JPS5946128B2 - variable resistance circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable resistance circuit constituted by an electronic circuit.

In particular, it is possible to obtain hyperbolic variable characteristics,
The present invention relates to a variable resistance circuit that can be controlled by a digital code signal or a pulse duration signal.

BACKGROUND ART Conventionally, circuits have been known in which a variable resistance value is obtained by controlling the equivalent resistance value appearing between the collector and emitter of a transistor or between the drain and source of a field effect transistor using an input signal to the base or gate electrode.

These devices directly utilize the characteristics of elements such as transistors and field-effect transistors, and have a narrow resistance variable range, and most of them do not provide simple responses to control signals, such as square-law characteristics or 372nd power percent characteristics. There are no drawbacks.

Additionally, these control signals are analog voltages or currents, which are often incompatible with the circuitry in which they are applied.

An object of the present invention is to provide a variable resistance circuit that has inversely proportional (hyperbolic) characteristics over a wide range to an input signal, regardless of the characteristics of elements such as field effect transistors or transistors.

Another object of the present invention is to provide a variable resistance circuit that can use a digital code signal or a pulse duration signal as an input control signal.

The present invention controls a loop circuit provided at the drain electrode and gate electrode of a field effect transistor, and controls the equivalent resistance generated between the drain electrode and source electrode of this field effect transistor and the reference connected in series with the source electrode. It is provided to utilize the sum of the resistors R6.

This will be explained in detail below using the drawings.

FIG. 1 is a circuit configuration diagram of an embodiment of the present invention.

In the figure, 1 and 2 are terminals for providing the resistance value of the variable resistance circuit, and 3 is an input signal terminal.

AHe Az G2 amplifier, F is variable potential conversion circuit, Q
indicates a field effect transistor, and Ro indicates a reference resistor.

Terminal 1 is led to variable potential conversion circuit F via buffer amplifier A1.

This control input is led from terminal 3, and the output is the differential amplifier A.
2 positive input terminal.

The output of amplifier A2 is coupled to the gate electrode of field effect transistor Q, and the source electrode is connected to the negative voltage of amplifier A2.

The source electrode is connected to a common potential via a reference resistor R6.

Field effect transistor Q is of N-channel type.

Here, the variable potential conversion circuit F may be an amplifier circuit or an attenuation circuit, and is a circuit that outputs a voltage obtained by multiplying the input voltage by a conversion rate X.

Specific examples will be described later in Examples.

To describe the operation of the circuit configured in this way, a voltage is applied between terminals 1 and 20, and at that time, terminals 1 and 20
Let i be the current flowing between terminals 1 and 2, and find the equivalent resistance R0 between terminals 1 and 2 as seen from the outside.

If the voltage at terminal 1 is El, then since amplifier A is just a buffer amplifier, the output is the same <El.

If the voltage at the output point of variable voltage conversion circuit F is R2, then E = E −X ・・・・・・・・・・・・・・・
.........(1) (where X is the conversion rate of the variable voltage conversion circuit F).

Amplifier A2 is a differential amplifier with a sufficiently large amount of feedback, and almost no current flows through the gate electrode of field effect transistor Q, so at the power point of both amplifiers A2, 1Ro=E2...・・・・・・・・・
・・・・・・・・・・・・(3)

(Equation 21, substituting equation (3) into equation (1), equivalent resistance value R
To find 8, we get 8.

That is, it is possible to obtain a variable resistance circuit whose equivalent resistance value changes in inverse proportion to the variable X.

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

In this example, the variable potential conversion circuit F is configured to be controlled by a digital code signal.

This variable potential conversion circuit F uses a ladder type digital-to-analog converter (for example, Analog Devices AD7520).
) is used, and the voltage ratio of the human output is controlled by a digital code signal.

Here, read the digital code string.

, Dl,...D, x=-(Do2° +D12-' +・-+D R2
-n.

FIG. 3 is a circuit configuration diagram of an embodiment of the present invention.

In this example, the variable potential conversion circuit F is configured to be controlled by the output of the counter CO.

By controlling in this way, it is possible to obtain a variable resistance value that shows changes as shown in FIG. 4 or FIG. 5.

FIG. 4 and FIG. 5 are diagrams showing changes in variable resistance value over time.

Further, in the example shown in FIG. 3, the output of the amplifier A2 is voltage-divided by the resistors R1 and R2 and is applied to the amplifier A3.

By appropriately selecting the values of R1 and R2, the variation width (range) of the variable resistance can be arbitrarily selected.

That is, in this example, the equivalent resistance value RF is (instead of → becomes.

FIG. 6 is a circuit configuration diagram of an embodiment of the present invention.

In this example, the variable potential conversion circuit F is configured to use an integrating circuit including an amplifier A3 to control the switch SW.

If the switch SW is controlled by a pulse time width signal with a period Ts and a duty TX, the resistance value RF can be varied by the pulse time width.

That is, the conversion rate X of this variable potential conversion circuit F is Therefore, the equivalent resistance value R9 is obtained from the formula (→).

Note that the circuit shown in FIG. 6 uses an inverting amplifier A4 because the polarity is inverted by the output of the variable potential conversion circuit F.

In addition, the same implementation is possible by using an attenuation circuit in the variable potential conversion circuit F and configuring a circuit that controls this by a pulse time width signal.

As mentioned above, it has a wider range of change than the equivalent resistance characteristic between the drain and source electrodes of a field effect transistor element alone, and changes hyperbolically in response to a human input signal, regardless of the characteristics of the element alone. It is possible to obtain a variable resistance circuit that can be used as a variable resistance circuit.

The circuit of the present invention has particularly excellent effects when used as a feedback circuit resistor of an operational amplifier or as a compensation resistor of various wave filters.

In addition to the configurations described in the above embodiments, the present invention can be implemented with various modified circuit configurations.

In particular, it goes without saying that countless combinations can be considered, such as inserting, omitting, or replacing a buffer amplifier, inverting amplifier, or attenuator, etc. in the current path according to the present invention, and accordingly swapping the positive and negative inputs of the amplifier.

In addition, although the above explanation shows an example using a QKN channel type field effect transistor, it can be applied to a P channel type, enhancement type or depletion type, or even if the source and drain electrodes are interchanged.
Correspondingly, by appropriately selecting the positive and negative inputs of the differential amplifier A2, the circuit of the present invention can be constructed in a similar manner.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit configuration diagram of an embodiment of the present invention. FIG. 2 is a circuit configuration diagram (digital code signal control) of an embodiment of the present invention. FIG. 3 is a circuit configuration diagram (binary counter control) of an embodiment of the present invention. FIGS. 4 and 5 are diagrams of generated resistance value waveforms. FIG. 6 is a circuit configuration diagram (pulse time width signal control) of an embodiment of the present invention. 1.2...Equivalent resistance terminal, 3...Input signal terminal, A
1-A4...Amplifier, Q...Field effect transistor, F...Variable potential conversion circuit, CO...Counter, R
o...: Reference resistor, R1, R2... Resistor, C.
...Capacitor.

Claims (1)

[Claims] 1 a field effect transistor, a resistor connected in series to the drain-source circuit of the field effect transistor, and a potential of the electrode of the drain and source of the field effect transistor to which the resistor is not connected controlled by an external input signal; a variable potential conversion circuit that multiplies a conversion rate and outputs the output voltage; an output voltage of the variable potential conversion circuit is applied to a non-inverting input terminal; and an inverting input terminal is connected to the resistor of the drain and source of the field effect transistor; a differential amplifier that outputs a control signal to the gate of the field effect transistor so that the electric potential of the electrode of the applied force is applied to make the electric potential of these two terminals equal, and the series circuit of the field effect transistor and the resistor; A variable resistance circuit with both ends as resistance developing terminals.