JPS6229926B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronic variable resistor that achieves a function equivalent to that of a mechanical variable resistor using an electronic circuit.

When testing the functionality of a semiconductor device, such as a linear IC, a variable resistor for adjustment may be required around the device. As such a variable resistor for adjustment,
Conventionally, mechanical variable resistors have been used.

The electronic variable resistor of the present invention is a variable resistor equivalent to a mechanical variable resistor configured using a fixed resistor and two amplifiers whose gain can be varied depending on an external signal, for example, a DC voltage. This method realizes a test method that is faster and has better controllability.

The electronic variable resistor of the present invention will be explained in detail below by citing a part of the semiconductor integrated circuit for FM stereo demodulation. As is well known, in a semiconductor integrated circuit for FM stereo demodulation, a variable resistor is generally connected externally in order to set the degree of separation between two demodulated stereo signals to the best point.

Figure 1 shows its standard circuit, in which two stereo signals S ₁ and S ₂ are input to the bases of transistors Q ₁ and Q ₂ , and the respective output signals S _p1 and S _p2 are input to the bases of transistors Q 1 and Q ₂ . Each of _{the two} collectors is taken out from the terminal as an output. At this time, it is necessary to connect a variable resistor V _R1 between the emitters of both transistors, adjust the degree of separation between the two output signals to the best point, and perform a degree of separation test. By the way, when the above-mentioned variable resistor V _R1 is a mechanical type, adjustment of the variable resistor V _R1 becomes a major hindrance when performing automatic measurement to automatically perform this separation degree test.

The present invention eliminates this obstacle and provides a second
The electronic variable resistor of the present invention will be explained in detail with reference to the drawings.

As shown, the electronic variable resistor of the present invention includes:
Non-inverting variable voltage gain amplifier (hereinafter referred to as amplifier) 1, 2, DC blocking capacitors 3, 4, 5,
6. It is constructed using fixed resistors 7 and 8. Note that 9 is an external signal source for gain control of the amplifiers 1 and 2, such as a DC power supply. In the electronic variable resistor of the present invention, the resistor 7 connected to the output terminal of the amplifier 1
and the capacitor 5 connected to the input terminal of the amplifier 2 are commonly connected to form a first terminal 10, and
One end of each of a capacitor 3 connected to the input terminal of the amplifier 1 and a resistor 8 connected to the output terminal of the amplifier 2 are commonly connected to form a second terminal 11. Note that the capacitances of capacitors 3, 4, 5, and 6 are C ₃ , C ₄ , C ₅ , C ₆ ,
Furthermore, when the resistance values of resistors 7 and 8 are R ₇ and R ₈ , there are C ₃ = C ₅ , C ₄ = C ₆ and
The relationship R ₇ = R ₈ is established.

FIG. 3 is a diagram illustrating the control characteristics of amplifiers 1 and 2, with the vertical axis showing the amplification voltage gain Gv _and the horizontal axis showing the external control voltage _Vc . Using amplifiers 1 and 2 having such control characteristics, _{the resistance values R 7 and R 8 of resistors 7 and 8 that set the variable resistance range are set to, for example, R 7 = R 8}
= 10KΩ, the equivalent resistance value R _E between the first terminal 10 and the second terminal 11 changes as follows depending on the external control voltage V _C .

For example, if the external control voltage V _C is set to 1.5V, the amplification voltage gain G _V of amplifiers 1 and 2 from Fig. 3 is
are 0.5 times each, and the equivalent resistance value R _O is 20K.
Ω, and when the control voltage V _C is set to 5V, the amplification voltage gains G _V of amplifiers 1 and 2 are each doubled, and the equivalent resistance value R _O is 5KΩ.

By the way, in the above embodiment, since the amplifiers with the same control characteristics are used, the values of the resistors 7 and 8 are set to be equal. However, when the control characteristics of the amplifiers 1 and 2 are set to be different, The resistance value may be set in accordance with this characteristic. For example, if the relationship R ₇ = 2R ₈ is established between the resistance values R ₇ and R ₈ , the amplification voltage gains G _V1 and G _V2 of amplifiers 1 and 2 under the same control voltage will be The control characteristics of amplifiers 1 and 2 may be set so that the relationship 2G _V1 =G _V2 is established.

As explained above, since the electronic variable resistor of the present invention can change the resistance value electronically, it can be used as a variable resistor required for functional testing of not only linear ICs but also various electronic circuits. If you use
It is possible to speed up functional testing.

Furthermore, the electronic variable resistor of the present invention can be widely used as one of the components of various electronic circuits, as an alternative to mechanical variable resistors.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a circuit in which a variable resistor is used, FIG. 2 is a diagram showing the configuration of an electronic variable resistor according to an embodiment of the present invention, and FIG. 3 is a diagram showing an example of an electronic variable resistor according to an embodiment of the present invention. FIG. 3 is a diagram showing an example of control characteristics of an amplifier used. 1, 2...Non-inverting voltage gain variable amplifier, 3-
6... DC blocking capacitor, 7, 8... Fixed resistor, 9... Control signal source, 10, 11... Terminal.

Claims (1)

[Claims] 1 Consists of a first capacitor, an amplifier whose voltage gain can be controlled with one end of the capacitor connected to the input side, and a series connection body of a second capacitor and a fixed resistor connected to the output side of the amplifier. First
A circuit section and a second circuit section having the same configuration as the first circuit section are connected in antiparallel, and the antiparallel connection points are the first and second terminals, and the first
and a means for supplying a voltage gain signal to an amplifier in the second circuit section, and the equivalent resistance value between the first and second terminals is varied by controlling the voltage gain of the amplifier. Electronic variable resistor.