal, 2 is a first current-voltage conversion circuit that converts the signal of the first photoelectric conversion element 1 into current-voltage, and 3 is A first amplifier circuit that amplifies the output signal of the first current-voltage conversion circuit 2, a comparator 4 that compares the output signal Vs of the amplifier circuit 3 and a reference voltage Vr, and reproduces and outputs as a signal output Vo. A light-shielded second photoelectric conversion element having the same structure as the conversion element 1, 6 is a second current-voltage conversion circuit that is the same as the first current-voltage conversion circuit 2, and 7 is a first current-voltage conversion circuit that is the same as the first amplification circuit 3. Two amplifier circuits. Further, 8 is a voltage dividing circuit that divides the outputs of the first amplifying circuit 3 and the second amplifying circuit 7 and outputs the potential at the midpoint thereof as the hold reference signal Vh, and 9 is the hold reference signal Vh from the voltage dividing circuit 8. It is a peak value hold circuit that holds the maximum value.

FIG. 4 is an operation waveform diagram for explaining FIG. In the figure, V1 is a transmission side drive pulse waveform for generating an optical signal of a light source (not shown), and Vs is a signal converted into a photocurrent by the first photoelectric conversion element 1, and further the first current-voltage conversion circuit 2 and The waveform is converted and amplified by the first amplifier circuit 3.

Vz is an output waveform of the second amplifier circuit 7.

Vr indicates the level of the reference voltage, and this value V
r and the output signal Vs are compared in magnitude by the comparator 4, and a predetermined binary output (high level or low level) is output and reproduced and output as the signal output Vo.

In this case, the output signal V depends on the operating characteristics of the first photoelectric conversion element 1, the first current-voltage converting circuit 2 and the second amplifying circuit 3 and the operating characteristics of the light source and the optical transmission line (not shown).
Since a time delay occurs in the rising and falling of s, the level of the reference voltage Vr is set so that the pulse width of the signal output V _O becomes equal to the pulse width of the transmission side drive pulse V1.
It is necessary to set the value to 1/2 of the pulse amplitude of.

Further, the pulse amplitude of the output signal Vs is reduced due to a decrease in the amplitude of the transmission side drive pulse V1 or fluctuations in the characteristics of the first photoelectric conversion element 1, the first current / voltage conversion circuit 2 and the first amplification circuit 3. May change.

In this example, even at this time, the reference voltage Vr of the comparator 4 holds the potential at the midpoint of the output signal Vs and the output signal Vz of the second amplifier circuit 7 by the voltage dividing circuit 8 and the peak value holding circuit 9. ing.

Since the output signal Vz has the same potential as the signal output Vs when no optical signal is input, the reference voltage Vz
r holds a value of 1/2 of the pulse amplitude of the output signal Vs, and the pulse width of the signal output Vo is kept equal to the pulse width of the transmission side drive pulse V1.

[0010]

Usually, since the optical signal input to the first photoelectric conversion element 1 is very small, the amplification factors of the current-voltage conversion circuits 2 and 6 and the amplification circuits 3 and 7 are set to be large. For this reason, the output signals Vs and Vz are likely to have noise. In particular, as shown in FIG. 5, when the output signal Vs is inverted, noise that enters both photoelectric conversion elements 1 and 5 through the power supply line appears as in-phase noise in the output signals Vs and Vz. At this time, the reference voltage Vr is Vh proportional to Vz.
Is held at a peak value, the level is set to a level different from the reference voltage Vr in the case where there is no original noise. Therefore, 1/2 of the pulse amplitude of the output signal Vs is set.
However, there is a drawback in that a deviation ΔS occurs in the pulse width of the signal output Vo due to the deviation from the value of.

Also, there is a time delay Δt from when the output signal Vs becomes equal to the reference voltage Vr until the signal output Vo changes.
Therefore, the frequency of the optical signal increases and the signal output Vo increases.
When the output signal Vs falls at the same time when the signal rises, or when the output signal Vs rises at the same time when the signal output Vo falls, it is particularly susceptible to noise.

In view of the above problems, the present invention aims to provide a photoelectric conversion device that is resistant to noise.

[0013]

As shown in FIGS. 1 and 2, the means for solving a problem according to the first aspect of the present invention is to convert an optical signal into an electric signal Vx.
A photoelectric conversion circuit A for converting the electric signal Vx to a reference voltage Vr2, a comparator 4 which inputs the electric signal Vx and a reference voltage Vr2 and outputs a predetermined binary output based on the magnitude relationship between them, and a reference voltage generation circuit B which determines the reference voltage Vr2. The reference voltage generating circuit B includes a peak value holding circuit 9 for holding the maximum value of the reference voltage Vr, and a plurality of resistors R for dividing the electric signal Vx to supply the peak value holding circuit 9 with the reference voltage Vr. The photoelectric conversion circuit A comprises a first voltage conversion circuit 1 for receiving an optical signal, and a voltage dividing circuit 12 for inputting a hold reference signal Vh as a base. A first current-voltage conversion circuit 2 for converting a signal into a current-voltage, a light-shielded second photoelectric conversion element 5 having the same structure as the first photoelectric conversion element 1, and the same as the first current-voltage conversion circuit 2 Has a structure and is shaded The second current-voltage conversion circuit 6 for converting the signal from the second photoelectric conversion element 5 into a current-voltage, the first output Va from the first current-voltage conversion circuit 2, and the second current-voltage conversion circuit 6 A differential amplifier circuit 1 that compares the second output Vb and cancels the noise of both outputs Va and Vb.
It is composed of 1 and 1.

According to a second aspect of the present invention, there is provided a means for solving the problems, wherein the differential amplifier circuit 11 according to the first aspect is configured to output the inverted output Vx and the non-inverted output Vy in a state where noise is eliminated. The inverted output Vx of the differential amplifier circuit 11 is input to the comparator 4 described in 1, and the inverted output Vx and the non-inverted output Vy of the differential amplifier circuit 11 are input to the voltage dividing circuit 12 according to claim 1. The peak value hold circuit 9 according to claim 1 is configured so that an output obtained by dividing the inverted output Vx and the non-inverted output Vy into three quarters by the voltage dividing circuit 12 is input. ..

According to a third aspect of the present invention, the photoelectric conversion circuit A, the comparator 4 and the reference voltage generating circuit B according to the first and second aspects are integrated in one chip.

[0016]

In the problem solving means according to claim 1, the received optical signal is converted into a current by the first photoelectric conversion element 1,
It is input to one side of the differential amplifier circuit 11 via the first current-voltage conversion circuit 2. In addition, the second photoelectric conversion element 5 that is shielded from light
The current from is also input to the other end of the differential amplifier circuit 11 via the second current-voltage conversion circuit 6. The differential amplifier circuit 11 is
The outputs Va and Vb from both current-voltage conversion circuits 2 and 6 are compared, and the comparator 4 and the voltage dividing circuit 1 of the reference voltage generating circuit B are compared.
Output to 2.

Here, the differential amplifier circuit 11 cancels out the noise of both the outputs Va and Vb from the current-voltage conversion circuits 2 and 6 and prevents their influence.

Then, the voltage dividing circuit 12 divides the electric signal Vx, which is not affected by noise, by the plurality of resistors R and outputs the hold reference signal Vh, which is the basis of the reference voltage Vr, to the peak value holding circuit 9 for peaking. The value hold circuit 9 holds the maximum value of the reference voltage Vr based on the hold reference signal Vh.

After that, the comparator 4 inputs the electric signal Vx which is not affected by noise and the reference voltage Vr2, and outputs a predetermined binary output according to the magnitude relationship.

In the problem solving means according to the second aspect, the pulse amplitude of the output signal Vx may change due to variations in the characteristics of the photoelectric conversion element 1, the current-voltage conversion circuit 2, and the amplification circuit 3, but the comparator 4 The reference voltage Vr2 is always output by the voltage dividing circuit 12 and the peak value holding circuit 9 as the output signal Vr.
Since the maximum value of the potential at the point of 3/4 between x and the output signal Vy which is the opposite phase output thereof is held, the reference voltage Vr2 has a value of 1/2 of the pulse amplitude of the pulse V1 of the output signal Vx. The pulse width of the signal output Vo is kept equal to the pulse width of the transmission side drive pulse V1.

In the problem solving means according to claim 3, all circuits 1, 2, 4, 5, 6, 9, 11, 1 of the photoelectric conversion device are provided.
Since 2 is integrated in one chip, the effect of noise is reduced, and since the characteristics of each photoelectric conversion element 1, 5 and each current-voltage conversion circuit 2, 6 match, the effect of canceling noise is further improved. growing.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit configuration diagram showing a photoelectric conversion device according to an embodiment of the present invention, and FIG. 2 is an operation waveform diagram in each part thereof. The same reference numerals as those in the conventional example shown in FIG. 3 indicate the same components.

In FIG. 1, A is a photoelectric conversion circuit for converting an optical signal into an electric signal Vx, B is a reference voltage generation circuit for determining a reference voltage Vr2 as a high / low comparison reference of the electric signal Vx, and 1 is transmission. A first photoelectric conversion element for receiving the received optical signal and converting it into an electric signal, 2 is a first current-voltage conversion circuit for converting a signal of the first photoelectric conversion element 1 into a current-voltage, and 5 is a first photoelectric conversion element 1. A light-shielded second photoelectric conversion element having the same structure, 6 is a second current-voltage conversion circuit having the same structure as the first current-voltage conversion circuit 2. Reference numeral 11 is a differential amplifier that receives the first output Va of the first current-voltage conversion circuit 2 and the second output Vb of the second current-voltage conversion circuit 6, and 4 is an inverted output signal Vx of the differential amplifier 11. Reference voltage Vr2
And a comparator similar to the conventional one which reproduces and outputs as a signal output Vo, and 12 denotes an inverted output signal Vx of the differential amplifier circuit 11.
And a voltage divider circuit that divides the non-inverted output signal Vy and outputs the potential at the 3/4 point as a hold reference signal Vh, and 9 is the same as the conventional one that holds the maximum value of the hold reference signal Vh from the voltage divider circuit 8. It is a peak value hold circuit of.

On one input side of the differential amplifier 11,
The output side of the current-voltage conversion circuit 2 on the one side is connected, and the output side of the current-voltage conversion circuit 6 on the other side is connected to the other input side of the differential amplifier 11. In addition, the differential amplifier 1
The inverted output of 1 is connected to one input side of the comparator 4.

The voltage dividing circuit 12 is composed of four resistors Ra to Rd having the same resistance value, one of which is a resistor R.
One end of a is connected to the contact between the inverting output of the differential inversion inverting device 11 and the comparator 4, and the other end is connected to the remaining resistors Ra to Rd. The resistors Rb to Rd are connected in series with each other, one end of which is connected to the non-inverting output of the differential amplifier 11 and the other end of which is connected to the input side of the peak value holding circuit 9.

Then, all the circuits 1, 2, 4, 5, 6,
9, 11, and 12 are monolithically integrated on one chip.

Next, the circuit operation of the photoelectric conversion device will be described.

In FIG. 2, V1 is a transmission side drive pulse waveform for generating an optical signal of a light source (not shown), Va is a waveform obtained by converting the signal into a photocurrent by the first photoelectric conversion element 1, and Vx is a difference. The inverted waveform is amplified by the dynamic amplifier circuit 11. Note that Vy shown in FIG. 1 is a non-inverted output waveform corresponding to Vx of the differential amplifier circuit 11. Also,
Vr2 indicates the level of the reference voltage. The value Vr2 and the output signal Vx are compared by the comparator 4 to determine whether they are equal to a predetermined value.
Value output (high level or low level) and signal output V
Reproduce and output as o.

In this case, the rising edge of the output signal Vx depends on the operating characteristics of the first photoelectric conversion element 1, the first current-voltage converting circuit 2, the differential amplifier circuit 11 and the operating characteristics of the light source and the optical transmission line (not shown). Since there is a time delay in the fall, it is necessary to set the reference voltage Vr2 to a value of 1/2 of the pulse amplitude of the output signal Vx so as to be equal to the pulse width of the pulse V1 of the signal output Vo.

Further, the pulse amplitude of the output signal Vx may change due to a decrease in the amplitude of the transmission side drive pulse V1 or a change in the characteristics of the first photoelectric conversion element 1 and the first current-voltage conversion circuit 2.

In the circuit of this embodiment, the comparator 4 is used even at this time.
The reference voltage Vr2 of the output voltage Vr2 of the voltage dividing circuit 12 and the peak value holding circuit 9 is always the potential at the 3/4 point of the output signal Vx and the output signal Vy which is the opposite phase output (hold reference signal Vr).
It holds the maximum value of h).

Since the midpoint potential Vk between the output signal Vx and the output signal Vy is the same potential as the signal output Vx when no optical signal is input, the hold reference signal Vh is 1 of the pulse V1 of the output signal Vx. Therefore, the reference voltage Vr2 holds half the value of the pulse amplitude of the pulse V1 of the output signal Vx, and the pulse width of the signal output Vo is the pulse of the transmission side drive pulse V1. Kept equal to width.

According to the present embodiment, when the output signal Vo is inverted, the noise that enters the photoelectric conversion elements 1 and 5 through the power supply line appears as the in-phase noise in the output signals Va and Vb. Output signal V for cancellation
Since no noise is generated in x and Vy, the peak value hold circuit 9 is not affected. Therefore, the reference voltage Vr2
Holds the value of 1/2 of the pulse amplitude of the output signal Vx, and the pulse width of the signal output Vo of the comparator 4 is the transmission side drive pulse V
Will be kept equal to one pulse width.

It is apparent from the above description that the noise has the same effect not only on the noise when the output signal is inverted but also on other external noises.

The present invention is not limited to the above embodiment, and it goes without saying that many modifications and changes can be made to the above embodiment within the scope of the present invention.

[0036]

As described above, according to the first aspect of the present invention, the differential amplifier circuit of the photoelectric conversion circuit includes the current-voltage conversion circuit for converting the signal from the light-receiving photoelectric conversion element into the current-voltage conversion, and the light-shielding circuit. Comparing both outputs with a current-voltage conversion circuit that converts the signal from the photoelectric conversion element that has been converted into a current voltage and canceling the noise, a photoelectric conversion device that is resistant to noise is provided without using a complicated circuit. can do.

According to the second aspect, the inverting output and the non-inverting output of the differential amplifier circuit are divided into three quarters by the voltage dividing circuit, and the reference voltage to be compared with the electric signal is determined based on the divided voltage. Therefore, even when configured as in claim 1,
The reference voltage to be compared with the electric signal is the maximum value of the electric signal, 2
Even if the amplitude value of the received optical signal and the amplitude value of the photoelectrically converted electrical signal change, the pulse width of the output signal is equal to the pulse width of the received pulse signal and stable extraction is possible. This makes it possible to prevent the pulse width from being affected by the time delay at the rise and fall of the output signal.

According to the third aspect, all the circuits of the photoelectric conversion device are integrated in one chip, so that it is convenient when the circuits are mounted on the substrate.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a photoelectric conversion device showing an embodiment of the present invention.

FIG. 2 is a waveform diagram showing the same operation.

FIG. 3 is a circuit configuration diagram of a conventional photoelectric conversion device.

FIG. 4 is a waveform diagram showing the same normal operation.

FIG. 5 is a waveform diagram showing an operation in a state in which the noise is also included.

[Explanation of symbols]

 1, 5 Photoelectric conversion element 2, 6 Current-voltage conversion circuit 4 Comparator 9 Peak value hold circuit 11 Differential amplifier circuit 12 Voltage dividing circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H03F 3/08 7328-5J

Claims (3)

[Claims] 1. A photoelectric conversion circuit for converting an optical signal into an electric signal, a comparator for inputting the electric signal and a reference voltage and outputting a predetermined binary output based on the magnitude relationship between the electric signal and a reference for determining the reference voltage. A reference voltage generating circuit, wherein the reference voltage generating circuit is a peak value holding circuit for holding the maximum value of the reference voltage, and an electric signal is divided by a plurality of resistors to serve as a basis of the reference voltage in the peak value holding circuit. A voltage dividing circuit for inputting a hold reference signal, wherein the photoelectric conversion circuit is a first photoelectric conversion element for receiving an optical signal, and a first current voltage for current-voltage converting the signal from the photoelectric conversion element. From the light-shielded second photoelectric conversion element having the same structure as the first current-voltage conversion circuit, and the light-shielded second photoelectric conversion element having the same structure as the conversion circuit, the first photoelectric conversion element Belief And a second current-voltage conversion circuit for converting the current-voltage into a first output from the first current-voltage conversion circuit and a second output from the second current-voltage conversion circuit, and a differential for canceling noise of both outputs. A photoelectric conversion device comprising an amplifier circuit. 2. The differential amplifier circuit according to claim 1 is configured to output an inverting output and a non-inverting output in a state in which noise is eliminated, and the comparator according to claim 1 includes a differential amplifier circuit The inverting output is input, the inverting output and the non-inverting output of the differential amplifier circuit are input to the voltage dividing circuit according to claim 1,
The photoelectric conversion according to claim 1, wherein the peak value hold circuit is configured to receive an output obtained by dividing the inverted output and the non-inverted output into three quarters by a voltage dividing circuit. apparatus. 3. A photoelectric conversion device according to claim 1, wherein the photoelectric conversion circuit, the comparator and the reference voltage generating circuit are integrated in one chip.