JP2000341095A - Comparator circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain proper comparison even when a high ground voltage or a high level other common mode noise is in existence by reducing the effect of the common mode noise such as the ground voltage between a signal supply source and a comparator without using a floating power supply. SOLUTION: A comparator CP is operated by a power supply with voltages +Vcc, -Vcc, compares a voltage at an input terminal T1 with a voltage at an input terminal T2 to produce an output in response to the magnitude correlation of them at an output terminal Tout. A voltage division resistor R1 is inserted between an input terminal L1 and the input terminal T1 and a voltage division resistor R2 is inserted between a ground potential point GND and a connection point between the voltage division resistor R1 and the input terminal T1. A voltage division resistor R1' is inserted between an input terminal L2 and the input terminal T2, and a voltage division resistor R2' is inserted between the ground potential point GND and a connecting point between the voltage division resistor R1' and the input terminal T2. A impedance matching resistor Z is inserted between the input terminals L1, L2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a comparator circuit using a voltage comparison type comparator for comparing voltages of input signals, and more particularly to a comparator circuit suitable for signal discrimination in a digital communication system.

[0002]

2. Description of the Related Art HDLC (High Level) which is a kind of protocol used for an online system of a computer.
DataLink Control) receiver circuit, or so-called 4
2. Description of the Related Art In a receiver circuit or the like of a wire communication channel (4W: 4 wire channel), a voltage comparison type comparator is used to compare a signal voltage of a digital signal or the like with a reference voltage to perform signal discrimination. This type of voltage comparison type comparator cannot operate normally unless the input signal voltage applied to the input terminal is within the range of the power supply voltage supplied to the comparator.

[0003]

When the comparator is connected to another device as in the above-described receiver circuit or the like, the common potential between the other device and the receiver circuit, that is, the ground potential (ground potential) difference. The operation of the comparator is easily affected by common mode noise based on the above. For example,
If the ground potential difference is large, it acts on the comparator as large common mode noise, and the input signal voltage may reach outside the range of the power supply voltage supplied to the comparator.

As described above, when the input signal voltage exceeds the positive power supply voltage of the power supply of the comparator or becomes lower than the negative power supply voltage, the comparator may perform a normal voltage comparison operation. I can no longer do it. Therefore, when the input signal voltage exceeds the range of the power supply voltage supplied to the comparator, the voltage comparison in the comparator does not operate normally, and when the comparator is used in a receiver circuit or the like, normal communication is not performed. Can not be performed.

In order to cope with such a problem, a floating power supply is generally used as a power supply section of a receiver circuit or the like. However, the circuit configuration becomes complicated and large-scale, and the receiver circuit and the like are included. This is a factor in increasing the manufacturing cost of the device.

The present invention has been made in view of the above circumstances, and reduces the influence of common mode noise such as a ground potential difference between a signal supply source and a comparator without using a floating power supply. It is an object of the present invention to provide a comparator circuit capable of performing a proper comparison operation even if the common mode noise is large.

[0007]

To achieve the above object, a comparator circuit according to a first aspect of the present invention comprises:
A comparator for comparing input voltages, and an input circuit provided at an input portion of the comparator and having voltage dividing means for dividing a common mode input voltage component are provided.

[0008] The voltage dividing means of the input circuit may include a voltage dividing resistor for dividing a common mode input voltage by resistance.

A comparator circuit according to a second aspect of the present invention has first and second input terminals, and compares an input voltage of the first input terminal with an input voltage of the second input terminal. A comparator; a first voltage-dividing resistor coupling a first signal input to a first input of the comparator;
A second voltage-dividing resistor coupled between a connection point between the voltage-dividing resistor and the first input terminal of the comparator and a common potential point;
A third voltage divider for coupling a second signal input to be compared with the first signal input to a second input of the comparator; and a third voltage divider and a second input of the comparator. A fourth voltage-dividing resistor coupled between the connection point with the end and the common potential point.

A comparator circuit according to a third aspect of the present invention has first and second input terminals, and compares an input voltage at the first input terminal with an input voltage at the second input terminal. A comparator having an inverting and non-inverting input terminal, connecting the non-inverting input terminal to a reference potential point, and amplifying a difference voltage obtained by subtracting the potential of the inverting input terminal from the input potential of the non-inverting input terminal. And an operational amplifier for outputting
A first voltage-dividing resistor coupling the signal input of the comparator to a first input terminal of the comparator, a connection point between the first voltage-dividing resistor and the first input terminal of the comparator, and an output terminal of the operational amplifier. A second voltage-dividing resistor coupled between the first and second signal-inputs, and a third voltage-dividing resistor coupling a second signal input to be compared with the first signal input to a second input of the comparator; A fourth terminal coupled between a connection point between the third voltage-dividing resistor and a second input terminal of the comparator and an output terminal of the operational amplifier.
A first potential detecting resistor coupled between a connection point between the first and second voltage dividing resistors and an inverting input terminal of the operational amplifier; A second potential detecting resistor coupled between a connection point of the third voltage dividing resistor and the fourth voltage dividing resistor and an inverting input terminal of the operational amplifier.

The first signal input and the third voltage dividing resistor are inserted between a connection point between the first signal input and the first voltage dividing resistor and a connection point between the second signal input and the third voltage dividing resistor. A terminating resistor for matching impedance between the first signal input and the second signal input may be further included.

In the comparator circuit according to the present invention, a voltage dividing means for dividing a common mode input voltage component is provided at an input portion of a comparator for comparing input voltages. In this comparator circuit, the common mode input signal component is divided by the voltage dividing means, so that the common mode allowable voltage range of the comparator circuit with respect to the input signal is substantially expanded, and the influence of common mode noise is reduced. Even if the ground potential difference or other common mode noise is large, an appropriate comparison operation is performed, and there is no need to use a floating power supply.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a comparator circuit according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 schematically shows a configuration of a comparator circuit according to a first embodiment of the present invention.

The comparator circuit shown in FIG. 1 includes a comparator CP, a first voltage dividing resistor R1 (the resistance value is also R1), a second voltage dividing resistor R2 (the resistance value is also R2), and a third voltage dividing resistor R2. A voltage dividing resistor R1 '(resistance value is also R1'), a fourth voltage dividing resistor R2 '(resistance value is also R2'), and an impedance matching resistor Z are provided.

The comparator CP operates with a power supply voltage of + Vcc and -Vcc, compares the voltage between the first and second input terminals T1 and T2, and outputs an output according to the magnitude relationship between the two to the output terminal Tout. Occurs. For example, when the voltage difference between the voltage of the first input terminal T1 and the voltage of the second input terminal T2 is positive, the voltage of the output terminal Tout becomes “H (high level)”.
When the voltage difference is negative, the voltage of the output terminal Tout becomes “L (low level)”. The voltage at the output terminal Tout is led out to the output terminal Lout and becomes the output of this comparator circuit.

Such a comparator CP is generally constituted by an operational amplifier (op-amp) which performs on / off switching by applying positive feedback. Conventionally, since the comparator CP is used alone, the input signal voltage is directly applied to the first and second input terminals T1 and T2.

The first input terminal L of the comparator circuit
1 and a first input terminal T1 of the comparator CP.
And a second voltage dividing resistor R1 is provided between a connection point between the first voltage dividing resistor R1 and the first input terminal T1 of the comparator CP and a common potential of 0 V, that is, the ground potential GND. R2 is inserted. Similarly, the second input terminal L
3 between the second input terminal T2 of the comparator CP and the second input terminal T2 of the comparator CP.
Is inserted, the third voltage dividing resistor R1 'is inserted.
A fourth voltage-dividing resistor R2 'is inserted between a connection point between the second input terminal T2 of the comparator CP and the ground potential GND.

Further, an impedance matching resistor Z for impedance matching of an input signal line is inserted between the first input terminal L1 and the second input terminal L2 of the comparator circuit.

Next, the function and operation of the comparator circuit configured as described above will be described in detail.

An input signal composed of a voltage signal from an input signal line is supplied to the first and second input terminals L1 and L2 of the comparator circuit, respectively. The voltage of the first input terminal L1 minus the second input terminal L2 Output from the output terminal Lout based on the voltage difference between these voltages.

The impedance matching resistor Z terminates an input line for supplying an input signal to the first and second input terminals L1 and L2, and performs impedance matching.

The first input terminal L1 and the ground potential GN
The common-mode input signal voltage given as a potential difference between D and D is divided by the first and second voltage dividing resistors R1 and R2, and R2 / (R1 + R2) is connected to the first input terminal T1 of the comparator CP. Given. A common mode input signal voltage given as a potential difference between the second input terminal L2 and the ground potential GND is divided by third and fourth voltage dividing resistors R1 'and R2', and R2 '/ (R1 '+ R
2 ') is provided to the second input terminal T2 of the comparator CP.

In this case, in order to equalize the voltage division ratio between the first input terminal L1 and the second input terminal L2, the resistance values of the voltage dividing resistors R1, R2, R1 'and R2' are each set to R1.
= R1 'and R2 = R2'. If the voltage division ratio between the first input terminal L1 and the second input terminal L2 does not have to be equal, each of the voltage dividing resistors R1, R2, R
The resistance values of 1 'and R2' may be set to appropriate values as desired.

At this time, the normal mode input signal voltage to the comparator CP, that is, the comparator CP
The potential difference between the first and second input terminals T1 and T2 is also reduced to R2 / (R1 + R2) times by the above-described voltage division. However, as long as the reduced amplitude of the input signal voltage can be detected by the comparator CP, the detection of the input signal is not hindered.

The specific operation of the above-described comparator circuit will be described in comparison with the case of the conventional configuration.

Conventionally, the input signal voltage has been directly supplied to a comparator substantially similar to the comparator CP shown in FIG. For example, when a signal exhibiting a substantially rectangular wave potential difference is applied between the input terminals L1 and L2, even if the voltage waveform of the input signal is distorted by the transmission characteristics of the transmission system, etc.
The “H” period and the “L” period are discriminated by a comparator,
Output as a proper rectangular wave of “H” and “L”.

In such a case, even if the input signal includes common mode noise including a predetermined voltage shift due to the ground potential difference, the amplitude of the input signal voltage is equal to the power supply voltage +
If it is between Vcc and -Vcc, that is, if it is within the normal operating range of the comparator, the common mode noise component is suppressed and an appropriate output signal can be obtained.

However, as shown in FIG. 5, since the input signal voltage includes common mode noise, the input signal voltage falls between the above-mentioned power supply voltages + Vcc and -Vcc, that is, outside the normal operation range of the comparator. When this happens, the comparator can no longer operate properly. For example, as shown in FIG. 6, an output signal of the comparator is mixed with an amplitude fluctuation component caused by common mode noise to obtain an appropriate output signal in the form of a rectangular wave. You will not be able to do it.

On the other hand, as shown in FIG. 1, first to fourth voltage dividing resistors R1, R
The operation in the case where a voltage dividing circuit composed of 2, R1 'and R2' is provided to constitute a comparator circuit is as follows.

When a signal exhibiting a substantially rectangular wave potential difference is applied between the input terminals L1 and L2, the input signal voltage becomes the first to fourth voltage dividing resistors R1, R2 and R as described above.
1 'and R2', the comparator C
The normal mode input signal voltage for P is R2 /
(R1 + R2) times. However, if the reduced voltage amplitude is within the range that can be detected by the comparator CP, the “H” period and the “L” period of the input signal are discriminated by the comparator CP, and “H” and “H” are output to the output terminal Lout. L ″ are output as appropriate rectangular waves alternately appearing.

The input terminal L of such a comparator circuit
As shown in FIG. 2, when input signal voltages including common mode noise are applied to the input terminals L1 and L2 as shown in FIG.
The input signal voltage is between the above-described power supply voltages + Vcc and -Vcc, that is, outside the normal operation range of the comparator.

However, in this case, the common mode component of the input signal is divided by the first to fourth voltage dividing resistors R1, R2, R1 'and R2', and the voltage dividing ratio R2 / (R1 +
R2), the input terminal T1 of the comparator CP
And T2. This comparator C
Since the voltage supplied to the input terminals T1 and T2 of P becomes a value between the power supply voltages + Vcc and -Vcc, that is, a value within the normal operation range of the comparator CP, the comparator CP can operate properly. That is, as shown in FIG. 2, the apparent normal operating range of the comparator circuit as a whole is the reciprocal thereof, that is, (R1 + R2) / depending on the voltage dividing ratio by the voltage dividing resistors R1, R2, R1 'and R2'.
This is equivalent to an enlargement in proportion to R2.

As described above, as long as the input signals supplied to the input terminals L1 and L2 are within the expanded normal operating range, the input signals include common mode noise including a predetermined voltage shift due to the ground potential difference. Also, if the amplitude of the divided input signal voltage falls within the normal operation range of the normal mode sensitivity of the comparator CP, the common mode noise component is suppressed, and an appropriate output signal can be obtained.

For this reason, from the output terminal Tout to the output terminal Lout
Is an appropriate rectangular wave-like signal in which an amplitude fluctuation component caused by common mode noise is not mixed as shown in FIG. 3, for example.

Thus, the input terminal T of the comparator CP
1 and T2, the common mode component of the voltage is divided by resistors R1, R2, R1 'and R2' to reduce the amount of voltage displacement caused by common mode noise. , Apparently the reciprocal of the resistance voltage division ratio, that is, (R1 + R2) / R
2, which can substantially correspond to a large ground potential difference with the input-side device.

In this way, the device is hardly affected by the ground potential difference and common mode noise, which are problems when receiving an input signal by connecting to another device, and it is not necessary to use a floating power supply. A reduction in the rate and a significant cost reduction can be achieved.

FIG. 4 schematically shows a configuration of a comparator circuit according to a second embodiment of the present invention. The second embodiment is a comparator circuit in which the midpoint potential of the input of the comparator CP is further fixed at 0V.

The comparator circuit shown in FIG. 4 has a comparator CP and a first comparator which are similar to those of the first embodiment shown in FIG.
Of the voltage dividing resistor R1 (resistance value R1), the second voltage dividing resistor R2
(Resistance value R2), the third voltage dividing resistor R1 '(resistance value R1'
= R1), a fourth voltage dividing resistor R2 '(resistance value R2'
= R2) and the impedance matching resistor Z
, An operational amplifier DA, a first potential detection resistor R3
(Resistance value R3) and a second potential detection resistor R3 ′ (resistance value R3 ′ = R3).

The comparator CP operates with the power supply voltages + Vcc and -Vcc, compares the voltage between the first and second input terminals T1 and T2, and outputs an output corresponding to the magnitude relationship between the two to the output terminal Tout. Occurs. For example, when the voltage difference between the voltage of the first input terminal T1 and the voltage of the second input terminal T2 is positive, the voltage of the output terminal Tout becomes “H (high level)”.
When the voltage difference is negative, the voltage of the output terminal Tout becomes “L (low level)”. The voltage at the output terminal Tout is led out to the output terminal Lout and becomes the output of this comparator circuit.

The first input terminal L of the comparator circuit
1 and a first input terminal T1 of the comparator CP.
Of the second input terminal L1.
3 between the second input terminal T2 of the comparator CP and the second input terminal T2 of the comparator CP.
Is inserted. A point between a connection point between the first voltage dividing resistor R1 and the first input terminal T1 of the comparator CP and a connection point between the third voltage dividing resistor R1 'and the second input terminal T2 of the comparator CP are connected. A series circuit of a second voltage dividing resistor R2 and a fourth voltage dividing resistor R2 'is inserted. The first voltage dividing resistor R1 ′ is connected between the first voltage dividing resistor R1 and the second voltage dividing resistor R2 and the third voltage dividing resistor R1 ′ and the fourth voltage dividing resistor R2 ′.
Is inserted in series with the potential detection resistor R3 and the second current detection resistor R3 '.

The operational amplifier DA amplifies and outputs a difference voltage obtained by subtracting the input potential at the inverting input terminal T01 from the input potential at the non-inverting input terminal T02. The inverting input terminal T01 of the operational amplifier DA is supplied with the potential of the connection point N0 between the first potential detecting resistor R3 and the second potential detecting resistor R3 ', and the non-inverting input terminal T02 of the operational amplifier DA has the ground potential GND. That is, it is connected to the reference 0 V potential point. Operational amplifier DA
Is connected to the connection point N1 between the second voltage dividing resistor R2 and the fourth voltage dividing resistor R2 '. Further, a first input terminal L1 and a second input terminal L of the comparator circuit
2, an impedance matching resistor Z for impedance matching of the input signal line is inserted.

In the comparator circuit having the above-described configuration, the operation of the comparator CP is basically the same as that of FIG. In this case, the midpoint potential obtained from the connection point N0 between the potential detection resistors R3 and R3 'having the same resistance value is changed to a ground potential G serving as a reference potential of 0V.
The differential voltage subtracted from ND is amplified by the operational amplifier DA, and the connection point N between the voltage dividing resistors R2 and R2 'having the same resistance value is obtained.
1 to control the midpoint potential of the input of the comparator CP. That is, the operational amplifier DA detects the input potential by the potential detection resistors R3 and R3 ', compares it with the ground potential GND, and pulls the midpoint of the input of the comparator CP to 0 V through the voltage dividing resistors R2 and R2'. ing.

In this way, the input terminals L1 and L
Even when the midpoint potential of the input signal input to 2 fluctuates due to common mode noise, the fluctuation can be effectively suppressed.

It is to be noted that the present invention is not limited to the configuration shown in the above-described embodiment.
By making the voltage dividing ratio by R2 and the voltage dividing ratio by the voltage dividing resistors R1 'and R2' different, the noise margin of the input terminals L1 and L2 is made different, or the voltage is divided by using a circuit element other than the resistor. If there is no problem such as impedance mismatch, the impedance matching resistor Z may be omitted.

[0046]

As described above, according to the present invention, the influence of common mode noise such as a ground potential difference between a signal supply source and a comparator is reduced without using a floating power supply, and the ground potential difference and other effects are reduced. A comparator circuit capable of performing a proper comparison operation even when the common mode noise is large can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram schematically showing a configuration of a comparator circuit according to a first embodiment of the present invention.

FIG. 2 is a schematic waveform diagram of an input signal for explaining an operation of the comparator circuit of FIG. 1;

FIG. 3 is a schematic waveform diagram of an output signal for explaining an operation of the comparator circuit of FIG. 1;

FIG. 4 is a diagram schematically showing a configuration of a comparator circuit according to a second embodiment of the present invention.

FIG. 5 is a schematic waveform diagram of an input signal for explaining an operation of a conventional comparator.

FIG. 6 is a schematic waveform diagram of an output signal for explaining an operation of a conventional comparator.

[Explanation of symbols]

 CP Comparator T1 First input terminal T2 Second input terminal Tout Output terminal DA Operational amplifier T01 Inverting input terminal T02 Non-inverting input terminal R1 First voltage dividing resistor (resistance value) R2 Second voltage dividing resistor (resistance value) R1 'Third voltage dividing resistor (resistance value) R2' Fourth voltage dividing resistor (resistance value) R3 First potential detecting resistor (resistance value) R3 'Second potential detecting resistor (resistance value) Z impedance Matching resistor L1 First input terminal L2 Second input terminal Lout Output terminal + Vcc Positive power supply voltage -Vcc Negative power supply voltage GND Ground potential

Claims (5)

[Claims] An input circuit provided at an input of the comparator, the input circuit including a voltage dividing means for dividing a common mode input voltage component;
A comparator circuit comprising: 2. The comparator circuit according to claim 1, wherein said voltage dividing means of said input circuit includes a voltage dividing resistor for dividing a common mode input voltage by resistance. 3. A comparator having first and second input terminals, for comparing an input voltage of the first input terminal with an input voltage of the second input terminal, and a first signal input to the comparator. A first voltage-dividing resistor coupled to a first input terminal of the comparator; and a second voltage-dividing resistor coupled between a connection point between the first voltage-dividing resistor and the first input terminal of the comparator and a common potential point. A third voltage-dividing resistor coupling a second signal input to be compared with the first signal input to a second input of the comparator; and a third voltage-dividing resistor. A fourth voltage-dividing resistor coupled between a connection point of the comparator with a second input terminal and a common potential point. 4. A comparator having first and second input terminals for comparing an input voltage of the first input terminal with an input voltage of the second input terminal, and an inverting and non-inverting input terminal. An operational amplifier having the non-inverting input terminal connected to a reference potential point, and amplifying and outputting a difference voltage obtained by subtracting the potential of the inverting input terminal from the input potential of the non-inverting input terminal; A first voltage-dividing resistor coupling a signal input to a first input terminal of the comparator; a connection point between the first voltage-dividing resistor and the first input terminal of the comparator; and an output terminal of the operational amplifier. A second voltage-dividing resistor coupled between: a third voltage-dividing resistor coupling a second signal input to be compared with the first signal input to a second input of the comparator; A connection point between a third voltage-dividing resistor and a second input terminal of the comparator; A fourth voltage-dividing resistor coupled between the output terminal of the operational amplifier, and a connection point between the first and second voltage-dividing resistors and an inverting input terminal of the operational amplifier. And a second potential coupled between a connection point between the third voltage dividing resistor and the fourth voltage dividing resistor and an inverting input terminal of the operational amplifier. And a detection resistor. 5. A power supply device, comprising: a connection point between the first signal input and the first voltage dividing resistor; and a connection point between the second signal input and the third voltage dividing resistor, The comparator circuit according to claim 3, further comprising a terminating resistor for matching impedance of the first signal input and the second signal input.