JPS61122787A - Function generating circuit - Google Patents

Abstract

PURPOSE:To obtain a function generator by a MOS-IC by actuating a switch for connecting a resistor to an amplifier so that the gain of the amplifier is changed when an output voltage exceeds a prescribed value. CONSTITUTION:Resistors R3, R5 are connected through switches SW1, SW2 between the inverted input terminal and output terminal of an amplifier APM1 in addition to a feedback resistor Rs and the output voltage Vout of the amplifier AMP1 is supervised by comparators COMP1, COMP2. When an input voltage VIN is close to the voltage Vc, the output is low, both the outputs of the comparators COM1, COM2 are high and both the switches SW1, SW2 are turned off. At that time, the gain is -R2/R1. If the input voltage is increased or dropped and exceeds a certain point, any one of the outputs of the comparators COM1, COM2 is turned to low, so that any one of the switches SW1, SW2 is turned on, the feedback resistance value is reduced and the gain is reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a function generation circuit, and in particular KMO3.
- It relates to a folded linear quantity generation circuit that can be effectively realized by an IC.

The function generating circuit according to the present invention is widely used in various control circuits and the like.

[Conventional technology]

As a conventionally well-known function generating circuit, there is one using diodes DI and D2, as shown in FIG. 2, for example. In FIG. 2, R11 to R6/ are resistors;
AMPII is an inverting amplifier. As is well known, the operating characteristics of this circuit are, for example, those shown by the solid line in FIG. In other words, when human power VxN=Vc, the output of operational amplifier AMPII is zero, so the output VO
ut=O. With both diodes DI and D2 off,
When the human power MIN increases, the human power VtX increases as the amplifier AMP
Gain = -R2 at the resistance part from the input point of II and VIN to the output point of the amplifier AMPII (hereinafter simply referred to as the amplifier)
It is amplified and inverted by 7R1' and becomes the output Vout. When the input WIN is higher than the predetermined value VtN6, the diode D1
Diode D1 becomes conductive when the potential difference across it reaches a value sufficient to turn on diode D1. As a result, R3' is connected in parallel with R2' as a negative feedback resistor of the amplifier AMPII.
will be connected. As a result, the gain of the amplifier 9 changes approximately to (R2'R3'/ (R2'+R) R1'. Therefore, when the input WIN becomes more than Vta@,
An output Wont having a slope different from that of the previous one is obtained. When the input WIN is below VC, the diode D2 side operates in the same manner as described above. Therefore, the characteristics shown in FIG. 3 are obtained.

[Problems to be Solved by the Invention] A function generating circuit having the above-mentioned functions is particularly suitable for MOS-IC.
However, there is a problem in that the PN junction diode cannot be formed on the same MOS-IC substrate. It is also possible to realize the above-mentioned function generation circuit by using the rectification characteristics of a MOS transistor instead of a diode, but there is a problem that a well-defined circuit cannot be obtained due to variations in startup characteristics, etc. There is. Therefore, conventionally, only the parts excluding the diode were realized with MOS-EC, and the diode had to be connected as an external component.
Problems have emerged that hinder the advantages of MOS-ICs, such as high integration and low cost, and also make the circuit configuration more complex.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention provides an amplifier, at least one switch provided in parallel with the amplifier, and a control provided corresponding to the switch for actuating the switch in response to the output level of the amplifier. a resistor associated with the switch and operatively connected to vary the gain of the amplifier in response to actuation of the switch; A function generating circuit is provided, which is characterized in that it defines the slope of a function.

[Effect]

In the present invention, conventional diodes are replaced by switches and control circuits that can be easily implemented in MO8 technology as part of the means for operating in response to human input signals to vary the gain of the amplifier.

〔Example〕

Examples of the present invention will be described below.

FIG. 1 is a diagram showing a function generating circuit as an embodiment of the present invention. In Figure 1, R1-R6 are resistors, AM
PI is an operational amplifier, COMPl, COMP2 are comparators, SWl, SW2 are analog switches, INVI
, rNV2 indicates an inverter. In the figure, the basic circuit configuration is the same as that in Figure 2, and the circuit elements R1 to R
6. The human MPI is similar to R1' to R6' and AMPII in FIG. However, analog switch SW1, inverter INVI, and comparator COMPI are used instead of diode D1 in Figure 82, and analog switch SW2, inverter INV2, and comparator CO are used instead of diode D2.
MP2 is connected as shown.

The circuit shown in FIG. 1 is formed as a MOS-IC.

In FIG. 1, analog switches SWI and SW2
Each integrates an NMOS analog switch and a PMOS analog switch connected in parallel. Basically, analog switches SWI and SW2 are each N.
Although it is possible to use only one of the MOS analog switch and PMOS analog switch, two of these switches are arranged in parallel for the main purpose of reducing the resistance when the switches SWI and SW2 are turned on. The NMOS analog switch and the PMOS analog switch operate simultaneously.

Therefore, inverters INVI and INV2 are provided at the outputs of the comparators COMPI and COMP2, respectively, and the NMOS analog switch and the PMOS analog switch of the analog switch SWI operate simultaneously in response to the output of the comparator COMPI. The same applies to the other side.

The operation of the circuit shown in FIG. M1 will be explained with reference to FIG.

In the initial state, analog switch SWI.

Both SW2 are off.

First, consider the case where an input VIN=V (of the same magnitude as the voltage vc applied to the non-inverting input terminal of the operational amplifier speaker MPI is applied. In this case, the output Vo of the amplifier AMP1 is
ut is zero. At this time, the comparator COMPI,
The outputs of COMP2 are both high (H) level.
The analog switches S'WI and SW2 remain off. At this time, the gain of the resistance portion (hereinafter simply referred to as the amplifier) from the input point of the amplifiers AMPI and vIN to the output point of the amplifier AMP1 is defined by -82/R1.

Next, when the input voltage MIN increases, the amplifier A with the above gain
An amplified and inverted output Vout is obtained by MP1. At this time, the voltage VA at point a also decreases.

Input voltage v! If N is even higher, the voltage V applied to the inverting input terminal of the comparator COMPI
When the voltage falls below C, the output of the comparator COMPI changes from the H level to the low (L) level. This low level signal turns on the υ analog switch sw1. Due to this conduction, the resistor R3 is connected in parallel with the amplifier speaker MPI, and the gain of the amplifier is approximately 1cmR2R3/(R2+R3)・Rt from the above-mentioned -R2/R1. Become. Therefore, if the input voltage vIN increases, an output Vout amplified by the latter gain can be obtained. The output Voutl when the analog switch SWI is switched is determined by the relationship.

As is clear from the above, breakpoint WIN =
Since outputs Vout with different amplification degrees can be obtained depending on the upper and lower sides of VIN&, a function approximated by a broken line can be generated.

The other circuit SW2 in FIG. INV2. COMP2 operates in the same manner as described above when the human power MIN is less than or equal to VC.

In other words, if the human power V[N is between VC and 'VtNb,
As mentioned above, the gain is defined by -R2/R1.
VHH, below, the gain is approximately −(Rz・Rs)/
It changes as (R2+R5)・R1. If the voltage at point b is vB in the case of , then the output Vout2 when the analog switch SW2 switches is defined as VB = VC.

This makes it possible to generate a function approximated by a broken line as shown by the solid line in FIG. VC is arbitrary, but Vc
=O, it is possible to generate a function that passes through the center O in FIG.

The slope of the function can be made arbitrary by adjusting the values of resistors R1, R2, R3 and R4.

The circuit of FIG. 1 also includes two sets of gain changing means, an analog switch SWI and an inverter INVI, in order to generate both positive and inverse functions for the input VIN.
, comparator COMPI, resistor R3, analog switch SW2, inverter INV2, comparator COMP2, and resistor R5 have been described, but only one of them can be provided. On the other hand, if it is desired to provide more breakpoints as shown by the broken lines in FIG. 3, a plurality of stages of gain changing means similar to those described above may be used.

Another embodiment of the invention is shown in FIG.

The circuit shown in FIG. 4 is different from the circuit shown in FIG.
y, Rs are connected. Also, ;Npa1/
-Evening COMP21. COMP22 and the analog switch 5W11.5WI2 are also connected with opposite characteristics to those shown in FIG. This indicates that any connection is acceptable.

The purpose of providing the former resistors R7 and R8 is to stabilize the operation of the comparators COMP21 and COMP22. That is, the voltage Va at point a is VINm
When it is in the vicinity, a slight fluctuation causes the comparator COMP
There is a possibility that the output of 21 will oscillate between the H level and the L level. Therefore, the resistor R7 is connected in series with the analog switch SWI 1 to create a voltage difference due to the voltage drop caused by the resistor R7, and the analog switch 5W11
This is aimed at stabilization during conduction. The same applies to the other side.

Incidentally, the gain when the analog switch 5W11 is conductive is given by the following equation.

The gain when the analog switch 5WI2 is conductive is expressed by the following formula: % The modification described in connection with FIG. 1 can be similarly applied to the circuit shown in FIG.

The above embodiments have been described mainly for the purpose of realizing MOS-IC, but the above-mentioned circuit is
Needless to say, the present invention is not limited to 8-IC implementation, and can be implemented using various other methods.

〔Effect of the invention〕

As described above, according to the present invention, a function generation circuit that can be implemented as an MO8-IC by taking advantage of the characteristics of the MO8-IC is provided.

[Brief explanation of the drawing]

FIG. 1 is a function generation circuit diagram as an embodiment of the present invention, FIG. 2 is a conventional function generation circuit diagram, FIG. 3 is a diagram showing function characteristics, and FIG. 4 is a diagram as another embodiment of the present invention. This is a function generation circuit diagram. (Explanation of symbols) 81 to R6...Resistor, AMPI...Operation amplifier, INVI, INV2...Inverter, COM
PI, COMP2... Comparator, SWI, S
W2...Analog switch.

Claims (1)

[Claims] 1. An amplifier, at least one switch provided in parallel with the amplifier, a control circuit provided corresponding to the switch and operating the switch in response to the output level of the amplifier; , a resistor provided corresponding to the switch and operatively connected to change the gain of the amplifier in response to actuation of the switch, the slope of the power function generated by the gain of the amplifier; A function generation circuit characterized in that it defines: 2. The function generating circuit according to claim 1, further comprising a resistor in series with the switch. 3. The function generating circuit according to claim 1 or 2, wherein the switch is an analog switch. 4. The function generating circuit according to claim 3, wherein the analog switch has two or more analog switches connected in parallel so that they operate simultaneously. 5. All the circuits are formed of MOS-ICs,
A function generating circuit according to claims 1 to 4.