JPH0554630B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a voltage discrimination circuit that can extract a voltage equal to the highest input voltage or the lowest input voltage among a plurality of analog input voltages.

(Prior Art) As a voltage discrimination circuit that discriminates the maximum value of an input analog voltage using a conventional operational amplifier, the one shown in FIG. 1 is known. In the figure, the outputs of operational amplifiers _A1 to _A3 are connected to diodes _D4 to _D6, respectively.
are respectively led to anodes, and their cathodes are connected in common to the output terminal 4. This output terminal 4 is connected by negative feedback to the negative input terminals of the operational amplifiers A ₁ to _{A 3} via protective resistors R ₁ to R ₃ . Analog input voltages are applied from input terminals ₁ to ₃ to the positive input terminals of operational amplifiers A 1 to A 3 , respectively.

Since the diodes D ₄ to D ₆ are inserted in the negative feedback loop, the forward voltage V _F of the diodes can be ignored. Since the cathodes of the diodes D ₄ to D ₆ are commonly connected, the operational amplifier A ₁ to which the highest voltage among inputs 1 to 3 is applied
One of _A3 , for example _A3 , acts as a voltage follower. However, since the potential of the negative input terminal of the remaining operational amplifiers A ₁ and A ₂ is higher than that of the positive input terminal, the output is saturated to the negative power supply side and is connected to the output terminal of the operational amplifiers A ₁ and A ₂ . The diodes D ₄ and D ₅ are reverse biased and disconnected from the output. As a result, the maximum voltage among a large number of analog input voltages is output.

However, when the number of inputs increases, one operational amplifier, one diode, and one resistor are required for each channel, and even if this circuit is integrated, it will require a considerable scale. ,
It has the disadvantage of high cost.

(Object of the Invention) An object of the present invention is to eliminate the above-mentioned drawbacks, to provide a highly accurate voltage discrimination circuit that can be configured with a small number of elements and is suitable for high-density integrated circuits.

(Structure of the Invention) A voltage discrimination circuit according to the present invention includes a plurality of voltage input terminals and a plurality of first transistors,
The respective collectors are commonly connected to the first circuit node, the respective bases are connected to corresponding ones of the plurality of voltage input terminals, and the respective emitters are connected to the second voltage input terminal through the first diode in the forward direction, respectively. a plurality of first transistors commonly connected to a circuit node, and a differential amplifier for the plurality of first transistors whose emitters are connected to the second circuit node through a second diode in the forward direction; a constant current source connected between the second circuit node and the power supply; and a constant current source connected between the first circuit node and the collector of the second transistor a first transistor and said second transistor;
an active load that converts a differential output with the transistor into a single-ended output, a feedback circuit that applies feedback from the output of the active load to the base of the second transistor, and an output terminal taken out from the output of the active load. It is characterized by including.

(Example) Next, an example of the present invention will be described using the drawings.

FIG. 2 is a circuit diagram of a first embodiment of the present invention.

This embodiment is an embodiment of a voltage discrimination circuit that outputs the higher voltage among the input voltages input to voltage input terminals 1 and 2, respectively.

This first embodiment has two voltage input terminals 1,
2, two first transistor groups Q ₁ and Q 2 whose collectors are commonly connected and whose bases are connected to voltage input terminals 1 and ₂ , respectively, and whose emitters are the emitters of the first transistor group Q ₁ and Q _2. A second transistor Q 3 is commonly connected to all of the transistors through diodes D ₁ , D ₂ , D ₃ respectively to form _a differential amplifier with the first transistor group Q ₁ , Q ₂ , and a second transistor Q ₃ emitter and the first transistor group Q ₁ ,
Common connection point _N1 with emitter of _Q2 and negative power supply terminal 6
a first constant current source I ₁ connected between the _first constant current source I ₁ and a _first transistor An active load consisting of transistors Q ₄ and Q ₅ that converts the differential output between the group and the second transistor into a single-ended output, and a feedback element Q ₆ that provides feedback from the output of this active load to the base of the second transistor. and an output terminal 4 connected to a common connection point _N2 between the active load and the feedback element. Note that capacitor C _F is for frequency compensation, 5 is a positive power supply terminal, and transistors Q ₄ and Q ₅ as active loads constitute a current mirror circuit.

In the circuit of the above embodiment, voltage input terminal 1,
If the input voltages input to 2 are V _IN1 and V _IN2 , |V _IN1 − V _IN2 | <V _BE + BV _EB0 (V _BE : Forward voltage between base and emitter, BV _EB0 : Reverse voltage between base and emitter. (withstand voltage), D ₁ to D ₃ can be omitted. That is, D ₁ to _{D 3} are inserted to widen the differential input voltage range between voltage input terminals 1 and 2.

In the above circuit configuration, of the transistors Q ₁ and Q ₂ to which an input voltage is applied to the base, the transistor to which the input voltage is higher is activated, and the other transistors are cut off. And the transistor
The activated transistor of Q ₁ and Q ₂ and the second transistor Q ₃ function as a differential amplifier. Then, it is converted into a single-ended signal by transistors Q ₄ and Q ₅ of the current mirror circuit that act as active loads, and the single-ended output is fed back to the base of Q ₃ via the emitter follower of transistor Q ₆ as a feedback element. Ru. That is, since the entire device operates as a voltage follower, the higher input voltage is output as is.

In this embodiment, an example of two-channel input is shown, but if necessary, the collectors of the transistors and diodes can be connected in common, the anodes of diodes are connected in series with their emitters, and the cathodes of transistors and diodes are connected in common. The number of input channels can be easily increased by increasing only the number.
Further, when this circuit is integrated, the input stage transistors Q ₁ to Q ₃ and diodes D ₁ to D ₃ are well matched and highly accurate can be obtained.

In the first embodiment, a voltage discrimination circuit that discriminates the maximum value of the input analog voltage was shown, but
By reversing the polarity of the transistor and the polarity of the current source, an analog voltage minimum value voltage discriminator circuit can be configured in exactly the same way.

FIG. 4 is a circuit diagram of a second embodiment of the present invention.

This embodiment is a circuit diagram that allows output with a constant gain for the maximum input voltage.The common connection between the emitter of transistor _Q6 and the base of transistor _Q3 is disconnected, and the output from the emitter of transistor _Q6 is It is connected to the reference potential point 7 via resistors R ₄ and R ₅ connected in series. The series connection point of resistors R ₄ and R ₅ is then connected to the base of transistor Q ₃ . and the emitter and resistor of transistor _Q6
The connection point of _R4 becomes output terminal 4. In the above circuit configuration, the higher voltage of the voltages V _IN1 and V _IN2 input to voltage input terminals 1 and 2 is (1+R ₄ /
R ₅ ) is multiplied and output to output terminal 4. Other circuit operations are the same as those in the embodiment shown in FIG.

(Effects of the Invention) As described above, according to the present invention, it is possible to obtain a voltage discriminator circuit that can be configured with a very small number of elements and has low power consumption and high accuracy, which is suitable for high-density integrated circuits. Moreover, by providing a forward diode between the emitter of each transistor constituting the differential amplifier and the constant current source, the differential input voltage range can be expanded.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an example of a conventional voltage discrimination circuit, and FIGS. 2 and 3 are circuit diagrams of first and second embodiments of the present invention, respectively. 1, 2, 3...Voltage input terminal, 4...Output terminal, 5...Positive power supply terminal, 6...Negative power supply terminal, 7...
…Reference voltage terminal, C _F …Capacitor, D ₁ to _{D 6} …
...Diode, I ₁ , I ₂ ... Constant current source, Q ₁ to _{Q 6} ...
Bipolar transistor, R ₁ to R ₃ ...resistance.

Claims (1)

[Claims] 1 a plurality of voltage input terminals and a plurality of first transistors, each collector of which is commonly connected to a first circuit node, each base of which is connected to a corresponding one of the plurality of voltage input terminals; The emitters of the plurality of first diodes are commonly connected to the second circuit node through the first diodes in the forward direction, respectively.
a second transistor whose emitter is connected to the second circuit node through a second diode in the forward direction to form a differential amplifier for the plurality of first transistors; a constant current source connected between the circuit node of and the power source;
an active load that is connected to the first circuit node and the collector of the second transistor and converts a differential output between the plurality of first transistors and the second transistor into a single-ended output; and the active load. A voltage discrimination circuit comprising: a feedback circuit that applies feedback to the base of the second transistor from the output of the active load; and an output terminal taken out from the output of the active load.