JP6407776B2 - Sensor drive circuit - Google Patents

Description

  The technology disclosed in this specification relates to a sensor drive circuit.

  Patent Document 1 and Patent Document 2 disclose a sensor drive circuit that supplies a power supply voltage to a sensor. When high-frequency noise (about 1 MHz to 400 MHz) is mixed in the power supply voltage supplied to the sensor, the sensor malfunctions due to the influence of the noise. For example, Patent Document 3 discloses a technique in which a sensor is surrounded by an electromagnetic shield to suppress radiation noise from the outside.

JP 2003-194579 A JP 2014-95656 A JP 2007-258670 A

  In such a sensor drive circuit, the power supply voltage terminal is connected to an external electric wire incorporated in the wire harness, and the power supply voltage is input through the external electric wire. Since the wire harness is exposed to the outside of the electromagnetic shield, radiation noise may enter from the external wire of the wire harness, and noise may be mixed into the power supply voltage. In addition to the external wires, the wire harness incorporates multiple signal wires, so that inductive noise enters the external wires for inputting power supply voltage from other signal wires, and noise is generated in the power supply voltage. May be mixed. There is a need for a technique for dealing with noise mixed in such a power supply voltage.

  An object of the present specification is to provide a sensor driving circuit capable of generating a voltage in which the influence of such noise is suppressed even when noise is mixed in the power supply voltage.

  One embodiment of the sensor drive circuit disclosed in this specification includes a reference voltage line, a power supply voltage line, an output voltage line, a constant current source, a differential pair transistor unit having first and second transistors, third and fourth An active load transistor portion having a transistor and a resistance element are provided. The constant current source, the first transistor, and the third transistor form a first series path that is connected in series between the reference voltage line and the power supply voltage line in this order. The constant current source, the second transistor, and the fourth transistor form a second series path that is connected in series between the reference voltage line and the power supply voltage line in this order. In the active load transistor portion, the third transistor is diode-connected, and the control electrode of the third transistor and the control electrode of the fourth transistor are connected. The resistance element is inserted between a first node where the first series path is connected to the power supply voltage line and a second node where the second series path is connected to the power supply voltage line. The output voltage wiring is connected to an output node between the second transistor and the fourth transistor.

  Since the resistance element is inserted between the first node and the second node, the voltage between the gate and the source of the fourth transistor is reduced by the voltage drop caused by the current flowing through the resistance element, and the current flowing through the second series path Is smaller than the current flowing through the first series path. The fourth transistor operates as an active load with respect to the second transistor, and the operating point is a linear region of the second transistor. As a result, even if noise is mixed in the power supply voltage of the power supply voltage wiring, fluctuations in the voltage of the output node can be suppressed. The sensor driving circuit can generate a voltage with reduced noise.

An example of the circuit diagram of a sensor and a sensor drive circuit is shown. The figure which superimposed the load line of the 4th transistor on the static characteristic of the 2nd transistor of a sensor drive circuit is shown. The other example of the circuit diagram of a sensor and a sensor drive circuit is shown.

  The technical features disclosed in this specification will be summarized below. The items described below have technical usefulness independently.

  One embodiment of the sensor drive circuit disclosed in this specification includes a reference voltage line, a power supply voltage line, an output voltage line, a constant current source, a differential pair transistor unit having first and second transistors, third and fourth An active load transistor portion having a transistor and a resistance element may be provided. For example, the first transistor and the second transistor may be n-type MOSFETs, and the third transistor and the fourth transistor may be p-type MOSFETs. The constant current source, the first transistor, and the third transistor form a first series path that is connected in series between the reference voltage line and the power supply voltage line in this order. The first series path may include other circuit elements as necessary. The constant current source, the second transistor, and the fourth transistor form a second series path that is connected in series between the reference voltage line and the power supply voltage line in this order. The second series path may include other circuit elements as necessary. In the active load transistor portion, the third transistor may be diode-connected, and the control electrode of the third transistor and the control electrode of the fourth transistor may be connected. The resistance element may be inserted between a first node where the first series path is connected to the power supply voltage line and a second node where the second series path is connected to the power supply voltage line. The output voltage wiring may be connected to an output node between the second transistor and the fourth transistor.

  The sensor drive circuit of the above embodiment may further include a next stage circuit. The next stage circuit is connected to the second node of the power supply voltage wiring and the output voltage wiring. When the voltage of the output voltage wiring is increased, the current of the power supply voltage wiring is increased and the voltage of the output voltage wiring is lowered. When trying to do so, the current of the power supply voltage wiring may be reduced. For example, the next stage circuit may be a source follower circuit. Such a next-stage circuit increases the current of the power supply voltage wiring when the voltage of the output voltage wiring is about to increase, and increases the voltage drop due to the resistance connected between the first node and the second node. Suppresses the increase in output voltage wiring voltage. Further, such a next-stage circuit reduces the current of the power supply voltage wiring when the voltage of the output voltage wiring is about to decrease, and the voltage drop due to the resistance connected between the first node and the second node is reduced. Reduces the voltage drop of the output voltage wiring. Thereby, the sensor drive circuit of the said embodiment can implement | achieve the noise suppression by the increase in drive capability and feedback control.

  The sensor driving circuit of the above embodiment may be configured such that a bias voltage having the same phase is input to the control terminal of the first transistor and the control terminal of the second transistor. More preferably, the sensor drive circuit of the above embodiment may be configured such that a fixed bias voltage is input to the control terminal of the first transistor and the control terminal of the second transistor. In this case, since there is no difference between the control voltages input to the first transistor and the second transistor, fluctuations in the voltage at the output node can be suppressed.

  As shown in FIG. 1, the sensor driving circuit 1 is a circuit that supplies a driving voltage Vout to the sensor 100, and includes a reference voltage wiring L1, a power supply voltage wiring L2, an output voltage wiring L3, a constant current source 2, a differential pair. A transistor unit 3, an active load transistor unit 4, a resistance element R1, and a next stage circuit 5 are provided. The sensor 100 has a plurality of impedance elements whose impedance changes depending on a physical quantity such as pressure, acceleration, or magnetism, and these are bridge-connected. The sensor drive circuit 1 and the sensor 100 are made into one chip.

  The reference voltage line L1 is connected to the reference voltage terminal T1. The ground voltage GND is input to the reference voltage terminal T1. The power supply voltage line L2 is connected to the power supply voltage terminal T2. The power supply voltage Vcc is input to the power supply voltage terminal T2.

  The differential pair transistor unit 3 includes a first transistor Tr1 and a second transistor Tr2. The first transistor Tr1 and the second transistor Tr2 are n-type MOSFETs. The active load transistor unit 4 includes a third transistor Tr3 and a fourth transistor Tr4. The third transistor Tr3 and the fourth transistor Tr4 are p-type MOSFETs.

  The constant current source 2, the first transistor Tr1, and the third transistor Tr3 are connected in series in this order between the reference voltage line L1 and the power supply voltage line L2. The constant current source 2, the second transistor Tr2, and the fourth transistor Tr4 are connected in series in this order between the reference voltage line L1 and the power supply voltage line L2. A series path composed of the constant current source 2, the first transistor Tr1, and the third transistor Tr3 is connected to a relatively upstream side of the power supply voltage wiring L2, and the constant current source 2, the second transistor Tr2, and the fourth transistor Tr4. The configured series path is connected to the relatively downstream side of the power supply voltage wiring L2.

  One end of the constant current source 2 is connected to the reference voltage line L1, and the other end is connected to both the source of the first transistor Tr1 and the source of the second transistor Tr2.

  The first transistor Tr1 is configured such that the source is connected to the constant current source 2, the drain is connected to the intermediate node Nint, and the fixed voltage VK is input to the gate. The third transistor Tr3 is configured such that the drain is connected to the intermediate node Nint, the source is connected to the first node N1 of the power supply voltage wiring L2, and the gate is connected to the gate of the fourth transistor Tr4. The third transistor Tr3 has a drain and gate short-circuited and is diode-connected.

  The second transistor Tr2 is configured such that the source is connected to the constant current source 2, the drain is connected to the output node Nout, and the fixed voltage VK is input to the gate. The fourth transistor Tr4 is configured such that the drain is connected to the output node Nout, the source is connected to the second node N2 of the power supply voltage wiring L2, and the gate is connected to the gate of the third transistor Tr3.

  The resistor element R1 has one end connected to the first node N1, the other end connected to the second node N2, and is configured to be inserted between the first node N1 and the second node N2.

  The next stage circuit 5 forms a source follower circuit and includes an n-type MOSFET fifth transistor Tr5. The fifth transistor Tr5 has a drain connected to the second node N2 of the power supply voltage wiring L2, a source connected to the sensor 100, and a gate connected to the output voltage wiring L3.

  Next, an operation for suppressing high frequency noise (about 1 MHz to 400 MHz) mixed in the power supply voltage Vcc by the sensor driving circuit 1 will be described. The high frequency noise suppressed by the sensor drive circuit 1 includes radiation noise and induction noise. An external electric wire incorporated in the wire harness is connected to the power supply voltage terminal T2, and the power supply voltage Vcc is input to the power supply voltage terminal T2 via the external electric wire. When radiation noise enters the external wire of the wire harness, the noise may be mixed into the power supply voltage Vcc. In addition to the external electric wire, a plurality of signal lines are incorporated in the wire harness. For this reason, when inductive noise enters from an external signal line to the external electric wire for inputting the power supply voltage Vcc, the noise may be mixed into the power supply voltage Vcc.

  Since the third transistor Tr3 is diode-connected, the voltage Vd1 at the intermediate node Nint follows the power supply voltage Vcc while the substantial threshold voltage of the third transistor Tr3 decreases. The voltage V1 at the second node N2 follows the power supply voltage Vcc while a voltage drop at the resistance element R1 is lowered due to the current flowing through the resistance element R1. For this reason, the gate-source voltage of the fourth transistor Tr4 becomes substantially constant even if the power supply voltage Vcc fluctuates, that is, even if noise is mixed in the power supply voltage Vcc. Further, the voltage drop at the resistance element R1 causes the voltage V1 at the second node N2 to be lower than the power supply voltage Vcc at the first node N1, so that the constant current source 2, the second transistor Tr2, and the fourth transistor Tr4 are connected in series. Is smaller than the current Id1 flowing through the series path of the constant current source 2, the first transistor Tr1, and the third transistor Tr3.

  FIG. 2 shows a load line of the fourth transistor Tr4 with respect to the second transistor Tr2. The voltage V1 of the second node N2 varies following the variation of the power supply voltage Vcc. For this reason, the rising voltage of the current Id2, that is, the rising voltage of the load line of the fourth transistor Tr4 when the current Id2 begins to flow greatly fluctuates corresponding to the fluctuation range of the voltage V1 of the second node N2. On the other hand, since the gate-source voltage of the fourth transistor Tr4 is constant, the current Id2 flowing through the fourth transistor Tr4, which is a p-type MOSFET, is increased with respect to the increase of the drain-source voltage (V1-Vd2). The characteristic becomes saturated. Therefore, as shown in FIG. 2, the fluctuation of the output voltage Vd2 at the output node Nout, which is the intersection of the characteristics of the second transistor Tr2 and the fourth transistor Tr4, is larger than the fluctuation of the voltage V1 at the second node N2. Get smaller. Thus, even if noise is mixed in the power supply voltage Vcc and the voltage V1 of the second node N2 varies greatly, the variation of the output voltage Vd2 output to the output node Nout is small.

  As shown in FIG. 1, the transistor Tr5 of the next-stage circuit 5 not only increases the driving capability but also operates to further suppress fluctuations in the output voltage Vd2 and generate a stable driving voltage Vout. The transistor Tr5 of the next stage circuit 5 increases the drawing current Id3 from the power supply voltage wiring L2 when the output voltage Vd2 is to increase. As a result, the voltage drop at the resistor element R1 increases, the voltage V1 at the second node N2 decreases, and an increase in the output voltage Vd2 is suppressed. On the other hand, the transistor Tr5 of the next-stage circuit 5 reduces the drawing current Id3 from the power supply voltage wiring L2 when the output voltage Vd2 tends to decrease. As a result, the voltage drop at the resistance element R1 is reduced, the voltage V1 at the second node N2 is increased, and the decrease in the output voltage Vd2 is suppressed. As described above, the transistor Tr5 of the next-stage circuit 5 can be feedback controlled so as to suppress the fluctuation of the output voltage Vd2 by inserting the resistance element R1 between the first node N1 and the second node N2. it can. The next-stage circuit 5 can increase the driving capability and can suppress fluctuations in the output voltage Vd2 by feedback control. As a result, even if noise is mixed in the power supply voltage Vcc, the sensor drive circuit 1 can supply the sensor 100 with the drive voltage Vout in which the influence of noise is suppressed.

  As described above, in order to suppress the fluctuation of the output voltage Vd2 of the output node Nout, it is desirable to increase the load resistance with respect to the second transistor Tr2. For example, in order to increase the load resistance with respect to the second transistor Tr2, the shape ratio (L / W) of the gate length (L) and the gate width (W) of the fourth transistor Tr4 is set to the gate length (L ) And the gate width (W) shape ratio (L / W). As shown in FIG. 3, in order to increase the load resistance for the second transistor Tr2, a resistor element R2 may be inserted between the drain of the fourth transistor Tr4 and the second node N2. Alternatively, the load resistance for the second transistor Tr2 may be increased by combining these.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings can achieve a plurality of objects at the same time, and has technical usefulness by achieving one of the objects.

1: Sensor drive circuit 2: Constant current source 3: Differential pair transistor section 4: Active load transistor section 5: Next stage circuit 6: Internal power supply 100: Sensor L1: Reference voltage wiring L2: Power supply voltage wiring L3: Output voltage wiring N1: First node N2: Second node Nint: Intermediate node Nout: Output node R1: Resistance element Tr1: First transistor Tr2: Second transistor Tr3: Third transistor Tr4: Fourth transistor Tr5: Fifth transistor

Claims (5)

A sensor driving circuit for providing a driving voltage to the sensor,
A reference voltage wiring, a power supply voltage wiring, an output voltage wiring, a constant current source, a differential pair transistor section having first and second transistors, an active load transistor section having third and fourth transistors, and a fixed resistance element,
The constant current source, the first transistor, and the third transistor constitute a first series path that is connected in series between the reference voltage line and the power supply voltage line in this order,
The constant current source, the second transistor, and the fourth transistor constitute a second series path connected in series in this order between the reference voltage line and the power supply voltage line,
In the active load transistor section, the third transistor is diode-connected, and the control electrode of the third transistor and the control electrode of the fourth transistor are connected,
The fixed resistance element is inserted between a first node where the first series path is connected to the power supply voltage line and a second node where the second series path is connected to the power supply voltage line,
The output voltage wiring is connected to an output node between the second transistor and the fourth transistor ;
The sensor drive circuit, wherein the drive voltage provided to the sensor is generated based on an output voltage of the output voltage wiring .   The output voltage wiring is connected to the second node of the power supply voltage wiring and the output voltage wiring, and when the voltage of the output voltage wiring is about to increase, the current of the power supply voltage wiring is increased. The sensor drive circuit according to claim 1, further comprising a next-stage circuit configured to reduce a current of the power supply voltage wiring when the power is to be reduced.   The sensor drive circuit according to claim 2, wherein the next stage circuit is a source follower circuit. The first transistor and the second transistor are n-type MOSFETs,
The sensor driving circuit according to claim 1, wherein the third transistor and the fourth transistor are p-type MOSFETs.   5. The sensor drive circuit according to claim 1, wherein a bias voltage having the same phase is input to a control terminal of the first transistor and a control terminal of the second transistor. 6.

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