JP2014095977A - Constant current driving circuit and constant current driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a constant current driving circuit and a constant current driving method that drivingly control a Hall element so that a current supplied to the Hall element has no variance.SOLUTION: A current driving unit 10 which supplies driving currents to a plurality of loads respectively on the basis of a reference current Ic includes: an amplifier 4 which has first and second input terminals and output terminals; a first transistor element NMC which has an input terminal connected to the first input terminal of the amplifier and a reference current generation part and a control terminal connected to the output terminal of the amplifier; a plurality of second transistor elements NM1 and NM2 which have input terminals connected to the plurality of loads respectively and also connected to the second input terminals of the amplifier and control terminals connected to the output terminal of the amplifier, and are paired with the first transistor element; and a plurality of voltage holding parts C1 and C2 which are connected to the control terminals of the plurality of second transistor elements respectively.

Description

  The present invention relates to a constant current driving circuit and a constant current driving method, and more particularly, to a constant current driving circuit and a constant current driving method for driving and controlling a Hall element so that a current flowing through the Hall element does not vary.

In general, the Hall element is a magnetoelectric conversion element using the Hall effect, and is widely used as various magnetic sensors and magnetic switches for detecting the position and rotation of a small precision brushless motor. This Hall effect is obtained by attaching input terminals I ₁ and I ₂ and output terminals O ₁ and O ₂ to a sensing part of a Hall element H having a thickness d made of a suitable semiconductor, and applying an input control voltage Ic from a power source Os. When a magnetic field having a magnetic flux density B is applied perpendicularly to the sensitive surface from the outside through the input terminals I ₁ and I ₂ , a potential difference (Hall voltage) V _H is generated between the output terminals O ₁ and O ₂ . There is a relationship of V _H = R _H / d · Ic · B (R _H is the Hall coefficient).
There are two types of driving methods for this type of Hall element: a constant current driving method and a constant voltage driving method. In the case of the constant current driving method, the Hall voltage V _H is expressed by the above-described equation, a constant current is supplied as the control current Ic, and the temperature characteristic of V _H depends on the temperature characteristic of R _H.

FIG. 1 is a configuration diagram of a constant current driving circuit for a Hall element using a conventional current mirror circuit, and is a circuit for driving a plurality of Hall elements at a constant current. The Hall element HE has a bridge resistance, and the V _HE increases as the current flowing through the Hall element is increased. The upper part of the Hall element is fixed at the reference voltage VREF in order to eliminate the dependency of the power supply voltage VDD. The magnitude of the reference voltage VREF is VDD> VREF. In order to pass a constant current through the Hall element, an NMOS for passing a current through the current mirror circuit is disposed below the Hall element. When the impedance of the Hall element is R _H , the drain voltage of the NMOS is VREF−R _H · I. When the drain voltage of the NMOS decreases, the NMOS becomes a linear region, the current mirror operation is not performed, and a constant current cannot be supplied.

When the power supply voltage VDD decreases, the reference voltage VREF also needs to be decreased. Since _RH • I is fixed, the drain voltage of the NMOS decreases, and a constant current cannot flow.
In order to solve this problem, for example, a current drive circuit described in Patent Document 1 has been proposed.
FIG. 2 is a configuration diagram of the constant current driving circuit for the Hall element disclosed in Patent Document 1. In FIG. This patent document 1 relates to a current drive circuit that drives and controls a plurality of white LEDs used as a backlight of a color liquid crystal display so that they all emit light uniformly. There are a plurality of circuits in parallel, and each current drive circuit supplies a current at an arbitrary ratio between the drain-source voltage of one transistor element and a reference current that flows a mirrored reference current from a current IREF that flows in a constant current generation circuit. By having a differential amplifier circuit for making the voltage between the drain and source of the other transistor element to flow the same, a uniform current can be mirrored to a plurality of MOS transistors, and the brightness of the current generating element of each current driving circuit can be increased. All are configured to be uniform.

  Further, for example, the one described in Patent Document 2 relates to a two-wire magnetic switch circuit using a constant current drive Hall element, and the Hall element is driven by a constant current by a constant current source. Further, for example, the one disclosed in Patent Document 3 relates to a motor Hall element abnormality protection circuit using a Hall element as a magnetic pole sensor, and is a Hall element for driving the Hall element as a motor magnetic pole sensor at a constant current. A control circuit is provided.

JP 2006-237382 A JP-A-8-17311 JP-A-8-47287

  However, the method disclosed in Patent Document 1 described above is a very useful method in a circuit that allows a constant current to flow even when the power supply voltage VDD decreases, but when driving a plurality of Hall elements, There is a problem that the current flowing through the Hall element varies due to the necessity of the number of control amplifiers AM, the current error having a plurality of current sources Ic, and the offset of the amplifiers.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a constant current driving circuit and a constant current driving method for driving and controlling a Hall element so as not to cause variations in current flowing through the Hall element. Is to provide.

  The present invention has been made to achieve such an object, and the invention according to claim 1 is a constant drive control for the plurality of loads so as not to cause variations in currents flowing through the plurality of loads. The current drive circuit includes a reference current generator (3) that generates a reference current (Ic), and a current driver (10) that supplies drive currents to the plurality of loads based on the reference current (Ic). The current driver (10) includes an amplifier (4) having first and second input terminals and an output terminal, and the input terminal is the first input terminal of the amplifier (4) and the reference current generator. A first transistor element (NMC) connected to (3) and having a control terminal connected to an output terminal of the amplifier (4); an input terminal connected to each of the plurality of loads; and the amplifier Second entry of (4) A plurality of second transistor elements (NM1, NM2,...) Connected to the terminal, having a control terminal connected to the output terminal of the amplifier (4) and paired with the first transistor element (NMC); A plurality of voltage holding portions (C1, C2...) Connected to the control terminals of the plurality of second transistor elements (NM1, NM2...), Respectively.

  The invention according to claim 2 is the invention according to claim 1, wherein the input terminals of the plurality of second transistor elements (NM1, NM2,...) And the second input of the amplifier (4). A plurality of first switches (SW11, SW12...) Connecting the terminals, a control terminal of the plurality of second transistor elements (NM1, NM2...), And an output terminal of the amplifier (4). And a plurality of second switches (SW12, SW22...) For connecting the two.

Further, according to a third aspect of the present invention, in the first or second aspect of the present invention, a third switch (SW13, SW23...) Is connected in parallel to each of the plurality of voltage holding units. It is characterized by that.
According to a fourth aspect of the present invention, in the first, second, or third aspect of the invention, the voltage holding unit is a capacitor.

The invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein the load is a Hall element.
According to a sixth aspect of the present invention, in the constant current driving method in the constant current driving circuit according to any one of the first to fifth aspects, the first step of obtaining a power-down state and the first Hall element side A second step of obtaining an adjustment state of the second, a third step of obtaining an adjustment state of the second Hall element side, and supplying a constant current to the first Hall element and the second Hall element to generate a magnetic field. A fourth step of obtaining a magnetic field measurement state to be measured, and the plurality of Hall elements are driven with a constant current by repeating the first to fourth steps.

  According to a seventh aspect of the invention, in the sixth aspect of the invention, in the first step, the reference voltage circuit (5), the current source (Ic), and the amplifier (4) are in a power-down state. The third switch (SW13, SW23) is on and the first and second switches (SW11, SW12, SW21, SW22) are off. In the second step, the reference voltage circuit (5) And the current source (Ic) and the amplifier (4) are in an operating state, and the first and second switches (SW11, SW12) and the third other switch (SW23) are on, The first and second other switches (SW21, SW22) and the third one switch (SW13) are off, and in the third step, the reference voltage circuit (5) and the current source (I ) And the amplifier (4) are in an operating state, the first and second other switches (SW21, SW22) are on, and the first and second switches (SW11, SW12) and the third switch Switch (SW13, SW23) is off, and in the fourth step, the reference voltage circuit (5) is in an operating state, the current source (Ic) and the amplifier (4) are in a power-down state, The first to third switches (SW11 to SW23) are off.

  According to the present invention, even if the power supply voltage VDD is lowered, a desired constant current is allowed to flow, since the current source and the control amplifier are common, there is no variation in the current value to be driven. Therefore, it is possible to realize a constant current driving circuit and a constant current driving method for controlling the driving of the Hall element so that the current flowing through the Hall element does not vary.

It is a block diagram of the constant current drive circuit of the Hall element using the conventional current mirror circuit. 1 is a configuration diagram of a constant current driving circuit for a Hall element disclosed in Patent Document 1. FIG. It is a circuit block diagram for demonstrating embodiment of the constant current drive circuit which concerns on this invention. It is a circuit block diagram for demonstrating the Example of the constant current drive circuit which concerns on this invention. It is a figure which shows the sequence of the constant current drive in the constant current drive circuit of this invention. FIG. 6 is a circuit state diagram showing a power-down state, and shows a period T0 in FIG. FIG. 6 is a circuit state diagram showing an adjustment state on the first Hall element (HE1) side, and shows a period T1 in FIG. FIG. 6 is a circuit state diagram showing an adjustment state on the second Hall element (HE2) side, and shows a period T2 in FIG. FIG. 6 is a circuit state diagram showing a magnetic field measurement state, and shows a period T3 in FIG.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 3 is a circuit configuration diagram for explaining an embodiment of a constant current driving circuit according to the present invention. In the figure, reference numeral 1 denotes a first Hall element (HE1) as a load, 2 denotes a second Hall element (HE2) as a load, 3 denotes a constant current source, 4 denotes a control amplifier (AM), and 5 denotes Reference voltage (VREF) circuit, 10 is a current driver, NMC is a first transistor, NM1, NM2,... Are a plurality of second transistors, and SW11 to SW22 are switches (SW).

The constant current drive circuit of the present embodiment is a circuit that drives a plurality of Hall elements 1 and 2 as a plurality of loads with a constant current, and is a circuit that allows a constant current to flow even when the power supply voltage VDD decreases. The current flowing through the Hall elements 1 and 2 as a plurality of loads is not varied.
That is, the constant current drive circuit of the present invention is a constant current drive circuit that drives and controls a plurality of loads so that current flowing through the plurality of loads does not vary, and the reference current generator 3 that generates the reference current Ic And a current drive unit 10 for supplying drive currents to a plurality of loads based on the reference current Ic.

  The current driver 10 includes an amplifier 4 having first and second input terminals and an output terminal, an input terminal connected to the first input terminal of the amplifier 4 and the reference current generator 3, and a control terminal connected to the amplifier 4. The first transistor element NMC connected to the output terminal and the input terminal of the first transistor element NMC are connected to the plurality of loads, and the second input terminal of the amplifier 4 is connected, and the control terminal is the output terminal of the amplifier 4 And a plurality of second transistor elements NM1 and NM2 paired with the first transistor element NMC, and a plurality of voltage holding units respectively connected to control terminals of the plurality of second transistor elements NM1 and NM2. C1 and C2.

In addition, a plurality of first switches SW11 and SW12 that connect input terminals of the plurality of second transistor elements NM1 and NM2 and a second input terminal of the amplifier 4, and a plurality of second transistor elements NM1 and NM2 are connected. A plurality of second switches SW12 and SW22 for connecting the control terminal and the output terminal of the amplifier 4 are provided.
The third switches SW13 and SW23 are connected in parallel to each of the plurality of voltage holding units.

  SWs are arranged at the drain and gate terminals of NMOSs (NM1, NM2) that drive the Hall elements 1 and 2, and capacitances (CAP) C1 and C2 are arranged at the gates. The control amplifier 4 is used similarly to Patent Document 1 described above to control the current to flow through the Hall element (SW is in the ON state). When the current value is determined, turn off SW. Since the capacitances C1 and C2 arranged at the gate of the NMOS hold the gate voltage for driving the NMOS, a desired current flows. This operation is similarly performed for a plurality of Hall elements.

  FIG. 4 is a circuit configuration diagram for explaining an embodiment of the constant current driving circuit according to the present invention, and shows a case where two Hall elements are used as a load and constant current driving is performed by an NMOS. In addition, the same code | symbol is attached | subjected to the component which has the same function as FIG. In FIG. 3, there are a plurality of Hall elements, whereas in FIG. 4, there are only two Hall elements. Further, SW13 and SW23 are provided in parallel with the capacitances C1 and C2.

  FIG. 5 is a diagram showing a constant current drive sequence in the constant current drive circuit of the present invention. As apparent from FIG. 5, the power-down state is shown in the T0 period, the adjustment state on the first Hall element (HE1) side is shown in the T1 period, and the second Hall element (HE2) side is shown in the T2 period. In the T3 period, the magnetic field measurement state is shown. Note that the state of each period is repeated as the period elapses.

  The constant current driving method of the present invention is a constant current driving method in the constant current driving circuit described above, a first step for obtaining a power-down state, a second step for obtaining an adjustment state on the first Hall element side, A third step of obtaining an adjustment state on the second Hall element side, and a fourth step of obtaining a magnetic field measurement state in which a constant current is supplied to the first Hall element and the second Hall element to measure a magnetic field. By repeating these first to fourth steps, the plurality of Hall elements are driven with constant current.

In the first step, the reference voltage circuit 5, the current source Ic, and the amplifier 4 are in a power-down state, the third switches SW13 and SW23 are on, and the first and second switches SW11, SW12, SW21, and SW22 are off. In the second step, the reference voltage circuit 5, the current source Ic, and the amplifier 4 are in an operating state, the first and second switches SW11 and SW12, and the third other switch SW23 are on, The first and second other switches SW21 and SW22 and the third one switch SW23 are off, and in the third step, the reference voltage circuit 5, the current source Ic, and the amplifier 4 are in the operating state, and the first and second switches The other two switches SW21 and SW2 are on, and the first and second switches SW11 and SW12 and the third switches SW13 and SW23 are off. In a fourth step, the reference voltage circuit 5 operating state, the current source Ic and the amplifier 4 is in a power-down state, the first to third switches SW11 to SW23 is off.
Below, each state mentioned above is demonstrated one by one.

<T0 period> (Power-down state)
FIG. 6 is a circuit state diagram showing the power-down state, and shows the period T0 in FIG. The VREF circuit, current source Ic, and control amplifier AM are in a power-down state, SW11, SW12, SW21, and SW22 are in an OFF state, and SW13 and SW23 are in an ON state. The A1 signal and the A2 signal are VSS (the charge holding capacitances C1 and C2 are in a discharge state).

<T1 period> (adjustment state on the first Hall element (HE1) side)
FIG. 7 is a circuit state diagram showing an adjustment state on the first Hall element (HE1) side, and shows a period T1 in FIG. The VREF circuit, current source Ic, and control amplifier AM are in an operating state, SW11 and SW12 are in an ON state, SW13 is in an OFF state, SW21 and SW22 are in an OFF state, and SW23 is in an ON state.
The B1 signal is determined by VREF-R _H · I. The control amplifier AM operates so that the BC signal becomes the same as the B1 signal. The AC signal and the A1 signal are connected by SW and are the gate voltages of MOSNMC and MOSNM1. Since the BC signal = B1 signal and the AC signal = A1 signal, the current flowing through the MOSNM1 is the same as that of the MOSNMC. The gate of the MOSNM1 has a charge holding capacitance C1, and the charge of the A1 signal is charged. The A2 signal remains at VSS.

<T2 period> (Adjustment state on the second Hall element (HE2) side)
FIG. 8 is a circuit state diagram showing an adjustment state on the second Hall element (HE2) side, and shows a period T2 in FIG. The VREF circuit, current source Ic, and control amplifier AM are in an operating state, SW11 and SW12 are in an OFF state, SW13 is in an OFF state, SW21 and SW22 are in an ON state, and SW23 is in an OFF state.
The B2 signal is determined by VREF-R _H · I. The control amplifier AM operates so that the BC signal becomes the same as the B2 signal. The AC signal and the A2 signal are connected by SW and are the gate voltages of MOSNMC and MOSNM2. Since the BC signal = B2 signal and the AC signal = A2 signal, the current flowing through the MOSNM2 is the same as that of the MOSNMC. The gate of the MOSNM2 has a charge holding capacitance C2, and the charge of the A2 signal is charged. The A1 signal keeps the charge charged in the charge holding capacitance C1 in the previous state.

<T3 period> (magnetic field measurement state)
FIG. 9 is a circuit state diagram showing the magnetic field measurement state, and shows the period T3 in FIG. The VREF circuit is in an operating state, the current source Ic and the control amplifier AM are in a power-down state, SW11 and SW12 are in an OFF state, SW13 is in an OFF state, SW21 and SW22 are in an OFF state, and SW23 is in an OFF state.
The charge holding capacitances C1 and C2 are charged with charges necessary for flowing a constant current through the respective MOSNM1 and NM2, and a desired current can be passed through the hall elements HE1 and HE2. In this state, the magnetic field is measured. (The signals of VHE1 and VHE2 are processed by a subsequent circuit.)
By repeating the above-described T0 to T3, the two Hall elements can be driven with a constant current. These states are shown in Table 1 below.

In the constant current driving circuit of the present invention, since the current source IC and the control amplifier AM are common, there is no current variation. Since the circuit operation is the same as that of Patent Document 1 described above, a desired constant current can flow even if VDD is lowered.
In the present embodiment, an example in which two Hall elements are driven has been described. However, the number of Hall elements that can be driven is not limited. Further, in this embodiment, an example of constant current driving with NMOS has been described. However, it is obvious that the driving MOS can be realized with PMOS. Further, the example in which the constant current driven element is a MOS has been described, but it is obvious that the element can be realized by other than the MOS. Further, the constant current driving circuit and the constant current driving method of the present invention can be applied to driving a sensor or LED using a bridge resistor other than the Hall element.

1 First Hall element (HE1)
2 Second Hall element (HE2)
3 Constant current source 4 Control amplifier (AM)
5 Reference voltage (VREF) circuit 10 Current drive unit

Claims (7)

In the constant current drive circuit that controls the drive of the plurality of loads so that the currents flowing to the plurality of loads do not vary,
A reference current generator for generating a reference current; and a current driver for supplying drive currents to the plurality of loads based on the reference current,
The current driver is
An amplifier having first and second input terminals and an output terminal;
A first transistor element having an input terminal connected to the first input terminal of the amplifier and the reference current generator, and a control terminal connected to the output terminal of the amplifier;
A plurality of input terminals connected to the plurality of loads, connected to the second input terminal of the amplifier, connected to the output terminal of the amplifier, and paired with the first transistor element. A second transistor element of
And a plurality of voltage holding units respectively connected to the control terminals of the plurality of second transistor elements.   A plurality of first switches that connect input terminals of the plurality of second transistor elements and a second input terminal of the amplifier; a control terminal of the plurality of second transistor elements; and an output terminal of the amplifier; The constant current drive circuit according to claim 1, further comprising a plurality of second switches for connecting the two.   The constant current drive circuit according to claim 1, wherein a third switch is connected in parallel to each of the plurality of voltage holding units.   The constant current drive circuit according to claim 1, wherein the voltage holding unit is a capacitor.   The constant current drive circuit according to claim 1, wherein the load is a Hall element. In the constant current drive method in the constant current drive circuit according to any one of claims 1 to 5,
A first step of obtaining a power-down state, a second step of obtaining an adjustment state on the first Hall element side, a third step of obtaining an adjustment state on the second Hall element side, and the first hall And a fourth step of obtaining a magnetic field measurement state in which a constant current is supplied to the element and the second Hall element to measure the magnetic field,
A constant current driving method, wherein the plurality of Hall elements are driven with constant current by repeating the first to fourth steps. In the first step, a reference voltage circuit, a current source, and an amplifier are in a power-down state, the third switch is on, and the first and second switches are off,
In the second step, the reference voltage circuit, the current source, and the amplifier are in an operating state, the first and second switches and the third other switch are on, and the first and second switches are on. The other switch of 2 and the third switch are off,
In the third step, the reference voltage circuit, the current source, and the amplifier are in an operating state, the first and second other switches are on, the first and second one switches, and the first step 3 switch is off,
7. The fourth step according to claim 6, wherein, in the fourth step, the reference voltage circuit is in an operating state, the current source and the amplifier are in a power-down state, and the first to third switches are off. Constant current drive method.

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