GB2125244A

GB2125244A - Absolute value amplifier

Info

Publication number: GB2125244A
Application number: GB8221481A
Authority: GB
Inventors: Masaji Usui
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1982-07-24
Filing date: 1982-07-24
Publication date: 1984-02-29
Also published as: AU561059B2; AU8569482A; GB2125244B; SE8204156D0; CA1202380A; SE8204156L; SE457130B

Abstract

A rectifier circuit includes three operational amplifiers (8, 9, 17), the first (8) of which is provided with feedback loops containing diodes (7, 18) of opposite polarity. The other op- amps (9, 17) are coupled to the output of the first one via the respective diodes, and to the circuit input via respective resistors 4, 15 having a value of twice that of the other resistors, so as to provide a positive going full wave rectified output at terminal 20, and a similar negative going output at terminal 12. <IMAGE>

Description

SPECIFICATION Input converting circuit This invention relates to converter circuits in which an input signal is converted into one suitable for an electrical device which is operated by the input signal, and more particuiarly to a circuit for converting the waveform of an input signal into positive and negative full-wave rectification waveforms. Such a circuit is employed as the input circuit of a protective relay device for instance.

A conventional input converting circuit of this type is as shown in Fig. 1. In Fig. 1, reference numerals 1 through 5 designate resistors; 6 and 7, diodes; and 8 and 9, operational amplifiers which form first and second operation circuits with the circuit elements 1 through 7 mentioned above.

The operation of the circuit thus organized will now be described.

In operation, a sinusoidal voltage V, as shown in Fig. 2a is applied through the resistor 1 to the inversion input terminal of the operational amplifier 8. When the non-inversion input terminal of the amplifier 8 is grounded, a voltage V2 is developed at the connecting point of the diode 7 connected to the output terminal of the amplifier 8 and the resistor 2 which serves as a feedback resistor. The waveform of the voltage V2 is half-wave rectified, as shown in Fig. 2b. When the voltage V1 is positive, the diode 6 connected between the input and output terminals of the operational amplifier 8 is rendered conductive, i.e., the input and output terminals are shortcircuited, as a result of which the voltage V2 is at O volts.When the voltage V1 is positive, the diode 7 blocks the flow of current to the input terminal of the operational amplifier through the resistor 2.

The voltage V2 is applied through the resistor 3 to the inversion input terminal of the operational amplifier 9, the non-inversion input terminal of which is grounded, and the output terminal 12 of the amplifier 9 is connected through the resistor 5 to the inversion input terminal of the same and is connected through the resistors 5 and 4 to the input terminal 10. As a result, a voltage V3 which if full-wave rectified as shown in Fig. 2c is developed at the output terminal 12.Therefore, if each of the resistances of the resistors 1, 2 and 3 is represented by R, the resistance of each of the resistors 4 and 5 is represented by 2R, then when V1 < O, V3=-V1, and when V1 < 0, V3=V1-2V2=V1-2V1=-V1 If a capacitor is connected in parallel with the resistor 5, which is feed-back resistor of the operational amplifier 9, then a voltage, which is obtained by smoothing the voltage V3. is provided at the output terminal 12.

The conventional input converting circuit is designed as described above. Therefore, in order to obtain full-wave rectification and waveform smoothing, the respective circuits described above must be provided.

An object of this invention is to eliminate the above-described drawback accompanying a conventional input converting circuit. More specifically, an object of the invention is to provide an input converting circuit in which one and the same circuit can provide a non-smoothed output, a smoothed output, or positive and negative outputs.

Fig. 1 is a circuit diagram showing a conventional input converting circuit; Figs. 2a-2c are waveform diagrams for describing the operation of the circuit of Fig. 1; Fig. 3 is a circuit diagram of a first example of an input converting circuit according to this invention; Figs. 4a-4e are waveform diagrams for describing the operation of the input converting circuit of Fig. 3; Figs. 5a and 5b are circuit diagrams showing second and third examples of the input converting circuit according to the invention; and Figs. 6a, 6b and 6d are waveform diagrams for describing the operation of the circuit of Fig. 5a.

Fig. 3 is a circuit diagram showing a first example of the input converting circuit according to the invention. In Fig. 3, those components which have been previously described with reference to Fig. 1 are therefore designated by the same reference numerals or characters. Further in Fig. 3, reference numeral 1 3 designated a resistor, one terminal of which is connected to the resistor 1. A resistor 14 has one terminal connected to the resistor 13, and a resistor 1 5 has one terminal connected to the input terminal 10.A resistor 1 6 has one terminal connected to the resistor 14 and 15, and an operational amplifier 1 7 has its inversion input terminal connected to the resistors 14, 15 and 16, a noninversion input terminal grounded, and an output terminal connected through the resistor 16 to the inversion terminal. Further in Fig. 3, reference numeral 1 8 designates a diode connected between the operational amplifier 8 and the connecting point 19 of the resistors 13 and 14; and 20, the output terminal of the operational amplifier 17.

The operation of the input converting circuit thus organized will now be described. It is assumed that the resistance of each of the resistors 13 and 14 is represented by R, the resistance of each of the resistors 1 5 and 1 6 is represented by 2R, and the resitances of the other resistors are the same as those described with reference to Fig. 1. The input voltage V1 is as shown in Fig. 4. When the voltage is positive, current flows in the resistors 1 and 1 3 and the diode 1 8 as indicated by the dotted line in Fig. 3.

Therefore, the voltage V4 at the connecting point 19 becomes -V1 (V4=-V1) (Fig. 4c). In this case, the output of the operational amplifier 8 equals -V1-(forward voltage drop across the diode 18).

Therefore, the diode 7 is non-conductive (off), and the voltage V2 at the connecting point 11 is OV which is equal to the voltage at the inversion input terminal of each of the operational amplifiers 8 and 9. (Fig. 4b). While the voltage V1 is negative, current flows through the diode 7 and the resistors 2 and 1 as indicated by the dot chain line in Fig. 3, and the voltage V2 at the connecting point 11 is -V1 (V2=-V1) (Fig. 4b).

In this operation, the diode 1 8 is nonconductive (off) and the voltage V4 at the connecting point 1 9 is OV. By repeating the above-described operation, the voltage V3 (Fig.

4d) at the output terminal 12 has a negative fullwave rectified waveform similarly as in the case of Fig. 1, and the voltage V5 (Fig. 4c) at the output terminal 20 has a positive full-wave rectified waveform.

In the first example described above, the resistor 5 is alone employed to feed back the output of the operational amplifier 9. However, a capacitor 21 may be connected in parallel to the resistor 5 as shown in Fig. 5a, to provide a smoothed output at the output terminal 12; and the same effect can be obtained by applying a reference voltage V ref through a resistor 22 to the inversion input terminal of the operational amplifier 9 as shown in Fig. 5b. However, it should be noted in this case that the inversion input terminals of the operational amplifier 9 and 17 are maintained at OV in a phantom manner similarly as in the case of the conventional circuit.

Fig. 6 is a diagram showing waveforms obtained with device of Fig. 5a.

As is apparent from the bore description, according to the invention, positive and negative full-wave rectification waveforms can be obtained simultaneously by employing three operational amplifiers in combination. The input converting circuit according to the invention, being simple in circuitry, can be manufactured at low cost.

Claims

1. An input converting circuit, comprising; a first operational amplifier for receiving an input signal through an inversion input terminal thereof and means for feeding back an output signal thereof to said inversion input terminal; first means for receiving an output signal of said first operational amplifier and means for feeding back an output signal of said first means to the inversion input terminal of said first operational amplifier and to an input of said first means; and second means for receiving an output signal of said first operational amplifier and means for feeding back an output signal of said second means to the inversion input terminal of said first operational amplifier and to an input of said second means.

2. A circuit as claimed in claim 1, wherein said feedback means for said first operational amplifier comprises first and second diodes of opposite polarity.

3. A circuit as claimed in claim 2, said first and second means comprising second and third operational amplifiers.

4. A circuit as claimed in claim 3, said second operational amplifier receiving an output of said first operational amplifier through said first diode.

5. A circuit as claimed in claim 3, said input of said first means comprising an inversion input terminal of said second operational amplifier.

6. A circuit as claimed in claim 3, said third operational amplifier receiving an output of said first operational amplifier through said second diode.

7. A circuit as claimed in claim 3, said input of said second means comprising an inversion input terminal of said third operational amplifier.

8. A circuit as claimed in claim 3, said feedback means for said second and third operational amplifiers comprising resistor means.

9. A circuit as claimed in claim 8, at least one of said feedback means including a capacitor coupled in parallel with said resistor means.

10. A circuit as claimed in claim 8, at least one of said feedback means inciuding resistor means having a reference voltage applied to that terminal thereof coupled to the inversion input terminal of the operational amplifier.

11. A circuit as claimed in claim 3, said second operational amplifier forming an integration circuit.