JPH1075217A - Current input type receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a receiver having wide versatility to various communication formats in a current input type receiver which is used for an optical communication system, based on infrared rays, for example. SOLUTION: A current/voltage coverting circuit 3 is connected through a capacitor C1 for coupling capacitances to a signal source circuit 2 comprising a photodiode 21 and a bias resistor 23 for forming a current signal source. A limiter amplifier 4 provided with a two-stage differential amplifier is connected to the output stage of the current/voltage converting circuit 3, further, a comparator 5 is connected to its output stage, and the block from the photodiode 21 to the input terminal of the comparator 5 is made into primary high-pass filter. Since there is capacitive coupling on the input side of the current/voltage converting circuit 3, the resistor 33 of the current/voltage converting circuit 3 contains no DC component so that conversion efficiency can be improved. Therefore, since the gain of the amplifier on the following stage can be reduced, an offset voltage can be removed by trimming and since it is not necessary to provide capacitve coupling as a result, the place to set a time constant is only one.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current input type receiver in which, for example, a photodiode is used as a current signal source in an optical communication system.

[0002]

2. Description of the Related Art As one of optical communication systems, a pulse signal based on infrared light is transmitted from a photodiode on a transmitting side.
Some receivers receive this infrared light and convert it into a current signal. FIG. 17 shows an example of a conventional receiver used for this type of optical communication. This receiver includes a signal source circuit 1 including a photodiode 10 as a current signal source and a bias power supply 11, and a photodiode on the emitter side. 10 is connected, a current-voltage conversion circuit 12 including a transistor 12b and a constant current source 12c having a resistor 12a connected to the collector side, a limiter amplifier 13 including two-stage amplifiers 13a and 13b, and a comparator 14. Have. 1
Reference numerals 5, 16, and 17 denote capacitors, and reference numeral 18 denotes a reference power supply.

In this receiver, the photodiode 10 receives a pulse signal transmitted from the transmitter 100 by infrared light, and a current flows through the photodiode 10 according to the received light signal. This current is converted into a voltage by the current-voltage conversion circuit 12, and the voltage pulse enters the comparator 14 through the limiter amplifier 13 and is extracted as a rectangular pulse.

By the way, between the current-voltage conversion circuit 12 and the amplifier 13a at the preceding stage of the limiter amplifier 13, between the amplifier 13a at the preceding stage of the limiter amplifier 13 and the amplifier 13b at the subsequent stage, and between the amplifier 13b at the latter stage and the comparator 14 Capacitors 15, 16, and 17 are interposed therebetween, and the respective components are capacitively coupled. The reason will be described below. First, a DC component may be superimposed on the output of the current-voltage conversion circuit 12 due to the influence of ambient light such as sunlight or a room light, and this becomes an offset voltage of the current-voltage conversion circuit 12. A capacitor 15 is provided on the output side of the current-voltage conversion circuit 12 to remove the voltage.

Since the light receiving intensity varies depending on the variation of the light source such as the light emitting diode, the magnitude of the current taken out from the photodiode 10 is, for example, 100 nA to 16 m.
There is considerable width with A. On the other hand, since the light emitting diode on the light emitting side and the photodiode on the light receiving side are slow in operation, if the frequency of the signal is high, a current based on light emission remains in the photodiode even if the pulse of the electric signal disappears. For this reason, when the light receiving intensity is strong (at the time of strong input), the current of the photodiode 10 on the light receiving side may not return to the zero level, and a residual current may be present.

FIG. 18 is a view showing this situation. Before the current flowing through the photodiode 10 returns to zero level, the photodiode 10 rises by receiving the next light pulse, and there is a residual current. Therefore, if the capacitor 15 is not provided, a voltage pulse output from the current-voltage conversion circuit 12 at the time of strong input may be connected.

The provision of the capacitors 16 and 17 further increases the gain of the amplifiers 13a and 13b because the current-voltage conversion efficiency of the current-voltage conversion circuit 12 cannot be increased. This is because a large offset voltage is generated at 13b, and this offset voltage must be removed. That is, in the current-voltage conversion circuit 12, since the value of the current flowing through the photodiode 10 has a considerably large width, in order to pick up a large current or a small current as a voltage pulse, it is omitted in the drawing. It must have a limiter function.

On the other hand, the resistor 12a of the current-voltage conversion circuit 12
Since the DC component flows as described above, the resistance value of the resistor 12a cannot be increased so much. If the resistance value is increased, a large voltage, for example, a voltage of about 1 V, is generated only by the DC component, and the output voltage swings off. Therefore, resistance 1
The resistance value of 2a is limited, and the current-voltage conversion efficiency cannot be increased.

As a method of removing the offset voltage, feedback may be applied instead of capacitive coupling, but in any case, a high-pass filter of the second or higher order must be used from the current signal source to the comparator. .

[0010]

By the way, recently, a high-speed mode communication format has been used, and it is necessary to shorten the time constant of the first stage capacitive coupling portion (capacitor 15). When the received signal disappears as shown in FIG. 19A, the voltage at the node A preceding the capacitor 16 tries to return to the zero level. For this reason, the voltage at the node B rises as shown in FIG.
When the reference voltage V18 is set, unnecessary pulses are generated as shown in FIG. 19C, which may cause an error. Therefore, there is a problem that the setting region of the reference voltage V18 is narrow. In addition, if the reference voltage V18 is increased, it becomes impossible to output a pulse with respect to an input having a weak received light intensity. Therefore, when securing a weak input characteristic, the setting region of the V18 is considerably narrowed.

In order to address such a problem, it is necessary to shorten the time constant of the capacitive coupling part as it goes to the subsequent stage to suppress the rise in the voltage of the node B when the signal is lost. However, some communication formats have a variable pulse width, for example, a pulse having a certain pulse width t and its two.
In some cases, both the pulse having the double pulse width 2t must be detected. In this case, if the time constant of the subsequent capacitive coupling portion becomes too short, the pulse width changes, so that the pulse width 2t is changed. Becomes indistinguishable from a pulse having a pulse width of 1t.

[0012] Because of this, the current-voltage conversion circuit 1
2. A method of preparing a plurality of circuits up to the limiter amplifier 13 and the comparator 14 and switching each circuit in accordance with the communication format has been adopted. Therefore, the number of components is large, and labor for mode switching is required.

The present invention has been made under such circumstances, and an object of the present invention is to provide a current input type receiver having a small number of parts and a high versatility.

[0014]

SUMMARY OF THE INVENTION A current input type receiver according to the present invention comprises a signal source circuit having a current signal source for receiving a pulse signal and outputting a current corresponding to the received signal; A current-voltage conversion circuit that is capacitively coupled and converts an AC component of the output current of the signal source circuit into a voltage;
A voltage amplifier connected to the output side of the voltage conversion circuit; and a comparator connected to the output side of the voltage amplifier and extracting a pulse signal corresponding to the transmission signal. The input impedance is set to be sufficiently smaller than the impedance of the signal source circuit.

The reason for setting the impedance in this way is to make most of the current from the current signal source flow into the current-voltage conversion circuit. As the current signal source, for example, a photodiode is used.

In the present invention, since the capacitive coupling exists at the preceding stage, the details will be described later.
For example, a configuration in which no capacitive coupling is provided at a stage subsequent to the current-voltage conversion circuit can be employed. Further, it is preferable that the signal source circuit includes a clamp circuit for suppressing a decrease in potential of the capacitive coupling portion on the signal source circuit side when the received signal disappears.

[0017]

FIG. 1 is a circuit diagram showing a basic circuit portion in a current input type receiver according to an embodiment of the present invention. In FIG. 1, reference numeral 21 denotes a photoelectric conversion element, for example, a photodiode serving as a current signal source. The anode side of the photodiode 21 is connected to a bias power supply 22 and the cathode side is connected to a bias power supply 24 via a bias resistor 23. I am. That is, the photodiode 21 is reverse-biased, and a current flows from the cathode to the anode by receiving light. Photodiode 21, bias power supplies 22, 24 and bias resistor 23
Corresponds to the signal source circuit 2.

The connection point between the photodiode 21 and the bias resistor 23 is connected to the base of an NPN transistor 31 via a capacitor C1, which is a capacitance component. The collector of the transistor 31 is connected to the constant current source 32, and the emitter is grounded. A resistor 33 is connected between the collector and the base of the transistor 31. The constant current source 32 is connected to a power supply whose power supply voltage is + VCC. Transistor 31, constant current source 32
The resistor 33 forms the current-voltage conversion circuit 3. That is, the current-voltage conversion circuit 3 is capacitively coupled to the signal source circuit 2 by the capacitor C1.

By the way, since the signal source circuit 2 and the current-to-voltage conversion circuit 3 are capacitively coupled, the current-voltage is lower than the impedance of the signal source circuit (impedance seen from the capacitor C1 toward the signal source circuit 2). The input impedance of the conversion circuit 3 must be sufficiently low. If the input impedance of the current-voltage conversion circuit 3 is large, the current from the photodiode 21 flows to the bias resistor 23 side and does not flow to the current-voltage conversion circuit 3. The above circuit satisfies this condition. The conversion efficiency of the current-voltage conversion circuit 3 is determined only by the resistance value of the resistor 33.

The reason is as follows. The signal source circuit 2 and the current-voltage conversion circuit 3 in FIG. 1 can be represented as an equivalent circuit shown in FIG. 2 in a small signal region. In FIG. 2, i is the current flowing through the photodiode 21, Vi is the voltage of the capacitor C1 on the signal source circuit 2 side, C1 is the capacitance of the capacitor C1 (having the same sign), R1 is the resistance value of the resistor 33, and R2 is the bias. The resistance value of the resistor 23, re is the resistance between the base and the emitter of the transistor 31, and V0 is the output voltage of the current-voltage conversion circuit 3. Assuming that S is jω, i and V0 are expressed by the following (Equation 1) and (Equation 2), respectively.

[0021]

(Equation 1)

[0022]

(Equation 2) From these (Equation 1) and (Equation 2), Vi and V0 are expressed by (Equation 3) and (Equation 4), respectively. If re is sufficiently smaller than R2, the current-voltage conversion circuit 3 Are represented by (Equation 5) and (Equation 6), respectively.

[0023]

(Equation 3)

[0024]

(Equation 4)

[0025]

(Equation 5)

[0026]

(Equation 6) Therefore, since Zi becomes re, it is sufficiently smaller than the impedance of the signal source circuit 2. Also, the conversion impedance Zt
Depends only on R1, the current-voltage conversion efficiency is determined by the resistance value R1 of the resistor 33.

Since the current-voltage conversion circuit 3 is capacitively coupled to the signal source circuit 2, no DC component flows through the resistor 33. Therefore, it is not necessary to consider that if the DC-current component flows through the current-voltage conversion resistor as in the related art, and if the resistance is increased, the output of the current-voltage conversion circuit 3 may be cut off, so that the resistance value of the resistor 33 is increased. Thus, high conversion efficiency can be obtained.

FIG. 1 shows a basic circuit configuration of the signal source circuit 2 and the current-voltage conversion circuit 3,
Actually, for example, it is designed based on a circuit configuration as shown in FIG. In the signal source 2, the anode side of the photodiode 21 is AC grounded, and a clamp circuit 25 in which diodes are connected in series is connected in parallel to a bias resistor 23. The clamp circuit 25 is a circuit for charging the node C when the potential of the node C decreases.

As a result, the voltage of the node C, that is, the reverse bias of the photodiode 21 is kept high, so that an increase in the capacitance component of the photodiode 21 can be suppressed, and high-frequency characteristics can be maintained. FIG. 4 shows the relationship between the parallel equivalent capacitance of the photodiode and the reverse bias voltage.

At a weak input, the current flowing from + VCC through the bias resistor 23 is very small, so that the photodiode 21 is biased at a potential close to VCC, but at a strong input, the input impedance of the current-voltage conversion circuit 3 and the signal source Since the current shunted by the impedance of the circuit 2 flows, the voltage of the node C also decreases. For this reason, the bias of the photodiode 21 is reduced, and in the worst case, the signal is not transmitted since the photodiode 21 is saturated.

FIG. 5A shows the potential of the node C and the current-voltage conversion circuit 3 when the clamp circuit 25 is not provided.
Is a simulation result showing that the potential of the node C continues to decrease. In the simulation, the output waveform of the current-voltage conversion circuit 3 is output. However, since the characteristics of the photodiode 21 are actually deteriorated, the waveforms are connected or the pulse width is widened.

On the other hand, FIG. 5B shows the clamp circuit 2
5 is a simulation result showing the potential of the node C and the output voltage of the current-voltage conversion circuit 3 when 5 is provided,
The bias of the photodiode is kept at VCC-VF (diode voltage) or higher.

As the signal source circuit 2, for example, as shown in FIG. 6, a photodiode 21 is connected to a high potential side, and a bias resistor 23 is connected to a low potential side.
One end of the capacitor C1 may be connected to the connection point of the first resistor 1 and the bias resistor 23, and the clamp circuit 25 may be connected in parallel with the bias resistor 23.

Further, in the current-voltage conversion circuit 3, the resistance 33
A clamp circuit including a transistor 35 is connected in parallel to the constant current source 34. That is, the base and the emitter of the transistor 35 are connected to the transistor 3
1 is connected to the collector and the base, respectively, and the collector of the transistor 35 is connected to + VCC. While a signal having a large light receiving intensity is being input, a current of, for example, 16 mA flows from the current-voltage conversion circuit 35 toward the signal source 2. At this time, the large current flows from the constant current source 34 through the resistor 33. If it flows, constant current source 3
4 is saturated, and the current-voltage conversion circuit 3 does not operate normally. Therefore, current is made to flow through the clamp circuit (transistor 35).

In this case, the current flowing through the constant current source 34 is considerably small, but since the base current of the transistor 31 is still large, the matching with the reference power supply of the limiter amplifier 4 is deteriorated as it is. That is, as will be described later, the reference power supply of the limiter amplifier 4 has the same circuit configuration as the current-voltage conversion circuit 3 so as to minimize the offset voltage. Therefore, if the base current of the transistor 31 is large, the matching between the two becomes poor.

Therefore, the transistor 36 is connected to the transistor 31 in Darlington connection, so that the base current of the transistor 31 is reduced and the voltage drop of the resistor 33 is suppressed. Reference numeral 37 denotes a bias resistor, and reference numeral 38 denotes a Schottky diode that clamps between the base and the collector of the transistor 31 to prevent saturation of the transistor 31.

The output terminal of the current-voltage conversion circuit 3 (the connection point between the collector of the transistor 31 and the constant current source 34) is connected to a limiter amplifier 4 serving as a voltage amplifier. Is connected to the comparator 5. The limiter amplifier 4 is configured, for example, as shown in FIG. Reference numeral 41 denotes a differential amplifier, which amplifies the difference between the output value of the current-voltage conversion circuit 3 and the potential of the reference power supply that determines the limiter value, and outputs the output lines 4 having opposite polarities.
2 and 43. The output lines 41 and 42 are input to the differential amplifier 44, and the output signal of the differential amplifier 44 is input to the comparator 5 as the output signal of the limiter amplifier 4.

FIG. 6 shows an actual circuit when the current-voltage conversion circuit 3 is incorporated in a receiver. Corresponding parts using the current-voltage conversion circuit 3 shown in FIG. 3 are denoted by the same reference numerals. The transistors 61, 62, and 63 are provided to supply current to the transistor that is the constant current source 32. The portion indicated by reference numeral 40 in FIG. 8 constitutes a reference power supply 40 for the amplifier 41 of the limiter amplifier 4. The reference power supply 40 is connected to the current-voltage conversion circuit 3 in order to minimize the offset voltage of the amplifier 41. It has the same configuration. The reference power supply 40 is not limited to the same configuration as the current-voltage conversion circuit 3.

In the limiter amplifier 4 shown in FIG. 7, the offset voltage of the preceding differential amplifier 41, that is, the output voltage of the limiter amplifier 4 and the output voltage of the comparator 5 when the input side of the current-voltage conversion circuit 3 is opened. The trimming circuit 7 adjusts the offset voltage so that the voltage between the reference power supply 50 and the reference power supply 50 becomes a certain value. Z
Reference numerals 1 and Z2 denote output impedances, respectively, which are output by the constant current sources 71 and 72 of the trimming circuit 7, respectively.
2 and 43 are drawn, and one of the constant current sources 71
By controlling the voltage drop due to the output impedance Z1, the offset voltage caused by the offset between the current-voltage conversion circuit 3 and the reference voltage 40, the offset between the amplifiers 41 and 44, and the difference between the output impedances Z1 and Z2 is removed.

FIG. 9 shows an example of a circuit in which the trimming circuit 7 is specifically designed. The current flowing through B1 is the sum of the currents flowing through the transistors 71 to 74. Transistors 72, 73, and 74 are transistors 75, 76, and 7, respectively.
When the transistor 7 is turned on, the transistor is turned on.
Metal fuses M1, M2, M on collector side of 6, 77
3 are provided, and these metal fuses M1, M
2. By turning off M3, transistors 75, 7
6, 77 become effective. Metal fuse M1, M2, M
3 is cut by supplying a predetermined current from each terminal of T1, T2, and T3. Therefore, the voltage between the output voltage of the limiter amplifier 4 and the voltage of the reference power supply 50 of the comparator 5 is a certain value (usually, a constant comparator is used to prevent the comparator output from changing due to noise or the like when there is no signal. Metal fuses M1, M2, M to be cut so that the offset voltage at the input is provided).
By determining the combination of the three, the offset voltage at the comparator input can be made constant. This operation is performed, for example, at the stage of a blow test performed when manufacturing an IC.

The offset voltage is trimmed by digital laser trimming (3 bits in this example) as shown in FIG. 9 or by direct laser trimming of the resistor, or by adjusting a resistance value by incorporating a variable resistor in the reference power supply 40. You may make it.

Next, the operation and effect of the above embodiment will be described. When an optical signal is transmitted from the transmitter 100 to the receiver via the communication cable, the current flowing through the photodiode 21 changes according to the light intensity of the received signal (optical signal), and the pulse generated by the transmitter 100 A current pulse signal corresponding to the signal is sent from the signal source circuit 2 to the current-voltage conversion circuit 3. Since the input impedance of the current-voltage conversion circuit 3 is sufficiently lower than the impedance of the signal source circuit 2, most of the current flowing through the photodiode 21 flows into the current-voltage conversion circuit 3.

Since the signal source circuit 2 and the current-voltage conversion circuit 3 are capacitively coupled, only the AC component of the current signal output from the signal source circuit 2 is input to the current-voltage conversion circuit 3. . The current input to the current-voltage conversion circuit 3 is converted into a voltage by a resistor 33, and the output voltage is amplified via a limiter amplifier 4 and further input to a comparator 5. The comparator 5 compares the input voltage with the reference voltage, and outputs a pulse signal corresponding to the pulse signal generated by the transmitter 100 from the output side. This pulse signal is input to a data processing circuit (not shown).

In this embodiment, since the input impedance of the current-voltage conversion circuit 3 is sufficiently lower than the impedance of the signal source circuit 2, the high-frequency current from the photodiode 21 passes through the capacitor C1 and flows through the current-voltage conversion circuit. Flow to 3. Therefore, even when the residual light that flows from the photodiode 21 at the time of strong input increases due to the presence of the residual light due to the delay of the extinction of the photodiode on the transmitter 100 side, the current-voltage conversion circuit 3 separates the current pulse. The strong input characteristics are excellent.

Since the DC component does not flow through the current-voltage conversion circuit 3, no voltage is generated due to the DC component unlike the conventional example, so that the resistance value R of the current-voltage exchange resistor 33 is reduced.
1 can be increased. That is, the current-voltage conversion efficiency is the signal source 2
Is not affected by the maximum input DC current, a high conversion efficiency can be obtained even if the resistance value R1 is increased. As a result, the gains of the differential amplifier 41 and the differential amplifier 44 of the limiter amplifier 4 at the subsequent stage can be reduced, so that the generation of the offset voltage in the limiter amplifier 4 can be suppressed, and it is possible to cope by trimming.

In the conventional circuit, as described above, the gain of the limiter amplifier 4 must be increased.
The offset voltages generated at 1 and 44 are so large that they cannot be handled by trimming, and therefore, the output stages of the amplifiers 41 and 44 need to be capacitively coupled. On the other hand, in the embodiment of the present invention, the offset voltage can be reduced by trimming.
No capacitive coupling is required on the subsequent stage, and the photodiode 2
From 1 to the input end of the comparator 5 is a primary high-pass filter (capacitive coupling is only one place). Therefore, since there is no problem such as a voltage increase when the light receiving signal is lost as shown in FIG. 19B, the setting range of the voltage of the reference power supply 50 of the comparator is widened, and the weak input characteristics are particularly improved.

Conventionally, there are a plurality of capacitive couplings, for example, three. If it is attempted to adjust the time constant of each capacitive coupling part according to a certain communication format, it is difficult to adjust the time constant, for example, it is incompatible with other communication formats. As a result, mode switching was required. However, according to the embodiment of the present invention, only one time constant needs to be set. Property is obtained.

Since the resistance value of the resistor 33 can be increased in the current-voltage conversion circuit 3, noise inside the circuit can be reduced. That is, when the gain is increased, the noise increases accordingly, but when the resistance value is doubled, the noise becomes 2
Because it requires ^1/2, so that the result noise is reduced as. Furthermore, since capacitive coupling is performed by external components, there is an advantage that the number of external components can be reduced.

An example of the main circuit constants of the receiver according to the embodiment of the present invention will be described below.
0 V, the range of the current flowing through the photodiode 21 is 10
0nA to 16mA, the capacity of the capacitor C1 is 2200p
F, the resistance value R1 of the resistor 33 is 20 kΩ, the gain of the differential amplifier 41 of the limiter amplifier 4 is 46 dB, and the gain of the differential amplifier is 20 dB.

Next, an operation test was performed in various communication formats using the receiver according to the embodiment of the present invention, and the output of the current-voltage conversion circuit 3 was measured.
The result shown in FIG. 16 was obtained. The signal on the upper side in the figure is a voltage pulse (transmission pulse) on the transmitter side, and emits light when falling. The lower signal is an output pulse (received pulse) of the current-voltage conversion circuit 3 of the receiver. One scale on the vertical axis in the transmission pulse is 5 V, and one scale on the vertical axis in the reception pulse is 500 mV. The upper right of each graph shows the applied communication format. SIR is Ser
ial InfraRed is an abbreviation for FIR.
st InfraRed, ASK is Ampl
It is an abbreviation of itude Shift Keying. As can be seen from the waveform diagrams shown in FIGS. 10 to 16, stable pulses can be obtained in any communication format, and it has been confirmed that the receiver of the embodiment of the present invention can be applied to these communication formats.

In the above, the signal source in the present invention is not limited to a photodiode as long as it receives a signal and outputs it as a current signal.

[0052]

According to the present invention, since the current-to-voltage conversion circuit is capacitively coupled to the signal source circuit, the conversion efficiency of the current-to-voltage conversion circuit can be increased, and the gain of the amplifying section at the subsequent stage can be increased accordingly. , The offset voltage can be suppressed. As a result, since everything from the signal source to the comparator can be configured as, for example, a primary high-pass filter, the versatility for the communication format is widened.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a basic configuration of a receiver according to an embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram equivalently showing the current-voltage conversion circuit in the embodiment.

FIG. 3 shows a signal source circuit and a current in the above embodiment.
FIG. 2 is a circuit diagram showing a voltage conversion circuit more specifically than FIG. 1.

FIG. 4 is a characteristic diagram showing a relationship between a reverse bias of a photodiode and a parallel equivalent capacitance.

FIG. 5 is a diagram illustrating a relationship between a node B and an output voltage of a current-voltage conversion circuit 3;

FIG. 6 is a circuit diagram showing another example of a signal source circuit diagram.

FIG. 7 is a circuit diagram showing an example of a limiter amplifier 4.

FIG. 8 is a circuit diagram showing a specific circuit example of a current-voltage conversion circuit and a reference power supply of a limiter amplifier.

FIG. 9 is a circuit diagram showing a trimming circuit for trimming an offset voltage of a limiter amplifier.

FIG. 10 is a waveform diagram showing an output waveform of a current-voltage conversion circuit together with a voltage waveform on the transmitter side using the receiver of the present invention.

FIG. 11 is a waveform diagram showing an output waveform of a current-voltage conversion circuit together with a voltage waveform on the transmitter side using the receiver of the present invention.

FIG. 12 is a waveform diagram showing an output waveform of a current-voltage conversion circuit together with a voltage waveform on the transmitter side using the receiver of the present invention.

FIG. 13 is a waveform diagram showing an output waveform of a current-voltage conversion circuit together with a voltage waveform on the transmitter side using the receiver of the present invention.

FIG. 14 is a waveform diagram showing an output waveform of a current-voltage conversion circuit together with a voltage waveform on the transmitter side using the receiver of the present invention.

FIG. 15 is a waveform diagram showing an output waveform of a current-voltage conversion circuit together with a voltage waveform on the transmitter side using the receiver of the present invention.

FIG. 16 is a waveform diagram showing an output waveform of a current-voltage conversion circuit together with a voltage waveform on the transmitter side using the receiver of the present invention.

FIG. 17 is a circuit diagram showing a conventional current input type receiver.

FIG. 18 is a current waveform diagram showing a state where a residual current remains in the photodiode on the receiver side because light emission from the photodiode on the transmitter side does not return.

FIG. 19 shows a node A and a node B in a conventional receiver.
FIG. 4 is a waveform chart showing a voltage waveform of FIG.

[Explanation of symbols]

 2 Signal Source Circuit 21 Photodiode 23 Bias Resistance C1 Capacitor 3 Current-Voltage Conversion Circuit 31 Transistor 32 Constant Current Source 33 Current-Voltage Conversion Resistance 4 Limiter Amplifier 41 Differential Amplifier 44 Differential Amplifier 7 Trimming Circuit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication H04B 1/06

Claims (4)

[Claims] 1. A signal source circuit having a current signal source for receiving a pulse signal and outputting a current corresponding to the received signal, and an AC component of an output current of the signal source circuit which is capacitively coupled to the signal source circuit. To a voltage, a voltage amplifier connected to the output of the current-voltage converter, and a pulse signal connected to the output of the voltage amplifier and corresponding to the transmission signal. And a comparator, wherein the input impedance of the current-voltage conversion circuit is set sufficiently smaller than the impedance of the signal source circuit. 2. The current input type receiver according to claim 1, wherein no capacitive coupling exists between the current / voltage conversion circuit and the input terminal of the comparator. 3. The current input type receiver according to claim 1, wherein the current signal source is a photoelectric conversion element that receives an optical pulse signal and outputs a current corresponding to the received signal. 4. The signal source circuit according to claim 1, wherein the signal source circuit includes a clamp circuit for suppressing a decrease in the potential of the capacitive coupling portion on the signal source circuit side when the received signal is lost. Or the current input type receiver according to 3.