JPH01119107A - Current control circuit - Google Patents

Abstract

PURPOSE:To realize a range finding arithmetic operation with high accuracy by controlling the collector current of the output transistor of a first current mirror circuit by regulating the emitter potential of the output transistor by a second current mirror circuit. CONSTITUTION:The collector current of a transistor(TR)3 that is the output of a current control circuit 21 controls the emitter potential of the TR3 by the second current mirror circuit being constituted by including TRs5, 6 and performs its switching. When the second current mirror circuit is set at a non- operating state, the first current mirror circuit being constituted by including the TRs3, 4, etc., is set at an operating state, and a current equivalent to the one on a constant current source 31 can be permitted to flow on the TR3 rapidly sufficiently by cutting off the TR5. In such a way, it is possible to switch a microcurrent at high speed and to realize the range finding arithmetic operation with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a distance measurement calculation circuit used in an automatic focusing mechanism of an imaging device, etc., in which a diode or a transistor is used for logarithmically compressing the output of a semiconductor device detection sensor. The present invention relates to a current control circuit that is suitably implemented when switching a bias current applied to a logarithmic compression element such as the above.

Background technology The endomorphic prior art is shown in FIG.

The semiconductor device detection sensor (hereinafter referred to as PSD) 1 is
It receives the light reflected by the subject, which is generated from a light source (not shown), and outputs a first current (1) and a second current (2) corresponding to the light receiving position on the light receiving surface. This current I
By calculating the light receiving position on the light receiving surface of PSDl from the ratio of I and I2, for example, i? from the imaging device to the subject. 1′! You can know the distance. First current ■1
is a current/voltage (hereinafter referred to as I/V) conversion circuit 2
is applied to the signal and converted into a signal voltage. I/V conversion circuit 2
The DC component of the output is removed by the capacitor C1, and the output is applied to the logarithmic compression circuit 3.

Capacitor C1 is connected via line 4 to transistor Ql
The collector of the transistor Q1 is connected at the connection point 5 to the cathode of a diode D1 provided as a logarithmic compression element. Further, the emitter of the transistor Q1 is connected to the output terminal of the operational amplifier 6. A reference voltage v1 is applied to the non-inverting input terminal of the operational amplifier 6.
is given, and the inverting input terminal is connected to line 4.

The line 4 is further connected to the transistor Q2 of the hold circuit 7.
collector is connected. The emitter of the transistor Q2 is grounded via a resistor R1, and its base is connected via a line 8 to one terminal of a switch circuit 9 which is turned on/off by the timing pulse S1.

A capacitor C2, one terminal of which is grounded, is connected to the line 8. The output of the operational amplifier 10 is given to the other terminal of the switch circuit 9, and the operational amplifier l
A reference voltage 2 is applied to the non-inverting input terminal of the transistor O. The collector potential of the transistor Q1 is applied to the inverting input terminal of the operational amplifier 10.

The power supply voltage VcC is applied to the anode of the diode D1, and the collector of the transistor Q3 of the current control circuit 11 is connected to the connection point 5 on the cathode side of the diode D1. The base of the transistor Q3 and the base of the transistor Q4 are commonly connected to the collector of the transistor Q5. The base and collector of transistor Q4 are short-circuited, and the collector is further connected to constant current source 12. In this way, transistor Q3. A current mirror circuit is configured including transistors Q4, and when the collector center of transistor Q5 becomes low level, transistors Q3 . Both transistors Q4 are conductive, so that a current equal to the current 3 flowing through the constant current source 12 flows through the collector of the transistor Q3.

Transistor Q3. Q4. A power supply voltage Vcc is applied to both emitters of Q5. Transistor Q5
The base of is connected to the connection point 13 connecting the resistors R2 and R3, and the terminal of the resistor R2 on the opposite side from the connection point 13 is
Power supply voltage Vcc is applied. A terminal of the resistor R3 on the opposite side from the connection point 13 is connected to one terminal of a switch circuit 14 that is turned on/off by the timing pulse S2, and the other terminal of the switch circuit 14 is grounded.

The potential on the cathode side of diode D1, that is, the connection point 5
The potential of is applied to the inverting input terminal of the operational amplifier 115 via the resistor R4, and the inverting input terminal of the operational amplifier 15 is
It is connected to its output terminal via a resistor R5. P.S.
The second electricity output by DI! Regarding I2, an arithmetic circuit 16 having the same configuration as that connected to the first current 11 is provided, and the output of the arithmetic circuit 16 is applied to the non-inverting input terminal of the operational amplifier 15 via a resistor R6.

The non-inverting input terminal of the operational amplifier 15 has a reference voltage ■3.
is given.

The switch circuit 9 is made conductive by a timing pulse Sl before a light source (not shown) emits infrared light. As a result, the potential appearing at the connection point 5 is fixed to the reference voltage 2, and a constant bias current IDI flows through the diode D1.

Furthermore, the output of the operational amplifier 10 is applied to the base of the transistor Q2, making the transistor Q2 conductive. Furthermore, the output voltage of the operational amplifier 10 is held in the capacitor C2. As a result, even after the switch circuit 9 is cut off, the base of the transistor Q2 remains at a fixed potential, and signal components contributing to background light that are not related to light reflected from the subject are removed from the PSDI output. Ru.

Thereafter, when infrared light is emitted, only signal components contributing to the reflected light from the object are applied to the base of the transistor Q1 and the inverting input terminal of the operational amplifier 6.

When the switch circuit 9 is cut off, the switch circuit 14 is subsequently cut off by the timing pulse S2. The switch circuit 14 is normally conductive, and at this time, the transistor Q5 is conductive, so the transistor Q
3. When the transistor Q4 is cut off and the switch circuit 14 is cut off, the transistor Q5 is cut off, and the current mirror circuit including the transistors Q3 and Q4 is activated. As a result, the collector of transistor Q3 has
A current equal to the current 3 flowing through the constant current source 12 will flow.

The current ■3 flowing through the constant current source 12 is the bias current ■ flowing through the diode D1. , and the bias current Io1 is no longer applied to the diode D1 due to conduction of the transistor Q3.

However, due to the carrier accumulation effect of the diode D1, the signal current Isl flowing through the diode D1 is
It changes immediately in response to a change in the potential at the connection point 5. That is, there is no delay in response due to the capacitance between both terminals of the diode D1, and the signal current Isl corresponding to the first current flows through the diode D1 with good response.

The switch circuit 14 is cut off, and the transistors Q3 and Q4
When the current mirror circuit including the circuit operates, infrared light is emitted, and as a result, the base of the transistor Q1 and the inverting input terminal of the operational amplifier 6 receive a current corresponding to the first current ■1. A signal is given. Due to the amplification effect of the operational amplifier 6 and the transistor Q1, the potential at the connection point 5 changes in accordance with the first current 1. Due to such a change in the potential at the connection point 5, the f3 current Isl corresponding to the first current 1 output from the PSD 1 flows through the diode D1. At this time, the voltage V D l between both terminals of the diode D1 is the saturation current factor of the diode D1. k: Boltzmann's constant T: absolute temperature q: electron charge. As a result, the potential at the connection point 5 becomes (Vcc
Vow>, and such a voltage is applied to the inverting input terminal of the operational amplifier 15 via the resistor R4. Similarly, the output of the arithmetic circuit 16 is as follows, and such a voltage is applied to the non-inverting input terminal of the operational amplifier 15 via the resistor R6. As a result, the output signal 0 of the operational amplifier 15 becomes 0, and the ratio of the signal currents Isl and Is2 corresponding to the first current 1 and the second current 2 is obtained.

The problem that the invention aims to solve The first and second currents It output by PSD 1.

(2) is normally about 1 nA, so the signal current Isl flowing through the diode D1 is about several 10 nA at most. Therefore, the bias current Io given to the diode D1
+ needs to be about 10 nA. Therefore, in the current control circuit 11, the current I3 flowing through the constant current source 12
has been encountered, for example, at 10rIA.

When switching such a small current,
After transistor Q5 is turned off, transistor Q3.
It takes a relatively long time to charge the capacitance between the base and emitter of Q4 before it becomes conductive, and furthermore, transistor Q5 is cut off from saturation, so that after switching circuit 14 is cut off by timing pulse S2, , transistor Q3. It takes about 1m5ec for Q4 to become conductive. However, in order to perform accurate distance measurement calculations, it is desirable that the calculation process be completed in as short a time as possible so that distance measurement calculations can be performed stably even with changes in external light. 11, it is desired that the switching of the collector current of transistor Q3 be performed as quickly as possible.

SUMMARY OF THE INVENTION An object of the present invention is to provide a current control circuit in which switching of a minute current is performed at high speed, and therefore enables highly accurate distance measurement calculations in, for example, a distance measurement calculation circuit.

Means for Solving the Problems The present invention provides a first current mirror circuit for screening an output transistor from which an output is taken out, and a second current mirror circuit comprising a transistor, which has an active state R/inactive state. and a second current mirror circuit, wherein the transistor is kept below saturation under active conditions, and the emitter potential of the output transistor of the first current mirror circuit is This current control circuit is characterized in that it is regulated by a second current mirror circuit, thereby controlling the collector current of the output transistor.

In the present invention for cattle, the transistor included in the second current mirror circuit is maintained below the saturation state when the second current mirror circuit is in the active state. This allows the second current mirror circuit to be switched between the active B/inactive state at a sufficiently high speed.

The first current mirror circuit is normally in an active state,
The emitter potential of the output transistor included in the first current mirror circuit is regulated by the second current mirror circuit. The second current mirror circuit is switched between the active state and the inactive state at a sufficiently high speed as described above, so that the collector current of the output transistor of the first current mirror circuit can be changed rapidly.

Embodiment 1 [2I is a current control circuit 2 which is an embodiment of the present invention.
FIG. 1 is an electrical circuit diagram showing the basic configuration of a distance measurement calculation circuit including FIG. Infrared light generated from a light source (not shown) is reflected by the subject, and a semiconductor device detection sensor (hereinafter referred to as PSD)
The first current 11 and the second current 12 form an image on a light-receiving surface (referred to as ) 22, and correspond to the image-forming position on the light-receiving surface.
are output respectively. In the distance measurement calculation circuit shown in FIG. 1, this current i1. The ratio of i2 is calculated. The first current 11 is applied to a current/voltage (hereinafter referred to as I/V) conversion circuit 23 and converted into a corresponding signal voltage. I
The DC component of the output of the /V conversion circuit 23 is removed by a capacitor C3, and the capacitor C3 is connected to the line 24.
1 of the logarithmic compression circuit 36 through the transistor T r
It is connected to the base of 1. The collector of the transistor Tri is connected at a connection point 25 to the cathode of a diode d1 provided as a logarithmic compression element.

The inverting input terminal of an operational amplifier 26 is connected to the line 24, and the output terminal of the operational amplifier 26 is connected to the transistor T.
connected to the emitter of ri.

In addition, the non-inverting input terminal of the operational amplifier 26 has a reference voltage ■
1 is given. The collector of the transistor Tr2 of the hold circuit 27 is further connected to the line 24. The emitter of the transistor Tr2 is grounded via a resistor r1, and its base is connected to one terminal of a switch circuit 28 that is turned on/off by the timing pulse T1. Further, a capacitor C4 whose other end is grounded is connected to a line 29 connecting the base of the transistor Tr2 and the switch circuit 28. The output of the operational amplifier 30 is applied to the other terminal of the switch circuit 28, the reference voltage 2 is applied to the non-inverting input terminal of the operational amplifier 30, and the voltage appearing at the connection point 25 is applied to the inverting input terminal of the operational amplifier 30. A potential is applied.

A power supply voltage VcC is applied to the anode of the diode d1, and a connection point 25 to which the cathode of the diode d1 is connected is connected to a PNP transistor included in the current control circuit 21, which is an output transistor. The collector of Tr3 is connected. The transistor T
The base of r3 is connected to the base of a PNP type transistor Tr4, and the collector of the transistor Tr4 is connected to one terminal of the constant current source 31. Further, the base of the transistor Tr4 is connected to the emitter of a PNP type transistor Tr8, and the base of the transistor Tr8 is connected to the collector of the transistor Tr4. The collector of the transistor Tr8 is grounded and the constant current source 3
The other terminal of 1 is also grounded. Transistor Tr3
．． The emitter of Tr4 is connected to a resistor r3. Power supply voltage VCC is applied via r4.

In this way, transistor Tr3. A first current mirror circuit is configured including Tr4, and the transistor T r 4 is normally conductive, so the first current mirror circuit is normally in a dynamic ft state.

The emitter of the transistor Tr3 is further connected to the collector of an NPN type transistor Tr5. The emitter of the transistor Tr5 is grounded, and its base is N
Along with the base of the PN type transistor Tr6, the NPN
The terminals are commonly connected to the collectors of the transistors Tr7.

The base and collector of the transistor Tr6 are short-circuited, and the constant current source 32 is connected to the collector.

In this way, transistor Tr5. A second current mirror circuit is configured including Tr6.

The emitter of transistor Tr7 is grounded, and its base is connected to resistor r5. It is connected to the connection point 33 that connects r6. The terminal of the resistor r6 opposite to the connection point 33 is grounded, and the terminal of the resistor r5 opposite to the connection point 33 is connected to one terminal of the switch circuit 34 which is turned on/off by the timing pulse T2. It is connected. The other terminal of the switch circuit 34 is supplied with the power supply voltage Vcc.

The potential appearing at the connection point 25 is applied to an inverting input terminal of an operational amplifier 35 via a resistor r7, and the inverting input terminal of the operational amplifier 35 is connected to its output terminal via a resistor r8. The second current 1 output by PSD'22
2, the I provided for the first current 11
/V' is provided with an arithmetic circuit 37 having the same configuration as the arithmetic circuit including a conversion circuit 23, a logarithmic compression circuit 36, a current control circuit 21, a hold circuit 27, etc.
The output of is given to the non-inverting input terminal of the operational amplifier 35 via the resistor r9. A reference voltage (2) is applied to the non-inverting input terminal of the operational amplifier 35.

Prior to infrared emission by the light source, timing pulse T1
is applied, and the switch circuit 28 becomes conductive. As a result, the potential of the connection point 25 is fixed to the reference voltage 2, and the transistor Tr2 becomes conductive.

The output current of the PSD 22 is normally about 1 nA, and the signal is amplified by the action of the transistor T r 1 and the operational amplifier 26, and the current flowing through the diode d1 is as follows.
It is approximately several 10 nA. Therefore diode d1
It is desirable that a current of about 10 nA be applied as a bias current before the signal from the PSD 22 is input to the logarithmic compression circuit 36. The aforementioned reference voltage v2 is therefore applied across the diode d1, for example 10n
It is chosen appropriately so that a current of A can flow through it.

When the switch circuit 28 is turned on and the potential at the connection point 25 is fixed to the reference voltage 2, the transistor Tr2 is turned on. After this, even when the switch circuit 28 is cut off, the operational amplifier 30 is connected to the capacitor C,1.
Since the output voltage of transistor T is held,
The base potential of r2 is fixed, so the transistor Tr2 is conductive. As a result, the signal of the portion corresponding to the background light that does not contribute to the reflected light of the light generated from the light source is removed, and only the signal of the portion corresponding to the reflected light from the subject is input to the base of the transistor Tr1 and the inverting input of the operational amplifier 26. It will be given to the terminal.

In the current control circuit 21, the switch circuit 34 is normally cut off, so the transistor Tr7 is cut off, and the second current mirror circuit including the transistors Tr5 and Tr6 is in the operating state. Therefore, in this state, the collector current of the transistor Tr5 is equal to the current flowing through the constant current source 32. The current flowing through the constant current source 32 may be selected to be, for example, about 12 μA, and in this case, the collector current of the transistor Tr5 is about 12 μA. At this time, as mentioned above, the collector current of the transistor T r 3 is so small that it can be ignored.

When the switching circuit 28 is cut off by the timing pulse T1, the switching circuit 34 is subsequently made conductive by the timing pulse T2, thereby causing the transistor T
r 7 conducts and therefore transistor T r 5
, T r 6 is 31! ! Cut off. transistor T
By blocking r5, the emitter potential of transistor Tr3 increases. As a result, a current equal to the current flowing through the constant current source 31 flows through the collector of the transistor Tr3.

The current flowing through the constant current source 31 is selected to be equal to the bias current flowing through the diode d1, and as described above, this bias current is selected to be about 10 nA, so the constant current source 31
The current flowing through is selected to be, for example, 10 nA.

By blocking the transistor Tr5, the transistor Tr3
Since a current of 10 nA will flow through the diode d1, no bias current will flow through the diode d1.
Due to the carrier accumulation effect of the diode d1, the current flowing through the diode d1 changes immediately in response to a change in the potential of the connection point 25. The potential at the connection point 25 can be varied by shutting off the switch circuit 28, and changes in response to the first current output from the PSD 22.

When the switch circuit 34 is turned on by the timing pulse T2, infrared light emission is subsequently performed. As a result, the PSD 22 receives the reflected light from the subject, and the first current 1 corresponding to the incident position of the reflected light on the light receiving surface is
1 and a second current 12. A signal corresponding to the first current 11 is applied to the base of the transistor Tri and the inverting input terminal of the operational amplifier 26. The signal current isl flowing through the diode d1 due to this signal changes in accordance with the collector current of the transistor Tr1, and thus corresponds to the first current 11.

The voltage Vdl between both terminals of the diode d1 is expressed as k: Boltzmann constant T: absolute temperature q: electron charge using the saturation current 10 of the diode d1. As a result, the potential appearing at the connection point 25 is
(Vcc-Vdl), and this voltage is applied to the inverting input terminal of the operational amplifier 35 via the resistor r7. Similarly, the output of the arithmetic circuit 37 becomes...(5), and the output 0 of the operational amplifier 35 becomes: In this way, the first and second
Output current i1. The current isl,is corresponding to the ratio of i2
The ratio of 2 will be found.

In the current control circuit 21, the resistor r3. The resistance value of r4 is chosen to be, for example, 10Ω. Transistor Tr4 is normally conductive, which causes resistor r4 to have a voltage of 10n.
A current of about A flows. Therefore, the voltage drop due to resistor R4 is 10 (kΩ) x 10 (n A ) = 0.1 (m V
) ...(7), and the transistor Tr7 is cut off, so the transistor Tr
5. When Tr6 is conductive, the collector current of transistor Tr5 is 12 μA, so the current flowing through resistor r3 is also about 12 nA, and the voltage drop due to resistor r3 is 10 (kΩ) x 12 (μA). )=120(mV
> -(8). Therefore, there is a difference of about 120 mV between the emitter potential of the transistor Tr3 and the emitter potential of the transistor Tr4.

Transistor Tr3. Since the bases of Tr4 are commonly connected, their potentials are the same, so the voltage Vo between the base and emitter of transistor Tr3 and the voltage V - m between the base and emitter of transistor Tr4 are the same.
It has the following relationship with K4: V tl'V'll@ko:2;;120...(9). On the other hand, transistor T
r3. Currents i3 and i4 flowing through each of Tr4 and the bases of transistors Tr3 and Tr4.
Due to the saturation current io between the emitters, the voltage VBt,
-1 becomes . Considering this in conjunction with the above formula 9,...(
12) Therefore, i 4 / i 3Σ100...
It turns out that (13) is obtained. Since the current i4 is about 1 OnA as described above, the current i3 is about 0.1 nA and the transistor Tr5. It can be seen that when the second current mirror circuit including Tr6 is operating, the current flowing through the transistor Tr3 is negligibly small.

When the switch circuit 34 is rendered conductive by the timing pulse T2, the transistor Tr7 is rendered conductive, thereby causing the transistors Tr5. Tr6 is cut off. At this time, the dynamic f% speed of the transistor Tr7 is sufficiently fast in order to shift from the cutoff state to the conduction state, and in P4K where the transistor Tr7 is cut off, the currents flowing through the transistors Tr5 and Tr6 are respectively 12n
Since the voltage is approximately A, none of the transistors is in a saturated state, and as the transistor Tr7 becomes conductive, the transistors Tr5. Tr6 is immediately cut off.

Although the emitter potential of the transistor Tr3 becomes equal to the emitter potential of the transistor Tr4 at a speed corresponding to the time constant determined by the resistance value of the resistor r3 and the capacitance of the transistor Tr5, the resistor r3 becomes equal to the emitter potential of the transistor Tr4 as described above. Since a small resistance value such as Ω is selected, the emitter potential of the transistor Tr3 rises sufficiently quickly to a potential equal to the emitter potential of the transistor Tr4, so that the collector current of the 1-transistor Tr3 becomes sufficiently fast<10 nA. That is, when the timing pulse T2 is applied and the switch circuit 34 becomes conductive, a current (10 nA) equal to the current flowing through the constant current source 31 immediately flows through the collectors of the transistors Tr1 to Tr3.

In this way, the collector current of the transistor Tr3 is switched sufficiently quickly, and therefore the bias current flowing through the diode d1 is switched sufficiently quickly.

As described above, in this embodiment, the collector current of the transistor Tr3, which is the output of the current control circuit 21, changes the emitter potential of the transistor Tr3 to the transistor Tr5. The switching is controlled by a second current mirror circuit including Tr6. The transistors Tr5.7r6 are turned on/off by the NPN type transistor Tr7, and the transistors Tr5.7r6 are turned on/off by the NPN type transistor Tr7. Since Tr6 is not in a saturated state even when it is conductive, it is immediately cut off when transistor Tr7 is conductive. Even when the second current mirror circuit is not in operation, the transistors Tr3. The first current mirror circuit, which includes transistor Tr4, etc., does not move and is in a deaf state.
3, it is sufficiently fast that the transistor Tr5 is cut off;
A current equal to the current flowing through the constant current source 31 flows. In this way, in the current control circuit 21, switching for a minute current of 10 nA is performed sufficiently quickly.

Effects As described above, according to the present invention, switching of minute currents is performed at high speed, and therefore, for example, in a distance measurement calculation circuit, highly accurate distance measurement calculation is possible.

[Brief explanation of the drawing]

FIG. 1 is an electrical circuit diagram of a ranging calculation circuit including a current control circuit 21 according to an embodiment of the present invention, and FIG. It is a circuit diagram. 21... Current control circuit, 27... Hold circuit, 3
1.32...constant current source, 34...switch circuit, 3
6... Logarithmic compression circuit, Tri to Tr7... Transistor, r1 to r6... Resistance agent Patent attorney Number of strokes Keiichi

Claims (1)

[Scope of Claims] A first current mirror circuit including an output transistor from which an output is taken out; and a second current mirror circuit including a transistor, the circuit being switched between an active state and an inactive state, a second current mirror circuit under which said transistor is held below saturation, the emitter potential of the output transistor of the first current mirror circuit being regulated by the second current mirror circuit; A current control circuit characterized in that the collector current of the output transistor is controlled thereby.