JPH05327432A - Voltage comparator circuit - Google Patents

Abstract

PURPOSE:To improve the offset voltage measurement accuracy. CONSTITUTION:In the case of making usual voltage comparison operation, an analog switch 2 is set to the OFF state, the voltage comparator 1 compares analog voltages inputted from analog input terminals 51, 52 by using the analog switch 2 and a resistor 3 without any affect. In the case of testing, the analog switch 2 is turned off by a control signal inputted from a test terminal 54 at the test and a noninverting input terminal and an inverting input terminal of the voltage comparator circuit 1 are short-circuited through the analog switch 2 and the resistor 3. The analog input terminal 51 connects to a current source 4 in this test and the analog input terminal 52 connects to a voltage source 5. The offset voltage Voff is obtained by a current Ia outputted from the current source 4 and a resistance R of the resistor 3. In order to measure the offset voltage Voff with high accuracy, only the accuracy of the current of the current source 4 is to be noticed of.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage comparison circuit, and more particularly to a voltage comparison circuit including a test circuit.

[0002]

2. Description of the Related Art A conventional voltage comparison circuit has an analog input terminal 59 as shown in the block diagram of FIG.
And 60, the analog voltages V ₁₂ and V _{13 of the} voltage sources 12 and 13 are input to the non-inverting input terminal and the inverting input terminal of the voltage comparison circuit 11, respectively, and the output voltage V is obtained as a comparison result of those analog voltages. _o is output from the output terminal 61.

In this conventional voltage comparison circuit, for example, when V ₁₂ <V ₁₃ , the output voltage V _δ is "L".
When the level is output and V ₁₂ > V ₁₃ , conversely, the “H” level is output as the output voltage V _o . However, in reality, variations in the characteristics occur due to "variation" in manufacturing the voltage comparison circuit and a problem of relative accuracy, and an error voltage occurs in the voltage comparison result. This error voltage is called the offset voltage _Voff . Due to the presence of this offset voltage, the range of the analog input voltage at which the output voltage V _o of the voltage comparison circuit 11 is output as the “L” level is V ₁₂ + V.
_off <V ₁₃ , and the range of the analog input voltage output as the output voltage V _δ at the “H” level is V ₁₂ + V
_off <V ₁₃ . Therefore, the voltage value of the offset voltage V _off is when the output voltage V _o of the voltage comparison circuit 11 changes from the “L” level to the “H” level or when the output voltage V _o changes from the “H” level to the “L” level. Analog input voltage is V
_12a and V _13a are given by the following equations.

V _off = V _12a −V _13a (1) The relationship of this equation (1) is shown in the graph of FIG.

Generally, in a voltage comparison circuit, it can be said that the offset voltage V _off has a better voltage comparison characteristic as the voltage value is closer to 0V. Therefore, the quality of the voltage comparison circuit itself is generally determined by the level of the offset voltage. In the conventional voltage comparison circuit, as means for determining the quality of the voltage comparison circuit, two analog voltages V ₁₂ and V ₁₃ to be compared are changed, and the output voltage V _δ at that time is measured,
When the output voltage V _o is changed to "H" level from the "L" level, "H" voltage value of V ₁₂ and V ₁₃ when changed to "L" level from the level and V _12a and V _13a
Substituting the voltage value of
Seeking _off .

[0006]

In the above-mentioned conventional voltage comparison circuit, as means for measuring the offset voltage in order to determine the quality of the voltage comparison circuit, two analog input voltages V _{12 to be} compared are used. It is necessary to change and input V ₁₃ and V ₁₃ . However, the level of this offset voltage V _off is generally several mV to several tens mV.
This is a voltage with a very small level, and therefore, there is a measurement defect that the voltage values themselves of the two analog voltages V ₁₂ and V ₁₃ input for measurement need to be set with high accuracy.

During measurement, the analog voltage V ₁₂
There is a drawback that the measurement accuracy of the offset voltage deteriorates due to the influence of noise and the like on V ₁₃ and V ₁₃ .

[0008]

The voltage comparison circuit of the present invention is a voltage comparison circuit for comparing and outputting two analog input voltages input to a non-inverting input terminal and an inverting input terminal, respectively. Is inserted and connected between the non-inverting input terminal and the inverting input terminal, and is configured to include at least a circuit element that is on / on controlled via a predetermined control signal.

The circuit element may be formed by a series connection of an analog switch which is on / off controlled via the control signal and a resistor having a predetermined resistance value. It may be formed by a CMOS analog switch which is on / off controlled via a control signal.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1A is a block diagram showing a first embodiment of the present invention. As shown in FIG. 1A, this embodiment has analog input terminals 51 and 52 and an output terminal 5.
3 and the test terminal 54 corresponding to the voltage comparison circuit 1
And an analog switch 2 and a resistor 3.

In FIG. 1A, when the voltage comparison circuit of the present embodiment performs a normal voltage comparison operation, the analog switch 2 is set to the off state, and at this time, the analog switch 2 is set. 2 and resistor 3
Since the voltage comparison circuit 1 is not affected by anything,
The circuit configuration is the same as that of the conventional voltage comparison circuit shown in FIG. 3, and the comparison operation of analog voltages input from the analog input terminals 51 and 52 is performed. Further, during the test, the analog switch 2 is turned off via a predetermined control signal input to the test terminal 54, and at this time, the analog switch 2 and the resistor 3 are connected.
Therefore, the non-inverting input terminal and the inverting input terminal of the voltage comparison circuit 1 are short-circuited. The circuit connection state at the time of this test is as shown in FIG.
The analog input terminal 51 is connected to the current source 4, and the analog input terminal 52 is connected to the voltage source 5. In this case, the ON resistance value of the analog switch 2 is sufficiently smaller than the resistance value of the resistor 3 and can be ignored, and the resistance value of the resistor 3 is R and the current value of the current source 4 is Is I and the voltage of the voltage source 5 is V, the non-inverting input voltage v ₁
And the inverting input voltage v ₂ are given by the following equations.

V ₁ = I · R + V ……………………………… (2) v ₂ = V …………………………………… (3) where When the value of the current I is changed to I → I _a , the non-inverting input voltage and the inverting input voltage are changed to v _1a and v _2a , respectively, and the output voltage V _o of the voltage comparison circuit 1 is changed. Then, the offset voltage V _off
Is given by the following equation.

[0014] _{V off = v 1a -v 2a =} (I a · R + V) -V = I a · R .................................... (4) Accordingly, the offset voltage V _off, the current source can be obtained 4 a current I _a that is output from the resistance value R of the resistor 3. In order to measure the offset voltage V _off with high accuracy, it is sufficient to pay attention only to the accuracy of the current value in the current source 4, and it is not necessary to use the voltage source 5 with high output voltage accuracy. In addition, the voltage source 5
Even if the output voltage fluctuates due to, there is no influence on the measurement accuracy of the offset voltage.

Next, FIG. 2 shows the second embodiment of the present invention.
It is a block diagram showing an example of. As shown in FIG. 2, the present embodiment corresponds to the analog input terminals 55 and 56, the output terminal 57 and the test terminal 58, and includes a voltage comparator circuit 6 and a CMOS analog circuit including an NMOS transistor 8 and a PMOS transistor 9. The switch 7 and the inverter 10 are provided.

The difference between this embodiment and the first embodiment is that a CMOS analog switch 7 formed by an NMOS transistor 8 and a PMOS transistor 9 is used as an analog switch, and in FIG. That is, the resistor 3 is eliminated. CM in general
The on-resistance value of the OS analog switch is about several tens of Ω to several tens of kΩ, and the value cannot be ignored.
For this reason, the resistor 3 in the first embodiment shown in FIG. 1 is eliminated and instead the on-resistance value of this CMOS analog switch 7 is used. This second
Also in the case of the embodiment described above, in the normal operation, the CMOS analog switch 7 is in the off state via the "H" level control signal input from the test terminal 58, and in the test, The control signal is input as a signal of "L" reher, and the CMOS analog switch 7 is set to the ON state. The operation in each case is the same as in the case of the above-described first embodiment, and the offset voltage measuring method during the test is also exactly the same.

[0017]

As described above, according to the present invention, an analog switch is provided between the non-inverting input terminal and the inverting input terminal of the voltage comparison circuit, and the non-inverting input terminal and the non-inverting input terminal of the voltage comparison circuit are provided during the test. By shorting the inverting input terminals through the analog switch and connecting the current source and the voltage source to the non-inverting input terminal and the inverting input terminal, respectively, the offset voltage is not affected by the noise level. There is an effect that the measurement accuracy of can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a block diagram showing a second embodiment of the present invention.

FIG. 3 is a block diagram showing a conventional example.

FIG. 4 is a diagram showing a relationship between an analog input voltage change and an output voltage in a conventional example.

[Explanation of symbols]

 1, 6, 11 Voltage comparison circuit 2 Analog switch 3 Resistance 4 Current source 5, 12, 13 Voltage source 7 CMOS analog switch 8 NMOS transistor 9 PMOS transistor 10 Inverter

Claims (3)

[Claims] 1. A voltage comparison circuit for comparing and outputting two analog input voltages input to a non-inverting input terminal and an inverting input terminal, respectively, wherein the voltage comparison circuit is inserted between the non-inverting input terminal and the inverting input terminal. A voltage comparison circuit comprising at least a circuit element which is connected and controlled to be turned on / on via a predetermined control signal. 2. The voltage comparison circuit according to claim 1, wherein the circuit element is formed by series connection of an analog switch which is on / off controlled via the control signal, and a resistor having a predetermined resistance value. .. 3. The voltage comparison circuit according to claim 1, wherein the circuit element is formed by a CMOS analog switch which is on / off controlled via the control signal.