JPS59208917A - Photoelectric conversion amplifying circuit - Google Patents

Abstract

PURPOSE:To improve the S/N and at the same time to decrease the number of elements by using two current mirrors a constant current source and a transistor to constitute a photoelectric converting amplifying circuit. CONSTITUTION:A transistor TR is connected in parallel to TRQ1 and Q2 constituting the 1st curent mirror, and an output is extracted out of the TR although an output terminal is not shown in the diagram. In other words, the base and the emitter of the TR are connected in common to the TRQ1 and Q2. Then a resistance is connected between the collector of the TR and an earth, and an output terinal can be extracted out of the collector of the TR. Otherwise an output can be extracted directly out of the base of a TRQ5. In such a constitution, it is not needed to flow an optical current produced by the steady light to a bias resistance of a conventional circuit. Thus the S/N can be greatly improvided. In addition, the number of elements can be decreased since the use of an operational amplifier is not needed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photoelectric conversion and amplification circuit that amplifies a photovoltaic current (hereinafter abbreviated as photocurrent) of a photodiode to obtain an output voltage.

Generally, the photocurrent photoelectrically converted by a photodiode varies in the range of several tens of picoamperes to several microamperes due to ambient light such as ambient light, so a logarithmic compression diode is used to narrow the output range. At the same time, it is common to provide good sensitivity even when the photocurrent is small. However, if the light input as the stationary light contains a pulsed optical signal, if the logarithmic compression diode is used, the pulsed optical signal will also be input superimposed on the stationary light. , it becomes difficult to detect pulsed optical signals, and a diode for logarithmic compression cannot be used. In this way, in the conventional technology, the relationship between the range due to the steady light and the amplification degree for detecting the pulsed optical signal is related to each other, so the circuit shown in FIG. 1 has to be used. It is in. In Fig. 1, SPD is the photodiode, R1 is the load resistance that converts the photocurrent into voltage, and El is the power supply for biasing the photodiode SPD.
C1 is a canopling capacitor that detects a pulsed optical signal, OP is an operational amplifier, R2 is a negative feedback resistor,
R2 represents a power supply for applying a bias voltage to the operational amplifier OP, VcC represents a power supply terminal, 0 represents an output terminal, and E represents a ground.

In FIG. 1, a photocurrent corresponding to steady light photoelectrically converted by a photodiode SPD flows through a resistor R1, is converted into a voltage, and power is consumed.

On the other hand, since the photocurrent corresponding to the pulsed optical signal is shunted and flows through the resistor R1 and the indenzer C1, the operational amplifier 0
It is obtained by amplifying the voltage to the output O of the operational amplifier 01) through the negative feedback resistor R2 of 1).

In this way, in the circuit shown in Figure 1, the pulsed photocurrent to be detected flows in a shunt manner through the resistor R1, capacitor C1, and resistor R2, so the pulsed photocurrent that flows through the resistor R1 and consumes power is loss, the S/N ratio decreases due to noise generated when the photocurrent corresponding to the steady light flowing through the resistor R1 is consumed, and the operational amplifier OP
Since it requires high input impedance and good frequency characteristics, it has drawbacks such as requiring a large number of elements.

The present invention was made in order to eliminate the above-mentioned drawbacks of the conventional technology, and by configuring a circuit using two current mirrors, one constant current source, and one transistor, the photocurrent can be used for biasing. It is an object of the present invention to provide a photoelectric conversion/amplification circuit which has many effects such as being able to improve the S/N ratio since the current does not need to be passed through the resistor, and requiring fewer elements than conventional circuits.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows an embodiment of the first invention of the present application, in which SPD is a photodiode and Ql.

C2 is the first. second PNP)
It is a transistor, and C2 has a base and a collector connected, and has a diode function. Q3 and C4 are the third. C3 is a fourth NPN transistor, and has a base and a collector connected, and has a diode function.

C5 is a fifth NPN I-transistor for negative feedback amplification;
IO is a constant current source, Vcc is a power supply terminal, and E is a ground terminal.

Although the output terminal is not shown in the figure, this output terminal is connected to the transistor Ql that constitutes the first current mirror.
, Q2 and connect a transistor in parallel to take out the output from the I.
A transistor may be provided whose base and emitter are commonly connected, a resistor may be connected between the collector of this transistor and ground, and the output terminal may be taken out from the collector of the transistor, or the output may be taken directly from the base of the transistor Q5. Furthermore, as shown in FIG. 3, a transistor Q6 whose base and emitter are commonly connected to the transistor Q5 and its output load resistor R5 may be provided, and the output may be taken out from the collector of the transistor Q6. This is the second invention (Claim 2) of the present application.

Further, the resistor R5 in FIG. 3 may be replaced with a second constant current source 1 as shown in FIG. 4, and this is the third invention (claim 3) of the present application. In this case, if resistor R5 is used for the output load as in the circuit shown in Figure 3, the output will fluctuate due to power supply voltage fluctuations.

The constant current source 11 is used to avoid problems such as increased power consumption and increased IC occupied area. In this case, the current from the second constant current source 11 and the collector of the transistor Q6 are The difference from the current is obtained as the output current.

In the first to third inventions of the present application, it is possible to greatly improve the S/N ratio since the photocurrent caused by cosmic light does not need to flow through the bias resistor R1 in the conventional circuit shown in FIG. In addition, since it is not necessary to use an operational amplifier as shown in FIG. 1, the number of elements can be greatly reduced.

Next, FIG. 5 shows the license fee of the fourth invention (Claim 4) of the present application, and in the figure, Ql and C2 are the first . The second PNP transistor C2 has its base and collector connected and has a diode function. C3°C4 is the third. C3 is a fourth NPN) transistor whose base and collector are connected and has a diode function.

C5 is the fifth NPN transistor for negative feedback amplification, R
3 is a first resistor for self-bias load connected to the emitter of transistor Q5, C6 is a sixth transistor for current amplification, and R4 is a second resistor for self-bias load connected to the emitter of transistor Q6. , C2 is a bypass capacitor connected to the emitter of transistor Q6, R5 is the third resistor of the output load, R0 is a constant current source, V
cc is a power supply terminal, 0 is an output terminal, and E is a ground terminal.

Here, the constant current source IO has a photocurrent corresponding to the cosmic light,
The photocurrents corresponding to the pulsed optical signals are added and set to a current value slightly larger than the expected maximum addition value.

Furthermore, to simplify the explanation, resistors R3 and R4 are assumed to have the same resistance value, and their values are the current values of the constant current source ■0 and R3 (
= R4) is the value obtained by subtracting the base-emitter voltage Vbe (C2) of transistor Q2 from the power supply voltage Vcc and the minimum collector-emitter voltage Vce (C5) when transistor Q5 is in the active region. Set the resistance values of R3 and R4 so that they are within the range. The resistance value of R5 is the voltage value obtained by multiplying the current value IO of the constant current source by the value of R4, and the minimum voltage value Vc4 (C6
) is subtracted from the power supply voltage Vcc, and as a result, the IO
The resistance value of R5 is set so that the voltage value obtained by multiplying by R5 is included. The value of C2 is set to a value that allows sufficient bypass in consideration of the frequency of the pulsed optical signal.

Next, we will invent the operation of this circuit.

First, when there is no optical input to the photodiode SPD, the current 0 of the constant current source becomes the Hoesmi current of the transistors Q5 and Q6, and the current is amplified by the transistor Q5, and the current mirror of the transistors Ql and Q2 is amplified. An amplified current is supplied to the current mirror of transistors Q3 and Q4 through the transistors Q3 and Q4. Then, the collector voltage of transistor Q4 becomes low, and transistors Q5 and Q6
Negative feedback is applied because the transistors operate to suppress the Hesumi current, and as a result, the collector currents of the transistors Q5 and Q6 become stable at a value of 0, which is approximately equal to the current value of the constant current source. At this time, I transistors Q5 and Q
A voltage is generated across resistors R3 and R4 respectively connected to the emitters of transistors Q5. An operation is performed to reduce the current amplification factor of Q6.

Next, when a photocurrent 1p corresponding to the steady light flows through the claw 1 diode SPD in the direction of the arrow shown in the figure, the photocurrent!
p flows in the direction in which the collector current of transistor Q3 increases, and at the same time acts so that the current supplied to the base currents of transistors Q5 and Q6 and the collector current of transistor Q4 is reduced by the photocurrent, and as a result, transistor Q5 The base current to Q6 acts in the direction of decreasing by twice the photocurrent. That is, the currents in each part of the circuit in this case are not shown in FIG. 5fa). However, since a self-bias load resistance acts on the emitters of the transistors Q5 and Q6, and the current amplification factors of the transistors Q5 and Q6 are reduced, no significant change occurs in the output voltage.

Next, when a photocurrent tp corresponding to a pulsed optical signal flows through the photodiode SPD, the photocurrent tp flows in the direction of increasing the collector current of the transistor Q3, and at the same time increases the base current of the transistors Q5 and Q6 and the transistor Q4. As a result, the base currents to the transistors Q5 and Q6 are reduced by twice the photocurrent.

That is, the alternating current of each part of the circuit in this case is shown in Figure 5 (bl
It becomes as shown in . At this time, since this photocurrent 2ip is given as a pulse, it can flow as the base current of the transistor Q6 through the bypass capacitor c2 via the emitter. Therefore, since the transistor Q6 operates with a high current amplification factor, the important thing here is to set the resistance values of the resistors R3 and R4 as large as possible so that the current 10 of the constant current source is sufficient. By lowering the voltage and giving a self-bias voltage to each emitter of transistors Q5 and Q6,
- Sufficient self-bias negative feedback is provided to transistors Q5 and Q6, and when a pulsed optical signal is input to photodiode sP[), transistors Q3. Q4
The value of the capacitor C2 is adjusted so that the pulse current change obtained as a change twice the pulsed photocurrent flowing through the photodiode SPD flows through the current mirror as a change in the base current of the transistor Q6. It is necessary to set this by considering the frequency of current change.

According to the photoelectric conversion amplifier circuit of the fourth invention of the present application, the S/N ratio obtained in the first to third inventions of the present application is
In addition to the two effects of improving the ratio and reducing the number of elements, the pulsed photocurrent to be detected can be directly extracted as a change in current that is twice as large as that of the conventional method shown in Figure 1. This has the effect that the photocurrent can be sent to the subsequent amplifier circuit with extremely reduced loss.

Although the fourth invention of the present application has been described above, FIG. The effect of this fifth invention over the conventional art is almost the same as that of the fourth invention.

As described above, according to the present invention, since the photoelectric conversion amplifier circuit is constructed using two current mirrors, one constant current source, and one transistor, the S/N ratio can be improved to reduce noise, and the operational amplifier As shown in Figure 5 or Figure 6, resistors R3 and R4 for self-bias loads are connected to transistors Q5 and Q6, and a capacitor is connected to C6. By connecting them, the pulsed photocurrent to be detected can be directly extracted as a double current change, and the loss caused by the pulsed photocurrent flowing through the resistor can be reduced.

[Brief explanation of the drawing]

Figure 2(a) is a diagram showing the distribution of steady current in each part of the circuit when steady light is received, Figure 2fbl is a diagram showing the distribution of pulsed current in each part of the circuit when pulsed light is received, and Figure 3 is FIG. 4 is a circuit diagram of an embodiment of the second invention of the present application, FIG. 5 is a circuit diagram of an embodiment of the third invention of the present application, and FIG. 5 is a circuit diagram of an embodiment of the fourth invention of the present application. Circuit diagram FIG. 6 is a circuit diagram of an embodiment of the fifth invention of the present application. SPD is the pho1 to diode, and Ql and C2 are the 1st. 2nd PNP) transistor, C
3 and C4 constitute a current mirror. 4th NP
N) transistor, ■0 is constant current source, C5 is fifth NP
N) transistor, C6 is the sixth NPN transistor, R3 and R4 are the first . The second resistor C2 is a bypass capacitor, R5 is a third resistor, and rl is a second constant current source. Agent Masuo Oiwa Figure 1 Figure 2 Figure 3 Figure 41g Figure 5 (Q) (b) Figure 6 Procedure amendment (method) % formula % 1. Indication of case Japanese Patent Application No. 84329/1984; 3 ．．
Representative of the person making the amendment Part 111 Part 5, Date of amendment order August 10, 1980 6, Subject of amendment - Brief explanation of drawings in the specification column 7, Contents of amendment (1) Description Page 19, lines 10-14, “Figure 2...
. . . A diagram showing distribution" is corrected to "Figure 2 is a circuit diagram of an embodiment of the first invention of the present application." -H

Claims (1)

[Claims] (1.1 A current mirror is configured by a first and a second transistor, the base and collector of the second transistor are connected, and the conductivity type is different from that of the first and second transistors. A current mirror is configured by a third and fourth transistor, the base and collector of the third transistor are connected, and the collector of the first transistor is connected to the third transistor.
The collector of the fourth transistor is connected to the collector of the transistor, and the anode of the four diode is connected to the connection point thereof, and the collector of the fourth transistor is connected to the constant current source, the cathode of the photodiode, and the first transistor and the transistor. bases of fifth transistors of different shapes are connected, the other end of the constant current source is interconnected with each emitter of the first and second transistors, and this connection point is connected to a power 1 terminal; Generally, the collector of the fifth transistor is connected to the collector of the second transistor, and the third, fourth, and third transistors are connected to each other. A photoelectric conversion amplifier circuit characterized in that the emitters of the fifth transistors are commonly connected and connected to a ground terminal. (2) A current mirror is configured by the first and second transistors, the base and collector of the second transistor are connected, and the first... A current mirror is configured by a third and fourth transistor having a different conductivity type from the second transistor, the base and collector of the third transistor are connected, and the collector of the first transistor is connected to the third transistor. The collector of the fourth
A constant current source, the cathode of the photodiode, and the base of a fifth transistor having a different conductivity type from the first transistor are connected to the collector of the first transistor, and the other end of the constant current source is connected to the first transistor. and each emitter of the second transistor, the connection point being connected to a power supply terminal, and the collector of the fifth transistor being connected to the collector of the second transistor; 4. The emitters of the fifth transistors are commonly connected to the ground terminal, and the sixth transistor having the same conductivity type as the fifth transistor has a
11. connected to the base of the fifth l-transistor, and the emitter of the sixth transistor connected to the ground terminal;
A photoelectric conversion characterized in that a collector of the sixth transistor is connected to a third resistor, a connection point thereof is connected to an output terminal, and the other end of the third resistor is connected to the power supply terminal. Amplification circuit. (3) A current mirror is configured by the first and second transistors, the base and collector of the second transistor are connected, and the first... A third and fourth transistor having a different conductivity type from the second transistor constitutes a Karen 1-mirror, the base and collector of the third transistor are connected, and the collector of the first transistor is connected to the third transistor.
The fourth
A constant current source, the cathode of the photodiode, and the base of a fifth transistor having a different conductivity type from the first transistor are connected to the collector of the transistor,
The other end of the constant current source is interconnected with each emitter of the first and second transistors, this connection point is connected to a power supply terminal, and the collector of the fifth transistor is connected to the collector of the second transistor. connected to the third
゜4th. The emitters of the fifth transistors are commonly connected to the ground terminal, and the bases of the sixth transistors having the same conductivity type as the fifth transistor are connected to the fifth transistor.
The emitter of the sixth transistor is connected to a ground terminal, the collector of the sixth transistor is connected to a second constant current source, and the connection point thereof is connected to an output terminal, A photoelectric conversion amplifier circuit, wherein the other end of the second constant current source is connected to the power supply terminal. (4) A current mirror is configured by the first and second transistors, the base and collector of the second transistor are connected, and the first... A current mirror is configured by a third and fourth transistor having a different conductivity type from the second transistor, the base and collector of the third transistor are connected, and the collector of the first transistor is connected to the third transistor. A constant current source is connected to the collector of the fourth transistor; The bases of the fifth transistor are connected to each other, the other end of the constant current source is interconnected to each emitter of the first and second transistors, this connection point is connected to the voltage terminal, and the fifth transistor The collectors of the transistors are connected to the collectors of the second transistor, the emitters of the third and fourth transistors are commonly connected to a ground terminal, and the emitter of the fifth transistor is connected to a first resistor. , the other end of the first resistor is connected to a ground terminal, the base of a sixth transistor having the same conductivity type as the fifth transistor is connected to the base of the fifth transistor, and the sixth transistor has the same conductivity type as the fifth transistor. The emitter of the sixth transistor is connected to a second resistor and a first capacitor, the other ends of the second resistor and the first capacitor are connected to the ground terminal, and the collector of the sixth transistor is connected to a second resistor and a first capacitor. A photoelectric conversion amplifier circuit, characterized in that it is connected to a third resistor, a connection point thereof is connected to an output terminal, and the other end of the third resistor is connected to the power supply terminal. (5) A current mirror is configured by the first and second transistors, the base and collector of the second transistor are connected, and the first... A current mirror is configured by a third and fourth transistor having a different conductivity type from the second transistor, the base and collector of the third transistor are connected, and the collector of the first transistor is connected to the third transistor. A constant current source is connected to the collector of the fourth transistor; The bases of the fifth transistors are connected, the other end of the constant current source is interconnected with each emitter of the first and second transistors, this connection point is connected to a power supply terminal, and the fifth transistor 1- The collector of the transistor is connected to the collector of the second transistor, the emitters of the third and fourth transistors are connected in common and connected to a ground terminal, and the emitter of the fifth transistor is connected to the first resistor. The other end of the first resistor is connected to the ground terminal, the base of a sixth transistor having the same conductivity type as the fifth transistor is connected to the base of the fifth transistor I, and the base of the sixth transistor is connected to the base of the fifth transistor I. The emitter of the sixth transistor is connected to a second resistor and a first capacitor, the other ends of the second resistor and the first capacitor are connected to the ground terminal, and the sixth transistor A photoelectric conversion amplifier characterized in that a collector of is connected to a second constant current source, a connection point thereof is connected to an output terminal, and the other end of the second constant current source is connected to the power supply terminal. circuit.