JP2732390B2 - Current output type comparator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current output type comparator, and more particularly to a current output type comparator which can easily maintain its output current at a minute constant current value.

[Prior Art] FIG. 3 is a connection diagram showing a conventional circuit, in which Q1, Q2, Q6, and Q7 are npn transistors, Q3, Q4, and Q, respectively.
5, Q8 is a pnp transistor, IE is a constant current circuit, R1,
R2, R3, R4, R5, R6 are resistors, VIN is the signal voltage, VTH is the threshold voltage, Ir is the collector current of Q1, IC3, IC7,
IC8 is the collector current of Q3, Q7, Q8, respectively. The collector connection point of Q7 and Q8 becomes the output terminal, and the load is connected between this output terminal and the ground.

A differential amplifier circuit is formed by a pair of transistors Q1 and Q2. The magnitude of VIN is controlled by cutting off the current of Q2 almost so that (Ir) = (IE), or by controlling the current of Q1. Let us consider the case of binary control of controlling whether (Ir) = 0 by almost cutting off. Here, (IE) indicates the current value of the constant current circuit IE. If you wrap it in other (), this applies.

That is, whether Q7 is cut off and operates as a current source that supplies a constant current IO from Q8 to the load, or operates as a current sink that passes a constant current from the load to Q7 (Q8 is then cut off). Consider the case of a current output type comparator.

In addition, since the operation as a current sink is similar to the operation as a current source, only the operation as a current source will be described below unless otherwise required.

When Q2 is cut off, Q4, Q5, Q6, and Q7 are also cut off.

Since (Ir) = (IE) and (IC3) = (Ir), and Q8 is connected as a current mirror of Q3, resistors R1 and R4
(IC8) = A (IC3) can be set by selecting the value of.

Since (IO) = (IC8), (IO) = A (IE) (1). Both A and (IE) are known and operate as a current source or sink of a given constant current. When the load is a capacitor, it can be charged or discharged with a predetermined constant current to generate a sawtooth wave.

[Problem to be Solved by the Invention] By the way, the value of the current IO represented by the equation (1) includes various errors. For example, since Ir includes the base currents of Q3 and Q8, it must be corrected.

FIG. 4 is a connection diagram showing a conventional circuit with such correction, in which the same reference numerals as those in FIG. 3 denote the same or corresponding parts, and Q9, Q10, Q11 denote Q3, Q8; Q4, Q5, respectively. A transistor provided to allow the base currents of Q6 and Q7 to flow, and since the base current flows through these transistors, this does not enter as an error.

However, there are still problems when using this comparator in a sawtooth wave light emitter. I would like to configure a load capacitor in an integrated circuit without using external components. Must be small enough. This means that Q8 operates in a small current region, that the value of the current amplification factor β is unstable, and that there is much variation due to manufacturing. Therefore, there is a problem that the value of A in the equation (1) becomes inaccurate and a desired saw-tooth liquid cannot be generated.

The present invention solves the above-mentioned problems in the conventional circuit,
It is an object of the present invention to provide a current output type comparator capable of supplying or absorbing a minute current at an accurate value.

Means for Solving the Problems According to the present invention, a current mirror circuit that generates a constant current that is A times the constant current IE and a current mirror circuit that generates a constant current that is B times the IE are provided. B) A constant current having the value of (IE) was output.

[Operation] With the configuration described above, A and B can make the value of AB accurate and small while maintaining the values of the appropriate operation ranges.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a connection diagram showing an embodiment of the present invention.
The same reference numerals as those in the drawing indicate the same or corresponding parts, and Q12, Q13, Q1
4 is an npn transistor, Q15 and Q16 are pnp transistors, R7, R8, R9, and R10 are resistors, and IC12 is Q12.
Shows the collector current of Q15 is connected as a current mirror of Q3, Q12 is connected as a current mirror of Q13, and Q16 is connected as a current mirror of Q4.

1 operate in the same manner as described with reference to FIG. If Q2 is cut off, Q4, Q5, Q6, Q7, Q16 are cut off and Q3, Q8, Q1
5, Since current flows through Q13, Q14, and Q12, (IO) = (IC8)-(IC12) ... (2).

By appropriately selecting the values of the resistors R1, R4, R7, R8, and R9, (IC8) = A (Ir) and (IC12) = B (Ir) can be obtained. In an actual case, R = 1 = R4 = R9 and A = 1, and the value of AB can be made a desired small value by selecting R7 and R8.

When Q1 is cut off, current flows through Q2, Q4, Q5, Q6, Q7, and Q16, and IO (in the direction opposite to the arrow in FIG. 1) becomes (IO) = (IC7)-(IC16), IC7) = D (I
r), (IC16) = E (Ir), and the value of DE can be a desired small value.

Q14 in FIG. 1 is provided for flowing the base currents of Q12 and Q13.

FIG. 2 is a connection diagram showing another embodiment of the present invention, in which the same reference numerals as in FIGS. 1 and 4 denote the same or corresponding parts, and the operation of Q9, Q10, Q11 The operation is the same as that of the transistors having the same reference numerals in FIG.

Although the embodiment shown in FIG. 1 shows a circuit capable of supplying a small constant current both as a current source and a current sink, depending on the purpose of use, only a small constant current is required for either the source or the sink. The current in the opposite case may not be a problem. When the present invention is used for such a purpose, it is possible to construct a circuit in which the circuit of FIG. 1 is appropriately omitted.

FIG. 5 is a connection diagram showing still another embodiment of the present invention.
Q16 is omitted from FIG.

When (IC8)> (IC12), it becomes the source of a minute constant current, and when (IC8) <(IC12), it becomes the sink. FIG. 6 is a connection diagram showing still another embodiment of the present invention, and Q12, Q13 and Q15 are omitted from FIG.

When (IC16)> (IC7), it becomes the source of a small constant current, and when (IC16) <(IC7), it becomes the sink.

[Effect of the Invention] As described above, according to the present invention, it is possible to configure a current output type comparator that can accurately output a small current value.

[Brief description of the drawings]

FIG. 1 is a connection diagram showing one embodiment of the present invention, FIG. 2 is a connection diagram showing another embodiment of the present invention, FIGS. 3 and 4 are connection diagrams showing a conventional circuit, and FIG. FIG. 6 is a connection diagram showing still another embodiment of the present invention. Q1, Q2, Q6, Q7, Q12, Q13 ... each is an npn transistor, Q
3, Q4, Q5, Q8, Q15, Q16 ... Each is a pnp transistor. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] An emitter of a pair of npn transistors Q1 and Q2 is connected to ground via a common constant current circuit, a signal voltage is applied to the base of Q1, and a threshold voltage is applied to the base of Q2. Differential amplifier, pnp transistor Q3 connected between power supply and collector of Q1 as load of Q1, pnp transistor Q4 connected between power supply and collector of Q2 as load of Q2 Q4 as current mirror for Q4 A pnp transistor Q5 connected to flow an emitter current proportional to the emitter current of Q5, connected between the collector of Q5 and ground as the load of Q5
The npn transistors Q6 and Q6 are connected to flow an emitter current proportional to the emitter current of Q6 as a current mirror to Q6.The npn transistors Q7 and Q3 are connected to flow an emitter current proportional to the emitter current of Q3 as a current mirror to Q3. a current output type comparator comprising a pnp transistor Q8, connecting the collectors of Q7 and Q8, and connecting this node to an output terminal and connecting a load between the output terminal and the ground, as a current mirror for Q4 Providing a pnp transistor Q16 connected to flow an emitter current proportional to the emitter current of Q4, connecting the collector of Q16 to the output terminal, and / or an emitter proportional to the emitter current of Q3 as a current mirror for Q3 A pnp transistor Q15 connected to allow current to flow, and Q15 And an npn transistor Q12 connected as a current mirror to Q13 so that an emitter current proportional to the emitter current of Q13 flows, and a collector of Q12 is connected to the output terminal. A current output type comparator characterized by being connected.