JPH0998033A - Current-to-voltage converter and optical receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current/voltage converter which can convert the current into the voltage are a wide range of power voltage while maintaining a clamp function. SOLUTION: A current/voltage converter consists of a transistor TR Q1 whose base is connected to an input terminal, a resistor R1 having one of its both ends connected to the collector of the TR Q1, a resistor R2 having one of its both ends connected to the resistor R1 with the other end connected to a power line VCC, a TR Q2 having the base connected to the connection point between both resistors R1 and R2 and the collector connected to a power line VCC, a constant current source I1 having one of its both ends connected to the emitter and the output terminal of the TR Q2 and the other end connected to the line VCC, a resistor R3 having one of its both ends connected to the emitter of the TR Q2 with the other end connected to the base of the TR Q1, a constant current source I2 having one of its both ends connected to a ground line GND, an electrostatic capacitor C1 having one of its both ends connected to the emitter of the TR Q1 with the other end connected to the line GND and the base connected to the collector of the TR Q1 respectively, and a TR Q3 having the emitter and the collector which are connected to the base of the TR Q1 and the line VCC respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current-voltage converter and an optical receiver, and more particularly to a transimpedance circuit for converting a received light signal into a voltage in a device using light as a communication medium. .

[0002]

2. Description of the Related Art In recent years, many devices using light as a communication medium have been developed, and an optical receiver that receives light and outputs a voltage is used for these devices. A current-voltage conversion circuit is required to convert the received light signal into a voltage in the optical receiver. A device using an optical receiver is driven by a commercial power source,
There are various types that are driven by battery power.
Therefore, it can be driven with a wide range of power supply voltage, and
A circuit capable of outputting a voltage having a wide dynamic range is desired.

FIG. 8 is a block diagram of an optical receiver according to a conventional example. In FIG. 8, 1 is a light receiving element that receives light such as infrared rays and generates a photocurrent. A photodiode (PD) is used as the light receiving element 1. 2 is a current-voltage conversion circuit for converting the photocurrent of the light receiving element 1 into a voltage. This conversion circuit 2 includes two npn-type bipolar transistors Q.
1, Q2, one diode D1, three resistors R1
~ R3.

The collector of the transistor Q1 is connected to one end of the resistor R1 and the base of the transistor Q2. The base (input) of the transistor Q1 is connected to the light receiving element 1, the cathode of the diode D1 and one end of the resistor R3, and the emitter thereof. Is connected to the ground line GND. Transistor Q2
Is connected to the power supply line Vcc, and its emitter is connected to the output, one end of the resistor R2, the other end of the resistor R3, and the anode of the diode D1. Resistance R1
Of the resistor R2 is connected to the ground line GND. R3 is called transimpedance.

The diode D1 clamps the voltage drop across the resistor R3. D1 turns on when the photocurrent Ipd flowing through the light receiving element 1 becomes large. At this time, the ON condition of D1 is that the voltage drop of the resistor R3 is the diode D
This is when the forward voltage drop VF of 1 is exceeded. When the diode D1 is turned on, a current flows from the transistor Q2 into the light receiving element 1 to fix the base potential of the transistor Q1 and prevent the collector potential from rising.

3 is an output voltage V of the current-voltage conversion circuit 2.
It is a DC voltage feedback circuit that feeds back 2 to the input. The feedback circuit 3 is composed of a differential amplifier and has an output voltage V2 and a reference voltage Vre.
The input potential of the transistor Q1 is controlled so that f has the same potential. Next, the operation of the optical receiver will be described. For example, when the light receiving element 1 receives light in which light and dark are alternately repeated, a photocurrent Ipd flows through the light receiving element 1. The photocurrent Ipd constitutes logic of “H” (high) level and “L” (low) level according to light and darkness of light.

For example, when the photocurrent Ipd does not flow, the current-voltage converter 2 includes transistors Q1, Q2 and resistors R1.
Since the negative feedback circuit is composed of 1 and R2, the DC potentials of the input V1 and the output V2 are the same potential (V1 = V2 = Vbe). On the other hand, when the photocurrent Ipd flows, ΔV2 = ΔIpd · R as the voltage change amount of the output V2 of the current-voltage converter 2.
3 is obtained. In this way, current-voltage conversion with R3 as the transimpedance can be performed. When the photocurrent Ipd flowing through the light receiving element 1 becomes large and the voltage drop across the resistor R3 exceeds the forward voltage VF of the diode D1, the diode D1 is turned on and a current is supplied from the transistor Q2 to the light receiving element 1. This clamps the transistor Q1.

The DC feedback amplifier 3 removes (cancels) the leak current of the light receiving element 1 and the offset current due to the extraneous light superimposed on the optical signal.

[0009]

However, in the current-voltage conversion circuit 2 of the conventional example, the diode D1 that clamps the transistor Q1 is connected to both ends of the resistor R3, so that there is the following problem. When the photocurrent Ipd shifts from the “H” level to the “L” level, the output waveform is tailed as shown in the broken line circled diagram in FIG. 8. This is because the parasitic capacitance inside the light receiving element 1 and the electric charge accumulated in the diode D1 are discharged. This electric charge is accumulated in the diode D1 which has passed the current through the light receiving element 1. When the input current is large, the output waveform is further tailed, which narrows the dynamic range of the current-voltage conversion circuit. Then, there is a possibility that the analog / digital conversion circuit or the like connected in the subsequent stage may malfunction. Further, if it takes a long time for the charges accumulated in the diode D1 to escape, the frequency response characteristic of the optical receiver deteriorates.

The diode D1 is a transistor Q1.
Needed to clamp. This is the light receiving element 1
When a large amount of light is applied to the
The base potential of the transistor Q1 drops to the potential of the ground line GND. As a result, Q1 deviates from the operating point. Therefore, Q1 is clamped. The current flowing through the transistor Q1 is determined by the power supply voltage and the load resistance R1 of Q1. Therefore, the current flowing through Q1 flows in proportion to the power supply voltage. As a result, if the power supply voltage drops extremely or, on the contrary, greatly increases, and the current flowing through Q1 changes, the frequency response characteristic of Q1 also changes. Q
The frequency response characteristic of 1 greatly changes the frequency output characteristic of the optical receiver. For this reason, when the current flowing in Q1 largely changes due to the power supply voltage, the frequency output characteristic of the optical receiver greatly changes.

Further, considering the operation limit of the current-voltage conversion circuit at low voltage driving, when the power supply voltage VCC becomes equal to or less than the voltage drop of the resistor R1 + 2 × Vbe + VF, the circuit does not operate. Therefore, it has been an obstacle to lowering the voltage of the optical receiver. Note that Vbe is the voltage between the base and emitter of Q1 and Q2. VF is diode D1
Is the voltage drop in the forward direction. Since the diode and the transistor in the same chip are formed by the same junction, VF≈Vbe.

The present invention was created in view of the problems of the conventional example, and it is possible to convert a current into a voltage with a wide range of power supply voltage while maintaining the clamp function. It is intended to provide a receiver and an optical receiver.

[0013]

A first current-voltage converter according to the present invention, as shown in FIG. 1 of the embodiment, includes a first transistor having a base connected to an input and one end of the first transistor. A first resistor connected to the collector of the first transistor; a second resistor having one end connected to the other end of the first resistor and the other end connected to a first power supply line; A second transistor connected to a connection point between the first resistor and the second resistor and having a collector connected to the first power supply line;
A first constant current source having one end connected to the emitter and output of the second transistor and the other end connected to a first power supply line; and one end connected to the emitter of the second transistor, and , A third resistor having the other end connected to the base of the first transistor, and a second resistor having one end connected to the emitter of the first transistor and the other end connected to a second power supply line. A current source, a capacitance having one end connected to the emitter of the first transistor and the other end connected to a second power supply line, and a base connected to the collector of the first transistor, and an emitter connected It is characterized by comprising a third transistor connected to the base of the first transistor and having a collector connected to the first power supply line.

In the first current-voltage converter of the present invention, a feedback circuit for detecting the voltage across the third resistor and adjusting the base potential of the first transistor is provided. To do. In the first current-voltage converter of the present invention, the feedback circuit is provided with a low-pass filter.

In the first current-voltage converter of the present invention, the value of the second resistor is set so that the third transistor is cut off when there is no input to the first transistor. Is characterized by. As shown in FIG. 4, the second current-voltage converter of the present invention has a gate connected to the collector of the first transistor and a source connected to the collector of the first transistor, instead of the third transistor. A field effect transistor having a drain connected to the first power supply line and connected to the base of the first transistor;
The field-effect transistor is adjusted to a threshold voltage larger than a voltage drop between the base and the emitter at which the second transistor is turned on.

A third current-voltage converter of the present invention, as shown in FIG. 5 for its embodiment, has a cathode connected to the collector of the first transistor in the first current-voltage converter. Further, a Schottky barrier diode having an anode connected to the base of the first transistor is provided. The fourth current-to-voltage converter of the present invention, as shown in FIG.
In the current-voltage converter, the diode having the cathode connected to the collector of the first transistor and the anode connected to the first power supply line is provided.

As shown in FIG. 7, a fifth current-voltage converter of the present invention has a first field effect transistor having a gate connected to an input and one end of the first field effect transistor. A first resistor connected to the drain of the transistor, a second resistor having one end connected to the other end of the first resistor and the other end connected to a first power supply line, and a gate connected to the first resistor Second field effect transistor connected to the connection point between the second resistance and the second resistance and the drain connected to the first power supply line, and one end connected to the source and the output of the second field effect transistor. A first constant current source having the other end connected to the first power supply line, one end connected to the source of the second field effect transistor, and the other end connected to the first field effect transistor. A third resistor connected to the gate,
A second constant current source having one end connected to the source of the first field effect transistor and the other end connected to a second power supply line; and one end connected to the source of the first field effect transistor. And a capacitance having the other end connected to the second power supply line, a gate connected to the drain of the first field effect transistor, and a source connected to the gate of the first field effect transistor, and , And a third field effect transistor having a drain connected to the first power supply line.

The sixth current-voltage converter of the present invention is characterized in that the threshold voltage of the third field effect transistor is adjusted to a value higher than the threshold voltage of the second field effect transistor. And An optical receiver according to the present invention includes a light receiving element that converts received light into a current, and a current-voltage conversion circuit that converts a current flowing in the photoelectric element into a voltage, and the current-voltage conversion circuit includes the first to first A sixth aspect of the present invention is characterized in that it comprises any one of a current-voltage converter, and achieves the above object.

The operation of the first current-voltage converter of the present invention will be described. For example, when no input current flows through the first transistor, the input and output DC potentials of the current-voltage converter have the same potential. The DC potentials of the input and the output are potentials obtained by subtracting the voltage drop of the resistor R2 and the voltage drop between the base and emitter of the second transistor from the power supply voltage.
The emitter potential of the first transistor is a DC voltage obtained by subtracting the voltage drop between the base and emitter of the first transistor from the input voltage of the current-voltage converter. Further, since the emitter of the first transistor is grounded in terms of an AC circuit due to the capacitance, this transistor circuit is a so-called grounded-emitter circuit.

Since the input voltage and the output voltage of the current-voltage converter have the same potential, the feedback circuit does not feed back the control signal to the input of the first transistor. On the other hand, the third transistor for clamping also undergoes the same process as the second transistor, and therefore the voltage drop between the base and the emitter is the same. Therefore, the base voltage of the third transistor is smaller than the base voltage of the second transistor by the voltage drop of the first resistor.
No collector current flows through the transistor. As a result, the third transistor does not perform the clamp operation.

Next, when the input current flows through the first transistor, the output of the current-voltage converter is ΔV2 = ΔI.
It becomes pd × R3. However, ΔV2 is a change in the output of the current-voltage converter, and ΔIpd is a change in the input current of the first transistor. R3 is a third resistor. In this way, the current-voltage conversion circuit using R3 as the transimpedance operates.

On the other hand, when the amplitude of the input current flowing through the first transistor is large, the collector current of the first transistor decreases and the collector potential rises. As a result, the third transistor draws a current from the power supply potential and clamps the first transistor. The output of the current-voltage converter at this time is ΔV2 = ΔIpd described above.
The relationship of × R3 is not established, and the output is V2 = VC
It becomes C-R2 · I1-Vbe. However, V2 is the DC output of the current-voltage converter, VCC is the power supply voltage, and R
2 is the second resistor, I1 is the current flowing through the first transistor, and Vbe is the base of the second transistor.
It is the voltage drop between the emitters.

Further, when the input current flowing through the first transistor changes from the "H" level to the "L" level, the charge accumulated in the base of the third transistor becomes
It is pulled out by the first transistor. Thus, according to the first current-voltage converter of the present invention, when the base input of the first transistor falls from the "H" level to the "L" level, the base-emitter of the third transistor is applied. Since the accumulated charge is extracted by the first transistor, the output waveform can be sharply lowered as compared with the case of using the clamp diode as in the conventional example.

Therefore, since the output waveform falls sharply as compared with the conventional example, the dynamic range of the current-voltage conversion circuit can be widened. Further, according to the first current-voltage converter of the present invention, the current flowing through the first transistor is determined by the first constant current source, so that even if the power supply voltage changes, The collector current can be kept constant. As a result, the frequency response characteristic of the first transistor becomes stable.

Further, according to the first current-voltage converter of the present invention, in consideration of the operation limit of the circuit at the time of driving at a low voltage, the power supply voltage VCC has a resistance drop (R1 + R2) + 2 ×.
The circuit can be operated until Vbe or less. Note that Vbe is the voltage drop between the base and emitter of the first transistor and the second transistor. Further, in the first current-voltage converter of the present invention, the feedback circuit that detects the voltage across the third resistor adjusts the base potential of the first transistor, so that a DC offset is superimposed on the input signal. If it was, you can remove it. Further, by providing a low-pass filter in the feedback circuit, the high cut frequency of the current-voltage converter can be determined. The low pass filter will pass signals of frequencies lower than this frequency.

According to the second current-voltage converter of the present invention, the field effect transistor provided in place of the third transistor has a value larger than the voltage drop between the base and the emitter at which the second transistor is turned on. Since the threshold voltage is adjusted to, the field effect transistor can be turned on when the input current becomes large. As a result, the resistor R1 that determines the operation of this field effect transistor
Can be omitted. Therefore, it contributes to the integration of the circuit.

According to the third current-voltage converter of the present invention, since the Schottky barrier diode is connected between the base and collector of the first transistor, the base potential of the first transistor is used as a reference. , It can prevent the voltage of the collector from dropping. Therefore, even when the input current is large, the collector voltage of the first transistor does not decrease, so that the circuit operation is stable.

According to the third current-to-voltage converter of the present invention, the diode includes the collector of the first transistor and the first transistor.
Since it is connected to the first power supply line, it is possible to prevent the collector voltage of the first transistor from lowering with respect to the first power supply line. Therefore, even when the input current is large, the collector voltage of the first transistor does not decrease as in the second current-voltage converter, so that the circuit operation is stable.

According to the fifth current-voltage converter of the present invention, in the first to fourth current-voltage converters, since the signal input circuit and the signal output circuit are composed of field effect transistors, Can be integrated. According to the sixth current-voltage converter of the present invention, the threshold voltage of the third field effect transistor is adjusted to a value larger than the threshold voltage of the second field effect transistor, so that the input current is large. Then, the third field effect transistor can be turned on. Thereby, the resistor R1 that determines the operation of the third field effect transistor can be omitted. Therefore, it contributes to the integration of the circuit.

According to the optical receiver of the present invention, since the current-voltage conversion circuit is composed of any one of the first-sixth current-voltage converters, it can be driven by a wide range of power supply voltage. Moreover, the dynamic range of the current-voltage converter can be expanded. In addition, the first of the current-voltage conversion circuit
Since the frequency response characteristic of the transistor becomes independent of the power supply voltage, the frequency output characteristic of the optical receiver is stable. In addition, the power supply voltage VCC has a resistance drop (R1 + R
2) Since the current-voltage conversion circuit can be operated until the voltage becomes equal to or less than + 2 × Vbe, it is possible to drive the photodetector at a low voltage.

[0031]

Next, an embodiment of the present invention will be described with reference to the drawings. 1 to 7 are explanatory views of the current-voltage converter and the optical receiver according to the embodiment of the present invention. (1) First Embodiment FIG. 1 is a configuration diagram of an optical receiver using a current-voltage converter according to a first embodiment of the present invention, and FIG.
The block diagram of the C feedback circuit is shown. In FIG. 1, reference numeral 11 is a light receiving element (photodiode: PD) that receives light such as infrared rays and generates a photocurrent. The light receiving element 11 utilizes the photoelectric effect of converting light into electric current.

Reference numeral 12 is a current-voltage conversion circuit for converting the current flowing through the light receiving element 11 into a voltage. The current-voltage converter circuit 12 comprises the first current-voltage converter of the present invention. 1, the conversion circuit 12 includes three npn-type bipolar transistors (hereinafter simply referred to as transistors) Q1 to Q3, three resistors R1 to R3, two constant current sources I1 and I2, and one capacitance. It consists of C1.

The transistor Q1 is an example of the first transistor, and its base (input) is connected to the light receiving element 11, the emitter of the transistor Q3 and one end of the resistor R3, and its collector is the base of the transistor Q3 and the resistor R1. Connect to each end. The emitter of the transistor Q1 is connected to the constant current source I1 and one end of the electrostatic capacitance C1, respectively. The constant current source I1 is an example of a first constant current source. The other end of the capacitance C1 is connected to the ground line GND. The capacitance C1 determines the low cut frequency of the transistor Q1.

The other end of the resistor R1 is connected to the base of the transistor Q2 and one end of the resistor R2, respectively. The other end of the resistor R2 is connected to the power supply line Vcc. The resistor R2 is preferably set to a value such that the transistor Q3 is cut off when there is no input to the transistor Q1. The transistor Q2 is an example of a second transistor, the collector of which is connected to the power supply line Vcc, and the emitter of which is connected to the output, the other end of the resistor R3, and the constant current source I2. The constant current source I2 is an example of a second constant current source, and the other end is connected to the ground line GND. The resistor R3 is called transimpedance.

The transistor Q3 is an example of the third transistor and constitutes a clamp transistor. Its collector is connected to the power supply line VCC. Transistor Q3
Is for clamping the transistor Q1. The transistor Q3 turns on when the photocurrent Ipd flowing through the light receiving element 11 becomes large. The ON condition of Q3 at this time is when the photocurrent Ipd increases, the collector current of Q1 decreases, and the collector voltage increases. When the transistor Q3 is turned on, the light receiving element 1
It is possible to prevent the collector potential from dropping by fixing the base potential of the transistor Q1 by flowing a current into the transistor 1.

Reference numeral 13 is a DC feedback circuit which detects the voltage across the resistor R3 and adjusts the base potential of the transistor Q1, and is an example of a feedback circuit. In FIG. 2A, the DC feedback circuit 13 includes a differential amplifier and an output circuit. The differential amplifier includes three pnp type bipolar transistors Q13 to Q15, two npn type bipolar transistors Q11 and Q12, and two constant current sources I.
It consists of 12, I12 and capacitance C11.

In FIG. 2A, the base of the transistor Q11 is connected to the-terminal, and the base of the transistor Q12 is connected to the + terminal. The emitters of the transistors Q11 and Q12 are connected to the constant current source I11. The collector of the transistor Q11 is connected to the collector of the transistor Q13. The collector of the transistor Q12 is connected to the collector of the transistor Q14. The base of transistor Q13 is transistor Q14
Of the transistor Q11. The emitters of the transistors Q13 and Q14 are the power line V
Connect to CC. The collector of the transistor Q14 is connected to the base of the transistor Q15 and one end of the electrostatic capacitance C11.
The other end of the capacitance C11 is connected to the ground line GND. The emitter of the transistor Q15 is connected to the power supply line Vcc. Its collector is connected to the output and a constant current source I12.

The DC feedback circuit 13 can keep the output DC potential constant by adjusting the base potential of the transistor Q1 constant. In FIG. 2B, 13A is a feedback circuit obtained by modifying the DC feedback circuit 13, and is provided with a filter resistor R11. The resistor R11 constitutes a low pass filter together with the electrostatic capacitance C11. The low-pass filter determines the high cut frequency of the DC feedback circuit 13.

Further, FIG. 3A shows a diagram comparing output waveforms of the optical receiver using the current-voltage converter according to each embodiment of the present invention and the conventional optical receiver. . FIG.
(B) shows frequency characteristics of the optical receiver according to each embodiment of the present invention. The vertical axis represents gain and the horizontal axis represents frequency. fL is the low cut frequency. The optical receiver is f
Passes signals with frequencies higher than L.

Next, the operation of the optical receiver using the current-voltage converter according to the first embodiment of the present invention will be described with reference to FIG. For example, when light (predetermined frequency) in which light and dark are alternately repeated is received by the light receiving element 11, a photocurrent Ipd flows through the light receiving element 11. The photocurrent Ipd constitutes logic of "H" (high) level and "L" (low) level according to light and darkness of light as shown in FIG.

For example, when the photocurrent Ipd does not flow in the transistor Q1, the DC potentials of the input V1 and the output V2 of the current-voltage conversion circuit 12 are the same potential. Input V1 and output V
The DC potential of 2 is a potential (≈VCC-R2) obtained by subtracting the voltage drop R2 · I1 of the resistor R2 and the voltage drop Vbe between the base and the emitter of the transistor Q2 from the power supply voltage VCC.
・ I1-Vbe).

The emitter potential of the transistor Q1 changes from the input voltage V1 of the current-voltage conversion circuit 12 to the transistor Q1.
The DC voltage (V1-Vbe) is obtained by subtracting the voltage drop between the base and the emitter of 1. Further, since the emitter of the transistor Q1 is grounded in the AC circuit by the capacitor C1, this transistor circuit is a so-called grounded-emitter circuit.

The DC feedback circuit 13 does not feed back the control signal to the input V1 of the transistor Q1 because the input V1 and the output V2 of the current-voltage conversion circuit 12 have the same potential. On the other hand, the base of clamp transistor Q3
The voltage drop Vbe between the emitters is
Since the voltage drop between the base and emitter of Q2 is larger than Vbe, no collector current flows through the transistor Q3.

Next, when the photocurrent Ipd flows through the transistor Q1, the output V2 of the current-voltage conversion circuit 12 is Δ
V2 = ΔIpd × R3. However, ΔV2 is a change in the output of the current-voltage conversion circuit 12, and ΔIpd is a change in the photocurrent Ipd flowing through the transistor Q1. R3 is the value of the resistor R3. In this way, the current-voltage conversion circuit using R3 as the transimpedance operates.

On the other hand, the photocurrent I flowing through the transistor Q1
When the amplitude of pd is large, the collector current of the transistor Q1 decreases and the collector potential rises. This causes the transistor Q3 to draw a current from the power supply potential and clamp the transistor Q1. The output V2 of the current-voltage conversion circuit 12 at this time is ΔV2 described above.
= ΔIpd × R3 no longer holds, and output V2
Becomes V2 = VCC-R2 · I1-Vbe.

However, V2 is D of the current-voltage conversion circuit 12.
C output, VCC is power supply voltage, R2 is resistor R
A value of 2, I1 is the current through transistor Q1, and Vbe is the base-emitter voltage drop of transistor Q2. Further, when the photocurrent Ipd flowing in the transistor Q1 changes from the “H” level to the “L” level, the charge accumulated in the base of the transistor Q3 becomes
It is pulled out by the transistor Q1.

As described above, according to the optical receiver using the current-voltage converter according to the first embodiment of the present invention, the photocurrent Ipd of the transistor Q1 changes from "H" level to "L" level. When changing, the electric charge accumulated in the base of the transistor Q3 is extracted by the transistor Q1, so that the output waveform sharply changes as shown in FIG. Can be brought down.

Therefore, since the output waveform falls sharply as compared with the conventional example, the dynamic range of the optical receiver can be widened. An analog / digital converter or the like connected in the subsequent stage can accurately convert the pulse width of the input signal into binary data. Further, according to the current-voltage converter of the present invention, the current flowing through the transistor Q1 is determined by the constant current source I1, so that the collector current of the transistor Q1 can be kept constant even if the power supply voltage changes. As a result, the transistor Q
Since the frequency response characteristic of 1 is stable, the frequency output characteristic of the optical receiver is also stable.

Further, according to the current-voltage converter of the present invention, considering the operation limit of the circuit when driven at a low voltage, the circuit is operated until the power supply voltage VCC becomes equal to or lower than the resistance drop (R1 + R2) + 2 × Vbe. Can be operated. In addition,
Vbe is a voltage drop between the base and emitter of the transistor Q1 and the transistor Q2. Therefore, it is possible to reduce the voltage of the optical receiver.

As a result, the voltage range of the driving power source is wide,
Moreover, an optical receiver having a wide dynamic range can be provided. In the current-voltage converter according to the present invention, the DC feedback circuit 13 that detects the voltage across the resistor R3 detects the voltage across the resistor R3 in the transistor Q1.
Since the base potential is adjusted by feeding back to the base of No. 3, it is possible to remove this when a DC offset (a signal component due to external light) is superimposed on the input signal.

In the DC feedback circuit 13A,
By providing the low-pass filter as shown in FIG. 2B, the high cut frequency fL of the current-voltage converter can be determined as shown in FIG. 3B. Further, in the embodiment of the present invention, as shown in FIG. 4, a field effect transistor TN is provided as a clamp transistor instead of the transistor Q3. Transistor T
The gate of N is connected to the collector of the transistor Q1, the source is connected to the base of the transistor Q1, and the drain thereof is connected to the power supply line VCC. Then, the transistor TN adjusts to a threshold value Vth larger than the voltage drop Vbe between the base and the emitter at which the transistor Q2 turns on.

In this way, the transistor TN can be turned on when the photocurrent Ipd is at the "H" level, which is much larger than the normal amplitude. As a result, the resistor R1 that determines the operating voltage of the transistor TN can be omitted, which contributes to circuit integration. (2) Second Embodiment FIG. 5 is a block diagram of an optical receiver using a current-voltage converter according to a second embodiment of the present invention. The second embodiment differs from the first embodiment in that the current-voltage converter 22 is provided with a Schottky barrier diode. In FIG. 5, reference numeral 22 is a current-voltage converter for converting the photocurrent Ipd flowing through the light receiving element 11 into a voltage.
The SBD is a Schottky barrier diode that prevents the collector voltage from dropping with reference to the base potential of the transistor Q1. The cathode of the SBD is connected to the collector of the transistor Q1 and its anode is connected to the base of the transistor Q1. Note that the same reference numerals and names as those in the first embodiment have the same functions, and therefore their explanations are omitted.

As described above, in the optical receiver using the current-voltage converter according to the second embodiment of the present invention, the Schottky barrier diode is connected between the base and collector of the transistor Q1. So transistor Q
It prevents the collector voltage from dropping with reference to the base potential of 1. As a result, even when the amplitude of the base input is large, the collector voltage of the transistor Q1 does not decrease, so that the circuit operation is stable.

(3) Third Embodiment FIG. 6 is a block diagram of an optical receiver using a current-voltage converter according to a third embodiment of the present invention. The third embodiment differs from the first embodiment in that the current-voltage converter 32 is provided with a constant voltage diode. In FIG. 6, reference numeral 32 is a current-voltage converter that converts the photocurrent Ipd flowing through the light receiving element 11 into a voltage. D11 is a diode that prevents the voltage of the collector of the transistor Q1 from dropping with reference to the power supply line Vcc. The cathode of D11 is connected to the collector of the transistor Q1 and its anode is connected to the power supply line Vcc. Note that the same reference numerals and names as those in the first embodiment have the same functions, and therefore their explanations are omitted.

In this way, according to the optical receiver using the current-voltage converter according to the third embodiment of the present invention, the diode D11 includes the collector of the transistor Q1 and the power supply line V.
Since it is connected to CC, it prevents the voltage of its collector from dropping with reference to the power supply line VCC. As a result, even when the amplitude of the base input is large, the collector voltage of the transistor Q1 does not drop as in the second embodiment, so that the circuit operation is stable.

(4) Fourth Embodiment FIG. 7 is a block diagram of an optical receiver using a current-voltage converter according to a fourth embodiment of the present invention. In the fourth embodiment, unlike the first embodiment, the transistors of the current-voltage converter 42 are n-type field effect transistors.

In FIG. 7, reference numeral 42 is a current-voltage converter for converting the photocurrent Ipd flowing through the light receiving element 11 into a voltage. The conversion circuit 42 includes three n-type field effect transistors (hereinafter simply referred to as transistors) TN1 to TN3, three resistors R1 to R3, two constant current sources I1 and I2, and 1
It consists of one capacitance C1. The transistor TN1 is an example of a first field effect transistor, and its gate (input) is connected to the light receiving element 11 and the source of the transistor TN3 and one end of the resistor R3, and its drain is the gate of the transistor TN3 and one end of the resistor R1. Connect to each. The source of the transistor TN1 is connected to the constant current source I1 and one end of the electrostatic capacitance C1. The other end of the constant current source I1 and the other end of the electrostatic capacitance C1 are connected to the ground line GND. The other end of the resistor R1 is connected to the gate of the transistor TN2 and one end of the resistor R2, respectively. The other end of the resistor R2 is connected to the power supply line Vcc. The resistor R2 is preferably set to a value such that the transistor TN3 is cut off when the transistor TN1 is not input.

The transistor TN2 is an example of a second field effect transistor, the drain of which is connected to the power supply line VCC, the source of which is the output and the other end of the resistor R3 and the constant current source I.
2 and 2 respectively. The other end of the constant current source I2 is connected to the ground line GND. The transistor TN3 is an example of the third field effect transistor, and constitutes a clamp transistor as in the first to third embodiments. Its drain is connected to the power supply line VCC. The transistor TN3 clamps the transistor TN1. The transistor TN3 turns on when the photocurrent Ipd flowing through the light receiving element 11 becomes large. The ON condition of TN3 at this time is T
This is when the gate potential of N1 decreases, the drain current of TN1 decreases, and the drain voltage increases. When the transistor TN3 is turned on, a current is supplied from the power supply line Vcc to the light receiving element 11 to fix the gate potential of the transistor TN1 and prevent the drain potential from decreasing. Note that the same reference numerals and names as those in the first embodiment have the same functions, and therefore their explanations are omitted.

Next, the operation of the optical receiver using the current-voltage converter according to the fourth embodiment of the present invention will be described. For example, when the photocurrent Ipd does not flow in the transistor TN1,
The DC potentials of the input V1 and the output V2 of the current-voltage conversion circuit 42 are the same potential. The DC potentials of the input V1 and the output V2 are substantially the voltage drop R2 of the resistor R2 from the power supply voltage VCC.
The potential becomes a potential (.apprxeq.VCC-R2.I1-Vth) obtained by subtracting I1 and the threshold Vth of the transistor TN2.

The source potential of the transistor TN1 is the current −
The DC voltage (V1-Vth) is obtained by subtracting the threshold value of the transistor TN1 from the input V1 of the voltage conversion circuit 42. Further, since the source of the transistor TN1 is grounded by the capacitor C1 in an AC circuit manner, this transistor circuit is a so-called source ground circuit. Further, since the input V1 and the output V2 of the current-voltage conversion circuit 42 have the same potential, D
The C feedback circuit 13 does not feed back the control signal to the input V1 of the transistor TN1. On the other hand, the threshold value Vth of the clamping transistor TN3 is the same as the other transistors TN1 and T3.
Since it is larger than the threshold value Vth of N2, another transistor TN
If the gate voltage higher than the gate voltages of 1 and TN2 is not input, the transistor TN3 does not turn on. Therefore, the drain current I1 does not flow through the transistor TN3 at this time.

Next, when the photocurrent Ipd flows through the transistor TN1, the output V2 of the current-voltage conversion circuit 42 is Δ
V2 = ΔIpd × R3. However, ΔV2 is the amount of change in the output of the current-voltage conversion circuit 42, and ΔIpd is the amount of change in the photocurrent Ipd flowing through the transistor TN1. R3 is the value of the resistor R3. In this way, the current-voltage conversion circuit using R3 as the transimpedance operates.

If the current when the photocurrent Ipd is at the “L” level is IpdL and the current when the photocurrent Ipd is at the “H” level is IpdH, then the change amount of the input current is ΔIpd =
Since it is IpdH-IpdL, the output V2 of the current-voltage conversion circuit 42 is ΔV2 = ΔIpd × R3. On the other hand, when the amplitude of the photocurrent Ipd flowing through the transistor TN1 is large, the drain current of the transistor TN1 decreases and the drain potential increases. As a result, the gate voltage of the transistor TN3 rises, turning on the transistor TN3, so that a current is drawn from the power supply potential to clamp the transistor TN1. Current-voltage conversion circuit 4 at this time
The output V2 of No. 2 does not hold the relationship of ΔV2 = ΔIpd × R3 described above, and the output V2 is V2 = VCC−
R2 · I1-Vth.

However, V2 is D of the current-voltage conversion circuit 42.
C output, VCC is power supply voltage, R2 is resistor R
2 is a value, I1 is a current flowing through the transistor TN1, and Vth is a threshold value of the transistor TN2. When the photocurrent Ipd flowing in the transistor TN1 changes from the “H” level to the “L” level, the charge accumulated in the gate of the transistor TN3 is extracted by the drain of the transistor TN1.

As described above, in the optical receiver using the current-voltage converter according to the fourth embodiment of the present invention, the gate input of the transistor TN1 changes from "H" level to "L" level. At this time, the electric charge accumulated in the gate of the transistor TN3 is extracted by the transistor TN1, so that the output waveform can be sharply lowered as in the first embodiment.

Therefore, as in the first embodiment,
The dynamic range of the current-voltage conversion circuit 42 can be widened. An analog / digital conversion circuit or the like connected to the subsequent stage of the optical receiver can accurately convert the pulse width of the input signal into binary data. Further, according to the current-voltage converter of the present invention, the transistor T
Since the current flowing through N1 is determined by the constant current source I1, the drain current of the transistor TN1 can be kept constant even if the power supply voltage changes. As a result, the frequency response characteristic of the transistor TN1 is stabilized, and the frequency output characteristic of the optical receiver is also stabilized.

Further, according to the current-voltage converter of the present invention, similarly to the first embodiment, in consideration of the operation limit of the circuit at the time of low voltage driving, the power supply voltage VCC causes the resistance drop (R1 + R2). ) The circuit can be operated until + 2 × Vth or less. Therefore, it is possible to reduce the voltage of the optical receiver. Note that Vth is a threshold voltage of the transistors TN1 and TN2.

As a result, like the first embodiment,
It is possible to provide an optical receiver having a wide driving power supply voltage range and a wide dynamic range. Further, since the current-voltage converter 42 is composed of the n-type field effect transistors TN1 to TN3, the circuit can be integrated. In the embodiment of the present invention, by adjusting the threshold value Vth of the transistor TN3 to a value larger than the threshold value Vth of the transistor TN2, when the photocurrent Ipd is at the “H” level which is much larger than the normal amplitude, The transistor TN3 can be turned on. As a result, the resistor R1 that determines the operating voltage of the transistor TN3 can be omitted. Therefore, the circuit can be integrated.

[0068]

As described above, according to the current-voltage converter of the present invention, when the base input of the first transistor changes, the charge accumulated in the base of the third transistor changes to the first charge. Since it is pulled out by the transistor, the output waveform can be sharply lowered as compared with the case of using the clamp diode as in the conventional example. Therefore, the dynamic range of the current-voltage converter can be widened.

According to another current-voltage converter of the present invention,
Since the Schottky barrier diode is connected between the base and collector of the first transistor, it is possible to prevent the voltage of the collector of the first transistor from dropping with reference to the base potential of the first transistor. Moreover, since the diode is connected between the collector of the first transistor and the first power supply line, the voltage of the collector can be increased with reference to the first power supply line. As a result, even if the amplitude of the base input is large, the collector voltage of the first transistor does not decrease, so that the circuit operation is stable.

According to the current-voltage converter of the present invention, the signal input circuit and the signal output circuit are composed of field effect transistors, so that the circuit can be integrated. According to the optical receiver of the present invention, the current-voltage conversion circuit includes the current-voltage conversion circuit of the present invention.
Since it is composed of the voltage converter, it is possible to widen the voltage range of the driving power supply and wide the dynamic range of the current-voltage converter.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical receiver using a current-voltage converter according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a DC feedback circuit according to each embodiment of the present invention.

FIG. 3 is a diagram comparing output waveforms of the optical receiver according to each embodiment of the present invention and an optical receiver of a conventional example, and a frequency characteristic diagram of the optical receiver.

FIG. 4 is a configuration diagram of an optical receiver using another current-voltage converter according to the first embodiment of the present invention.

FIG. 5 is a configuration diagram of an optical receiver using a current-voltage converter according to a second embodiment of the present invention.

FIG. 6 is a configuration diagram of an optical receiver using a current-voltage converter according to a third embodiment of the present invention.

FIG. 7 is a configuration diagram of an optical receiver using a current-voltage converter according to a fourth embodiment of the present invention.

FIG. 8 is a configuration diagram of an optical receiver using a current-voltage converter according to a conventional example.

[Explanation of symbols]

1, 11 ... Light receiving element, 2, 12, 22, 32, 42 ... Current-voltage conversion circuit, 3, 13 ... DC feedback circuit, Q1 to Q3, Q11, Q12 ... Npn type bipolar transistor, Q13 to Q15 ... pnp Type bipolar transistors, TN1 to TN3 ... N type field effect transistors, R
1 to R3 ... resistors, I1, I2, I11, I12 ... constant current source,
C1, C11 ... Capacitance.

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

Claims (10)

[Claims] 1. A first transistor having a base connected to an input, a first resistor having one end connected to a collector of the first transistor, one end connected to the other end of the first resistor, and A second resistor having the other end connected to the first power supply line, a base connected to the connection point of the first resistance and the second resistance, and a collector connected to the first power supply line. A second constant current source, one end of which is connected to the emitter and output of the second transistor and the other end of which is connected to a first power supply line; and one end of which is the emitter of the second transistor. And a third resistor having the other end connected to the base of the first transistor, one end connected to the emitter of the first transistor, and the other end connected to the second power supply line. Second constant current source, and one end of the first transistor Connected to the emitter of the motor, and a capacitance connected to the other end to a second power supply line, a base connected to the collector of said first transistor,
Connecting the emitter to the base of the first transistor,
A current-voltage converter comprising a third transistor having a collector connected to the first power supply line. 2. A current circuit according to claim 1, further comprising a feedback circuit for detecting a voltage across the third resistor and adjusting a base potential of the first transistor.
Voltage converter. 3. The current-voltage converter according to claim 2, wherein the feedback circuit is provided with a low-pass filter. 4. The current value according to claim 1, wherein the value of the second resistor is set so that the third transistor is cut off when there is no input to the first transistor. Voltage converter. 5. Instead of the third transistor, a gate is connected to the collector of the first transistor, a source is connected to the base of the first transistor, and
A field effect transistor having a drain connected to the first power supply line is provided, and the field effect transistor is adjusted to a threshold voltage larger than a base-emitter voltage at which the second transistor is turned on. The current-voltage converter according to claim 1. 6. A Schottky barrier diode having a cathode connected to the collector of the first transistor and an anode connected to the base of the first transistor. Current-voltage converter. 7. A current-voltage converter according to claim 1, further comprising a diode having a cathode connected to the collector of the first transistor and an anode connected to the first power supply line. vessel. 8. A first field effect transistor having a gate connected to an input, a first resistor having one end connected to a drain of the first field effect transistor, and one end connected to the other end of the first resistor. A second resistance connected to the first power supply line and the other end connected to the first power supply line; a gate connected to the connection point of the first resistance and the second resistance; and a drain connected to the first power supply line. A second field effect transistor connected to the first field effect transistor, and a first field effect transistor having one end connected to a source and an output of the second field effect transistor and the other end connected to a first power supply line.
Constant current source, a third resistor having one end connected to the source of the second field effect transistor and the other end connected to the gate of the first field effect transistor, and one end of the first resistor A second constant current source connected to the source of the field effect transistor and having the other end connected to the second power supply line; one end connected to the source of the first field effect transistor and the other end A capacitance connected to a second power supply line, a gate connected to the drain of the first field effect transistor, a source connected to the gate of the first field effect transistor, and a drain connected to the first field effect transistor. A current-voltage converter comprising a third field effect transistor connected to a power line. 9. The current according to claim 8, wherein the threshold voltage of the third field effect transistor is set to a value higher than the threshold voltages of the first and second field effect transistors. A voltage converter. 10. A light receiving element for converting received light into a current, and a current for converting current flowing through the photoelectric element into a voltage.
And a voltage conversion circuit, wherein the current-voltage conversion circuit is claim 1, claim 2, claim 3, claim 4, claim 5, claim 6, claim 7, claim 8 or claim 9. An optical receiver comprising a current-voltage converter according to any one of 1.