JPS6225287B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current mirror circuit that can vary the current reversal ratio, and particularly aims to provide a current mirror circuit suitable for use in field strength display circuits of radio receivers, etc. It is something.

Conventionally, a current mirror circuit as shown in FIG. 1 is known. This is done by passing a constant current _I0 through the constant current source 1, causing the current _I0 to flow through the diode 2, and obtaining an inverted current _I1 correlated to the current _I0 at the collector of the transistor 3. . At this time, by setting the emitter area ratio of diode 2 and transistor 3 to l, I ₁ =l·I ₀ . (For example, if l=1, the collector current I ₁ of transistor 3 becomes I ₀ ; if l=2, I ₁ becomes 2I _0. ) Therefore, the current mirror circuit of FIG. By matching the characteristics of the diode 2 and the characteristics of the transistor 3, it is possible to obtain a current that accurately maintains a predetermined relationship with the current flowing through the diode 2, so it is often used in ICs (integrated circuits).

However, the circuit shown in FIG. 1 has the disadvantage that it cannot be used in cases where the inversion ratio needs to be changed in response to changes in the reference current. For example, in the field strength display circuit of a radio receiver, it is necessary to send a signal (current) corresponding to the magnitude of the field strength to the field strength display meter, but if the inversion ratio is constant, the field strength The relationship with the display meter input signal became constant, and appropriate display could not be performed.

The present invention has been made in view of the above points, and will be described below based on embodiments with reference to the drawings. Second
The figure shows the principle of the present invention, in which 4 is a first PNP transistor whose emitter is connected to a power supply line 5 and its collector is connected to a current output terminal 6; 7 is a base, emitter, and collector are the base of the first transistor 4, respectively. , a second PNP transistor connected to the emitter and collector, 8 a reference diode connected between the emitter and base of the first transistor 4, and 9 a switch 10 and a diode 11 connected in parallel with the reference diode 8. The series circuit 12 is a constant current circuit for providing forward current to at least the reference diode 8.
Therefore, the diodes and transistors used are all set to have the same emitter area, and the current flowing through the constant current circuit 12 is
I is set to ₀ .

If the switch 10 is now closed, two diodes 8 and 11 are connected in parallel between the bases and emitters of the first and second transistors 4 and 7. A current of I ₀ /2 flows through each of them. Therefore, a current of I ₀ /2 flows through the first and second transistors 4 and 7, respectively, so that an output current of I ₀ can be obtained at the output terminal 6.

Also, if the switch 10 is open,
Only the reference diode 8 is connected between the bases and emitters of the first and second transistors 4 and 7, and a current equal to the current I ₀ flowing through the constant current circuit 12 flows through the reference diode 8. Therefore, a current of I ₀ flows through the first and second transistors 4 and 7, respectively, so that an output current of 2I ₀ can be obtained at the output terminal 6. Therefore, the current mirror circuit in FIG. 2 can be used as a current mirror circuit with an inversion ratio of "1" or as a current mirror circuit with an inversion ratio of "2" by controlling the switch from the outside. I can do it. In the current mirror circuit shown in Fig. 2, n transistors are provided whose bases, emitters, and collectors are connected in common, and a series circuit of a switch and a diode is connected to m transistors.
If the m switches are controlled by a single control signal or by m mutually independent control signals, it can be used as a circuit with multiple inversion ratios. It can be explained in the same way.

FIG. 3 shows one embodiment of the present invention.
3 is a first transistor having a base, emitter, and collector; 14 is the first transistor 13;
and a second transistor 15 whose base, emitter, and collector are commonly connected; a second transistor 15 serving as a reference bias means whose collector is connected to the input terminal 16 and whose base is connected to its own collector via the emitter-base path of the transistor 17; 3 transistors, 1
8 is a fourth transistor whose base and collector are commonly connected to the third transistor 15 and serves as a biasing means.
A fifth transistor, 16, constitutes an electronic switch whose collector-emitter path is inserted between the power supply 20 and the emitter of the fourth transistor 18 and whose base is connected to the control input terminal 21; An input terminal to which a current source for supplying forward current to the third transistor is connected; 22 indicates the first and second transistors 13 and 1;
This is an output terminal for outputting the collector current flowing through 4. Note that the transistors 23, 24 and 25
is for matching and has the same characteristics as the fifth transistor 19 which operates as an electronic switch.

Next, the operation will be explained. Assuming that a current of _I0 is flowing out from the input terminal 16 by a current source (not shown), and no current is flowing to the control input terminal 21, the fifth transistor 19 is fully conductive, and the effect of the transistor 17 is 3rd and 4th
An equal current of I ₀ /2 flows through transistors 15 and 18 . Therefore, a current of I ₀ /2 equally flows through the first and second transistors 13 and 14, and a current of I ₀ is obtained at the output terminal 22. Therefore, when the fifth transistor 19 is fully conductive, the third
The current mirror circuit shown in the figure operates as a current mirror circuit with a current reversal ratio of "1".

Furthermore, if a signal sufficiently small (a negative signal may be applied) relative to the power supply voltage is applied to the control input terminal 21, the fifth transistor 19 will be completely non-conductive, and the fourth transistor 18 will be completely non-conductive. Current stops flowing. Therefore, all of the current I ₀ flowing to the input terminal 16 flows through the third transistor 15, and as a result, the current I ₀ equally flows through the first and second transistors 13 and 14. Therefore, a current of 2I ₀ is obtained at the output terminal 22, and the current mirror circuit shown in FIG. 3 becomes a current mirror circuit with a current reversal ratio of "2".

Since the fifth transistor 19 can take an active state between a fully conductive state and a completely non-conductive state, the current reversal ratio can be adjusted by applying a continuously changing control signal to the control input terminal 21. It can be freely changed between "1" and "2", and various applications are possible.

For example, if the current mirror circuit shown in FIG. 3 is used in a field strength display circuit of a radio receiver, it is possible to expand the linear display range. For example, in a conventional current mirror circuit with a fixed current reversal ratio, the linear display range was narrow as shown by the dotted line in Figure 4, but by using the current mirror circuit in Figure 3 according to the present invention, A current that changes according to a signal corresponding to the electric field strength (for example, the signal indicated by the dotted line in FIG. 4) is applied to the input terminal 16, and a signal corresponding to the electric field strength is applied to the control input terminal 21. The electric field strength at which the fifth transistor 19 transitions from the saturated state to the active state is set at point A in FIG. If set to B, the distance between the points A and B can be made into a substantially straight line, and the overall straight line display range can be expanded.

As described above, since the current mirror circuit according to the present invention can freely change the current reversal ratio, it is possible to obtain a signal depending on how it is used.
It is an excellent device that can have a large degree of freedom, especially by considering the control method.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing a conventional current mirror circuit.
FIG. 2 is a circuit diagram showing the basic principle of the invention, FIG. 3 is a circuit diagram showing an embodiment of the invention, and FIG. 4 is a characteristic diagram for explaining the invention. Explanation of main drawing numbers, 4, 7, 13, 14, 15,
18, 19...transistor, 8, 11...diode, 10...switch.

Claims (1)

[Claims] 1 At least the base and collector are connected in common, and the emitter is connected to the power supply line.
transistor and its base
The base is connected to the bases of the n transistors in order to apply a forward bias between the emitters,
a transistor whose emitter is connected to a power supply line and which serves as a reference bias means; a current source that provides a forward current to the transistor which serves as the reference bias means; and a base and collector connected to the base and collector of the transistor which serves as the reference bias means, respectively. m transistors connected to each other, for giving forward current to the m transistors, m control transistors connected to the emitters of the m transistors, and for controlling the m control transistors. a control input terminal to which a control signal is applied, and an output terminal connected to a common collector of the n transistors, and controls the current flowing through the transistor serving as the reference bias means in accordance with the control signal. . A power supply mirror circuit, characterized in that the output terminal is configured to generate an output current n times as large as the current flowing through the transistor serving as the reference bias means.