JP2012026959A - Sensor threshold determination circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sensor threshold determination circuit for acquiring a digital output with hysteresis characteristics which are independent of the resistance of a sensor with respect to the external input of a sensor.SOLUTION: This sensor threshold determination circuit is configured to generate a sensor threshold voltage Vx by setting the voltage of a terminal VPX or VNX as a reference potential by using a voltage drop as the product of output impedance RSUM1 and RSUM2 of an impedance conversion circuit 170 and sensor bias currents ±IB. Thus, it is possible to obtain a digital output with hysteresis characteristics which are independent of a sensor resistance R with respect to a sensor external input BIN. Thus, it is not necessary to consider the matching of mutual resistance elements, and it is possible to relax constraint on the flowing direction of driving currents or the arrangement of elements or the like.

Description

  The present invention relates to a sensor threshold value determination circuit, and more particularly to a sensor threshold value determination circuit that outputs a digital value having a hysteresis characteristic that does not depend on the resistance of a sensor with respect to an external input of the sensor.

  There is a sensor threshold value determination circuit that determines a threshold value necessary for digitizing the outputs of various sensors. First, the circuit configuration of the conventional sensor threshold value determination circuit 100 will be described with reference to FIG. 5 includes a four-terminal sensor 120, a sensor drive current detection circuit 130, a sensor bias current output circuit 140, a bias current switching circuit 150, and a voltage comparator 160. Composed. A bias current IB generated by the sensor bias current output circuit 140 is supplied to the output terminal of the four-terminal sensor 120. As a result, a voltage drop of ROUT × IB that is the product of the sensor output impedance ROUT that is the output impedance of the four-terminal sensor 120 and the bias current IB is obtained. The sensor threshold value determination circuit 100 is a circuit for obtaining a digital output having a hysteresis characteristic with respect to the sensor external input BIN input to the four-terminal sensor 120 by using this voltage drop.

  The four-terminal type sensor 120 is a four-terminal type sensor having two sensor input terminals and two sensor output terminals VP and VN, or a sensor having a circuit configuration equivalent to the four-terminal type sensor. A magnetoresistive element, a strain sensor, a pressure sensor, a temperature sensor, or an acceleration sensor. The four-terminal sensor 120 has sensor resistances R1 to R4. Based on the displacement of two outputs of the current I1 flowing through the resistors R1 and R2 and the current I2 flowing through the sensor resistors R3 and R4, for example, a permanent magnet, An absolute value of magnetic flux density generated from a coil or the like is detected, or a magnetic resistance or distortion is detected.

The sensor drive current detection circuit 130 has a drive current detection resistor RS to which the sensor drive voltage VCC is applied, and detects the sensor drive current I for driving the four-terminal sensor 120.
The sensor bias current output circuit 140 includes an operational amplifier 141 for amplifying the sensor drive current I, a PMOS transistor 142 for switching switching for performing an amplification operation, and a bias current output resistor RB to which the sensor drive voltage VCC is applied. And is configured.
The sensor drive current I is detected by using the drive current detection resistor RS, and the sensor drive current I is determined by a ratio of K to 1 determined by the combination of the drive current detection resistor RS, the bias current output resistor RB, and the operational amplifier 141. A current mirror circuit that outputs the amplified current is configured to generate a sensor bias current IB that is a predetermined (1 / K = RS / RB) times the sensor drive current I.

  The plus input terminal of the operational amplifier 141 is connected between the drive current detection resistor RS to which the sensor drive voltage VCC of the sensor drive current detection circuit 130 is applied and the input terminal of the four-terminal sensor 120. The negative input terminal of the operational amplifier 141 is connected between the source of the PMOS transistor 142 and the bias current output resistor RB. The output terminal of the operational amplifier 141 is connected to the gate of the PMOS transistor 142. The drain of the PMOS transistor 142 is connected to the output terminal of the four-terminal sensor 120 via the switches SW 1 and SW 2 of the bias current switching circuit 150. The generated bias current IB is output from the drain of the PMOS transistor 142 to the bias current switching circuit 150.

The bias current switching circuit 150 has a bias that is 1 / K times the sensor driving current I generated by the sensor bias current output circuit 140 according to the output state (“High” level or “Low” level) of the voltage comparator 160. The operation is switched so that the current IB is discharged (flowed in the positive direction) or drawn (flowed in the negative direction).
The voltage comparator 160 has a positive input terminal connected to the sensor output terminal VP and a negative input terminal connected to the sensor output terminal VN. The output terminal is connected to the gate of the switch SW1 and the gate of the switch SW2 via the inverter 151. Then, by comparing the two output voltages output from the four-terminal sensor 120, the output voltage of the four-terminal sensor 120 is output as a digital value Dout.

In the conventional sensor threshold value determination circuit 100, the sensor drive current I is detected using the drive current detection resistor RS, and the sensor drive current I is detected by the drive current detection resistor RS, the bias current output resistor RB, and the operational amplifier 141. A current mirror circuit that outputs a current amplified at a ratio of K to 1 determined by the combination is configured to generate a sensor bias current IB that is 1 / K of the sensor drive current I.
Here, with reference to FIG. 6, it will be described that hysteresis can be provided by the bias current IB. FIG. 6 is a circuit diagram showing a circuit configuration of a sensor threshold value determination circuit 100 ′ that is equivalent to the sensor threshold value determination circuit 100 when the switch SW2 of the bias current switching circuit 150 is turned on and the switch SW1 is opened.

  First, for ease of explanation, the resistance value of the driving current detection resistor RS that detects the sensor driving current I is compared with the resistance value of the sensor resistor R that is a combined resistance of the sensor resistors R1 to R4 of the four-terminal sensor 120. Think of it as a very small value. Thereby, the drive terminal voltage VCC2 of the 4-terminal sensor 120 becomes equal to the sensor drive voltage VCC. From the result derived later, it can be seen that the threshold voltage for outputting the output voltage of the sensor as the digital value Dout does not depend on the sensor drive voltage VCC. Therefore, in general, the drive for detecting the sensor drive current I is performed. The resistance value of the current detection resistor RS may be an arbitrary value.

  Although the case where the bias current IB flows into the output terminal of the four-terminal sensor 120 is considered, conversely, the bias current IB may flow out of the output terminal of the four-terminal sensor 120. The state when the switch SW1 is turned on and the switch SW2 is opened is the sensor output terminal which is the voltage of the output terminal of the four-terminal sensor 120 by replacing the sensor resistors R1, R2 and the sensor resistors R3, R4 in the following description. What is necessary is just to replace the voltage of VP with the voltage of the sensor output terminal VN.

As shown in FIG. 6, when the currents I1 and I2 are determined, the following equations (1a) to (1c) are established.
I1 = (VCC-VP) / R1 (1a)
I2 = VCC / (R3 + R4) (1b)
VP / R2 = I1 + IB (1c)
Solving this for VP,
VP = (VCC / R1 + IB) / (1 / R1 + 1 / R2) (2)
It becomes. Since the voltage comparator 160 performs a switching operation when the voltage of the sensor output terminal VP = the voltage of the sensor output terminal VN, the following equation (3) is established.
(VCC / R1 + IB) / (1 / R1 + 1 / R2)
= R4 × VCC / (R3 + R4) (3)

Here, in the four-terminal sensor 120, the sensor resistances R1 to R4 are out of balance according to the sensor input BIN applied from the outside, and R1 = R4 = R + ΔR, R2 = R3 = R−ΔR, or R1 = R4. = R−ΔR, R2 = R3 = R + ΔR, and it can be considered that the sensor output voltage VH = the voltage of the sensor output terminal VP−the voltage of the sensor output terminal VN is generated. For example, in the case of a hall sensor, the sensor output voltage VH is a hall electromotive force generated by the sensor external input BIN. From this, R1 = R4 = R + ΔR, R2 = R3 = R−ΔR, and substituting into the above equation (3),
(VCC / (R + ΔR) + IB) / (1 / (R + ΔR) + 1 / (R−ΔR))
= (R + ΔR) × VCC / (R−ΔR + R + ΔR) (4)
It becomes. When ΔR / R that satisfies the above equation (4) is obtained,
ΔR / R = VCC / (R × IB) × (SQRT (1+ (R × IB / VCC) ² ) −1)
≈ VCC / (R × IB) × (1+ (R × IB / VCC) ² / 2-1)
= R x IB / (2 x VCC) (5)
It becomes. The sensor output voltage VH of the four-terminal sensor 120 is usually in the output range of several hundred μV to several tens of mV. The drive voltage VCC of the four-terminal sensor 120 is about 1V to 5V. R × IB is several tens of mV at most. Therefore, the term R × IB / VCC in the above formula (5) is a value sufficiently smaller than 1. As described above, the threshold voltage can be determined from the currents I1 and I2 of the four-terminal sensor 120 and the bias current IB.

  Next, a flow for determining the threshold voltage using a voltage drop of the product (IB × ROUT) of the output impedance ROUT of the four-terminal sensor 120 and the bias current IB will be described. The output impedance ROUT of the four-terminal sensor 120 as viewed from the voltage VP of the output terminal of the four-terminal sensor 120 is given by the following equation (6) by connecting the sensor resistance R1 and the sensor resistance R2 in parallel.

ROUT = R1 × R2 / (R1 + R2) (6)
Here, if R1 = R + ΔR and R2 = R−ΔR,
ROUT = (R + ΔR) × (R−ΔR) / (R + ΔR + R−ΔR)
= (R / 2) × (1- (ΔR / R) ² ) (7)
It becomes. ΔR / R is normally considered to be 0.1 or less, so if the second order term is ignored, ROUT = R / 2 (8)
It becomes. The product of the sensor output impedance ROUT and the bias current IB is R × IB / 2. Since the sensor output voltage VH is a differential voltage between the voltage at the sensor output terminal VN and the voltage at the sensor output terminal VP, the following equation (9) is obtained.

VH = VCC × R4 / (R3 + R4) −VCC × R2 / (R1 + R2) (9)
As before, if R1 = R4 = R + ΔR and R2 = R3 = R−ΔR,
VH = VCC × (R + ΔR) / (R−ΔR + R + ΔR) −VCC ×
(R−ΔR) / (R + ΔR + R−ΔR) = VCC × ΔR / R (10)
It becomes. Since the voltage comparator 160 switches when the voltage of the sensor output terminal VP = the voltage of the sensor output terminal VN, the following equation (11) is established.
VCC × ΔR / R = R × IB / 2 (11)
Therefore,
ΔR / R = R × IB / (2 × VCC) (12)
It becomes. As shown in the above formulas (5) and (12), even when considered from the currents I1 and I2 of the four-terminal sensor 120 and the bias current IB, or the sensor output impedance ROUT and the bias current IB The same result was obtained when considering from the product.

  In the description so far, for the sake of easy understanding, it is assumed that the resistance of the sensor is R1 = R4 = R + ΔR and R2 = R3 = R−ΔR. However, even if the sensor resistances R1 to R4 remain unbalanced, Does not lose sex. Further, even if the four-terminal sensor 120 is a Hall element that generates a voltage internally without changing its resistance value, the threshold voltage is determined by the product of the sensor output impedance ROUT and the bias current IB. Can be applied as is.

Here, the sensor bias current IB in the above equations (5) and (12) is a current obtained by multiplying the sensor drive current I determined by the sensor voltage VCC and the sensor resistance R by 1 / K times. Therefore, when VCC / R / K is substituted into the bias current IB in the above equation (5),
ΔR / R = R × VCC / R / K / (2 × VCC)
= 1 / (2 x K) (13)
become that way. In the above equation (13), what is important is that the threshold voltage changes depending only on the constant K. The constant K is given by the resistance ratio or the transistor mirror ratio. Therefore, if the constant K is determined, the threshold voltage is determined as one value, which means that there is no variation or change with time.

Also, attention is focused on the change in threshold voltage due to temperature fluctuation. In order to make the temperature fluctuation of the threshold voltage constant with respect to the sensor external input BIN, the constant K needs to have a characteristic equivalent to the temperature characteristic of the sensor resistance R.
The voltage compared by the voltage comparator 160 is the sensor output voltage VH of the four-terminal sensor 120 and the threshold voltage (R × IB / 2) obtained by the above equation (11). Since the sensor output voltage VH is a Hall electromotive force, if the Hall constant is RH and the sensor thickness is t, the Hall electromotive force is generally defined as RH / t × I × BIN. It can be seen that the Hall electromotive force is determined by RH / t and the sensor drive current I. In other words,
RH / t × I × BIN = R × IB / 2
BIN = R × IB / (2 × (RH / t × I)) (14)
It becomes. Here, since the bias current IB is 1 / K times the sensor driving current I,
BIN = R × I / K / (2 × (RH / t × I))
= R / (2 × K × (RH / t)) (15)

  From the above equation (15), it can be seen that the sensor external input BIN is affected by the temperature characteristics of the Hall constant RH, the sensor thickness t, and the sensor resistance R. Here, the temperature characteristics of RH / t are determined by the process of manufacturing the Hall element. The RH / t often has a small variation with respect to a temperature variation, while the sensor resistance R often has a very large variation with respect to the temperature variation. Therefore, ignoring the temperature characteristic of RH / t, by setting the constant K in consideration of the temperature characteristic of the sensor resistance R, it is possible to make the sensor external input BIN constant regardless of temperature fluctuations.

JP 2001-108480 A

  As described above, the fact that the sensor external input BIN depends on the sensor resistance R means that if the elements of the sensor resistance R and the bias current output resistance RB are not matched, the absolute value of the sensor external input BIN This means that variations and fluctuations due to temperature characteristics occur. Therefore, the drive current detection resistor RS in FIG. 5 has no temperature characteristics, or an external resistor is selected, and the bias current output resistor RB is the same as the sensor resistor R. Had to be used.

However, in this case, there is a problem in that it is restricted by the direction in which the drive current flows and the arrangement of elements. In addition, since the sensor resistance R is often determined in advance in terms of the shape of the element and the location of the element, there is a problem that the layout in consideration of matching between such resistance elements is limited.
In view of the above problems, an object of the present invention is to provide a sensor threshold value determination circuit capable of outputting a digital value having hysteresis characteristics that do not depend on the resistance of a sensor with respect to an external input of the sensor. And

The drive device according to the present invention is configured as follows in order to achieve the above object.
A first sensor threshold value determination circuit according to the present invention includes a sensor drive current detection unit that detects a sensor drive current for driving a sensor, and the sensor drive current detected from the sensor drive current detection unit is multiplied by a predetermined amount. A sensor bias current output means for outputting a bias current, an impedance conversion means for converting the output impedance of the sensor into a predetermined impedance, and a sensor output voltage output from the sensor are compared, and the sensor output voltage is converted into a digital value. And a voltage comparison unit that outputs the threshold voltage for output as the digital value by allowing the bias current to flow with respect to the output impedance after conversion.

  According to the first sensor threshold value determination circuit, the impedance conversion means converts the output impedance of the sensor. Then, by passing a bias current to the converted output impedance, the threshold voltage is determined using a voltage drop of the product of the converted output impedance and the bias current. This makes it possible to obtain a digital output having a hysteresis characteristic that does not depend on the resistance of the sensor with respect to the external input to the sensor.

In the second sensor threshold value determining circuit according to the present invention, the sensor is a four-terminal type sensor having two input terminals and two output terminals, and the impedance conversion means is the four-terminal type sensor. Two outputs connected to the output terminal, converting at least one of the two output impedances of the four-terminal type sensor into a predetermined impedance, and outputting from the impedance converting means based on the comparison result of the voltage comparing means Bias current switching means for switching the flow of the bias current so as to flow the bias current to any one of the impedances is provided.
According to the second sensor threshold value determining circuit, the impedance conversion unit converts at least one of the two output impedances of the four-terminal sensor into a predetermined impedance, and then converts the impedance by the bias current switching unit. It becomes possible to flow a bias current only to the output impedance.

The third sensor threshold value determining circuit according to the present invention is characterized in that the impedance converting means converts both of two output impedances of the four-terminal sensor into a predetermined impedance.
According to said 3rd sensor threshold value determination circuit, an impedance conversion means converts both two output impedances of a 4-terminal type sensor into predetermined | prescribed impedance.

In the fourth sensor threshold value determination circuit according to the present invention, the bias current switching means may be configured to apply the bias current to one of two output impedances after conversion based on a comparison result of the voltage comparison means. The flow of the bias current is switched so as to flow.
According to the fourth sensor threshold value determination circuit, the bias current switching unit switches the amplified sensor drive current from one output of the bias current switching unit to one of the two outputs of the impedance conversion unit. . As a result, as described above, it is possible to output a digital value having a hysteresis characteristic that does not depend on the resistance of the sensor, with respect to the external input to the sensor.

The fifth sensor threshold value determining circuit according to the present invention is characterized in that the impedance converting means converts one of two output impedances of the four-terminal sensor into a predetermined impedance.
According to the fifth sensor threshold value determination circuit, the impedance conversion unit converts one of the two output impedances of the four-terminal sensor into a predetermined impedance.

  A sixth sensor threshold value determining circuit according to the present invention comprises sensor bias sink current output means for outputting a negative bias current with respect to the bias current, and the bias current switching means is provided with a comparison result of the voltage comparison means. On the basis of this, the flow of the bias current is switched so as to discharge or draw the bias current with respect to the output impedance after conversion.

  According to the sixth sensor threshold value determining circuit, the sensor bias sink current output means outputs a negative bias current with respect to the bias current. Then, the bias current switching means switches so that the amplified sensor drive current is discharged from the output of the bias current switching means to the output of the impedance conversion means, or is drawn from the output of the impedance conversion means to the output of the bias current switching means. Shed. As a result, as described above, it is possible to output a digitizer value having a hysteresis characteristic independent of the resistance of the sensor, with respect to the external input to the sensor.

In a seventh sensor threshold value determining circuit according to the present invention, the output impedance converting means includes an output voltage amplifying circuit for amplifying the sensor output voltage with a predetermined gain, and a sensor output amplified by the output voltage amplifying circuit. And an impedance conversion resistance element for determining the threshold voltage on the basis of a voltage.
According to the seventh sensor threshold value determination circuit, first, the sensor output voltage is output by an output voltage amplifier circuit that combines, for example, a circuit configuration of a voltage follower using an operational amplifier and a configuration of a non-inverting amplifier circuit using an operational amplifier and a resistor. Is amplified with a predetermined gain. Furthermore, if a bias current is passed through the impedance conversion resistance element, the threshold voltage can be determined based on the amplified sensor output voltage.

In an eighth sensor threshold value determination circuit according to the present invention, the sensor drive current detection means includes a drive current detection resistance element for detecting the sensor drive current, and the sensor bias current output means includes the sensor A drive current amplification circuit for outputting the bias current obtained by multiplying the drive current by a predetermined value, a bias current output resistance element, and a switching element; the sensor drive current detection means; and the sensor bias current output means; To form a current mirror circuit.
According to the eighth sensor threshold value determination circuit, it is possible to generate a bias current to flow to the output impedance after conversion in the mirror circuit.

In a ninth sensor threshold value determination circuit according to the present invention, the sensor is any one of a Hall element, a magnetoresistive element, a strain sensor, a pressure sensor, a temperature sensor, and an acceleration sensor.
According to said 9th sensor threshold value determination circuit, it becomes possible to use for various sensors irrespective of the kind of sensors, such as a Hall element, a magnetoresistive element, and a distortion sensor.

  According to the present invention, it is possible to output a digital value having a hysteresis characteristic independent of the resistance of the sensor with respect to the external input of the sensor. For this reason, it is not necessary to consider matching between the resistances of the sensor. Therefore, when manufacturing an IC (Integrated Circuit) with a built-in sensor, restrictions due to the direction in which the drive current flows, the arrangement of elements, and the like are relaxed, and productivity can be increased.

1 is a circuit diagram showing a configuration of a sensor threshold value determination circuit 10 according to a first embodiment of the present invention. FIG. 5 is a circuit diagram showing a circuit configuration of a sensor threshold value determination circuit 10 ′ that is equivalent to the sensor threshold value determination circuit 10 when the switch SW1 of the bias current switching circuit 150 is turned on and the switch SW2 is opened. It is a circuit diagram which shows the structure of the sensor threshold value determination circuit 20 which concerns on 2nd Embodiment of this invention. It is a circuit diagram which shows the structure of the sensor threshold value determination circuit 30 which concerns on 3rd Embodiment of this invention. It is a circuit diagram which shows the circuit structure of the conventional sensor threshold value determination circuit 100. 4 is a circuit diagram showing a circuit configuration of a sensor threshold value determination circuit 100 ′ that is equivalent to the sensor threshold value determination circuit 100 when the switch SW2 of the bias current switching circuit 150 is turned on and the switch SW1 is opened. FIG.

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. In each drawing referred to in the following description, components equivalent to those in the other drawings are denoted by the same reference numerals.
[First Embodiment]
First, the circuit configuration of the sensor threshold value determination circuit 10 according to the first embodiment of the present invention will be described with reference to FIG. The sensor threshold value determination circuit 10 shown in FIG. 1 is configured to further include an impedance conversion circuit 170 in addition to the components constituting the sensor threshold value determination circuit 10 shown in FIG.

The impedance conversion circuit 170 includes operational amplifiers 171 and 172, resistors RG1 and RG2, and impedance conversion resistors RSUM1 and RSUM2.
The operational amplifier 171 is for amplifying one of the output voltages of the four-terminal sensor 120 with a predetermined gain, and the sensor output terminal VP is connected to the plus input terminal. Further, the node between the resistors RG1 and RG2 is connected to the negative input terminal. The operational amplifier 171 includes a resistor RG1 and a resistor RG2 to form a non-inverting amplifier circuit that amplifies a signal with reference to the voltage at the terminal VNX.

  The operational amplifier 172 is for amplifying one of the output voltages of the four-terminal sensor 120 with a predetermined gain, and the sensor output terminal VN is input to the plus input terminal. Further, the node between the resistor RG1 and the terminal VNX is connected to the negative input terminal. The operational amplifier 172 constitutes a voltage follower (unity gain buffer) that outputs the input voltage as it is. Therefore, the gain is 1.

The resistor RG1 is connected between the negative input terminal of the operational amplifier 171 and the negative input terminal of the operational amplifier 172. The resistor RG2 is connected between the negative input terminal of the operational amplifier 171 and the terminal VPX of the operational amplifier 171.
The impedance conversion resistor RSUM1 is connected between a terminal VNX connected to the output terminal of the operational amplifier 172 and a terminal VSUMN connected to the negative input terminal of the voltage comparator 160. The impedance conversion resistor RSUM2 is connected between the terminal VPX connected to the operational amplifier 171 and the terminal VSUMP connected to the positive input terminal of the voltage comparator 160.

  The impedance conversion circuit 170 is a combination of a voltage follower circuit configuration using an operational amplifier 172 and a non-inverting amplifier circuit configuration using an operational amplifier 171, a resistor RG 1, and a resistor RG 2. The configuration of the impedance conversion circuit 170 need not be a non-inverting amplifier circuit composed of the operational amplifier 171, the resistor RG1, and the resistor RG2, and the resistors RG1 and RG2 are eliminated, and the operational amplifier 171 is connected to the operational amplifier 172. Similarly, a voltage follower configuration may be used. In the case of this configuration, the gain of the impedance conversion circuit 170 is 1.

  In the sensor threshold value determination circuit 10 as well, as in the sensor threshold value determination circuit 100 shown in FIG. 5, the sensor drive current detection circuit 130 and the sensor bias current output circuit 140 constitute a current mirror circuit. The current mirror circuit outputs a sensor bias current IB obtained by multiplying the sensor drive current I by a predetermined (1 / K = RS / RB). Then, the bias current IB is passed through the impedance conversion resistors RSUM1 and RSUM2 of the impedance conversion circuit 170 to generate the sensor threshold voltage Vx = IB × RSUM1 and the sensor threshold voltage Vy = IB × RSUM2. A voltage A × VH obtained by amplifying the electromotive force VH generated in the four-terminal sensor 120 by the sensor external input BIN by a gain A (= 1 + RG2 / RG1) times by the impedance conversion circuit 170 and the sensor threshold voltages Vx and Vy are voltages. Comparison is performed by the comparator 160. As a result, a digital output having hysteresis characteristics independent of the sensor resistance R, the sensor drive voltage, and the sensor drive current can be obtained with respect to the sensor external input BIN.

  A feature of the sensor threshold value determination circuit 10 according to the first embodiment is that the sensor drive current IB generated by the sensor drive current detection circuit 130 and the sensor bias current output circuit 140 is switched to have hysteresis by the bias current IB. When SW1 becomes conductive and the switch SW2 is opened, it is discharged to the impedance conversion resistor RSUM1 of the impedance conversion circuit 170. Thus, the sensor threshold voltage Vx = IB × RSUM1 is generated at both ends of the impedance conversion resistor RSUM1 of the impedance conversion circuit 170 with reference to the voltage of the terminal VNX. In the description of the present embodiment, the case where the bias current IB is discharged to the impedance conversion resistor RSUM1 is considered, but conversely, the bias current IB may be drawn from the impedance conversion resistor RSUM1.

Here, with reference to FIG. 2, it will be described that the bias current IB and the impedance conversion circuit 170 can provide hysteresis. FIG. 2 is a circuit diagram showing a circuit configuration of a sensor threshold value determination circuit 10 ′ that is equivalent to the sensor threshold value determination circuit 10 when the switch SW1 of the bias current switching circuit 150 is turned on and the switch SW2 is opened.
The impedance conversion circuit 170 amplifies a differential voltage VH between the voltage at the sensor output terminal VP and the voltage at the sensor output terminal VN at a gain A times between the terminal VPX and the terminal VNX with reference to the voltage at the terminal VNX. Has a function for. At the same time, the operational amplifiers 171 and 172 have a small output impedance. Since the output impedance of each operational amplifier is small, the output impedance that can be seen when the bias current IB is discharged is only the impedance conversion resistor RSUM1. Therefore, the output impedance that appears when the bias current IB is discharged is converted from the output impedance R / 2 of the four-terminal sensor 120 to RSUM1.

  Next, the output impedance when the switch SW1 is opened and the switch SW2 is turned on is similarly the impedance conversion resistor RSUM2. In this case, the sensor threshold voltage Vx = IB × RSUM2 is generated in the impedance conversion resistor RSUM2 with reference to the voltage of the terminal VPX. The state when the switch SW2 becomes conductive and the switch SW1 is opened may be considered by replacing the impedance conversion resistor RSUM1 and the impedance conversion resistor RSUM2 in the following description.

Representing the bias current IB again using the drive current detection resistor RS, the bias current output resistor RB, and the sensor drive current I,
IB = I × RS / RB (16)
It becomes. Here, when the sensor threshold voltage Vx is obtained using the above equation (16),
Vx = I × RS / RB × RSUM1 (17)
It becomes. The voltage determined by the voltage comparator 160 is obtained by using the impedance conversion circuit 170 to obtain a sensor output voltage VH generated between the sensor output terminal VP and the sensor output terminal VN obtained by magnetic input to the four-terminal sensor 120 by a gain A. The multiplied voltage and the sensor threshold voltage Vx obtained by the above equation (17). The sensor external input BIN is obtained from A × VH and Vx.
A × RH / t × I × BIN = I × RS / RB × RSUM1
BIN = 1 / (A × (RH / t) × (RB / RSUM1) × (1 / RS)) (18)

  As can be seen from the above equation (18), the sensor external input BIN does not depend on the sensor resistance R. This means that it is not necessary to consider matching between the sensor resistance R and other resistances. Here, since the gain A is determined by the resistance RG1 and the resistance RG2, any element may be selected. The same applies to the bias current output resistor RB and the impedance conversion resistors RSUM1 and RSUM2. Further, as the driving current detection resistor RS, a resistor having a small temperature characteristic or an external resistor may be used. In this way, it is possible to arbitrarily determine the shape and element arrangement location of elements that originally need matching.

[Second Embodiment]
Next, the circuit configuration of the sensor threshold value determination circuit 20 according to the second embodiment of the present invention will be described with reference to FIG.
The sensor threshold value determination circuit 20 shown in FIG. 3 includes a sensor bias sink current output circuit 180 in addition to the components constituting the sensor threshold value determination circuit 10 shown in FIG.
The sensor bias sink current output circuit 180 includes NMOS transistors 181 and 182. The gate of the NMOS transistor 181 is connected to the gate of the NMOS transistor 182, and the drain of the NMOS transistor 182 is connected to the terminal VSUMN, so that the sensor bias current -IB can be generated.

  In addition to the addition of the sensor bias sink current output circuit 180, the sensor bias current output circuit 240 is configured to include a PMOS transistor 143 in addition to the elements included in the sensor bias current output circuit 140. The bias current switching circuit 250 includes a switch SW3 in addition to the elements included in the bias current switching circuit 150. The impedance conversion circuit 270 does not include the impedance conversion resistor RSUM2 among the elements included in the impedance conversion circuit 170.

  The drain of the PMOS transistor 143 that generates the bias current IB of the sensor bias current output circuit 240 is connected to the drain and gate of the diode-connected NMOS transistor 181 of the sensor bias sink current output circuit 180 via the switch SW2 of the bias current switching circuit 250. Connected to. As a result, a current that sinks to the sensor bias current IB can be output.

  The terminal VCOMP connected to the output terminal of the voltage comparator 160 is connected to the gate of SW1 of the bias current switching circuit 250, the gate of SW2 and the gate of the switch SW3 via the input terminal of the inverter 151, respectively. As a result, the sensor bias current IB discharged from the impedance conversion resistor RSUM1 in accordance with the digital value Dout output from the terminal VCOMP connected to the voltage comparator 160 is the sensor bias current − drawn from the impedance conversion resistor RSUM1. It becomes possible to switch to IB.

  In the sensor threshold value determination circuit 10 according to the first embodiment, the bias current IB is applied to the impedance conversion resistors RSUM1 and RSUM2 which are output impedances of the impedance conversion circuit 170 in order to give the digital value Dout hysteresis by the bias current IB. Although the sensor threshold value determination circuit 20 according to the second embodiment is characterized by using the bias current switching circuit 250 and the sensor bias sink current output circuit 180, the sensor threshold value according to the first embodiment This is the point that the impedance conversion resistor RSUM2 of the impedance conversion circuit 170 of the determination circuit 10 is eliminated. Then, the sensor bias current IB is discharged or drawn only to the impedance conversion resistor RSUM1.

Even if only the impedance conversion resistor RSUM1 is provided as in the impedance conversion circuit 270 of the sensor threshold value determination circuit 20 according to the second embodiment, the same expression as Expression (18) can be realized.
The state when the switch SW2 is turned on and the switch SW1 is opened may be considered by replacing the impedance conversion resistor RSUM1 with -RSUM1 in the same analysis as in the above equation (18).

[Third Embodiment]
Subsequently, a circuit configuration of the sensor threshold value determination circuit 30 according to the third embodiment of the present invention will be described with reference to FIG. The sensor threshold value determination circuit 30 shown in FIG. 4 is configured to have each part constituting the sensor threshold value determination circuit 20 shown in FIG. However, the impedance conversion circuit 370 is different from the elements of the impedance conversion circuit 170 in that it does not include the impedance conversion resistor RSUM1.
First, the drain of the PMOS transistor 143 that generates the bias current IB is connected to the drain and gate of the diode-connected NMOS transistor 181 of the sensor bias sink current output circuit 180 via the switch SW2 of the bias current switching circuit 250. As a result, a current that sinks to the sensor bias current IB can be output. The process so far is the same as the sensor threshold value determination circuit 20 according to the second embodiment.

The gate of the NMOS transistor 181 is connected to the gate of the NMOS transistor 182, and the drain of the NMOS transistor 182 is connected to the terminal VSUMP, so that the sensor bias current -IB can be generated.
The terminal VCOMP connected to the voltage comparator 160 is connected to the gate of SW1 of the bias current switching circuit 250, the gate of SW2 via the input terminal of the inverter 151, and the gate of the switch SW3. When the bias current is switched by the bias current switching circuit 250, the sensor bias current IB discharged to the impedance conversion resistor RSUM2 can be switched to -IB depending on the state of the terminal VCOMP connected to the device 160.

The sensor threshold value determination circuit 20 according to the second embodiment uses the bias current switching circuit 250 and the sensor bias sink current output circuit 180 to discharge or draw the sensor bias current IB only to the impedance conversion resistor RSUM1. Met. Thereby, the digital value Dout is given hysteresis by the bias current IB. The characteristic point of the sensor threshold value determination circuit 30 according to the third embodiment is that the sensor bias current IB is not discharged to both the impedance conversion resistors RSUM1 and RSUM2 as in the sensor threshold value determination circuit 20 according to the second embodiment. The sensor bias current IB is discharged or drawn only to the impedance conversion resistor RSUM2. Even when only the impedance conversion resistor RSUM2 is provided as in the impedance conversion circuit 370 of the sensor threshold value determination circuit 30 according to the third embodiment, the same as the above-described equation (18) can be realized.
The state when the switch SW2 is turned on and the switch SW1 is opened may be considered by replacing the impedance conversion resistor RSUM2 with -RSUM2 in the same analysis as Expression (18).

[Modification]
As described above, the sensor threshold value determination circuit described above can output a digital value having a hysteresis characteristic that does not depend on the resistance of the sensor, but a temperature compensation circuit or the like is intentionally provided after the sensor threshold value determination circuit. Thus, the output accuracy of the sensor can be increased.
[Summary]
In each of the first to third embodiments, the threshold voltage Vx is generated at the reference potential of the terminal VPX or VNX using the product of the output impedances RSUM1 and RSUM2 of the impedance conversion circuit and the sensor bias current ± IB. . As a result, a digital output having a hysteresis characteristic independent of the sensor resistance R with respect to the sensor external input BIN can be obtained. Therefore, it is not necessary to consider matching between the resistance elements.

  A four-terminal sensor, or a sensor having a circuit configuration equivalent to the four-terminal sensor, and sensor thresholds of various sensors such as a Hall element, a magnetoresistive element, a strain sensor, a pressure sensor, a temperature sensor, and an acceleration sensor It can be integrated into an IC as a decision circuit.

10, 20, 30 Sensor threshold value determination circuit 110 Sensor drive voltage source 120 Four-terminal sensor 130 Sensor drive detection circuit 140, 240 Sensor bias current output circuit 150, 250 Bias current switching circuit 160 Voltage comparators 170, 270, 370 Impedance conversion Circuits 171 and 172 Operational amplifiers RG1 and RG2 Resistors RSUM1 and RSUM2 Impedance conversion resistors 180 Sensor bias sink current output circuit

Claims (9)

Sensor driving current detecting means for detecting a sensor driving current for driving the sensor;
Sensor bias current output means for outputting a bias current obtained by multiplying the sensor drive current detected from the sensor drive current detection means by a predetermined value;
Impedance conversion means for converting the output impedance of the sensor into a predetermined impedance;
Voltage comparison means for comparing the sensor output voltage output from the sensor and outputting the sensor output voltage as a digital value;
With
A sensor threshold value determining circuit for determining a threshold voltage to be output as the digital value by causing the bias current to flow with respect to the output impedance after conversion. The sensor is a four-terminal sensor having two input terminals and two output terminals,
The impedance converter is connected to an output terminal of the four-terminal sensor, converts at least one of two output impedances of the four-terminal sensor into a predetermined impedance,
Bias current switching for switching the flow of the bias current so that the bias current flows to one of the two output impedances output from the impedance conversion unit based on the comparison result of the voltage comparison unit The sensor threshold value determination circuit according to claim 1, further comprising: means.   3. The sensor threshold value determining circuit according to claim 2, wherein the impedance converting means converts both of two output impedances of the four-terminal sensor into a predetermined impedance.   The bias current switching unit switches the flow of the bias current so that the bias current flows to one of the two output impedances after conversion based on the comparison result of the voltage comparison unit. The sensor threshold value determination circuit according to claim 3.   3. The sensor threshold value determining circuit according to claim 2, wherein the impedance converting means converts one of two output impedances of the four-terminal sensor into a predetermined impedance. Sensor bias sink current output means for outputting a negative bias current with respect to the bias current;
The bias current switching means switches the flow of the bias current so as to discharge or draw the bias current with respect to the output impedance after conversion based on a comparison result of the voltage comparison means. Item 4. The sensor threshold value determination circuit according to Item 3. The output impedance converting means includes
An output voltage amplification circuit for amplifying the sensor output voltage with a predetermined gain;
A resistance element for impedance conversion for determining the threshold voltage with reference to the sensor output voltage amplified by the output voltage amplifier circuit;
The sensor threshold value determination circuit according to claim 1, comprising: The sensor drive current detection means has a drive current detection resistance element for detecting the sensor drive current,
The sensor bias current output means includes a drive current amplification circuit for outputting the bias current obtained by multiplying the sensor drive current by a predetermined value, a bias current output resistance element, and a switching element.
8. The sensor threshold value determination circuit according to claim 1, wherein a current mirror circuit is configured by the sensor drive current detection unit and the sensor bias current output unit.   The sensor threshold according to any one of claims 1 to 8, wherein the sensor is any one of a Hall element, a magnetoresistive element, a strain sensor, a pressure sensor, a temperature sensor, and an acceleration sensor. Decision circuit.

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