JPS62118624A - Limiter circuit - Google Patents

Abstract

PURPOSE:To obtain a flat limiter characteristic by connecting a cathode of the 1st diode and the 1st resistor, an anode of the 2nd diode and the 2nd resistor in series respectively, connecting the anode of the 1st diode and the cathode of the 2nd diode to an output terminal of an operational amplifier and connecting the other terminal of the 1st and 2nd resistors to the output of a feedback resistor so as to use the connecting point as the output terminal of the operational amplifier circuit. CONSTITUTION:The 1st resistor R1 and the cathode of the 1st diode D1, and the 2nd resistor R2 and the anode of the 2nd diode D2 are connected in series respectively, the anode of the 1st diode D1 and the cathode of the 2nd diode D2 are connected to the output terminal of the operational amplifier A1 at a connecting point (b), the other terminal of the 1st and 2nd resistors R1, R2 not connected to the diodes D1, D2 is connected to the output point (e) of the feedback resistor Rf and the point is used as the output point of the operational amplifier A1. Further, an input resistor Ri is connected to an inverting input of the operational amplifier A1 and the feedback resistor Rf is provided to the feedback circuit.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a limiter circuit, and in particular, the positive output saturation voltage and negative output saturation voltage of an operational amplifier can be set independently, and a flat amplitude can be achieved. This is a limiter circuit that allows you to wander the limiting characteristics.

(Prior Art) Conventionally, various specific circuits for realizing the limiter function have been considered, such as a circuit that separately supplies a saturation voltage to an output terminal, a shunt limiter circuit, and a feedback limiter circuit. FIG. 2a shows the simplest and typical circuit configuration of a feedback limiter circuit. Here, an input voltage Ei is applied to the negative input terminal of the operational amplifier A1 through an input resistor Ri. This negative input terminal is connected to the output terminal by a resistor R4 through a diode D°2.

On the other hand, the operational amplifier A is connected from the output terminal through the feedback resistor Rf.
A feedback circuit is provided which is connected to the negative input terminal of .

Also, +E2 from the power supply terminal to bring the lower limit saturation value.
is applied to the connection point between the resistor R4 and the cathode of the diode D'2 through the resistor R3, and -E1 is applied from the power supply terminal to provide the upper limit saturation value to the resistor R'2 through the resistor R'1. , the anode of the diode D°, and the cathode of the diode D゛, is connected to the operational amplifier AI.
connected to the negative input terminal of The positive input terminal of operational amplifier A is grounded. If the total input voltage Ei is zero, the diodes D' and D'2 are in the off state, and the output voltage Eo
is zero, but when a positive voltage is gradually added to the input voltage Ei, when the diodes D' and D'2 are off, they are negative-phase multipliers with a gain of -Ri, so the gain is proportional to the input voltage. A negative output voltage gradually appears. This state is the second
The figure shows the linear region B'-C-D'.

When the input voltage is further increased, diode D°2 is turned on, R4 is connected in parallel to the feedback resistor Rf, and the region A'-B'
is formed. The saturation voltage value is sloped compared to that of resistor R4, and therefore the saturation voltage changes from the point where the input voltage turns on diode D2. The same applies when the input voltage Ei is a negative voltage (a problem to be solved by the invention).In the conventional feedback limiter circuit shown above, the limiter characteristic after the diode is turned on is that the input voltage increases in positive and negative directions. Accordingly, the slope output becomes proportional to the parallel resistance value of the feedback resistor Rf and the resistor R°2 or the resistor R4, and there is a drawback that flat characteristics cannot be achieved.

(Means for Solving the Problems) In consideration of the above points, in this invention, the output saturation voltage can be made flat, and the power supply for providing the saturation value can be the power supply of the operational amplifier. The saturation values can be set independently for positive and negative values, and the number of passive elements included in the feedback circuit is further reduced.

That is, the present invention is an operational amplifier in which a feedback circuit from an output side to an input side includes only passive elements consisting of a resistor and a diode in addition to a feedback resistor, and the passive element includes a first diode. The cathode of the first diode and the first resistor, and the anode of the second diode and the second resistor are connected in series, respectively, and the anode of the first diode and the cathode of the second diode are connected to the output of the operational amplifier. By connecting the other side of the first resistor and the second resistor to the output side of the feedback resistor and using it as the output terminal of the arithmetic circuit, flat limiter characteristics can be obtained, and the output The present invention is characterized in that the saturation value can be set independently for the positive and negative voltages.

(Function) Thus, the limiter characteristic in this invention is formed by the power supply voltage necessary to operate the operational amplifier and the resistor and diode included in the feedback circuit, and the saturation value of the output voltage is It is determined by the value of the passive element connected from the output terminal of the operational amplifier to the feedback circuit with reference to the power supply voltage.

(Embodiment) Next, the present invention will be explained with reference to an embodiment circuit configuration diagram shown in FIG. 1A and a characteristic curve diagram shown in FIG. 1S.

For convenience, the parts corresponding to Figure 2a and +3 are indicated by the same reference numerals.

First, the connections of the passive elements are the first resistor R1 and the cathode of the first diode D1, and the second resistor R2 and the second diode D1.
The anodes of the diodes D2 are connected in series, the anodes of the first diode D1 and the cathodes of the second diode D2 are connected to the output terminal of the operational amplifier A1 at the connection point, and the first and second resistors are connected in series. R, R2 diode DID2
The other end on the side not connected to is connected at the output side point e of the feedback resistor Rf to form the output circuit of the operational amplifier A1.

Further, an input resistor R; is connected to the negative input terminal of the operational amplifier A1, and a feedback resistor Rf is also provided in the feedback circuit. The positive input terminal is grounded.

When an input voltage Ei is applied to the operational amplifier configured as described above, an output voltage Eo appears. The relationship between the input voltage Ei and the output voltage Eo is that when the diode D1 or D2 is on, it is an inverse multiplier, so EO = -Saku1・E
Represented by i. This shape i is in the linear region B-C-D of Figure 1, and when the input voltage Ei is zero, the output voltage Eo is also zero, but if a positive or negative voltage is gradually added to the input voltage Ei, Rf At this time, the output voltage Eo gradually becomes a negative voltage and a positive voltage in proportion to the input voltage Ei with a slope of -1F.

When the input voltage Ei is further increased, the output voltage Eo reaches a certain voltage that depends on the power supply voltage of the operational amplifier A1, Vc, the resistors R,, R2, the feedback resistor Rf, and the load resistor R, saturate.

That is, the resistors R, , connected to the output terminal of the operational amplifier A1,
The resistance value of R2 is R,, R2, the forward voltage of diode DI + D2 is V PDl, V FD2, the maximum output voltage amplitude of operational amplifier A1 is 10 VON, and the load resistance is R.
When it is L, the saturation voltage ±Eos at the output terminal is expressed as follows.

That is, when the output voltage Eo, which gradually increases due to the input voltage Ei, reaches the set saturation voltage value ±F,os, the input voltage E
Even if i increases, the output voltage Eo is saturated at a value of EO5.

Therefore, the values of the resistors R and R2 provided in the feedback circuit are (1) (2)
) by selecting the saturation value E of the output voltage EO.
ON can be set independently for the positive side and the negative side.

In addition, in the above embodiment, the limiter function and characteristics due to the operation of this passive element were explained, but by including the resistors R1+R2 in series with the output terminal, the output current of the operational amplifier can be suppressed below the maximum rated value, and the operational It can protect the amplifier from overload current damage.

In other words, the maximum allowable load current of the operational amplifier is IO5 (effects of the invention). A simple circuit configuration consisting of only the power supply voltage necessary to operate the amplifier and the diodes and resistors necessary to operate the feedback amplifier, and a special voltage source to bring the saturation value. A limiter circuit with nearly ideal flat characteristics can be obtained without having a saturated voltage, and the saturation voltage can be set independently for positive and negative voltages.

[Brief explanation of drawings]

FIG. 1a is a block diagram of a limiter circuit according to an embodiment of the present invention;
The figures are the input/output characteristic curve diagram of Figure 1a, Figure 2a is the configuration diagram of a typical limiter circuit used conventionally, and Figure 2 (2)
I11 is the input/output characteristic curve diagram of FIG. 2a. In the figure, A1 is an operational amplifier, DID2 is a diode, Ri is an input resistance, Rf is a feedback resistance, and R and R2 are saturation value setting resistances.

Claims (1)

[Claims] (1) In an operational amplifier, the feedback circuit from the output side to the input side includes only a passive element consisting of a resistor and a diode in addition to the feedback resistor, and the passive element is a first diode. The cathode of the first diode and the first resistor are connected in series, and the anode of the second diode and the second resistor are connected in series, and the anode of the first diode and the second resistor are connected in series.
The cathode of the diode is connected to the output terminal of the operational amplifier, and the other sides of the first resistor and the second resistor are connected to the output side of the feedback resistor, and the output terminal of the operational circuit is connected to the output terminal of the operational amplifier. A limiter circuit characterized in that the positive side saturation voltage and the negative side saturation voltage of the output can be independently set by doing so.