VOLTAGE COMPARATOR OF A TYPE OF LOW POWER COMSUMPTION

Abstract: Current supply circuits (23), (24) having switching ele­ ments are inserted on the power supply side (31) and on the power return wire side (32) of a differential amplifier means (10) in a voltage comparator, and are turned on or off. This makes it possible to obtain a voltage comparator which inter­ mittently operates at high speeds consuming a reduced amount of electric power.

Description: The present invention relates to a low electric power consumption voltage comparison circuit utilized in an electronic circuit for a pulse encoder or the like. Conventional voltage comparison devices using differential amplification circuits are shown in Fig. 1, Fig. 2, and Fig. 3. In Fig. 1, an operational amplifier 50 operating as a voltage comparison device is shown. The operational amplifier 50 is supplied with electric power from a +V electric power source 21 through an electric power supply feeder 51, and the electric power returns to a negative terminal 22 (usually ground potential) of the power source through an electric power return feeder 52. Also, an input signal S(IN) is supplied between a noninverting input terminal 53 and an inverting input terminal 54, and an output is obtained at an output terminal 55. The use of such a voltage comparison device in the form of an operational amplifier, which is usually part of an integrated circuit, presents a problem in that the device has a comparatively large electric power consumption since it includes the differential amplification circuit. Particularly, when electric power is supplied from a cell or the like to the above circuit, the effect is remarkable. For this reason, as shown in Fig. 2, a circuit is known wherein the electric power is supplied as a pulse S (PULSE) from a pulse source 58 only when a voltage comparison is performed. In this example, an input signal S(IN) from signal source 15 is applied between the noninverting input terminal 53 and the inverting input terminal 54, and a bias voltage V (BIAS) from a bias source 26 is applied to the inverting input terminal 53. The circuit diagram of the differential amplification circuit in this circuit is shown in Fig. 3. In this example of the circuit, the differential amplification circuit is constituted with two transistors 56 and 57 connected to each other at their emitters, resistors 62 and 63 connected to the collectors of the transistors 56 and 57, respectively, and a resistor 61 connected to the emitters of the transistors 56 and 57. In the circuit of Fig. 3, the pulse source 58 of Fig. 2 is replaced by a switch 60 which is inserted in the electric power supply feed circuit and controlled to turn the voltage of the electric power source 21 ON or OFF. Thus the voltage comparison circuit operates intermittently, and the output is obtained at a terminal 65. If the circuits as shown in Fig. 2 and Fig. 3 are used, the electric power consumption can be suppressed to a low value. However, when electric power is not being supplied, almost all of the circuits are reduced to the potential of the return side of the electric power source, that is, usually ground potential. When power is again supplied to enable the voltage comparator, a high speed rise to a required potential cannot be performed as a certain time lag is necessary, and thus high speed intermittent operation is difficult to achieve. JP-A-5471542 describes a voltage comparator circuit having a low current consumption. A comparator circuit is connected to a first power supply terminal by a first transistor and to a second power supply terminal by a pair of second transistors which are arranged in parallel. The period for which power is supplied to the comparator circuit is limited by controlling the period for which the first transistor is conductive. The second transistors are provided to assist in reducing malfunctions due to noise but are not switched to limit power consumption. US-A-4309627 describes a voltage comparison circuit in which power consumption is reduced by inserting switching elements arranged to enable the comparison circuit only when a sampling pulse signal is received. Portions of the comparison circuit remain electrically connected to power supply terminals at all times however. It is an object of the present invention to obtain a voltage comparison device with which it is possible to achieve low electric power consumption and to operate intermittently at a high speed. According to the present invention, there is provided a voltage comparison device comprising a differential amplification means having a noninverting input terminal and an inverting input terminal, for amplifying differentially an input signal and for generating an output signal; first and second voltage sources; an electric power supply feeder for connecting said differential amplification means to said first voltage source; an electric power return feeder for connecting said differential amplification means to said second voltage source; a first electric current supply circuit including a switching element inserted in the said electric power supply feeder; and a second electric current supply circuit including a switching element inserted in the said electric power return feeder, whereby means are provided for switching said first and second electric current supply circuits such that said switching elements are simultaneously switched ON and simultaneously switched OFF. As mentioned above, as electric current switch circuits are provided at the electric power supply side and the electric power return side of the differential amplification means in the voltage comparison device, and electric power is intermittently supplied only when necessary by turning ON the electric current switches, the electric power consumption can be reduced. Also, when the differential amplification circuit is turned OFF and disconnected from the power supply by the two electric current switches, it is in a floating condition. Thus when it is switched to the operating condition by turning ON the electric current switches, a high speed response and thus a high speed intermittent operation can be achieved. BRIEF EXPLANATION OF DRAWINGS Figs. 1 and 2 are circuit diagrams of conventional voltage comparison devices; Fig. 3 is a circuit diagram of a differential amplification portion according to a conventional voltage comparison device which operates intermittently; Fig. 4 is a circuit diagram of a differential amplification circuit and peripheral associated circuits in a low electric power consumption voltage comparison device according to an embodiment of the present invention; Figs. 5 and 6 are circuit diagrams of the low electric power consumption voltage comparison device in Fig. 4; and Fig. 7 is a circuit diagram according to another embodiment of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION A low electric power consumption voltage comparison device according to an embodiment of the present invention is shown in Figs. 4 and 5. In Fig. 5, an electric current supply circuit is provided in an operational amplifier type differential amplification circuit, which constitutes the voltage comparison device and can be turned ON or OFF by applying a control signal S (ON/OFF) to an external switching control terminal 30. Electric current switches 23, 24 are inserted in the electric power supply side and the electric power return side in the differential amplification circuit 10, and the electric power source of the differential amplification circuit can be connected or disconnected as necessary. In the circuit of Fig. 5, an input is applied between a noninverting input terminal 12 and an inverting input terminal 13, and an output is obtained at an output terminal 20. A voltage from +V electric power source 21 as a first electric power source is supplied through an electric power supply feeder 31. The electric power return feeder 32 is connected to a ground potential V (GROUND) at a ground point 22. Fig. 6 is a diagram corresponding to the above-mentioned Fig. 2. An input signal 15 to be operated upon is applied between input terminals 12, 13 of the circuit of Fig. 6 and the inverting input terminal 13 is connected to an electric power source 26 for supplying the bias voltage V (BIAS). The control signal S (PULSE) is applied from a pulse source 33. The differential amplification circuit 10 is the same as that in Fig. 6. In Fig. 4, the circuit diagram of the differential amplification circuit and the peripheral portion thereof is shown. The differential amplification circuit 10 comprises transistors 16 and 17 and resistors 18 and 19 connected to the collectors of the transistors 16 and 17, respectively. The emitters of the transistors 16 and 17 are connected to each other. The base of the transistor 16 is connected to the noninverting input terminal 12 and the base of the transistor 17 is connected to the inverting input terminal 13. The electric power from the +V electric power source 21 is connected to the terminals of the resistors 18 and 19, which are connected to the transistors 16 and 17, through an electric current switch 23. The emitters of the transistors 16 and 17 are grounded through another electric current switch 24. Control terminals through which the electric current switches 23 and 24 are controlled to turn ON or OFF are connected to the terminal 30 for switching. The collector of the transistor 17 is connected to an output terminal 14. The connections regarding the input signal 15 and the electric power source 26 for the bias voltage are substantially the same as those in the circuit of Fig. 3. For example, a transistor circuit constituting a constant-current circuit can be used as the electric current switches 23 and 24. If the electric current switches are switched from an OFF state to an ON state, since the differential amplification circuit 10 is in a floating state when in the OFF state, the voltage of each portion of the circuit quickly reaches the normal state in the operating condition by using the above-mentioned differential amplification circuit 10. Therefore, a high speed intermittent operation can be carried out. In Fig. 7, a circuit diagram of a low electric power consumption voltage comparison device according to another embodiment of the present invention is shown. The device of Fig. 7 comprises transistors Q1 to Q17. The transistors Q1 to Q7, Q15, and Q16 are used for electric current switching. The electric power source 21 usually supplies +5 volts and one terminal is connected to the ground 22. The transistor Q1 is made conductive or nonconductive by receiving the external ON or OFF switching signal. The transistor Q1 is made conductive by receiving +5 volts at the base thereof and the transistor Q2 is also made conductive, whereby the transistor Q5 becomes conductive. Then a connecting point 42 to which the bases of the transistors Q3, Q4, Q6, Q7, and Q15 are connected is set at approximately +4.4 volts, which is about 0.6 volts lower than +5 volts. Simultaneously, a connecting point 43 connected to the base of the transistor Q5 and the collector of the transistor Q3 is set at approximately +3.8 volts, which is about 1.2 volts lower than +5 volts. Also, the base of the transistor Q16 is set at approximately +0.6 volts. Thus, all of the transistors for electric current switching become conductive, and moreover, the transistors Q10, Q11, and Q14 are made conductive. As mentioned above, when the transistor Q1 is conductive, the electric current switching transistors become conductive, and electric power is supplied to a differential amplification circuit constituted by the transistors Q8 and Q9, and is supplied to the transistors Q10, Q11, and Q17, which constitute the output circuit of the differential amplification circuit. The differential amplification circuit receives an input at terminals 12 and 13 and supplies the output to an output terminal 41 through the collector of the transistor Q17 and a power amplification circuit comprising the transistors Q12, Q13, and Q14. In the device of Fig. 7, when the ON signal is not applied to the switching terminal 30, little electric power is consumed, and when the ON signal is applied, each portion is quickly set at the potential appropriate to the operation state. Thus, a high speed intermittent operation can be performed. In addition, the transistor Q17 and a diode connected to the base thereof constitute a current-Miller circuit.

Claims: A voltage comparison device comprising a differential amplification means (10) having a noninverting input terminal (12) and an inverting input terminal (13), for amplifying differentially an input signal and for generating an output signal; first and second voltage sources (21, 22); an electric power supply feeder (31) for connecting said differential amplification means to said first voltage source; an electric power return feeder (32) for connecting said differential amplification means to said second voltage source; a first electric current supply circuit (23) including a switching element inserted in the said electric power supply feeder; and a second electric current supply circuit (24) including a switching element inserted in the said electric power return feeder, characterised in that means are provided for switching said first and second electric current supply circuits such that said switching elements are simultaneously switched ON and simultaneously switched OFF. A device as set forth in claim 1 wherein each said first and second electric current supply circuit comprises a constant-current circuit. A device as set forth in claim 1 or 2, wherein said switching elements in said first and second electric current supply circuits comprise transistors.

Inventors: ISHIDA, HIROSHI 2-2-73, MATSUBARA-CHO
Applicants: FANUC LTD.
Application year: 1985
Main classification: G01R19
IPC codes: H03K5, G01R19