# Patent

## Title
Motor driving circuit

## Abstract

A motor driving circuit may include a Hall sensor configured to generate a Hall signal according to the position of a rotor of a motor to be driven; a Hall bias circuit; an analog amplifier configured to amplify the Hall signal; an A/D converter configured to convert the Hall signal into a digital signal; an amplitude control circuit configured to adjust the amplitude of the digital signal; a control signal generating unit configured to generate a control signal to be used to drive the motor; and a driver circuit configured to drive the motor according to the control signal. The components may be monolithically integrated on a single semiconductor substrate. The amplitude control circuit may include an amplitude correction circuit; and a target amplitude judgment circuit configured to adjust the gain of the analog amplifier.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a motor driving apparatus.
2. Description of the Related Art
As a cooling fan motor, a spindle motor configured to rotationally drive an optical or a magnetic disk, or a capstan motor employed in a tape recording apparatus, a DC motor is employed. Typical DC motors each include a rotor having a permanent magnet and a stator having a coil. By controlling electric current to be supplied to the coil, such a DC motor is rotationally driven.
In order to detect the rotational position of the rotor of the DC motor, a Hall sensor (Hall element) is employed. Such a Hall sensor generates a pair of Hall signals that change in a complementary manner according to the position of the rotor of the motor (which will be collectively referred to simply as a “Hall signal”). Hall sensor mounting motors are known including a Hall sensor mounted on a stator.
A motor driving circuit switches the polarity of the driving voltage to be supplied to the coil based upon the Hall signal, and uses the Hall signal to generate a control signal for controlling a regeneration period. In a case in which such a Hall signal has a sine waveform or a trapezoidal waveform according to change in the magnetic polarity of the rotor, the motor driving circuit is capable of gradually changing the driving voltage and the magnetic polarity to be applied to the coil using the change in the voltage of the Hall signal detected before and after each switching timing, thereby providing reduced motor driving noise. Such an arrangement is also referred to as “soft switching”.
RELATED ART DOCUMENTS
Patent Documents
[Patent document 1]


    Japanese Patent Application Laid Open No. 2005-224100


However, such a Hall sensor has temperature characteristics such that the amplitude of the Hall signal decreases at a low temperature or increases at a high temperature. Furthermore, the Hall signal is subject to the effects of irregularities in gaps between the Hall sensor and the rotor, irregularities in such Hall sensors themselves, irregularities in circuits, and its environment. Accordingly, in a case in which such a Hall signal is used to perform a timing control operation for driving a motor, such an arrangement can lead to a problem of fluctuation in the regeneration period, a problem in that the Hall signal has an insufficient amplitude to handle a comparator, and so forth. In order to solve such a problem, manufacturers of Hall sensor mounting motors must perform selection of Hall sensors, and must perform a gap control operation giving consideration to the Hall sensors.
SUMMARY OF THE INVENTION
The present invention has been made in view of such a situation. It is an exemplary purpose of an embodiment of the present invention to provide a motor driving technique configured to be resistant to the effects of irregularities in Hall sensors.
A motor driving circuit according to an embodiment of the present invention comprises: a Hall sensor configured to generate a Hall signal which comprises a first signal and a second signal that are complementary, according to the position of a rotor of a motor to be driven; a Hall bias circuit configured to supply a Hall bias signal to the Hall sensor; an analog amplifier configured to amplify the Hall signal; a target amplitude judgment circuit configured to adjust the gain of the analog amplifier so as to change the amplitude of the Hall signal to be amplified; a control signal generating unit configured to generate a control signal to be used to drive the motor, based upon the Hall signal amplified by the analog amplifier; and a driver circuit configured to drive the motor according to the control signal. The aforementioned components are monolithically integrated on a single semiconductor substrate.
With such an embodiment, by adjusting the gain of the analog amplifier configured to amplify the Hall signal, such an arrangement is capable of stabilizing the amplitude of the signal to be input to the control signal generating unit, thereby allowing the motor to be appropriately driven.
Another embodiment of the present invention also relates to a motor driving circuit. The motor driving circuit comprises: a Hall sensor configured to generate a Hall signal which comprises a first signal and a second signal that are complementary, according to the position of a rotor of a motor to be driven; a Hall bias circuit configured to supply a Hall bias signal to the Hall sensor; an analog amplifier configured to amplify the Hall signal; a target amplitude judgment circuit configured to adjust the Hall bias signal so as to change the amplitude of the Hall signal to be amplified; a control signal generating unit configured to generate a control signal to be used to drive the motor, based upon the Hall signal amplified by the analog amplifier; and a driver circuit configured to drive the motor according to the control signal. The aforementioned components are monolithically integrated on a single semiconductor substrate.
With such an embodiment, by adjusting the bias signal to be applied to the Hall sensor, such an arrangement is capable of stabilizing the amplitude of the signal to be input to the control signal generating unit, thereby allowing the motor to be appropriately driven.
Yet another embodiment of the present invention relates to a cooling apparatus. The cooling apparatus comprises: a fan motor; and a driving circuit according to any one of the aforementioned embodiments, configured to drive the fan motor.
Yet another embodiment of the present invention relates to an electronic device. The electronic device comprises: a processor; and the aforementioned cooling apparatus configured to cool the aforementioned processor.
It is to be noted that any arbitrary combination or rearrangement of the above-described structural components and so forth is effective as and encompassed by the present embodiments.
Moreover, this summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features.



BRIEF DESCRIPTION OF THE DRAWINGS
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:
FIG. 1 is a circuit diagram which shows a configuration of an electronic device including a driving IC according to a first embodiment;
FIG. 2 is a circuit diagram which shows a configuration of an offset correction circuit;
FIG. 3 is a waveform diagram which shows the operation of the offset correction circuit;
FIGS. 4A and 4B are circuit diagrams each showing an example configuration of an amplitude correction circuit shown in FIG. 1;
FIGS. 5A through 5F are circuit diagrams showing the respective blocks of the driving IC shown in FIG. 1;
FIGS. 6A through 6C are circuit diagrams each showing a configuration of a driving IC according to a second embodiment;
FIG. 7 is a circuit diagram which shows a part of a configuration of a driving IC according to a third embodiment;
FIG. 8 is a graph which shows a PWM control operation of the driving IC shown in FIG. 7;
FIG. 9 is a circuit diagram which shows an example configuration of a PWM instruction logic conversion circuit;
FIGS. 10A and 10B are graphs each showing the operation of the PWM instruction logic conversion circuit shown in FIG. 9;
FIG. 11 is a block diagram which shows a configuration of a cooling apparatus employing a driving IC according to a fourth embodiment;
FIG. 12 is a circuit diagram which shows a modification of the driving IC shown in FIG. 11;
FIG. 13 is a circuit diagram which shows a configuration of a driving IC according to a fifth embodiment;
FIG. 14 is a circuit diagram which shows a part of a modification of the driving IC shown in FIG. 13; and
FIG. 15 is a diagram which shows a further generalized configuration of the driving IC shown in FIG. 13.



DETAILED DESCRIPTION OF THE INVENTION
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.
First Embodiment
FIG. 1 is a circuit diagram which shows a configuration of an electronic device 1 including a driving IC 100 according to a first embodiment. The electronic device 1 is configured as a desktop computer, a laptop computer, a workstation, a game device, an audio device, a video device, or the like, for example, and includes a cooling apparatus 2 and a CPU (Central Processing Unit) 4. The cooling apparatus 2 includes a fan motor 6 arranged such that it faces the CPU 4, and a driving IC 100 configured to drive the fan motor 6.
The driving IC 100 is configured as a function IC integrated on a single semiconductor chip. The driving IC 100 is connected to a Hall sensor 8 arranged at a position at which it receives the magnetic field from the rotor of the fan motor 6, in addition to being connected to the fan motor 6 to be driven. A Hall bias voltage VHB is applied to the Hall sensor 8. The Hall sensor 8 generates a Hall signal comprising a complimentary first signal S1 (H+) and second signal S2 (H−) according to the position of the rotor of the fan motor 6. The Hall sensor 8 may be configured as a built-in component of the driving IC 100.
The driving IC 100 includes a first A/D converter ADC1, a second A/D converter ADC2, a differential conversion circuit 14, an offset correction circuit 16, an amplitude control circuit 18, a control signal generating unit 24, and a driver circuit 26.
The driving IC 100 receives the first signal S1 and the second signal S2 from the Hall sensor 8 via Hall input terminals HP and HN, respectively. The first A/D converter ADC1 and the second A/D converter ADC2 respectively perform analog/digital conversion of the first signal S1 and the second signal S2 of the Hall signal, so as to generate a third signal S3 (SHP) and a fourth signal S4 (SHN) in the form of digital signals.
The downstream signals of the first A/D converter ADC1 and the second A/D converter ADC2 are each configured as 8-bit binary data, for example. The differential conversion circuit 14 generates a single-ended fifth signal S5 according to the difference between the third signal S3 and the fourth signal S4. The differential conversion circuit 14 is configured as a digital subtractor.
In a case in which there is no offset of the Hall signal H+ and H−, the fifth signal S5 has a waveform which repeatedly alternates between a positive state and a negative state with the zero point as the center. However, if there is such an offset, the fifth signal S5 has a waveform that swings with the offset value as the center, leading to adverse effects on the downstream operation. Specifically, this leads to a problem in that each switching timing at which the driving phase of the fan motor 6 is to be switched cannot be detected normally, and a problem in that each period for which a soft switch driving operation is to be performed in order to switch the phase cannot be detected normally. In order to solve such a problem, the offset correction circuit 16 performs digital signal processing so as to correct the offset of the fifth signal S5, thereby generating a sixth signal S6.
FIG. 2 is a circuit diagram which shows a configuration of the offset correction circuit 16. The offset correction circuit 16 includes an offset correction circuit 50 and an offset amount control unit 52. The offset correction circuit 50 is configured as a digital adder/subtractor, and is configured to shift the fifth signal S5 by summing the fifth signal S5 and a correction amount ΔCMP or by subtracting the correction amount ΔCMP from the fifth signal S5, and outputs the resulting signal as the sixth signal S6. The offset amount control unit 52 generates data that indicates the correction amount ΔCMP based upon the sixth signal S6.
FIG. 3 is a waveform diagram which shows an operation of the offset correction circuit 16. FIG. 3 shows a sixth signal S6 when such an offset has not been completely canceled out. A sampling unit 54 included in the offset amount control unit 52 performs data sampling of a value DPEAK at a timing T1 in the vicinity of the peak of the sixth signal S6, and performs data sampling of a value DBOTTOM at a timing T2 in the vicinity of the bottom of the sixth signal S6. Such a sampling operation is performed at least once for every peak and every bottom of the sixth signal S6. With the offset correction circuit 16 shown in FIG. 1, data sampling is performed multiple times, e.g., four times, for every peak and every bottom of the sixth signal S6. A timing detection circuit 90 detects a timing at which the sampling unit 54 is to perform a sampling operation, and outputs a timing control signal S90 which indicates the timings T1 and T2 thereof.
The cycle of the Hall signal H+ and H− changes over time according to the rotational speed of the fan motor 6. Accordingly, in an operation for acquiring the amplitude of the Hall signal H+ and H−, the timings T1 and T2 of the occurrence of the peak and the bottom of the sixth signal S6 change according to the rotational speed. Accordingly, the timing detection circuit 90 is required to have a function for detecting the timings T1 and T2 according to the rotational speed.
For example, the timing detection circuit 90 may include a counter, a calculation unit, a latch circuit, and a comparator. The counter measures the period of the fifth signal, the period of the sixth signal that corresponds to the fifth signal, or the period of the seventh signal. The calculation unit multiples the count value that corresponds to the period thus measured by a coefficient that corresponds to a desired timing, and instructs the latch circuit to store the value thus calculated. The comparator may assert a timing signal every time the count value of the counter reaches the value held by the latch circuit.
The offset amount control unit 52 determines the correction amount ΔCMP based upon the peak values DPEAK and the bottom values DBOTTOM thus sampled. Specifically, the integrator 56 is configured to sequentially sum the peak values DPEAK and the bottom values DBOTTOM. The correction amount determining unit 58 outputs a correction amount ΔCMP that corresponds to the sum result X. For example, the correction amount determining unit 58 determines the correction amount ΔCMP as a value obtained by multiplying the sum result X by a predetermined coefficient, e.g., a gain G= 1/10. In a case in which the predetermined coefficient is set to 2n, the correction amount determining unit 58 may be configured as a bit shifter circuit.
The integrator 59 integrates the correction amount ΔCMP, and outputs the resulting value to the offset correction circuit 50.
The offset correction circuit 16 calculates the offset of the input signal S5, and has a feedback loop configured to subtract the offset thus calculated such that the offset of the output signal becomes zero. An integrator 59 having an integrating function is included in the feedback loop. The offset calculation is executed once per cycle of the electrical angle of the Hall sensor. Accordingly, the cycle of the electrical angle of the Hall sensor matches the sampling frequency at which the integrator 59 operates. The offset correction circuit 16 demonstrates the characteristics of a high-pass filter.
If the offset of the Hall signal is zero, the sum total X of the data thus sampled is zero. In a case in which there is a positive offset of the Hall signal H+ and H−, the sum total X results in a positive value. In a case in which there is a negative offset of the Hall signal H+ and H−, the sum total X results in a negative value.
For example, let us consider a case in which there is a positive offset of the Hall signal H+ and H−. In this case, let us say that the peak value has been sampled four times, with the peak values being DPEAK 10, 10, 10, and 10, and that the bottom value has been sampled four times, with the bottom values being DBOTTOM−5, −5, −5, and −5. In this case, the data sum total X is 10×4−5×4=20. Thus, the correction amount ΔCOMP is represented by a value obtained by multiplying the sum total 20 by 1/10, i.e., 2. The offset correction circuit 50 subtracts the correction amount ΔCOMP=2 from the fifth signal S5. The output X of the integrator 56 is reset for every cycle of the Hall signal.
The offset correction circuit 16 repeatedly performs such an operation for every cycle of the Hall signal, thereby providing an offset-free sixth signal S6 with zero as the center.
Returning to FIG. 1, the amplitude control circuit 18 stabilizes the amplitude of the sixth signal S6 to a predetermined target value REF, and generates the absolute value thereof so as to generate a seventh signal S7. FIG. 1 shows an arrangement in which an amplitude correction circuit configured to stabilize the amplitude and an absolute value circuit 22 configured to generate the absolute value are connected in series in this order. The order of the amplitude stabilization operation and the absolute value generating operation is not restricted in particular. Accordingly, the absolute value circuit 22 may be arranged upstream of the amplitude correction circuit 20.
FIGS. 4A and 4B are circuit diagrams each showing an example configuration of the amplitude correction circuit 20 shown in FIG. 1. The amplitude correction circuits 20a and 20b shown in FIGS. 4A and 4B are each configured as a multiply-add calculation unit including a digital multiplier 30 and a coefficient control unit 32, and are each configured to perform an automatic gain control operation (AGC).
The digital multiplier 30 multiplies an input signal S30 thereof by a variable coefficient K. The coefficient control unit 32 compares the amplitude A of an output signal S32 of the digital multiplier 30 with the target value REF. When the amplitude A is greater than the target value REF, the coefficient control unit 32 reduces the variable coefficient K by ΔK. When the amplitude A is smaller than the target value REF, the coefficient control unit 32 raises the variable coefficient K by Δk.
The coefficient control unit 32a shown in FIG. 4A includes an amplitude detection unit 34, a digital subtractor 36, a sign judgment unit 38, a digital adder 40, and a delay circuit 42. The amplitude detection unit 34 samples the value of the signal S32 at either a peak timing or a bottom timing of the waveform of the output signal S32 of the digital multiplier 30, or otherwise at both timings thereof, and generates amplitude data S34 which represents the amplitude of the output signal S32 of the digital multiplier 30. The sampling timing may be indicated by a timing control signal S90 generated by the aforementioned timing detection circuit 90.
The digital subtractor 36 generates an eighth signal S8 (=REF−A) which represents the difference between the amplitude A of the output signal S32 of the digital multiplier 30 and the target value REF. The sign judgment unit 38 outputs a positive or negative predetermined value Δk according to the sign of the eighth signal S8. Specifically, when the sign of the eighth signal S8 is positive, i.e., when REF>A, the sign judgment unit 38 outputs a positive predetermined value Δk (e.g., +1). When the sign of the eighth signal S8 is negative, i.e., when REF<A, the sign judgment unit 38 outputs a negative predetermined value Δk (e.g., −1). It should be noted that, when the amplitude A is equal to the target value REF, i.e., the difference therebetween is zero, the predetermined value Δk may be set to any one of 0, +1, and −1.
The digital adder 40 generates the sum of the predetermined value Δk output from the sign judgment unit 38 and the variable coefficient K. The delay circuit 42 delays the output data S40 of the digital adder 40 by one sampling time, and outputs the resulting data to the digital adder 40 and the digital multiplier 30.
With such a configuration shown in FIG. 4A, such an arrangement is capable of changing the coefficient in increments of constant steps Δk according to the magnitude relation between the amplitude A and the target value REF. Thus, the system converges to a state in which the amplitude A matches the target value REF. That is to say, such an arrangement is capable of stabilizing the amplitude A to a constant value.
Also, an arrangement may be made in which the target value REF is divided by the value of the input signal S30 of the digital multiplier 30, and the input signal S30 is amplified with a gain that corresponds to the division result, whereby the amplitude of the output signal S32 of the digital multiplier 30 can be made to match the target value REF. However, such a method requires a division operation. The amplitude correction circuit 20 according to the embodiment is capable of maintaining the amplitude without involving such a division operation. Thus, such an arrangement has an advantage of a reduced circuit area in comparison with an arrangement employing a divider.
By selecting a suitable value as the target value REF, such an arrangement provides a coefficient control unit 32 having a further simplified configuration. Specifically, the target value REF is preferably set to a value configured as binary data, with all the lower m bits being set to 1 or 0. In other words, the target value is preferably set to a boundary value immediately before a carry or borrow occurs.
FIG. 4B shows an arrangement in which the target value REF is set to [01000000] (the lower six bits are set to all-zero) or [00111111] (the lower six bits are set to all-one), i.e., an arrangement in which the target value REF is set to approximately half the positive full scale of the amplitude A. The coefficient control unit 32b shown in FIG. 4B includes a calculation unit 44 instead of the digital subtractor 36 and the sign judgment unit 38 shown in FIG. 4A.
The calculation unit 44 outputs the positive or negative predetermined value Δk based upon a predetermined bit (lower (m+1)-th bit) of the data S34 that represents the amplitude A of the output signal S32 of the digital multiplier 30. The calculation unit 44 monitors the upper two bits A[7:6] of the amplitude A. When A[7:6] matches “01”, the calculation unit 44 outputs Δk=−1. When A[7:6] matches “00”, the calculation unit 44 outputs Δk=+1. With such an arrangement, the most significant bit (lower (m+2)-th bit) is redundant. Thus, the calculation unit 44 may generate a predetermined value Δk based upon only the lower (m+1)-th bit, i.e., A[6].
If the target value REF is assumed to be “01000000”, when REF=A, the calculation unit 44 outputs Δk=+1. If the target value REF is assumed to be “00111111”, when REF=A, the calculation unit 44 outputs Δk=−1.
As described above, by selecting a particular desired value as the target value REF, such an arrangement is capable of controlling the coefficient K using only a bit comparison operation. Thus, such an arrangement provides a simplified circuit configuration of the amplitude correction circuit 20 in comparison with an arrangement shown in FIG. 4A.
Returning to FIG. 1, the control signal generating unit 24 receives the seventh signal S7 from the amplitude control circuit 18, and generates a control signal SCNT (S60, S64) based upon the seventh signal S7 thus received. For example, the control signal generating unit 24 includes an FG signal generating unit 60, a pulse modulator 64, and a calculation unit 68.
The FG signal generating unit 60 generates a control signal (which will also be referred to as the “FG signal”) which is set to a first level (e.g., high level) during the first half period of the Hall signal, and to a second level (e.g., low level) during the second half period thereof. For example, the FG signal generating unit 60 switches the level of the control signal S60 every time the seventh signal S7 straddles a threshold value TH0 in the vicinity of zero point.
It should be noted that, in a case in which there is a need to detect the switching between the driving period and the regeneration period, such an arrangement may include a regeneration period detection comparator configured to compare the seventh signal S7 with a predetermined threshold value THI. With such an arrangement, the output signal of the regeneration period detection comparator is set to the first level (low level) during the regeneration period, and is set to the second level (high level) during the driving period.
The calculation unit 68 is arranged upstream of the pulse modulator 64. The calculation unit 68 multiples the seventh signal S7 by a duty ratio control signal SDUTY which represents a duty ratio for when the fan motor 6 is to be PWM driven, i.e., the rotational speed of the fan motor 6.
For example, the pulse modulator 64 generates the control pulse signal S64 having a duty ratio that corresponds to the level of the seventh signal S7′. For example, the pulse modulator 64 includes a PWM comparator and an oscillator. The oscillator generates a cyclic signal having a triangle waveform or a sawtooth waveform. The oscillator may be configured as a digital counter, for example. The frequency of the control pulse signal S64 is preferably set to be higher than the audible band in order to prevent the occurrence of unpleasant audible noise that can be recognized by the user of the electronic device 1, and, specifically, is preferably set to be 20 kHz or more. Giving consideration to irregularities in the circuit, the frequency of the control pulse signal S64 is preferably set to be double the aforementioned frequency, i.e., on the order of 50 kHz or more. The PWM comparator compares the seventh signal S7′ having an amplitude that has been adjusted by the calculation unit 68 with a cyclic signal so as to generate the control pulse signal S64 that has been subjected to pulse-width modulation.
The configuration of the pulse modulator 64 is not restricted in particular. The pulse modulator 64 may be configured using a counter, for example.
The driver circuit 26 drives the fan motor 6 according to the control signal SCNT (S60, S64). The driver circuit 26 includes a logic unit 26a, a pre-driver circuit 26b, and an H-bridge circuit 26c, for example. The configuration of the driver circuit 26 is not restricted in particular. Also, the driver circuit 26 may be configured using the same circuit as that of a driver IC configured as a conventional analog circuit.
The driver circuit 26 alternately selects either a pair of oppositely positioned switches M1 and M4 or a pair of oppositely positioned switches M2 and M3 according to the level of the FG signal S60. In the regeneration period, the driver circuit 26 performs PWM driving (soft switching) of the selected switch pair of the H-bridge circuit according to the control pulse signal S64. Furthermore, in the driving period, the driver circuit 26 performs PWM driving of the fan motor 6, with a duty ratio that corresponds to the target torque.
The above is the configuration of the driving IC 100. Next, description will be made regarding the operation thereof.
FIGS. 5A through 5F are waveform diagrams which show the operations of the respective blocks of the driving IC 100 shown in FIG. 1. As shown in FIG. 5A, the offset of the fifth signal S5 is corrected by the offset correction circuit 16. Subsequently, as shown in FIG. 5B, the amplitude control circuit 18 performs a correction operation such that the amplitude of the sixth signal S6 matches the target value REF. Subsequently, as shown in FIG. 5C, the amplitude correction circuit 20 generates the absolute value of the sixth signal S6, thereby generating the seventh signal S7.
The FG signal generating unit 60 generates the FG signal S60 shown in FIG. 5D based upon the seventh signal S7. As shown in FIGS. 5E and 5F, the pulse modulator 64 generates the control pulse signal S64 subjected to pulse-width modulation by comparing the seventh signal S7′ with the cyclic signal S66, for example.
There is a difference in the amplitude of the seventh signal S7′ between a case shown in FIG. 5E and a case shown in FIG. 5F. FIG. 5E shows a case in which the duty ratio control signal SDUTY is set to 1 (i.e., to 100%). FIG. 5F shows a case in which the duty ratio control signal SDUTY is set to be smaller than 1. It can be understood that the amplitude of the seventh signal S7′ changes according to the change in the value of the duty ratio control signal SDUTY, and the duty ratio of the control pulse signal S64 changes according to the change in the amplitude of the seventh signal S7′.
The driver circuit 26 drives the fan motor 6 according to the control signal SCNT (S60, S64). With the driving IC 100 shown in FIG. 1, by converting the Hall signal S1 and S2 into digital data, by canceling out the offset of the Hall signal, and by performing amplitude correction, such an arrangement is capable of driving the fan motor 6 while reducing the effects of irregularities in the Hall sensor, and so forth.
Also, the driving IC 100 can be configured as a digital circuit. Thus, with such an arrangement, the circuit can be miniaturized by means of a semiconductor manufacturing process, thereby providing the advantage of chip shrink as compared with a case in which the driving IC 100 is configured as an analog circuit. Thus, such an arrangement provides such a driving IC 100 having a reduced size and with reduced costs. Furthermore, such an arrangement performs a digital signal operation, thereby providing an advantage of being resistant to effects of irregularities in circuit elements as compared with conventional driving ICs configured as an analog circuit.
Typical driving ICs configured as an analog circuit amplify the Hall signal H+ and H− with a high gain in order to reduce the effects of the offset of the Hall signal H+ and H− or to reduce the effects of irregularities in the amplitude thereof. This leads to distortion of the peak and the bottom of a signal (which will be indicated by “S7*”) that corresponds to the seventh signal shown in FIG. 1, as indicated by the line of dashes and dots shown in FIG. 5E, which results in the signal S7* having a waveform similar to a trapezoidal waveform. The signal S7* has an excessively steep slope in each phase switching period. Accordingly, it is difficult to gradually change the duty ratio of a signal that corresponds to the control pulse signal S64 as shown in FIG. 5E.
In contrast, with the driving IC 100 shown in FIG. 1, the duty ratio of the control pulse signal S64 can be gradually changed. Thus, such an arrangement is capable of smoothly switching the phase, thereby reducing noise that occurs in the fan motor 6.
Second Embodiment
Description will be made in the second embodiment regarding a rotational driving control operation for the fan motor 6 according to the temperature or an external control signal. FIGS. 6A through 6C are circuit diagrams each showing a configuration of a driving IC 100 according to the second embodiment.
In FIG. 6A through 6C, the same circuit blocks as those shown in FIG. 1 are not shown as appropriate. FIG. 6A is a circuit diagram which shows a configuration of a driving IC 100a configured to perform a rotational driving control operation according to the temperature.
The driving IC 100a includes a thermistor terminal TH, a third A/D converter ADC3, and a control instruction circuit 72.
The thermistor terminal TH is connected to a thermistor RTH biased by a reference voltage VREF. The thermistor terminal TH receives, as an input signal, an analog temperature detection voltage VTH that corresponds to the temperature. The third A/D converter ADC3 performs analog/digital conversion of the temperature detection signal VTH so as to generate a ninth signal S9 (STH) configured as a digital signal that corresponds to the temperature. According to the ninth signal S9, the control instruction circuit 72 generates a tenth signal S10 which indicates the duty ratio to be used to perform PWM driving. As the temperature becomes higher, the value of the tenth signal S10 also becomes higher, and as the temperature becomes lower, the value of the tenth signal S10 also becomes lower. The tenth signal S10 is a signal that corresponds to the duty ratio control signal SDUTY shown in FIG. 1. The tenth signal S10 is input to the calculation unit 68 included in the control signal generating unit 24.
As a result, the control pulse signal S64 generated by the control signal generating unit 24 is subjected to pulse width modulation according to the temperature. The driver circuit 26 performs a PWM driving operation for the fan motor 6 according to the control pulse signal S64, i.e., according to the tenth signal S10.
With the driving IC 100a shown in FIG. 6A, such an arrangement is capable of raising the rotational speed of the fan motor 6 according to an increase in the temperature, thereby appropriately cooling the CPU 4.
FIG. 6B is a circuit diagram which shows a configuration of a driving IC 100b configured to perform a rotational speed control operation according to an external duty ratio control voltage. The duty ratio control voltage VDUTY has a level that corresponds to the duty ratio to be used to perform PWM driving of the fan motor 6, i.e., a level that corresponds to the target value of the rotational speed. The duty ratio control voltage VDUTY is input to a duty ratio control terminal DUTY.
A fourth A/D converter ADC4 performs analog/digital conversion of the duty ratio control voltage VDUTY so as to generate an eleventh signal S11 configured as a digital signal. According to the eleventh signal S11, the control instruction circuit 78 generates a twelfth signal S12 which represents the duty ratio to be used to perform PWM driving.
With the driving IC 100b shown in FIG. 6B, such an arrangement is capable of controlling the rotational speed of the fan motor 6 according to the external control voltage VDUTY. Thus, such an arrangement provides a flexible platform to the designer of the cooling apparatus 2.
FIG. 6C is a circuit diagram which shows a configuration of a driving IC 100c configured to perform a rotational speed control operation according to the temperature and an external duty ratio control voltage. The driving IC 100c shown in FIG. 6C has a configuration obtained by combining the configurations of the driving ICs 100a and 100b shown in FIGS. 6A and 6B. Based upon both the ninth signal S9 and the eleventh signal S11, a control instruction combining circuit 80 generates a thirteenth signal S13 which represents the duty ratio to be used to perform PWM driving. With the driving IC 100c shown in FIG. 6C, such an arrangement is capable of controlling the rotational speed of the fan motor 6 based upon the control voltage VDUTY and the temperature.
Third Embodiment
In some cases, heat generation of a CPU to be cooled, the temperature thereof, the thermal runaway threshold voltage thereof, and so on, differ for each CPU. Accordingly, the rotational speed of the cooling fan is preferably set in a flexible manner according to the target to be cooled. Description will be made in the third embodiment regarding a technique for providing a flexible rotational speed control operation.
FIG. 7 is a circuit diagram which shows a part of a configuration of a driving IC 100d according to a third embodiment
The driving IC 100d shown in FIG. 7 includes a PWM pulse signal input terminal PWM instead of the duty ratio control terminal DUTY shown in FIGS. 6B and 6C. An external PWM signal PWM subjected to pulse width modulation is input to the PWM pulse signal input terminal PWM. The driving IC 100 performs PWM driving of the fan motor 6 according to the duty ratio of the external PWM signal. The duty ratio of the external PWM signal PWM is set in a range of 0 to 100%.
The driving IC 100d performs a PWM driving operation for the fan motor 6 according to the duty ratio of the external PWM signal PWM and the temperature temp. FIG. 8 is a graph which shows a PWM control operation of the driving IC 100d shown in FIG. 7. In FIG. 8, the horizontal axis represents the duty ratio (input duty ratio DUTYIN) of the external PWM signal, and the vertical axis represents the duty ratio (output duty ratio DUTYOUT) of the PWM driving operation.
As shown in FIG. 8, when the input duty ratio is lower than the minimum duty ratio MINDUTY, the driving IC 100d drives the fan motor 6 with a minimum duty ratio MINDUTY. When the input duty ratio DUTYIN is higher than the minimum duty ratio MINDUTY, the output duty ratio DUTYOUT is raised according to the slope α, which is determined by the temperature. The slope α is set as follows.

temp>TUPPER  (1)

α0=1

temp<TLOWER  (2)

αn=(MIN100P−MINDUTY)/(100−MINDUTY)

TLOWER≦temp≦TUPPER  (3)

The slope αk in this range is switched in a stepwise manner, such as n=16 levels, for example, according to the temperature temp. That is to say, αk is represented by the Expression αk=(α0−αn)/n×k.
Returning to FIG. 7, the driving IC 100d receives analog voltages that indicate MIN100P, MINDUTY, TLOWER/and TUPPER.
The driving IC 100d includes a reference power supply 114, A/D converters ADC3, and ACD5 through ADC7, a PWM instruction logic conversion circuit 116, and a control instruction combining circuit 80.
The reference power supply 114 generates a reference voltage VREF, and outputs the reference voltage VREF thus generated via a reference voltage terminal REF. The reference voltage VREF is divided by external resistors R2, R3, and R4, so as to generate a thermistor control minimum output duty setting voltage VMINT and a PWM control minimum output duty setting voltage VMINP. The thermistor control minimum output duty setting voltage VMINT and the PWM control minimum output duty setting voltage VMINP thus generated are input to a thermistor control minimum output duty setting input terminal MINT and a PWM control minimum output duty setting input terminal MINP, respectively. The reference voltage VREF is divided by internal resistors R10 and R11, thereby generating a reference voltage VREF′.
The A/D converters ADC5 through ADC7 respectively perform analog/digital conversion of the voltages VREF′, and VMIP, so as to generate data signals SREF, SMINT, SMINP and SSS. Adder-subtractors ADD10 through ADD12 respectively subtract the data SREF from the data signals SMINT, SMINP, STH, and STSS, so as to shift these data signals, thereby generating data signals MIN100P, MIN_DUTY, and temp.
The PWM instruction logic conversion circuit 116 generates a data signal SPWM which indicates a value that corresponds to the duty ratio of the external PWM signal. The PWM instruction logic conversion circuit 116 converts the PWM signal having a duty ratio of 0 to 100% into an L-bit signal S. For example, in a case in which L=7, the 0 to 100% duty ratio is converted into a digital value of 0 to 127.
The control instruction combining circuit 80 generates a duty ratio control signal SDUTY based upon the control data SPWM, the data signals MIN100P, MIN_DUTY, and temp.
The control instruction combining circuit 80 includes a slope calculation unit 141, a first calculation unit 142, a second calculation unit 143, a third calculation unit 144, a sign judgment unit 145, and a selector 146.
The slope calculation unit 141 calculates the slope a based upon the aforementioned rules.
The first calculation unit 142 subtracts MIN_DUTY from the data SPWM. The second calculation unit 143 multiples the output data of the first calculation unit 142, i.e., (SPWM−MIN_DUTY) by the slope α. The third calculation unit 144 generates the sum of MIN_DUTY and α×(SPWM−MIN_DUTY).
The sign judgment unit 145 judges the sign of the calculation result obtained by the first calculation unit 142, i.e., (SPWM−MIN_DUTY). When the sign is positive, i.e., when SPWM>MINDUTY, the selector 146 selects the data α×(SPWM−MIN_DUTY)+MIN_DUTY input via the input (0). When the sign is negative, the selector 146 selects the data MIN_DUTY input via the input (1). The output data SDUTY of the selector 146 is output to a pulse modulator.
With the driving IC 100d shown in FIG. 7, such an arrangement is capable of appropriately controlling the rotational speed of the fan motor 6 based upon the external PWM signal PWM and the temperature according to the characteristics shown in FIG. 8. Specifically, by means of a digital control operation, such an arrangement is capable of independently setting the minimum rotational speed of the fan motor 6 and the temperature dependence of the rotational speed thereof.
FIG. 9 is a circuit diagram which shows a configuration of the PWM instruction logic conversion circuit 116. The PWM instruction logic conversion circuit 116 includes a level conversion circuit 150 and a digital filter 152.
The high level of the external PWM signal PWM is converted into 1, and the low level thereof is converted into 0. In order to provide such an operation, the external PWM signal may be input to a CMOS as an input signal. The level conversion circuit 150 multiples the external PWM signal converted into a 1/0 binary signal by a coefficient 2L. When L=7, the external 1/0 PWM signal is converted into a 128/0 signal, and the resulting signal is input to the digital filter 152 arranged as a downstream component.
The digital filter 152 is configured as a first-order IIR (Infinite Impulse Response) low-pass filter, and includes a fourth calculation unit 153, a delay circuit 154, and a fifth calculation unit 156, arranged in series.
The delay circuit 154 has a bit width (L+n), and delays the output data of the fourth calculation unit 153 by a delay time TCLK in synchronization with the clock signal CLK having the predetermined period TCLK.
The fourth calculation unit 153 multiples the output data of the delay circuit 154 by a coefficient 2−n. The constant n determines the frequency characteristics of the low-pass filter. The fifth calculation unit 156 and the fifth calculation unit 156 may each be configured as a bit shifter configured to bit-shift the input data.
The fourth calculation unit 153 generates the sum of the output data of the level conversion circuit 150 and the output data of the delay circuit 154, subtracts the output data of the fifth calculation unit 156 from the resulting data, and outputs the calculation result to the delay circuit 154.
FIGS. 10A and 10B are graphs each showing an operation of the PWM instruction logic conversion circuit shown in FIG. 9. FIG. 10A shows the data signal SPWM when the external PWM signal has a duty ratio of 50%. The gain (responsiveness) of the feedback loop and the ripple in the data signal SPWM, change according to change in the filtering coefficient n.
Description will be made regarding the frequency fCLK of the clock signal CLK. In a case in which the duty ratio of the external PWM signal is converted into an L-bit signal, the duty ratio is preferably converted with 1⁄2L precision or lower. For example, in a case in which the duty ratio of the external PWM signal is converted into an L=7−bit signal (0-127), the duty ratio is preferably converted with precision of 1/128 (approximately 1% precision) or lower. Assuming that the carrier frequency fPWM of the PWM signal is 28 kHz, by setting the frequency fCLK of the clock signal CLK to be 2L (=128) times the carrier frequency fPWM of the PWM signal, i.e., to be 3.6 MHz or more, such an arrangement is capable of generating a data signal SPWM for every cycle of the external PWM signal without missing any data. Such an arrangement prevents the occurrence of beating.
Next, description will be made regarding the filtering coefficient n. FIG. 10B is a graph which shows the low-pass filter characteristics of the PWM instruction logic conversion circuit 116. In order to suppress ripple in the output data SPWM to 1 step or less, the required gain G is on the order of 1/128=−42 dB. An arrangement in which n=12 provides a removal efficiency on the order of −38.5 dB when the carrier frequency fPWM of the external PWM signal PWM is 21 kHz. As the carrier frequency fPWM becomes higher, such an arrangement provides higher removal efficiency.
Fourth Embodiment
FIG. 11 is a block diagram which shows a configuration of a cooling apparatus 2 employing a driving IC 100e according to a fourth embodiment. The driving IC 100e according to the fourth embodiment employs the techniques described in the aforementioned first through third embodiments. Description will be made below regarding each block of the driving IC 100e. 
A power supply terminal Vcc and a ground terminal GND are each connected to an external power supply 3, and respectively receive the power supply voltage and the ground voltage.
A band gap reference circuit 102 generates a reference voltage VBGR. An internal power supply 104 is configured as a linear regulator, for example. The internal power supply 104 receives the reference voltage VBGR, and generates a stabilized internal power supply voltage VDDINT according to the value of the reference voltage VBGR. A self-running oscillator circuit 106 generates a clock signal CLK having a predetermined frequency.
A power on/reset circuit 108 generates a power on/reset signal SPOR by comparing the power supply voltage Vcc with a predetermined threshold voltage. A low-voltage malfunction prevention circuit (UVLO: Under Voltage Lock Out) 110 generates a UVLO signal SUVLO by comparing the power supply voltage Vcc with a predetermined threshold voltage. These signals SPOR and SUVLO are used to protect the circuit.
A Hall bias power supply 112 generates a Hall bias voltage VHB, and outputs the Hall bias voltage VHB thus generated via a Hall bias terminal HB. The Hall bias voltage VHB is supplied to a Hall sensor 8.
The driving IC 100 has a soft start function for gradually raising the rotational speed at the start of rotation of the fan motor 6. The period of the soft start operation is determined according to a soft start period setting voltage VTSS. External resistors R5 and R6 divide the reference voltage VREF so as to generate the soft start period setting voltage VTSS, and input the soft start period setting voltage VTSS thus generated to a soft start period setting input terminal SS. An A/D converter ADC8 performs analog/digital conversion of the soft start setting voltage VTSS so as to generate a data signal STSS. An adder-subtractor ADC13 subtracts the data SREF from the data signal STSS so as to shift the data STSS, and outputs the data STSS′ thus obtained.
Based upon the signal STSS′ which indicates the soft start period, a soft start setting circuit 122 generates a soft start setting signal SSS which gradually rises over time, with a slope that corresponds to the value of the signal STSS′.
A quick start detection circuit 118 detects if the stationary state of the motor is due to the external PWM signal PWM or if it is due to abnormal motor operation. In a case in which the stationary state of the motor is due to the external PWM signal PWM, the lock protection function is disabled. Such a quick start function allows the motor to start to rotate immediately after the PWM signal “H” is input when the motor has entered the stationary state due to the PWM signal.
The control instruction combining circuit 80 receives the signals SMINT′, SMINP′, STH′, SPWM, and SQS, and combines these signals thus received so as to generate a control signal SDUTY which indicates the duty ratio to be used to perform a PWM driving operation for the fan motor 6.
An external detection resistor Rs is connected to an output current detection terminal RNF. A voltage drop (detection voltage) VCS occurs at the detection resistor Rs according to the current Im that flows through the fan motor 6. The detection voltage VCS is input to a detection current input terminal CS of the driving IC 100. A ninth A/D converter ADC9 converts the detection voltage VCS into a digital-valued detection signal SCS. A current limit setting circuit 120 generates data SIMAX which represents the upper limit of the current Im that flows through the fan motor 6.
Adder-subtractors ADD15 and ADD16 sequentially subtract the signals SIMAX and SSS from the detection signal SCS so as to generate a current upper limit signal SCS′. The current upper limit signal SCS′ limits the duty ratio with which the fan motor 6 is PWM driven, and limits the current Im that flows through the fan motor 6 to be equal to or lower than a current value that corresponds to the signal SIMAX. Furthermore, such an arrangement provides a soft start operation when the motor is started.
A calculation unit 82 generates an FG signal (S60) based upon the seventh signal S7 output from the amplitude control circuit 18 as described above. An open collector output circuit 138 outputs the FG signal via a rotational speed pulse output terminal FG.
The driving IC 100 includes a lock protection function. A lock protection/automatic restoration circuit (which will be referred to as the “lock protection circuit” hereafter) 128 monitors the FG signal, detects a stationary state due to abnormal motor operation, and generates a detection signal (lock alarm signal) AL that indicates this abnormal state. An open collector output circuit 140 outputs the lock alarm signal AL via a lock alarm output terminal AL.
A thermal monitor circuit 124 monitors the chip temperature of the driving IC 100, and generates a chip temperature voltage VT that corresponds to the chip temperature. An A/D converter ADC10 performs analog/digital conversion of the chip temperature voltage VT, so as to generate a chip temperature signal ST. When the chip temperature signal ST is higher than a predetermined threshold value, i.e., when the driving IC 100 is in an abnormal temperature state, a thermal shutdown circuit 126 asserts a thermal shutdown signal TSD.
The calculation unit 82 multiplies the seventh signal S7 by the duty ratio control signal SDUTY and the current upper limit signal SCS′ so as to generate the control signal S7′. Furthermore, when the lock alarm signal AL or the thermal shutdown signal THD is asserted, the calculation unit 82 sets the level of the control signal S7′ to zero so as to stop the supply of electric power to the fan motor 6.
The above is the configuration of the driving IC 100e. With the driving IC 100e, such an arrangement is capable of controlling the rotational speed of the fan motor 6 according to the duty ratio of the external PWM signal and the temperature. Furthermore, such an arrangement provides such a soft start function, a lock protection function, and a quick start function, by means of a single function IC.
FIG. 12 is a circuit diagram which shows a modification of the driving IC shown in FIG. 11. Description will be made regarding only the point of difference from an arrangement shown in FIG. 11. A driving IC 100f includes a control instruction serial data input terminal SDT. The terminal SDT is connected to external memory 9 or an external CPU. Data that corresponds to at least one of the data SMINT, SMINP, STSS, and SIMAX described with reference to FIG. 8 is input to the control instruction serial data input terminal SDT. A reception circuit 84 receives serial data SDT, and outputs the serial data STD thus received to the control instruction combining circuit 80. The memory 9 may be configured as a built-in component of the driving IC 100f. 
Furthermore, a detection resistor Rs is configured as a built-in component of the driving IC 100f. The output data SCS of the A/D converter ADC9 is input to the control instruction combining circuit 80. The control instruction combining circuit 80 generates a duty ratio control signal SDUTY such that the detection signal SCS does not exceed the current limit setting value included in the serial data SDT.
With the driving IC 100f shown in FIG. 12, by supplying the data from the memory or CPU to the control instruction serial data input terminal SDT, such an arrangement is capable of changing the settings of the driving IC 100f. 
Fifth Embodiment
FIG. 13 is a circuit diagram which shows a configuration of a driving IC 100g according to a fifth embodiment. The technique described in the present embodiment may be combined with any one of the aforementioned driving ICs.
In the present embodiment, the Hall sensor 8 is integrated on the same semiconductor chip as the driving IC 100g. 
The signal level of the Hall signal S1 and S2 output from the Hall sensor 8 integrated on a semiconductor chip is miniscule. Accordingly, there is a need to amplify the Hall signal S1 and S2 such that the signal levels thereof are within the dynamic ranges of the first A/D converter ADC1 and the second A/D converter ADC2. Accordingly, the driving IC 100g further includes an analog amplifier 13 configured to amplify the Hall signal S1 and S2 received from the Hall sensor 8. Furthermore, a Hall bias circuit 11 is configured as a voltage source configured to supply a Hall bias voltage VHB to the Hall sensor 8, or is configured as a current source configured to supply a Hall bias current (IHB).
With such a system, the sensitivity of the Hall element 8 greatly fluctuates due to process irregularities, fluctuation in the temperature, and other effects. Accordingly, the amplitude of the Hall signal fluctuates on the order of several times to several hundred times due to this fluctuation in its sensitivity. That is to say, there is a need to adjust the amplitude of the Hall signal in increments of individual ICs. Furthermore, there is a need to perform such amplitude adjustment according to changes in temperature. It should be noted that this problem has not been recognized as a typical problem by those skilled in this art. Rather, this problem has been first recognized by the present inventors.
In order to solve such a problem, the driving IC 100g shown in FIG. 13 uses the analog amplifier 13, arranged upstream of the first A/D converter ADC1 and the second A/D converter ADC2, as a second amplitude correction means configured to adjust the amplitude of the Hall signal S1 and S2.
That is to say, the analog amplifier 13 is configured as a variable gain amplifier. The gain g of the analog amplifier 13 is adjusted such that the amplitude of the Hall signal S1′ and S2′ input to the first A/D converter ADC1 and the second A/D converter ADC2 approaches a predetermined target level.
With such a circuit, the gain g of the analog amplifier 13 is adjusted according to an instruction value received from a downstream digital block. For example, such an arrangement allows the gain g of the analog amplifier 13 to be switched between 100, 200, 400, 600, 800, and 1000. Specifically, on a signal line of the digital block, a circuit (target amplitude judgment circuit) 21 configured to control the amplitude of the Hall signal S1 and S2 is provided. For example, the target amplitude judgment circuit 21 compares the amplitude level of the output signal of the amplitude correction circuit 20 with a reference value REF. When the amplitude level of the output signal of the amplitude correction circuit 20 is lower than the reference value REF, the target amplitude judgment circuit 21 raises the gain g of the analog amplifier 13, and when the amplitude level is higher than the reference value REF, the target amplitude judgment circuit 21 lowers the gain g of the analog amplifier 13. As the amplitude level to be compared with the reference value REF, the aforementioned amplitude data S34 may be used.
The above is the configuration of the driving IC 100g. The driving IC 100g performs amplitude correction in both the analog stage and the digital stage. In such an analog stage, coarse amplitude adjustment is preferably provided. On the other hand, in such a digital stage, fine amplitude adjustment is preferably provided.
The driving IC 100g is capable of appropriately adjusting the amplitude of the Hall signal S1 and S2 output from the Hall sensor 8 such that these signal components settle within the dynamic ranges of the first A/D converter ADC1 and the second A/D converter ADC2 even if the amplitude of the Hall signal S1 and S2 fluctuates.
Furthermore, the target amplitude judgment circuit 21 configured to perform gain adjustment of the analog amplifier 13 is provided in the digital block. Such an arrangement results in only a small increase in the circuit area to provide the target amplitude judgment circuit 21.
By configuring the Hall element 8 as a built-in component of the driving IC 100g, such an arrangement does not require the Hall input terminals HP and HN, thereby allowing the number of pins to be reduced by 2. This provides a great advantage that compensates for the increased circuit area due to the analog amplifier 13 being arranged as an additional component. Furthermore, this provides a great advantage to a driving circuit for a fan motor which is required to be configured with a reduced size.
Also, the following modification can be conceived with respect to the driving IC 100g shown in FIG. 13.
The amplitude to be monitored by the target amplitude judgment circuit 21 is not restricted to the output signal S6′ of the amplitude correction circuit 20. Also, the target amplitude judgment circuit 21 may monitor other signals on the digital signal processing path, such as the output signal S5 of the differential conversion circuit 14, the output signal S6 of the offset correction circuit 16, and the output signal S7 of the absolute-value circuit 22.
The amplitude correction performed in the analog stage is not restricted to the adjustment of the gain g of the analog amplifier 13. For example, by changing the Hall bias signal generated by the Hall bias circuit 11 according to the output signal of the target amplitude judgment circuit 21, such an arrangement may directly adjust the Hall signal S1 and S2 generated by the Hall sensor 8.
Also, the target amplitude judgment circuit 12 may be configured as an analog circuit. FIG. 14 is a circuit diagram which shows a part of a modification of the driving IC shown in FIG. 13. With such a modification, a target amplitude judgment circuit 21h is configured as an analog circuit which is upstream of the first A/D converter ADC1 and the second A/D converter ADC2. The target amplitude judgment circuit 21h includes a low-pass filter 23, a peak hold circuit 25, and a comparator 27.
The low-pass filter 23 performs filtering of the Hall signal amplified by the analog amplifier 13. The low-pass filter 23 may receive only one of the differential components of the Hall signal amplified by the analog amplifier 13, as shown in FIG. 14. Also, the low-pass filter 23 may receive both of the differential components of the Hall signal. The peak hold circuit 25 holds the peak value of the output signal of the low-pass filter 23, i.e., the amplitude of the Hall signal. The comparator 27 compares the amplitude thus held with a target amplitude value VREF/and controls the gain g of the analog amplifier 13 according to the comparison result.
The target amplitude judgment circuit 21 may change the Hall bias signal generated by the Hall bias circuit 11, instead of or in addition to the control operation for controlling the gain g of the analog amplifier 13.
Description has been made with reference to FIG. 13 or 14 regarding an arrangement in which the Hall signal is converted into a digital value, and the control signal SCNT is generated by means of digital signal processing. Also, the control signal generating unit 24 may perform analog signal processing in order to generate a signal to be used to drive the fan motor 6. FIG. 15 is a circuit diagram which shows a further generalized configuration of a driving IC 100i. 
A control signal generating unit 24i receives a seventh signal from an intermediate signal processing unit 15, and performs analog signal processing or digital signal processing on the seventh signal thus received so as to generate a control signal SCNT. In a case in which digital signal processing is performed, the intermediate signal processing unit 15 includes A/D converters ADC1 and ADC2 configured to convert an analog Hall signal S1′ and S2′ into a digital value. Also, the intermediate signal processing unit 15 may include either an offset correction circuit 16 or an amplitude control circuit 18, or both of these circuits, as necessary.
In a case in which the control signal generating unit 24i performs analog signal processing, such an arrangement requires neither of the A/D converters ADC1 and ADC2. Also, the intermediate signal processing unit 15 may be eliminated. Also, the intermediate signal processing unit 15 may perform an operation that is equivalent to at least one of the operation of the offset correction circuit 16 or the operation of the amplitude control circuit 18. In this case, the driver circuit 26 may be configured as an analog circuit.
The target amplitude judgment circuit 21i adjusts the gain of the analog amplifier 13 so as to change the amplitude of the Hall signal S1′ and S2′ to be amplified. The target amplitude judgment circuit 21i adjusts the gain of the analog amplifier 13 based upon a signal selected from among the signals that can be acquired on a path from the output of the analog amplifier 13 up to the input of the control signal generating unit 24i, such that the amplitude of the seventh signal S7 input to the control signal generating unit 24i approaches a predetermined value (broken line a in FIG. 15). For example, the target amplitude judgment circuit 21 may perform a gain control operation based upon the signal S1′ (or S2′ or both S1′ and S2′) amplified by the analog amplifier 13 (broken line a1 in FIG. 15). Also, the target amplitude judgment circuit 21 may perform a gain control operation based upon an internal signal of the intermediate signal processing unit 15 (broken line a2 in FIG. 15).
Also, the target amplitude judgment circuit 21i may adjust the amplitude of the Hall signal input to the control signal generating unit 24i by changing the Hall bias signal generated by the Hall bias circuit 11 (broken line b in FIG. 15), instead of the gain control operation for the analog amplifier 13. With such an arrangement, the target amplitude judgment circuit 21i adjusts the Hall bias signal based upon the amplitude of a signal selected from among the signals that can be acquired on a path from the output of the analog amplifier 13 up to the input of the control signal generating unit 24i, such that the amplitude of the seventh signal S7 input to the control signal generating unit 24i approaches a predetermined value (broken line b in FIG. 15). For example, the target amplitude judgment circuit 21 may adjust the Hall bias signal based upon the amplitude of the signal S1′ (or S2′ or both of S1′ and S2′) amplified by the analog amplifier 13 (broken line b1 in FIG. 15). Also, the target amplitude judgment circuit may adjust the Hall bias signal based upon an internal signal of the intermediate signal processing unit 15 (broken line b2 in FIG. 15).
As described above, with such an arrangement in which the Hall sensor 8 is integrated in the driving IC 100, by controlling the gain of the analog amplifier 13, or by adjusting the Hall bias signal, such an arrangement is capable of stabilizing the amplitude level of the signal S7 input to the control signal generating unit 24i. 
The above-described embodiment has been described for exemplary purposes only, and is 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 has been made in the embodiments regarding an arrangement in which the fan motor to be driven is configured as a single-phase driving motor. However, the present invention is not restricted to such an arrangement. Also, the present invention can be applied to the driving operation for other kinds of motors.
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.

## Claims

1. A motor driving circuit comprising:
a Hall sensor configured to generate a Hall signal which comprises a first signal and a second signal that are complementary, according to the position of a rotor of a motor to be driven;
a Hall bias circuit configured to supply a Hall bias signal to the Hall sensor;
an analog amplifier configured to amplify the Hall signal;
an A/D converter configured to convert the Hall signal amplified by the analog amplifier into a digital signal;
an amplitude control circuit configured to adjust the amplitude of the digital signal;
a control signal generating unit configured to generate a control signal to be used to drive the motor, based upon an output of the amplitude control circuit; and
a driver circuit configured to drive the motor according to the control signal,
wherein the aforementioned components are monolithically integrated on a single semiconductor substrate, and wherein
the amplitude control circuit comprises:
an amplitude correction circuit configured to stabilize the amplitude of the digital signal; and
a target amplitude judgment circuit configured to adjust the gain of the analog amplifier based on the result of comparing the output of the amplitude correction circuit with a reference value.

2. A motor driving circuit according to claim 1, wherein the target amplitude judgment circuit is configured to adjust the gain of the analog amplifier such that the amplitude of the Hall signal amplified by the analog amplifier approaches a predetermined value.

3. A motor driving circuit comprising:
a Hall sensor configured to generate a Hall signal which comprises a first signal and a second signal that are complementary, according to the position of a rotor of a motor to be driven;
a Hall bias circuit configured to supply a Hall bias signal to the Hall sensor;
an analog amplifier configured to amplify the Hall signal;
an A/D converter configured to convert the Hall signal amplified by the analog amplifier into a digital signal;
an amplitude control circuit configured to adjust the amplitude of the digital signal;
a control signal generating unit configured to generate a control signal to be used to drive the motor, based upon an output of the amplitude control circuit; and
a driver circuit configured to drive the motor according to the control signal,
wherein the aforementioned components are monolithically integrated on a single semiconductor substrate;
and wherein the amplitude control circuit comprises
an amplitude correction circuit configured to stabilize the amplitude of the digital signal; and
a target amplitude judgment circuit configured to adjust the Hall bias signal so as to change the amplitude of the Hall signal to be amplified by the analog amplifier, based on the result of comparing the output of the amplitude correction circuit with a reference value.

4. A motor driving circuit according to claim 3, wherein the target amplitude judgment circuit is configured to adjust the Hall bias signal such that the amplitude of the Hall signal amplified by the analog amplifier approaches a predetermined value.

5. A cooling apparatus comprising:
a fan motor; and
a driving circuit configured to drive the fan motor, wherein the driving circuit comprises:
a Hall sensor configured to generate a Hall signal which comprises a first signal and a second signal that are complementary, according to the position of a rotor of a motor to be driven;
a Hall bias circuit configured to supply a Hall bias signal to the Hall sensor;
an analog amplifier configured to amplify the Hall signal;
an A/D converter configured to convert the Hall signal amplified by the analog amplifier into a digital signal;
an amplitude control circuit configured to adjust the amplitude of the digital signal;
a control signal generating unit configured to generate a control signal to be used to drive the motor, based upon an output of the amplitude control circuit; and
a driver circuit configured to drive the motor according to the control signal,
wherein the aforementioned components are monolithically integrated on a single semiconductor substrate; and wherein
the amplitude control circuit comprises:
an amplitude correction circuit configured to stabilize the amplitude of the digital signal; and
a target amplitude judgment circuit configured to adjust the gain of the analog amplifier based on the result of comparing the output of the amplitude correction circuit with a reference value.

6. An electronic device comprising:
a processor; and
a cooling apparatus configured to cool the processor, wherein
the cooling apparatus comprises:
a fan motor; and

a driving circuit configured to drive the fan motor, and wherein the driving circuit comprises:
a Hall sensor configured to generate a Hall signal which comprises a first signal and a second signal that are complementary, according to the position of a rotor of a motor to be driven;
a Hall bias circuit configured to supply a Hall bias signal to the Hall sensor;
an analog amplifier configured to amplify the Hall signal;
an A/D converter configured to convert the Hall signal amplified by the analog amplifier into a digital signal;
an amplitude control circuit configured to adjust the amplitude of the digital signal;
a control signal generating unit configured to generate a control signal to be used to drive the motor, based upon an output of the amplitude control circuit; and
a driver circuit configured to drive the motor according to the control signal,
wherein the aforementioned components are monolithically integrated on a single semiconductor substrate, and wherein
the amplitude control circuit comprises:
an amplitude correction circuit configured to stabilize the amplitude of the digital signal; and
a target amplitude judgment circuit configured to adjust the gain of the analog amplifier based on the result of comparing the output of the amplitude correction circuit with a reference value.

7. A cooling apparatus comprising:
a fan motor; and
a driving circuit configured to drive the fan motor, wherein the driving circuit comprises:
a Hall sensor configured to generate a Hall signal which comprises a first signal and a second signal that are complementary, according to the position of a rotor of a motor to be driven;
a Hall bias circuit configured to supply a Hall bias signal to the Hall sensor;
an analog amplifier configured to amplify the Hall signal;
an A/D converter configured to convert the Hall signal amplified by the analog amplifier into a digital signal;
an amplitude control circuit configured to adjust the amplitude of the digital signal;
a control signal generating unit configured to generate a control signal to be used to drive the motor, based upon an output of the amplitude control circuit; and
a driver circuit configured to drive the motor according to the control signal,
wherein the aforementioned components are monolithically integrated on a single semiconductor substrate;
and wherein the amplitude control circuit comprises
an amplitude correction circuit configured to stabilize the amplitude of the digital signal; and
a target amplitude judgment circuit configured to adjust the Hall bias signal so as to change the amplitude of the Hall signal to be amplified by the analog amplifier, based on the result of comparing the output of the amplitude correction circuit with a reference value.

8. An electronic device comprising:
a processor; and
a cooling apparatus configured to cool the processor, wherein
the cooling apparatus comprises:
a fan motor; and

a driving circuit configured to drive the fan motor, and wherein the driving circuit comprises:
a Hall sensor configured to generate a Hall signal which comprises a first signal and a second signal that are complementary, according to the position of a rotor of a motor to be driven;
a Hall bias circuit configured to supply a Hall bias signal to the Hall sensor;
an analog amplifier configured to amplify the Hall signal;
an A/D converter configured to convert the Hall signal amplified by the analog amplifier into a digital signal;
an amplitude control circuit configured to adjust the amplitude of the digital signal;
a control signal generating unit configured to generate a control signal to be used to drive the motor, based upon an output of the amplitude control circuit; and
a driver circuit configured to drive the motor according to the control signal,
wherein the aforementioned components are monolithically integrated on a single semiconductor substrate;
and wherein the amplitude control circuit comprises
an amplitude correction circuit configured to stabilize the amplitude of the digital signal; and
a target amplitude judgment circuit configured to adjust the Hall bias signal so as to change the amplitude of the Hall signal to be amplified by the analog amplifier, based on the result of comparing the output of the amplitude correction circuit with a reference value.