JPH05291957A - One-chip comparator with comparison reference changeover switch - Google Patents

Abstract

PURPOSE:To allow the comparator to make voltage comparison with high accuracy while receiving an input reference voltage in matching with an analog input voltage by setting two-way of comparison being comparison between external two input voltages and comparison between an external input voltage and an internal reference voltage as a comparison reference input to the comparator. CONSTITUTION:When a comparison start signal is outputted from a comparator control circuit 12, comparison is implemented between analog input voltages V1 and V2 independently of an internal reference voltage Vr. The result is stored to a bit (n) of a comparator register 14 as 1-bit digital value. A CPU reads the data via a data bus 13 to recognize the result of comparison. When a terminal 11c is thrown to the position of a terminal 11b in a switch 11, an analog input voltage V1 and the internal reference voltage Vr are given to inputs to the comparator. In this case, a digital value corresponding to the internal reference signal Vr is set to the register 14, and the comparator 10 receiving the internal reference voltage Vr by a resistor ladder 16 and a switch tree 15 makes voltage comparison of the voltage Vr with the analog input voltage V1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a one-chip comparator whose comparison standard can be set freely.

[0002]

2. Description of the Related Art As is well known, a comparator is a device or circuit that determines the magnitude relationship between two analog input voltages and outputs the result. FIG. 4 is a diagram showing a temporal change in operation of the comparator circuit. In the figure, the operation is as follows. That is, Vin is an input voltage from the outside and changes with time. On the other hand, Vr is a reference voltage, which serves as a judgment reference for voltage comparison of the comparator. Then, the output of the comparator is inverted at to. When the input voltage Vin is lower than or equal to the reference voltage Vr when the time t <to, the comparator output is “0” in this example. When time t> to, since the input voltage Vin is higher than the reference voltage Vr, the comparator output is inverted and becomes “1”.

FIG. 5 is a typical block diagram of a conventional comparator circuit. In the figure, 10 is a comparator for performing voltage comparison, and 12 is a comparator control circuit for controlling the operation and stop of the comparator. Reference numeral 13 is a data bus connecting to a central processing unit (not shown: hereinafter abbreviated as CPU) of the one-chip microcomputer, and 14 is an n + 1-bit length comparator register capable of setting an arbitrary digital value. Reference numeral 15 is a switch tree that is turned on / off according to the value of the bit set in the comparator register, and 16 is a resistor ladder that divides the voltage between the power supply voltage Vcc and Vss by resistance. Generate Vr.

The operation of the comparator circuit incorporated in the conventional one-chip microcomputer will be described. First, the digital value corresponding to the internal reference voltage Vr to be compared is written in the comparator register 14. An internal reference voltage Vr determined by the power supply voltage and the selected resistance ladder value is given to the comparator 10 as a comparison reference.
When the comparison start signal is output by the comparator control circuit 12, the voltage comparison is started. The comparator 10 compares the input voltage Vin with the internal reference voltage Vr and stores the result as a digital value in bit n of the comparator register 14. By reading the value of this bit n, it can be known whether the input voltage is higher or lower than the internal reference voltage.

[0005]

Since the comparator incorporated in the conventional microcomputer is configured as described above, the input voltage can be compared and judged only with respect to the internal reference voltage, and the comparator can be externally determined. There was a problem that the voltage comparison between the two input voltages cannot be performed.

The present invention has been made in order to solve the above problems, and is a one-chip comparator incorporated in a microcomputer or the like, which compares a conventional internal reference voltage and two external input voltages. It is an object of the present invention to obtain a one-chip comparator capable of both voltage comparisons.

[0007]

The one-chip comparator according to the present invention has a switch for selecting an internal reference voltage or an external reference voltage as a reference input for comparison.

[0008]

In the one-chip comparator according to the present invention, the input comparison reference voltage set by the changeover switch is
It serves as a reference for the other measurement input.

[0009]

EXAMPLES Example 1. An embodiment of the present invention will be described below with reference to the drawings. 1 is a block diagram of a comparator circuit according to an embodiment of the present invention. Reference numeral 11 is a switch circuit for switching between the analog input voltage V2 and the internal reference voltage Vr, 11a is an analog input voltage terminal, and 11b.
Is an internal reference voltage terminal, and 11c is an input terminal to the comparator.

In the switch 11, when the terminal 11c is connected to the terminal 11a, the analog input voltages V1 and V2 are connected to the input of the comparator 10. If the comparison start signal is output from the comparator control circuit 12 in this state, the analog input voltages V1 and V2 are compared regardless of the internal reference voltage Vr. The result is stored in bit n of the comparator register 14 as a 1-bit digital value. The comparison result can be known by the CPU (not shown) reading through the data bus 13.

In the switch 11, when the terminal 11c is connected to the terminal 11b, the analog input voltage V1 and the internal reference voltage Vr are connected to the input of the comparator. In this case, a digital value corresponding to the internal reference voltage Vr is set in the comparator register 14, and the internal reference voltage Vr is set by the resistor ladder 16 and the switch tree 15.
Occurs. The comparator 10 compares the internal reference voltage Vr with the analog input voltage V1. In this state, the measurement circuit is exactly the same as the conventional one. By switching the switch 11 as described above, it is possible to select both of the two external inputs and the conventional internal reference voltage.

Example 2. In the first embodiment, the switching between the analog input voltage V2 and the internal reference voltage Vr is shown as a simple switch 11, but the selection circuit using the voltage control switch shown in FIG.

FIG. 2 will be described below. Reference numeral 21 is a data flip-flop (hereinafter abbreviated as D / F / F), which is 2
2a and 22b are transmission gates.
Then, by the control signal applied to the control terminals 11a and 11b, the switch is turned on / off as if the switch is connected / disconnected. An inverter element 23 inverts the input signal and outputs it. In this case, the inversion of ON / OFF of the gates 22a and 22b is guaranteed. 1
1a, 11b and 11c are switches 11 in FIG.
Corresponds to the terminal.

"0" or "1" is set in the D / F / F 21 from the CPU (not shown) via the data bus 13. For example, when the D / F / F 21 is set to "0", the transmission gate 22a becomes active, and therefore the transmission gate 22b becomes non-active. At this time, the gate 22a becomes conductive and only the analog input voltage V2 is connected to the comparator 10. Conversely, when the D / F / F 21 is set to "1", the transmission gate 22a becomes non-active, the transmission gate 22b becomes active, the gate 22b becomes conductive, and the internal reference voltage Vr is connected to the comparator 10.

As described above, by setting a digital value in the D / F / F 21, either the analog voltage V2 or the internal reference voltage Vr can be selected, and can be freely selected by software designation. ..

Embodiment 3. Further, in the first embodiment, the comparator circuit in which the switch 11 for switching the analog input voltage V2 and the internal reference voltage Vr is added to the setting of the comparison reference input has been described, but the power supply to the resistor ladder 16 is set to the power supply voltage Vcc. A comparator circuit to which a switch circuit for switching the input reference voltage Vref is added will be described. Example 3 will be described below with reference to the drawings. V in FIG.
ref / V2 serves as both the input reference voltage Vref and the analog input voltage V2, and the switch 31 is Vref / V2.
The voltage supplied to the resistance ladder 16 can be selected by switching the V2 terminal and the power supply voltage Vcc terminal. Switch 3
The terminal 31a in 1 is connected to the Vref / V2 terminal, 31b is connected to the power supply voltage Vcc, and 31c is connected to the resistance ladder 16.

The Vref / V2 terminal is connected to the input reference voltage Vr.
When used as ef, switch 31
By switching to connect 1a and 31c, the internal reference voltage Vr generates a voltage corresponding to the value set in the comparator register 14 between Vref and Vss. The comparator 10 compares the internal reference voltage Vr with the analog input voltage V1. When the analog input voltage V1 is a minute level, the input reference voltage Vre
By inputting a low voltage, which is optimal for comparison with the analog voltage V1, to f, the voltage comparison is performed more accurately.
When the switch 31 is switched to connect 31b and 31c, the internal reference voltage Vr is generated between the power supply voltage Vcc and Vss. Analog input voltage V1 is Vc
This is effective when there is a large amplitude between c and Vss.

Example 4. In the third embodiment, two changeover switches are provided, but one may be provided. That is, the changeover switch 11 is eliminated and 11c and 11b are connected. In this case, the changeover switch 31 is set to 31a and 31
When operated so as to connect c, a comparison reference voltage corresponding to the value set by the register 14 is obtained between Vref and Vss. The changeover switch in the third and fourth embodiments may be a switch that can be selected by the software designation described in the second embodiment.

[0019]

As described above, according to the present invention, as the comparison reference input of the comparator, between the two external input voltages,
Since two types of comparison, the comparison with the internal reference voltage, can be switched and set, an input reference voltage matching the analog input voltage is given, and there is an effect that the voltage comparison can be performed accurately.

[Brief description of drawings]

FIG. 1 is a block diagram of a one-chip comparator circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a changeover switch which can be changed over by software designation.

FIG. 3 is a block diagram of a one-chip comparator circuit according to another embodiment of the present invention.

FIG. 4 is a diagram showing a temporal change in operation of a comparator.

FIG. 5 is a block diagram of a comparator circuit incorporated in a conventional one-chip microcomputer.

[Explanation of symbols]

 10 Comparator 11 Switch Circuit 12 Comparator Control Circuit 14 Comparator Register 15 Switch Tree 16 Resistor Ladder 21 Data Flip-Flop 22 Transmission Gate 23 Inverter 31 Switch Circuit

Claims (1)

[Claims] 1. A one-chip comparator with a comparison reference changeover switch, comprising a switch for switching and setting an internal reference voltage and an external reference voltage to a reference input for comparison.