JP2002131343A - Minimum value detection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize a circuit for detecting a minimum value among a plurality of given signals with high precision. SOLUTION: To input terminals T1-T3, cathodes of input diodes D1-D3 are connected individually. The anodes of the input diodes D1-D3 are connected to a non-inverting input terminal of an operation amplifier OP. The output of the operation amplifier OP is connected to the non-inverting input terminal via a resistor R1 and connected to an inverting input terminal via a resistor R2. The inverting input terminal of the operation amplifier OP is connected to the anode of a diode D0. The cathode of the diode D0 is grounded via a resistor R3 and connected to an output terminal Tout. The resistance value ratio between the resistors R1 and R2 is designed so that the ON voltage of the input diode inputting a minimum voltage approximately matches with the ON voltage of the diode D0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a circuit for detecting a minimum value among a plurality of given signals.

[0002]

2. Description of the Related Art Conventionally, there has been known a circuit for detecting a minimum value among a plurality of given signals in electric equipment or electronic equipment. For example, this type of circuit is used in applications where the worst value is detected from the outputs of a plurality of sensors.

FIG. 2A is a circuit diagram of an example of an existing minimum value detection circuit. This circuit is generally a wired-OR
It is called a circuit or a diode OR circuit, and a diode is provided for each input terminal.
Specifically, signals input from the input terminals T1 to T3 are supplied to the cathodes of the corresponding diodes D1 to D3, respectively. On the other hand, the anodes of the diodes D1 to D3 are electrically connected to each other.

In this configuration, assuming that a signal (for example, a voltage value) supplied to the input terminal T3 is smaller than a signal supplied to the other input terminals, a current supplied from the power supply flows at least through the diode D3. Will be. Therefore, in this case, this circuit is connected to the “input terminal T
3 + ON voltage of diode D3 ".

As described above, since the output of the circuit shown in FIG. 2A is added with the ON voltage of the diode, the minimum value of the input signal cannot be accurately detected. FIG.
(b) is a circuit diagram of another example of the existing minimum value detection circuit. This circuit corresponds to the diode D of the circuit shown in FIG.
This is realized by replacing 1 to D3 with ideal diodes. The ideal diode is configured using an operational amplifier, and has a function of canceling the ON voltages of the diodes D1 to D3. Here, since each operational amplifier operates so that the potentials of its inverting input terminal and non-inverting input terminal coincide with each other, the resistors R1 and R2
By appropriately setting the ratio of the diodes D1 to
The ON voltage of D3 is cancelled.

By using this circuit, it is possible to accurately detect the minimum value of the input signal. However, this circuit has the drawback that the number of components is large and the circuit scale is large.

[0007]

As described above, the circuit for detecting the minimum value among a plurality of given signals has been increased in circuit scale in order to increase the detection accuracy. An object of the present invention is to reduce the size of a circuit that accurately detects a minimum value among a plurality of given signals.

[0008]

A minimum value detection circuit according to the present invention is configured to detect a minimum value among a plurality of given signals, and includes a plurality of input diodes to which the plurality of signals are input. An input circuit for outputting the minimum value of the plurality of signals, and a cancel circuit for canceling the influence of the ON voltage of the input diode from the minimum value output from the input circuit.

According to the above configuration, the influence of the ON voltage of the input diode is canceled by the cancel circuit, so that the minimum value among a plurality of given signals can be accurately detected. Further, since the cancel circuit cancels the influence of the ON voltages of the plurality of input diodes at once, the circuit scale is small.

[0010] The cancel circuit is fed back so that the minimum value output from the input circuit is given to the first input terminal and the value of the second input terminal matches the value of the first input terminal. A minimum value having an operational amplifier to be controlled and a diode connected to a second input terminal of the operational amplifier, wherein the influence of the ON voltage of the input diode is canceled via a diode provided in a cancel circuit thereof May be output. Further, the operational amplifier may be designed such that an ON voltage of the input diode and an ON voltage of a diode provided in the cancel circuit match each other.

[0011]

FIG. 1 is a circuit diagram of a minimum value detection circuit according to an embodiment of the present invention. This circuit has a plurality of input terminals T1 to T3 and an output terminal Tout, detects a minimum value of signals given to the input terminals T1 to T3, and outputs it from an output terminal Tout. The signal applied to each input terminal is, for example, a voltage signal.

The input terminals T1 to T3 are connected to the cathodes of input diodes D1 to D3, respectively. The anodes of the input diodes D1 to D3 are connected to the non-inverting input terminal of the operational amplifier OP. That is, the input diodes D1 to D3 constitute a wired OR circuit (diode OR circuit).

The output of the operational amplifier OP is connected to its non-inverting input terminal via a resistor R1 and to its inverting input terminal via a resistor R2. The inverting input terminal of the operational amplifier OP is connected to the anode of the diode D0. The cathode of the diode D0 is grounded via a resistor R3 and the output terminal T
connected to out.

The diode D0 is provided to cancel the ON voltage of the input diodes D1 to D3. The basic value of the bias current of the diode D0 is determined by the resistance of the resistor R3. Further, the resistor R1
The ratio between the resistance value of the resistor R2 and the resistance value of the resistor R2 is designed according to, for example, the number of input signals (that is, the number of input terminals). Specifically, the ratio of the resistance values of the resistors R1 and R2 is designed so that the ON voltage of the input diode to which the minimum voltage is applied and the ON voltage of the diode D0 approximately match.

Next, the operation of the minimum value detection circuit having the above configuration will be described. In the above configuration, the operational amplifier OP supplies a bias current to the input diodes D1 to D3 via the resistor R1, and also supplies a bias current to the diode D0 via the resistor R2. On the other hand, each input diode D
The input terminals T corresponding to the cathodes of 1 to D3 respectively
Signals to be detected (hereinafter, "detection voltages") are applied through 1 to T3. Here, the input diode D1
D3 constitute a wired OR circuit. Therefore, the non-inverting input terminal of the operational amplifier OP receives a voltage obtained by adding the ON voltage of the input diodes D1 to D3 to the minimum voltage among the detection voltages applied to this circuit. For example, assuming that the detection voltage input via the input terminal T3 is smaller than the detection signal input via the other input terminals, the non-inverting input terminal of the operational amplifier OP is connected to the "detection voltage applied to the input terminal T3". (Voltage + ON voltage of input diode D3).

The operational amplifier OP operates by feedback control such that the potential of its non-inverting input terminal and the potential of its inverting input terminal match each other. That is, the potential of the inverting input terminal of the operational amplifier OP is “the minimum voltage among the plurality of detection voltages + the ON voltage of the input diode to which the minimum voltage is given”. Therefore, the ON voltage of the input diode to which the minimum voltage is given and the diode D
Assuming that the ON voltage of 0 coincides with the ON voltage of the diode D0, the ON voltage of the input diode is canceled by the ON voltage of the diode D0, and the output of the output terminal Tout coincides with the minimum voltage. That is, for example,
Assuming that the minimum voltage is applied via the input terminal T3,
ON voltage of input diode D3 and ON of diode D0
If the voltages match each other, the minimum voltage is output from the output terminal Tout.

Here, in the minimum value detection circuit of the present embodiment, the resistance values of the resistors R1 and R2 are adjusted so that the ON voltage of the input diode to which the minimum voltage is applied and the ON voltage of the diode D0 approximately match. The ratio is designed.
Therefore, this circuit can output an accurate minimum value from which the influence of the ON voltages of the input diodes D1 to D3 has been removed.

Next, a method of designing the minimum value detection circuit having the above configuration will be described. In the circuit having the above configuration, if the current flowing through the diode D0 is "Ia" and the potential of the output terminal Tout is "Vo", the following equation (1) is obtained. If the current flowing through the resistor R1 is "Ib",
The following equation (2) is obtained.

Ia = Vo / R3 (1) Ib = (R2 / R1) .Ia (2) The current Ib flows through the input diodes D1 to D3. That is, the current Ib is controlled by the input diodes D1 to D3.
Is the sum of the currents flowing through Therefore, if the respective detection voltages applied to the input terminals T1 to T3 have substantially the same value, the input diodes D1 to D3
The currents flowing through 3 are almost identical to each other. In this case, the current Ib is three times the current flowing through each input diode.

On the other hand, if the variation in the detection voltage applied to the input terminals T1 to T3 is large and the detection voltage applied to one input terminal is sufficiently smaller than the detection voltage applied to the other two input terminals, Current flows only through the input diode connected to the input terminal. In this case, the current Ib matches the current flowing through the input diode.

In consideration of these points, the minimum value of the current Ib is a current value flowing through the input diode to which the minimum voltage is input. On the other hand, the maximum value of the current Ib is a value obtained by integrating the number of input diodes with the value of the current flowing through the input diode to which the minimum voltage is input. Here, in the minimum value detection circuit of the present embodiment, the current flowing through the input diode to which the minimum voltage is input and the current flowing through the diode D0 need to match each other. Therefore, the range of the current Ib is given by the following equation (3). Note that “n” is the number of input diodes, and in the example shown in FIG. 1, “n = 3”.

Ia ≦ Ib ≦ n · Ia (3) The resistance values of the resistors R1 and R2 are calculated according to the above (2)
It is determined according to the formula and the formula (3). That is, the resistance R
1 and the resistance value of the resistor R2 are such that the current Ib is in accordance with the above equation (3),
The N voltages are determined so as to be substantially the same as each other. At this time, the ratio of the resistance values of the resistors R1 and R2 ((2)
The expression "R2 / R1" is, for example, the input terminals T1 to T3.
A value close to the number of input diodes is set when the variation in the detection voltage applied to the input terminals is small, and "1" when the variation in the detection voltage applied to the input terminals T1 to T3 is large.
May be set to a value close to. Further, the resistance values of the resistors R1 and R2 may be calculated by simulation or the like, or they may be obtained while adjusting during the actual machine test.

The output voltage of the operational amplifier OP is set to "Vp
, The following equation (4) is obtained. Therefore, when designing this minimum value detection circuit, care must be taken so that the voltage Vp does not exceed the power supply voltage of the operational amplifier OP. Vp = {1+ (R2 / R3)}. Vo (4) In the above embodiment, the minimum value of the three input voltages is detected by providing three input diodes.
The present invention is not limited to this. That is, the present invention is applicable to a circuit that detects a minimum value when n inputs are provided by providing n (n is an integer of 2 or more) input diodes.

[0024]

According to the present invention, the influence of the ON voltage of a plurality of input diodes can be canceled with a simple configuration, and thus the circuit for accurately detecting the minimum value of a given plurality of signals can be miniaturized. Is achieved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a minimum value detection circuit according to an embodiment of the present invention.

FIGS. 2A and 2B are circuit diagrams of an existing minimum value detection circuit.

[Explanation of symbols]

 D (D0 to D3) Diode R (R1 to R3) Resistor OP Operational amplifier

Claims (4)

[Claims] 1. A minimum value detection circuit for detecting a minimum value among a plurality of given signals, the circuit comprising a plurality of input diodes to which the plurality of signals are inputted, and a minimum value among the plurality of signals. A minimum value detection circuit comprising: an input circuit that outputs a value; and a cancel circuit that cancels the influence of the ON voltage of the input diode from the minimum value output from the input circuit. 2. The minimum value detection circuit according to claim 1, wherein the input circuit includes a plurality of input terminals to which the plurality of signals are respectively applied and one output terminal, and the plurality of input terminals include: The cathodes of the corresponding input diodes are connected, and the anodes of the plurality of input diodes are connected to the output terminal. 3. The minimum value detection circuit according to claim 1, wherein the cancel circuit is configured to supply a minimum value output from the input circuit to a first input terminal, and to provide the second input terminal with a minimum value. An operational amplifier that performs feedback control so that the value of the terminal matches the value of the first input terminal; and a diode that is connected to the second input terminal of the operational amplifier, and is provided in the cancel circuit. A minimum value is output via the diode in which the influence of the ON voltage of the input diode is canceled. 4. The minimum value detection circuit according to claim 3, wherein the operational amplifier is designed such that an ON voltage of the input diode and an ON voltage of a diode provided in the cancel circuit match each other. .