JPH04340813A - Reference voltage selecting circuit - Google Patents

Abstract

PURPOSE:To obtain a reference voltage selecting circuit by which a desired reference voltage signal can be efficiently selected and outputted in a stable state for a long term from among a plurality of reference voltage signals. CONSTITUTION:Each reference voltage signal IN1-INn generated between each resistance of a resistance array 2, is inputted to an analog multiplexer 8, and the desired reference voltage signal is selected and outputted by the above mentioned analog multiplexer 8 according to a selection signal Bn outputted from a priority encoder 10. Then, the desired reference voltage signal is inputted to a comparator 7 as an input signal b, and compared with an input signal a by the comparator 7, and a comparator output signal b is outputted.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a reference voltage selection circuit that switches and selects any desired reference voltage using a mechanical switch.

0002

2. Description of the Related Art FIG. 4 is a diagram of a conventional reference voltage selection circuit. In the figure, 1 is a reference voltage generation circuit, 2 is a resistor array that divides the voltage generated by the reference voltage generation circuit 1, or a resistor that replaces it, and 3 is a voltage that is divided by the resistor array 2 or a resistor that is a substitute for it. 4 is a pull-up resistor, 5 is a buffer amplifier,
6 is a low-pass filter, and 7 is a comparator.

Next, the operation of the conventional circuit according to the above configuration will be explained. A voltage generated by a reference voltage generation circuit 1 is applied to both ends of a resistor array 2 configured by connecting a plurality of resistors having different resistance ratios in series. As a result, the reference voltage is divided in a plurality of ways according to the resistance ratio of each resistor, and is input to a multi-input single-output mechanical switch.

The mechanical switch 3 switches the output switching contact to an arbitrary input point, selects a desired divided voltage output, and uses it as a reference voltage. This selected reference voltage is input to the buffer amplifier 5 for impedance conversion, but the mechanical switch 3 stops at a halfway point to prevent the voltage from being selected and the input terminal of the buffer amplifier 5 to be in a floating state. Therefore, the input of the buffer amplifier 5 is pulled up to a stable potential by the pull-up resistor 4.

The reference voltage that has passed through the buffer amplifier 5 passes through a low-pass filter 6 and is input to a comparator 7 to which the input signal a is input. In this comparator 7, the input signal b, which is a reference voltage, is compared with the input signal a, and if the input signal a>input signal b, the comparator 7
is activated and output signal b is output. Note that the low-pass filter 6 is for absorbing noise generated when the mechanical switch 3 is switched.

[0006]

Since the conventional reference voltage selection circuit is constructed as described above, when the mechanical switch 3 selectively outputs the reference voltage, the following problems arise. First, a pull-up resistor is required to prevent the mechanical switch from floating, and therefore, adding a pull-up resistor deteriorates the accuracy of voltage division. In addition, a low-pass filter is required to absorb noise during switching of the mechanical switch, which increases the response speed. In addition, the current flowing through a mechanical switch is very small, and the reference voltage may also be low, so a mechanical switch with a very low minimum load current/voltage is required, and since it is a mechanical switch, it is susceptible to vibration. There were problems such as:

The present invention was made in order to solve the above-mentioned problems, and it is an object of the present invention to provide a reference voltage selection circuit that can improve the voltage division accuracy of the reference voltage and output a stable reference voltage without delay. purpose.

[0008]

[Means for Solving the Problems] A reference voltage selection circuit according to the present invention includes a reference voltage generation circuit that generates a reference voltage;
A resistor array that divides and outputs the generated reference voltage according to the resistance ratio between multiple resistors connected in series, and a multiplexer that inputs each divided voltage and selects and outputs a predetermined divided voltage as a reference voltage. a mechanical switch that switches and outputs each reference voltage selection signal, and a priority that is connected to the output terminal of the mechanical switch and that converts the reference voltage selection signal output from a predetermined output terminal into a selection signal for the multiplexer and outputs it. It is equipped with an encoder.

[0009]

[Operation] According to the present invention, by using an analog multiplexer with no mechanical movement as a circuit that selects and outputs a reference voltage from a resistor array, signals can be output stably over a long period of time and there is no noise generation. This eliminates the need for a low-pass filter in the output stage, resulting in faster response speed.

0010

【Example】

Example 1. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit configuration diagram of a reference voltage selection circuit according to this embodiment. In the figure, the same reference numerals as in FIG. 4 indicate the same or corresponding parts. In the figure, 8 is an analog multiplexer that selects the voltage divided by the resistor array 2 or a resistor replacing it, 9 is a mechanical switch, and 10 is a signal selected by the mechanical switch 9, which encodes the signal with priority, A priority encoder 11 selects the input of the analog multiplexer 8, and 11 is a pull-up resistor.

Next, the operation of the conventional circuit according to the above configuration will be explained. A voltage generated by a reference voltage generation circuit 1 is applied to both ends of a resistor array 2 configured by connecting a plurality of resistors having different resistance ratios in series. As a result, the reference voltage is divided in a plurality of ways according to the resistance ratio of each resistor, and is input to the analog multiplexer 8.

In this manner, with the divided reference voltages being input to each input terminal of the analog multiplexer 8,
When outputting a reference voltage of a desired value, the operator switches the mechanical switch 9 to the desired reference voltage selection position as shown in FIG. As a result, selection signals corresponding to each selection input terminal of the priority encoder 10 and the output terminal of the mechanical switch 9 to which the selection signal was output are input. Note that when the mechanical switch 9 is switched, a constant current flows through the resistor array 11 in order to maintain contact reliability of the switch.

Next, the selection signal An inputted to the priority encoder 10 is encoded and inputted into the selection signal Bn to the analog multiplexer 8, and this selection signal Bn causes the analog multiplexer 8 to select the reference voltage selected by the mechanical switch 9 side. INx
is selected and output to the comparator 7 as input signal b. At that time, if the input signal of the comparator 7 is input signal a>input signal b, the comparator 7 works and the output signal b
is output.

Example 2. In the above embodiment, the mechanical switch 9 and the priority encoder 10 are independent, but as shown in FIG.
, a rotary code switch 12 having the functions of the priority encoder 10 may be used, and the same effect as the above embodiment can be achieved.

[0015]

As described above, according to these inventions, the analog multiplexer 8, which has no mechanical movement, is used as a circuit that selects and outputs a desired reference voltage from the reference voltages divided into various values by the resistor array. This allows the reference voltage to be output with high precision and in a stable state over a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a reference voltage selection circuit according to an embodiment of the present invention.

FIG. 2 is an analog multiplexer selection signal correspondence table corresponding to the switch of the present invention.

FIG. 3 is a circuit diagram showing a reference voltage selection circuit according to another embodiment of the present invention.

FIG. 4 is a circuit diagram showing a conventional reference voltage selection circuit.

[Explanation of symbols]

1 Reference voltage generation circuit 2 Resistor array 7 Comparator 8 Analog multiplexer 9 Mechanical switch 10 Priority encoder 11 Pull-up resistor array

Claims (1)

[Claims] Claim 1: A reference voltage generation circuit that generates a reference voltage; a resistor array that divides and outputs the generated reference voltage according to a resistance ratio between a plurality of series-connected resistors; A multiplexer that selects and outputs a predetermined divided voltage as a reference voltage, a mechanical switch that switches and outputs each reference voltage selection signal, and a reference voltage that is connected to the output terminal of the mechanical switch and output from a predetermined output terminal. A reference voltage selection circuit comprising: a priority encoder that converts a voltage selection signal into a selection signal for the multiplexer and outputs the same.