Driving circuit for voice coil motor having a first driver coupled to a first end of a coil and a second driver coupled to a second end of the coil
10141880 ยท 2018-11-27
Assignee
Inventors
Cpc classification
International classification
G02B27/64
PHYSICS
Abstract
With a driving current as I.sub.DRV, with a reference voltage as V.sub.REF, and with a gain as k, a current detection circuit generates a detection voltage V.sub.S represented by V.sub.S=V.sub.REF+kI.sub.DRV. An error amplifier amplifies a difference between the detection voltage V.sub.S and a control voltage that indicates a position of the VCM so as to generate an error voltage V.sub.ERR. A first driver switches the driving current I.sub.DRV between a source current and a sink current with respect to one end of the coil according to the error voltage V.sub.ERR. A second driver switches the driving current I.sub.DRV between a sink current and a source current with respect to the other end of the coil according to the error voltage V.sub.ERR. The driving circuit allows an external circuit to set the level of the reference voltage V.sub.REF.
Claims
1. A driving circuit that supplies a bi-directional driving current to a voice coil motor, the driving circuit comprising: a current detection circuit structured to generate a detection voltage V.sub.S represented by V.sub.S=V.sub.REF+kI.sub.DRV, with the driving current as I.sub.DRV, with a reference voltage as V.sub.REF, and with a gain as k; an error amplifier structured to amplify a difference between the detection voltage V.sub.S and a control voltage that indicates a position of the voice coil motor so as to generate an error voltage; a first driver having its output to be coupled to a first end of a coil of the voice coil motor, and structured to switch the driving current between a state in which the driving current flows as a source current and a state in which the driving current flows as a sink current according to the error voltage; and a second driver having its output to be coupled to a second end of the coil of the voice coil motor, and structured to switch the driving current between a state in which the driving current flows as a sink current and a state in which the driving current flows as a source current according to the error voltage, wherein a level of the reference voltage V.sub.REF is settable externally.
2. The driving circuit according to claim 1, wherein the current detection circuit comprises: a detection resistor arranged on a path of the driving current; a first operational amplifier; a first resistor arranged between a first input terminal of the first operational amplifier and a first end of the detection resistor; a second resistor arranged between a second input terminal of the first operational amplifier and a second end of the detection resistor; a third resistor arranged between an output terminal of the first operational amplifier and the first input terminal of the first operational amplifier; and a fourth resistor having one end connected to the second input terminal of the first operational amplifier and another end to which the reference voltage is applied.
3. The driving circuit according to claim 1, further comprising: a first D/A converter structured to convert, into the control voltage configured as an analog signal, digital control data that is received from an external processor and that indicates the position; and a second D/A converter structured to convert, into the reference voltage configured as an analog signal, correction data that is received from the external processor and that indicates the reference voltage.
4. The driving circuit according to claim 2, wherein the detection resistor is arranged between the first end of the coil and an output terminal of the first driver, or otherwise between the second end of the coil and an output terminal of the second driver.
5. The driving circuit according to claim 2, wherein an on resistance of a transistor that forms an output stage of the first driver and an on resistance of a transistor that forms an output stage of the second driver are used as the detection resistor.
6. The driving circuit according to claim 2, wherein a known DC resistance component of the voice coil motor is used as the detection resistor.
7. The driving circuit according to claim 1, wherein the error amplifier comprises: a second operational amplifier having a first input terminal to which the control voltage is input; a first capacitor arranged between a second input terminal and an output terminal of the second operational amplifier; and a fifth resistor having a first end connected to the second input terminal of the second operational amplifier and a second end to which the detection voltage V.sub.S is applied.
8. The driving circuit according to claim 1, wherein the first driver comprises a non-inverting amplifier that amplifies the error voltage with a predetermined common voltage as a reference voltage so as to apply a first driving voltage to the one end of the coil, and wherein the second driver comprises an inverting amplifier structured to amplify the error voltage with the common voltage as a reference voltage so as to apply a second driving voltage to the other end of the coil.
9. The driving circuit according to claim 1, wherein the first driver comprises: a first voltage-dividing circuit structured to divide, with a predetermined voltage division ratio, a voltage difference between a first output voltage that develops at the one end of the coil and a predetermined common voltage; and a first amplifier that comprises a first push-pull output stage including a high-side transistor and a low-side transistor, and structured to control the high-side transistor and the low-side transistor of the push-pull output stage such that the voltage obtained by voltage division by means of the first voltage-dividing circuit approaches to the error voltage, and wherein the second driver comprises: a second voltage-dividing circuit structured to divide, with a predetermined voltage division ratio, a voltage difference between a second output voltage that develops at the other end of the coil and the error voltage; and a second amplifier that comprises a second push-pull output stage including a high-side transistor and a low-side transistor, and structured to control the high-side transistor and the low-side transistor of the push-pull output stage such that the voltage obtained by voltage division by means of the second voltage-dividing circuit approaches to the common voltage.
10. A driving circuit that supplies a bi-directional driving current to a voice coil motor, the driving circuit comprising: a current detection circuit structured to generate a detection voltage V.sub.S that corresponds to the driving current; an error amplifier structured to amplify a difference between the detection voltage V.sub.S and a control voltage that indicates a position of the voice coil motor so as to generate an error voltage; a first driver having its output to be coupled to a first end of a coil of the voice coil motor, and structured to switch the driving current between a state in which the driving current flows as a source current and a state in which the driving current flows as a sink current according to the error voltage; and a second driver having its output to be coupled to a second end of the coil of the voice coil motor, and structured to switch the driving current between a state in which the driving current flows as a sink current and a state in which the driving current flows as a source current according to the error voltage, wherein the driving circuit is capable of superimposing a shift voltage that is settable by means of an external circuit on at least one of the control voltage and the detection voltage V.sub.S, and wherein the error amplifier generates the error voltage such that the control voltage approaches to the detection voltage after the shift voltage is superimposed on at least one of the control voltage and the detection voltage.
11. The driving circuit according to claim 10, wherein the current detection circuit generates a detection voltage V.sub.S represented by V.sub.S=V.sub.REF+kI.sub.DRV, with the driving current as I.sub.DRV, with a reference voltage as V.sub.REF, and with a gain as k, and wherein the level of the reference voltage V.sub.REF is settable according to correction data received from an external processor.
12. The driving circuit according to claim 10, wherein the control voltage is obtained by adding a shift voltage that corresponds to correction data received from an external processor to a voltage that corresponds to digital control data that indicates a position of the voice coil motor received from the external processor.
13. The driving circuit according to claim 10, wherein the control voltage is obtained as a voltage by adding correction data received from an external processor to, or otherwise by subtracting the aforementioned correction data from, digital control data that indicates a position of the voice coil motor received from the external processor, and by converting the digital value thus obtained into an analog voltage.
14. The driving circuit according to claim 10, further comprising an adder arranged as an upstream stage of the error amplifier, and structured to add a shift voltage that corresponds to correction data received from an external processor to, or otherwise subtracts the aforementioned correction data from, the detection voltage.
15. The driving circuit according to claim 10, wherein an offset voltage of the error amplifier is adjustable according to correction data received from an external processor.
16. The driving circuit according to claim 1, monolithically integrated on a single semiconductor substrate.
17. A lens module comprising: a focusing lens; a voice coil motor arranged such that a moving element thereof is coupled with the focusing lens; and the driving circuit according to claim 1, structured to drive the voice coil motor.
18. A lens module comprising: an image stabilization lens; a voice coil motor arranged such that a moving element thereof is coupled with the image stabilization lens; and the driving circuit according to claim 1, structured to drive the voice coil motor.
19. An electronic device comprising: the lens module according to claim 17; and an image acquisition element structured to acquire an image based on light that has passed through the lens module.
20. An electronic device comprising: the lens module according to claim 18; and an image acquisition element structured to acquire an image based on light that has passed through the lens module.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) Embodiments will now be described, by way of example only, with reference to the accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several Figures, in which:
(2)
(3)
(4)
(5)
DETAILED DESCRIPTION OF THE INVENTION
(6) The invention will now be described based on preferred embodiments which do not intend to limit the scope of the present invention but exemplify the invention. All of the features and the combinations thereof described in the embodiment are not necessarily essential to the invention.
(7) In the present specification, the state represented by the phrase the member A is connected to the member B includes a state in which the member A is indirectly connected to the member B via another member that does not substantially affect the electric connection therebetween, or that does not damage the functions or effects of the connection therebetween, in addition to a state in which the member A is physically and directly connected to the member B. Similarly, the state represented by the phrase the member C is provided between the member A and the member B includes a state in which the member A is indirectly connected to the member C, or the member B is indirectly connected to the member C via another member that does not substantially affect the electric connection therebetween, or that does not damage the functions or effects of the connection therebetween, in addition to a state in which the member A is directly connected to the member C, or the member B is directly connected to the member C.
(8)
(9) The lens module 502 is provided in order to provide a so-called autofocus function. The lens module 502 includes a focusing lens 512 and an actuator 510. The lens 512 is held such that it can be moved in the optical axis direction. The actuator 510 controls the position of the lens 512 according to an instruction value S1 received from the CPU 508.
(10) Light (an image) is input to the image acquisition element 504 after it has passed through the lens 512. The image processing processor 506 reads out the image data from the image acquisition element 504.
(11) The CPU 508 determines the target position to which the focusing lens 512 is to be set, based on the image read out by the image processing processor 506, such that the image that has passed through the focusing lens 512 forms an image on the image acquisition element 504. Furthermore, the CPU 508 outputs an instruction value S1 to the actuator 510 according to the target position thus determined.
(12) The above is the overall configuration of the electronic device 500. Next, description will be made regarding a specific configuration of the lens module 502.
(13)
(14) The lens module 502 includes a voice coil motor (VCM) 200 and a driving circuit 2.
(15) The VCM 200 is configured as an actuator that provides positioning of the focusing lens (512 in
(16) The driving circuit 2 includes output terminals OUT+ and OUT, a power supply terminal PVDD, a ground terminal PGND, and an interface terminal IF.
(17) A power supply voltage V.sub.DD is supplied to the power supply terminal PVDD. A ground voltage V.sub.GND is supplied to the ground terminal PGND. The interface terminal IF is connected to the external CPU 508 via a bus. The CPU 508 supplies, to the driving circuit 2, control data D.sub.CNT which indicates a stroke amount (target position, displacement) for the moving element of the VCM 200.
(18) A coil L1 of the VCM 200 to be driven is connected between the output terminals OUT+ and OUT. The driving circuit 2 supplies a bi-directional driving current I.sub.DRV to the coil L1 of the VCM 200 according to the control data D.sub.CNT, so as to control the position of the moving element. When the driving current I.sub.DRV that flows through the coil L1 is zero, the moving element comes to a stop at the predetermined reference position. When the driving current I.sub.DRV flows through the coil L1 in the positive direction, the position of the moving element is changed in the first direction according to the current value. Conversely, when the driving current I.sub.DRV flows through the coil L1 in the negative direction, the position of the moving element is changed in the second direction according to the current value. Description will be made in the present embodiment with the direction in which the driving current I.sub.DRV flows from the output terminal OUT+ to the output terminal OUT as the positive direction.
(19) The driving circuit 2 includes a current detection circuit 10, an error amplifier 20, a first driver 30, a second driver 40, a logic unit 50, a first D/A converter 52, a second D/A converter 54, and a buffer 56.
(20) The logic unit 50 includes an interface circuit that transmits and receives data or instructions between it and the CPU 508, and a register or the like that stores the data received from the CPU 508.
(21) The current detection circuit 10 detects the driving current I.sub.DRV that flows through the coil L1, and generates a detection voltage V.sub.S that corresponds to the driving current I.sub.DRV. The detection voltage V.sub.S is represented by the following Expression (2) using a gain k and a reference voltage V.sub.REF.
V.sub.S=V.sub.REF+kI.sub.DRV(2)
(22) For example, the current detection circuit 10 includes a detection resistor R.sub.NF, a first resistor R1, a second resistor R2, a third resistor R3, and a fourth resistor R4.
(23) The detection resistor R.sub.NF is arranged on a path of the driving current I.sub.DRV. For example, the detection resistor R.sub.NF is arranged between the second end of the coil L1 and the output terminal of the second driver 40. Alternatively, the detection resistor R.sub.NF may be arranged between the first end of the coil L1 and the output terminal of the first driver 30. A voltage drop V.sub.NF occurs at the detection resistor R.sub.FN in proportion to the driving current I.sub.DRV.
(24) The first resistor R1 is arranged between the first input terminal (inverting input terminal) of a first operational amplifier 12 and a first end E1 of the detection resistor R.sub.NF. The second resistor R2 is arranged between the second input terminal (non-inverting input terminal) of the first operational amplifier 12 and a second end E2 of the detection resistor R.sub.NF. The third resistor R3 is arranged between the output terminal and the first input terminal (inverting input terminal) of the first operational amplifier 12. The fourth resistor R4 is arranged such that its one end is connected to the second input terminal (non-inverting input terminal) of the first operational amplifier 12 and such that the reference voltage V.sub.REF is applied to its other end.
(25) In the following description, V1 represents an electric potential at the first end E1 of the detection resistor R.sub.NF, and V2 represents an electric potential at the second end E2 of the detection resistor R.sub.NF. When the relation (R1=R2=Ra) and the relation (R3=R4=Rb) hold true, the detection voltage V.sub.S is represented by the following Expression (3).
V.sub.S=V.sub.REF+Rb/Ra(V2V1)(3)
(26) By substituting Expression (3) into Expression (4), Expression (5) is obtained.
V.sub.NF=V2V1=R.sub.NFI.sub.DRV(4)
V.sub.S=V.sub.REF+Rb/RaR.sub.NFI.sub.DRV(5)
(27) Thus, the gain k of the current detection circuit 10 is represented by (Rb/RaR.sub.NF).
(28) It should be noted that the configuration of the current detection circuit 10 is not restricted to such a configuration shown in
(29) The first D/A converter 52 converts the control data D.sub.CNT, which is received by the logic unit 50 from the CPU 508, into an analog control voltage V.sub.CNT. The control voltage V.sub.CNT indicates a target stroke amount to be applied to the moving element of the VCM 200.
(30) The driving circuit 2 according to the present embodiment is configured to allow an external circuit to set the level of the reference voltage V.sub.REF. Specifically, the logic unit 50 is configured to receive, from the CPU 508, correction data D.sub.REF that indicates the reference voltage V.sub.REF. The second D/A converter 54 converts the correction data D.sub.REF received by the logic unit 50 into the analog reference voltage V.sub.REF.
(31) The error amplifier 20 amplifies a difference between the control voltage V.sub.CNT that indicates the position value for the voice coil motor and the detection voltage V.sub.S so as to generate an error voltage V.sub.ERR. For example, the error amplifier 20 may be configured as an integrator. For example, the error amplifier 20 includes a second operational amplifier 22, a first capacitor C1, and a fifth resistor R5.
(32) The control voltage V.sub.CNT is input to the first input terminal (non-inverting input terminal) of the second operational amplifier 22. The first capacitor C1 is arranged between the second input terminal (inverting input terminal) and the output terminal of the second operational amplifier 22. The fifth resistor R5 is arranged such that its first end is connected to the second input terminal (inverting input terminal) of the second operational amplifier 22, and such that the detection voltage V.sub.S is applied to its second end.
(33) It should be noted that the configuration of the error amplifier 20 is not restricted to such an arrangement shown in
(34) The first driver 30 is connected to one end of the coil L1 of the voice coil motor 200. The first driver 30 switches the driving current I.sub.DRV according to the error voltage V.sub.ERR, between a state in which the driving current I.sub.DRV flows as a source current and a state in which the driving current I.sub.DRV flows as a sink current.
(35) The second driver 40 operates with the reverse phase of the first driver 30. The second driver 40 is connected to the other end of the coil L1 of the voice coil motor 200. Furthermore, the second driver 40 switches the driving current I.sub.DRV according to the error voltage V.sub.ERR, between a state in which the driving current I.sub.DRV flows as a sink current and a state in which the driving current I.sub.DRV flows as a source current.
(36) The buffer 56 outputs a predetermined common voltage V.sub.COM. The first driver 30 includes a non-inverting amplifier that performs amplification without inversion of the error voltage V.sub.ERR with the common voltage V.sub.COM as a reference voltage, and that applies a first driving voltage V.sub.O+ to the first end of the coil L1. In contrast, the second driver 40 includes an inverting amplifier that performs amplification with inversion of the error voltage V.sub.ERR with the common voltage V.sub.COM as a reference voltage, and that applies, to the second end of the coil L1, a second driving voltage V.sub.O having the reverse phase of the first driving voltage V.sub.O+.
(37) More specifically, the first driver 30 includes a first voltage-dividing circuit 32 and a first amplifier 34. The first voltage-dividing circuit 32 includes resistors R11 and R12, and divides the voltage difference between the first output voltage V.sub.O+ at the first end of the coil L1 and the predetermined common voltage V.sub.COM using a predetermined voltage division ratio. The first amplifier 34 includes a push-pull output stage comprising a high-side transistor MH and a low-side transistor ML. The first amplifier 34 controls the high-side transistor MH and the low-side transistor ML included in its push-pull output stage such that a voltage V.sub.FB+ obtained by the first voltage-dividing circuit 32 approaches to the error voltage V.sub.ERR.
(38) The second driver 40 includes a second voltage-dividing circuit 42 and a second amplifier 44. The second amplifier 44 includes resistors R21 and R22, and divides the voltage difference between the second output voltage V.sub.O at the second end of the coil L1 and the error voltage V.sub.ERR using a predetermined voltage division ratio. The second amplifier 44 includes a push-pull output stage comprising a high-side transistor MH and a low-side transistor ML. The second amplifier 44 controls the high-side transistor MH and the low-side transistor ML included in its push-pull output stage such that a voltage V.sub.FB obtained by the second voltage-dividing circuit 42 approaches to the common voltage V.sub.COM.
(39) The above is the configuration of the driving circuit 2. Next, description will be made regarding the operation thereof.
(40) Description will be made assuming that the control data D.sub.CNT output from the CPU 508 is configured as 10-bit data having a value ranging between 0x000(0) and 0x3FF (1023). As shown in
V.sub.CNT=V.sub.H(X/1023)
(41) The driving circuit 2 generates the driving voltages V.sub.O+ and V.sub.O by means of a feedback loop including the error amplifier 20 such that the detection voltage V.sub.S matches the control voltage V.sub.CNT.
(42) As described above, the detection voltage V.sub.S is represented by Expression (3). Thus, the driving current I.sub.DRV is feedback controlled so as to approach a target value represented by the following Expression.
I.sub.DRV=(V.sub.CNTV.sub.REF)/k.
(43) The control voltage V.sub.CNT is supplied in a voltage range between 0 and V.sub.H. Thus, the maximum value I.sub.MAX of the driving current I.sub.DRV is represented by I.sub.DRV=(V.sub.HV.sub.REF)/k, and the minimum value I.sub.MIN is represented by I.sub.DRV=V.sub.REF/k. The width of the range of the driving current I.sub.DRV, which is represented by I=I.sub.MAXI.sub.MIN, is also represented by V.sub.H/k, which is a constant value regardless of the reference voltage V.sub.REF.
(44) That is to say, with the driving circuit 2 shown in
(45) The driving circuit 2 is configured to be capable of setting the reference voltage V.sub.REF to be supplied to the current detection circuit 10, according to the reference data D.sub.REF received from the CPU 508 configured as an external component. The reference voltage V.sub.REF is required to have only a low resolution as compared with the control voltage V.sub.CNT. Accordingly, the number of bits of the second D/A converter 54 may be on the order of 8 bits. In this case, the reference data D.sub.REF is configured as 8-bit data.
(46) With the reference data D.sub.REF in decimal notation as Y, the reference voltage V.sub.REF is represented by the following Expression.
V.sub.REF=V.sub.HY/255V.sub.H(4Y)/1023
(47) That is to say, when the control data D.sub.CNT is equal to a value obtained by multiplying the reference data D.sub.REF by 4 (obtained by bit shifting the reference data D.sub.REF by 2 bits toward the upper bit side), the driving current I.sub.DRV becomes zero.
(48)
(49) The maximum value I.sub.MAX and the minimum value I.sub.MIN of the driving current I.sub.DRV are represented by the following Expressions.
I.sub.MAX=I/1023(1023(Y4))
I.sub.MIN=I/1023(Y4)
(50) The above is the operation of the driving circuit 2.
(51) With the driving circuit 2, such an arrangement is capable of setting the ratio between the negative driving current I.sub.MIN and the positive driving current I.sub.MAX to a desired value. This allows a common driving 2 circuit to drive various kinds of VCMs 200. Also, such an arrangement allows various kinds of platforms to employ such a common driving circuit 2 to drive the VCM 200.
(52) The driving circuit 2 is capable of setting the minimum driving current I.sub.MIN to 0 mA, or otherwise of setting the maximum driving current I.sub.MAX to 0 mA. That is to say, such an arrangement is capable of generating the driving current I.sub.DRV in only one direction. Thus, the driving circuit 2 can be employed as a driving circuit for the spring return method. That is to say, by employing such a common driving circuit 2, such an arrangement allows the user to operate a given platform regardless of whether the platform employs a bi-directional driving method or a spring return method. Such an arrangement provides reduced design time.
(53) Next, description will be made regarding a specific example of an electronic device 500.
(54) With the aforementioned driving circuit 2, changing the reference voltage V.sub.REF is equivalent to superimposing, on the detection voltage V.sub.S, a shift voltage that can be set by means of an external circuit. Furthermore, the same effect can be provided by superimposing, on the control voltage V.sub.CNT instead of the detection voltage V.sub.S, a shift voltage that can be set by means of an external circuit. By extending this idea, the following technical idea can be derived.
(55) That is to say, the driving circuit 2 may be configured to be capable of superimposing a shift voltage, which can be set by means of an external circuit, on at least one from among the control voltage V.sub.CNT and the detection voltage V.sub.S. Furthermore, the error amplifier 20 may preferably generate the error voltage V.sub.ERR such that the control voltage V.sub.CNT is equal to the detection voltage V.sub.S after a shift voltage is superimposed on at least one from among the control voltage V.sub.CNT and the detection voltage V.sub.S.
(56) Thus, by adjusting the value of the shift voltage, such an arrangement is capable of freely setting the range in which the driving current I.sub.DRV can be set according to the control voltage V.sub.CNT. This technical idea includes the following specific embodiments.
(57) 1. A shift voltage that can be set according to correction data received from an external circuit is superimposed on (is added to or otherwise subtracted from) the detection voltage V.sub.S. This embodiment includes the following techniques.
(58) 1.1 The reference voltage V.sub.REF is configured as a variable voltage. This technique has been described in the embodiment.
(59) 1.2 An analog adder/subtractor unit is provided as an upstream stage of the error amplifier 20, so as to add the shift voltage that corresponds to the correction data D.sub.REF to, or otherwise to subtract the shift voltage from, the detection voltage V.sub.S. Furthermore, the output voltage of the analog adder/subtractor unit is output to the error amplifier 20.
(60) 2. A shift voltage that can be set according to correction data received from an external circuit is superimposed on (is added to or otherwise subtracted from) the control voltage V.sub.CNT. This embodiment includes the following techniques.
(61) 2.1 An analog adder/subtractor unit is arranged between the error amplifier 20 and the first D/A converter 52 so as to add a shift voltage that corresponds to the correction data D.sub.REF to, or otherwise to subtract the shift voltage from, the control voltage V.sub.CNT. Furthermore, the output voltage of the analog adder/subtractor unit is output to the error amplifier 20.
(62) 2.2 Digital calculation is performed on the control data D.sub.CNT and the correction data D.sub.REF, each configured as digital data, so as to generate a digital value. The digital value thus obtained is D/A converted by means of the first D/A converter 52 into an analog value. The analog value thus converted is supplied to the error amplifier 20.
(63) 3. The input offset voltage of the error amplifier 20 (second operational amplifier 22) is configured as a variable voltage. Furthermore, the offset voltage of the error amplifier 20 is adjusted according to the correction data received from an external processor.
(64) Description has been made regarding the present invention with reference to the embodiments. The above-described embodiments have been described for exemplary purposes only, and are by no means intended to be interpreted restrictively. Rather, it can be readily conceived by those skilled in this art that various modifications may be made by making various combinations of the aforementioned components or processes, which are also encompassed in the technical scope of the present invention. Description will be made below regarding such modifications.
Modification 1
(65) Description has been made in the embodiment regarding an arrangement in which the first driver 30 and the second driver 40 provide linear driving of the VCM 200. However, the VCM 200 may be PWM driven. That is to say, the first driver 30 and the second driver 40 may generate pulse driving voltages V.sub.O+ and V.sub.O, respectively. Furthermore, the first driver 30 and the second driver 40 may adjust the duty ratios of the driving voltages V.sub.O+ and V.sub.O, respectively, according to the error voltage V.sub.ERR.
Modification 2
(66) Description has been made in the embodiment regarding an arrangement in which the detection resistor R.sub.NF is arranged between the second driver 40 (first driver 30) and the coil L1. However, the position of the detection resistor R.sub.NF is not restricted to such a position. The detection resistor R.sub.NF may be arranged in series with the high-side transistor MH between the output terminal OUT+(OUT) and the power supply line. Also, the detection resistor R.sub.NF may be arranged in series with the low-side transistor ML between the output terminal OUT+ (OUT) and the ground line. Also, the on resistances of the transistors (MH, ML) that form an output stage of the first driver 30 and/or the on resistances of the transistors (MH, ML) that form an output stage of the second driver 40 may be used as the detection resistor R.sub.NF.
(67) Also, in a case in which the DC resistance component (parasitic resistance) of the VCM 200 is a known value, the DC resistance component may be used as the detection resistor R.sub.NF. The voltage across both ends of the VCM 200 is represented by the sum of the voltage drop that occurs at the resistance component and the back electromotive force that occurs across the inductance L1. Thus, the current detection circuit 10 may eliminate the back electromotive force that occurs at the coil L1 from the voltage across both ends of the VCM 200, so as to detect the voltage drop that occurs at the resistance component. Such a current detection circuit may be configured using known techniques.
Modification 3
(68) Description has been made in the embodiment regarding an arrangement in which the CPU 508 supplies the digital control data D.sub.CNT and the digital reference data D.sub.REF. However, the present invention is not restricted to such an arrangement. For example, at least one pin is provided to the driving circuit 2 in order to allow the reference voltage V.sub.REF to be set. Specifically, the reference voltage V.sub.REF may be set according to a combination of pins (which indicates high-level voltage, low-level voltage, or otherwise high impedance). Also, the driving circuit 2 may receive, from an external circuit, the reference voltage V.sub.REF configured as an analog signal.
Modification 4
(69) Description has been made in the embodiment regarding a lens module for focusing. However, the usage of the driving circuit 2 is not restricted to such an application. For example, the VCM 200 may drive a lens employed for image stabilization.
(70) While the preferred embodiments of the present invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the appended claims.