PWM driver, method for generating PWM signal, actuator system and camera module

Abstract

A PWM driver is provided that can reduce noise caused by a PWM-controlled OIS / AF actuator on a camera module. The PWM driver for generating a PWM signal for driving a lens includes: a PWM signal generator for generating a reference PWM signal that switches at a predetermined period; a receiving unit for receiving a mask signal defining a switching disable period; and a modulation unit for generating an actual PWM signal by not switching the reference PWM signal during the switching disable period defined by the mask signal.

Description

Technical Field

[0001] The present invention relates to a PWM driver, a method for generating a PWM signal, an actuator system, and a camera module, and more specifically, to a PWM driver for generating a PWM signal for driving a lens, a method for generating a PWM signal, an actuator system, and a camera module. Background Technology

[0002] Electronic devices such as smartphones and small cameras include optical image stabilization (OIS) / auto-focus (AF) actuators for external control of camera units. For example, SMA wires are known to be used as actuators. In this case, the SMA wire is used to drive the OIS of the camera's optical image by tilting the camera unit, which includes the camera's lens elements and image sensor. In this case, the OIS / AF actuator of the electronic device outputs a signal modulated by a pulse width modulation (PWM) signal (hereinafter referred to as the "PWM signal"). The PWM signal is a signal that switches between a high (H) state and a low (L) state at a predetermined period. In the actuator, the SMA wire is driven by this PWM signal to move the lens elements in the desired direction.

[0003] PWM technology is a good candidate for controlling OIS / AF actuators because it can reduce the power consumption of the camera module. However, the repetition of the H and L levels of the PWM signal output from the PWM driver increases electrical and magnetic noise. Since the OIS / AF actuator is implemented close to the image sensor used to move the lens unit, the noise of the PWM driver can affect the image signal. Summary of the Invention

[0004] This invention provides a method for mitigating noise on a camera module caused by a PWM-controlled OIS / AF actuator.

[0005] According to a first aspect, a PWM driver for generating a PWM signal for driving a lens includes:

[0006] A PWM signal generator is used to generate a reference PWM signal that switches at a predetermined period.

[0007] The receiving unit is used to receive the mask signal that defines the switching prohibition period;

[0008] A modulation unit is used to generate an actual PWM signal by not switching the reference PWM signal during the switching disable period defined by the mask signal.

[0009] According to this implementation, the actual PWM signal is generated by not switching the reference PWM signal during the switching disable period. Therefore, the influence of noise on the pixel output AD conversion can be eliminated, without being limited by the combination of the PWM carrier frequency and the AD conversion period.

[0010] In one possible implementation of the first aspect, the PWM signal generator generates the reference PWM signal based on the movement of the lens.

[0011] Based on this implementation, the movement of the lens, such as the lens's acceleration, velocity, and position, can be considered to generate a PWM signal.

[0012] In one possible implementation of the first aspect, the generator acquires motion information from a gyroscope sensor that detects the movement of the lens.

[0013] According to this implementation, the PWM signal generator can generate the reference PWM signal based on motion information from a gyroscope sensor that detects the movement of the lens.

[0014] In one possible implementation of the first aspect, the switching prohibition period is based on a control signal set for analog-to-digital conversion of an image captured by an image sensor.

[0015] According to this implementation, the output level of the actual PWM signal can be maintained during one cycle of the AD conversion operation.

[0016] In conjunction with one possible implementation of the first aspect, the PWM driver further includes a counter for increasing or decreasing a counter value of the number of clock pulses based on the H state or L state of the actual PWM signal, wherein the modulation unit is configured to switch the actual PWM signal based on the counter value to minimize the absolute value of the counter value outside the switching disable period.

[0017] According to this implementation, the counter indicates the duration by which the output H / L state period differs from the H / L state period of the reference PWM signal. Taking the measurement results into account, the actual PWM signal can be switched.

[0018] In one possible implementation of the first aspect, the range of the counter corresponds to the period of the reference signal for the analog-to-digital conversion.

[0019] This implementation method can suppress counter overflow.

[0020] In one possible implementation of the first aspect, the modulation unit switches the actual PWM signal when the counter value overflows during the switching disable period.

[0021] Based on this implementation, PWM control can continue to be performed with lower noise while reducing the impact of counter overflow.

[0022] In one possible implementation of the first aspect, the mask signal is generated based on control signals used for analog-to-digital conversion of images captured by an image sensor.

[0023] According to this implementation, the switching disable period can be set by a mask signal so that the PWM state does not change in one cycle of the CDS, and the noise caused by the PWM state change in the AD conversion of the image sensor is suppressed.

[0024] In one possible implementation of the first aspect, the switching disable period is configured such that the actual PWM signal does not switch during the conversion process of converting the analog signal of the image captured by the image sensor into a digital output.

[0025] According to this implementation, the switching disable period can be set so that the PWM state does not change during one cycle of the CDS.

[0026] In one possible implementation of the first aspect, the PWM driver further includes a monitor for instructing the modulation unit to switch the actual PWM signal based on the reference PWM signal and the actual PWM signal.

[0027] According to this implementation, the modulation unit can generate the actual PWM signal based on the output of the duty cycle error monitor and the reference PWM signal.

[0028] In one possible implementation of the first aspect, the monitor instructs the modulation unit to switch the actual PWM signal so that the actual PWM signal approaches the duty cycle of the reference PWM signal.

[0029] According to this implementation, the average duty cycle can be the same as the duty cycle of the reference PWM signal.

[0030] In one possible implementation of the first aspect, the PWM driver further includes a mask generation unit for generating the mask signal.

[0031] According to this implementation method, the mask generation unit can be implemented in the PWM driver.

[0032] According to a second aspect, an actuator system is provided, the actuator system comprising:

[0033] The PWM driver according to any implementation of the first aspect;

[0034] A lens unit for driving the lens based on the actual PWM signal generated by the actual PWM driver.

[0035] According to the third aspect, a camera module is provided.

[0036] The actuator system according to the second aspect;

[0037] An imaging unit for capturing images using a lens driven by the actuator system.

[0038] According to the fourth aspect, a method for generating a PWM signal for driving a lens is provided, comprising:

[0039] Generate a reference PWM signal that switches at a predetermined period;

[0040] Receive the mask signal that defines the switching of the prohibition period;

[0041] The actual PWM signal is generated by not switching the reference PWM signal during the switching disable period defined by the mask signal.

[0042] According to this implementation, the actual PWM signal is generated by not switching the reference PWM signal during the switching disable period. Therefore, the influence of noise on the pixel output AD conversion can be eliminated, without being limited by the combination of the PWM carrier frequency and the AD conversion period.

[0043] In one possible implementation of the fourth aspect, the step of generating the reference PWM signal is based on the movement of the lens.

[0044] In one possible implementation of the fourth aspect, the step of generating the reference PWM signal obtains motion information from a gyroscope sensor that detects the movement of the lens.

[0045] Regarding one possible implementation of the fourth aspect, the switching prohibition period is based on a control signal set for analog-to-digital conversion of the image captured by the image sensor.

[0046] Regarding one possible implementation of the fourth aspect, the method further includes:

[0047] Based on the H state or L state of the actual PWM signal, the counter value of the number of clock pulses is increased or decreased, wherein the step of generating the reference PWM signal is based on the counter value to minimize the absolute value of the counter value outside the switching disable period.

[0048] In one possible implementation of the fourth aspect, the range of the counter corresponds to the period of the reference signal for the analog-to-digital conversion.

[0049] In one possible implementation of the fourth aspect, when the counter value overflows during the switching disable period, the step of generating the actual PWM signal switches the actual PWM signal.

[0050] In one possible implementation of the fourth aspect, the mask signal is generated based on control signals used for analog-to-digital conversion of images captured by an image sensor.

[0051] In one possible implementation of the fourth aspect, the switching disable period is set such that the actual PWM signal does not switch during the conversion process of converting the analog signal of the image captured by the image sensor into a digital output.

[0052] In one possible implementation of the fourth aspect, the step of generating the actual PWM signal includes switching the actual PWM signal based on the reference PWM signal and the actual PWM signal.

[0053] In one possible implementation of the fourth aspect, the step of generating the actual PWM signal switches the actual PWM signal so that the actual PWM signal is close to the duty cycle of the reference PWM signal.

[0054] In one possible implementation of the fourth aspect, the method further includes the step of generating the mask signal. Attached Figure Description

[0055] To more clearly describe the technical solutions in the embodiments, the accompanying drawings required for describing this embodiment are briefly described below. Obviously, the drawings in the following description only depict some possible embodiments, and those skilled in the art can still obtain other drawings from these drawings without creative effort. In the drawings:

[0056] Figure 1 A schematic diagram of the electrical connections of SMA-OIS is shown.

[0057] Figure 2 The time-division driven configuration is shown.

[0058] Figure 3 The time variation of the PWM signal used to drive the SMA filament is shown.

[0059] Figure 4 The Bode plot of the correlated double sampling (CDS) filter is shown.

[0060] Figure 5The configuration of a CMOS image sensor is shown, where the column ADC of the pixel column performs CDS.

[0061] Figure 6 The signal diagram in the CDS implemented on the CMOS image sensor is shown.

[0062] Figure 7 An example configuration of a lens actuator system is shown.

[0063] Figure 8 A schematic diagram is shown of the signals used to perform CDS in the ADC and the PWM signals used for OIS driving.

[0064] Figure 9 A block diagram of a lens actuator system with a waveform modulator provided in one embodiment is shown.

[0065] Figure 10 A waveform diagram is shown to explain the waveform operation of the waveform modulator.

[0066] Figure 11 The relationship between the RAMP signal and the ACT_PWM signal used for AD conversion is shown.

[0067] Figure 12 A state transition diagram provided by one embodiment is shown.

[0068] Figure 13 A schematic diagram of the operating waveform is shown in the case of duty cycle error monitor overflow.

[0069] Figure 14 A state transition diagram provided by one embodiment is shown.

[0070] Figure 15 A block diagram of a lens actuator system with a waveform modulator is shown.

[0071] Figure 16 A signal diagram of a lens actuator system provided in one embodiment is shown. Detailed Implementation

[0072] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0073] In the following description, the use of PWM-controlled SMA actuators is described as a representative example.

[0074] (First Embodiment)

[0075] First, refer to Figures 1 to 4 The operating principle of this embodiment is described.

[0076] Figure 1 This is a schematic diagram of the electrical connections of SMA-OIS. (For example...) Figure 1 As shown, the controller 204 for controlling the OIS and the OIS actuator 202 are connected by wires. Each of the shape memory alloy (SMA) wires 102a, 102b, 102c and 102d is connected to one of the PWM sources 206a, 206b, 206c and 206d via one of the amplifiers 210 for driving.

[0077] To heat the wires, current can be applied to the SMA wires via a corresponding PWM source 206a, 206b, 206c, and 206d. This current should be controlled using a PWM method to reduce its significant power consumption. Furthermore, a temperature sensor 208 is used in this system to measure the temperature of each wire, improving its control accuracy. The system incorporates the temperature sensor 208 and is driven by a time-sharing drive (…). Figure 2 and Figure 3 The structure of multiple SMA wires 120 driven by the camera module reduces the size of the camera module.

[0078] PWM sources 206a, 206b, 206c, and 206d generate PWM signals based on the temperature of the connected SMA filaments measured by temperature sensor 208. This system, intended to realize a miniature camera module, can control the position of the movable unit 110 because each of the SMA filaments 102a, 102b, 102c, and 102d can shrink its own length by heating.

[0079] Figure 2 The time-division drive configuration is shown. Figure 2 In this configuration, SMA wire 304 includes four SMA wires: WIRE0, WIRE1, WIRE2, and WIRE3. Wires WIRE0, WIRE1, WIRE2, and WIRE3 have resistance values ​​r0, r1, r2, and r3, respectively. One end of wires WIRE0, WIRE1, WIRE2, and WIRE3 is connected to an analog-to-digital converter (ADC) 302 and a temperature sensor 308. If the SMA wires are considered as resistors with temperature characteristics, the temperature can be estimated from the output voltage by determining the voltage divider output of the SMA wires and the resistor included in the temperature sensor 308 for measurement. This output voltage is converted into a digital value by the ADC 302.

[0080] The other end of SMA wire WIRE0 is connected to transistor 306a, whose gate is connected to the PWM source 206a of the output PWM signal PWM0. The other end of SMA wire WIRE1 is connected to transistor 306b, whose gate is connected to the PWM source 206b of the output PWM signal PWM1. The other end of SMA wire WIRE2 is connected to transistor 306c, whose gate is connected to the PWM source 206c of the output PWM signal PWM2. The other end of SMA wire 3 is connected to transistor 306d, whose gate is connected to the PWM source 206d of the output PWM signal PWM3. Current flows when the PWM signal at the gate of the transistor input is turned on. By using PWM sources 206a to 206d to turn transistors 306a to 306d on / off, current from transistors 306a to 306d is supplied to SMA wire 304.

[0081] Figure 3 The time variations of the PWM signals used to drive SMA filaments WIRE0, WIRE1, WIRE2, and WIRE3 are shown. Figure 3 As shown, the temperature of each SMA wire in WIRE0, WIRE1, WIRE2, and WIRE3 should be calculated based on the ADC input voltage, which is proportional to the measurement of each SMA wire. A clamping force is generated by electrically heating the SMA wire 304, and this clamping force is used as the lens driving force for the driving lens. Here, the length of one cycle (PWM carrier cycle) of the four PWM signals is the same. Furthermore, the four PWM signals go high at different times. Additionally, the four PWM signals can have different duty cycles. This method generally has the advantages of easily reducing the size and weight of electronic devices and achieving relatively large forces.

[0082] Next, we will describe the noise generated during analog-to-digital (AD) conversion used in image sensors such as CCD and CMOS image sensors in cameras. Among this noise, kTC noise, Vth offset, and 1 / f noise are well-known. To counteract several types of noise, correlated double sampling (CDS) is typically implemented on the ADC in an image sensor. In CDS operation, double sampling is performed on the reset level (reset sample) and the signal level (signal sample), and the output signal is defined as the difference between the reset sample and the signal sample. This operation can eliminate the noise typically contained between the reset sample and the signal sample. The frequency response of CDS is defined as the time interval T between the two samples, as follows:

[0083]

[0084] Figure 4 This is the Bode plot of the CDS (Catalyst Detector) based on the above formula. In the plot, the vertical axis represents the gain (dB) of the frequency response, and the horizontal axis represents the frequency (1 / T). The solid lines are drawn based on the CDS transfer function. These lines are approximated by dashed lines. Figure 4 As shown, CDS exhibits the transmission characteristics of a bandpass filter. Specifically, it acts as a high-pass filter in the frequency range below 1 / 2T and completely cancels out the frequency components of n / T.

[0085] Next, refer to Figure 5 and Figure 6 This will describe the CDS implemented in a CMOS image sensor. Figure 5 A configuration of a CMOS image sensor is shown, in which the ADC of a pixel column performs CDS. The CMOS image sensor 600 includes a row decoder and driver 608, a pixel array 602, a comparator 604, a counter 605, a buffer 606, a RAMP generator 610, and a counter clock 612. The pixel array 602 includes a plurality of pixels. Each pixel has a photodiode and a floating diffusion (FD), and the FD stores the charge acquired by the photodiode. The pixel rows are driven by signals from the row decoder and driver 608. The voltages of the pixel outputs from the pixel array 602 are compared with the voltages of the RAMP signals from the RAMP generator 610 in the comparator 604, and the time of change of the comparator output is output to the buffer 606 via the counter 605.

[0086] Here, the RAMP signal is a control signal used for analog-to-digital conversion of the image captured by the image sensor. Counter 605 counts the number of pulses from counter clock 612. Specifically, counter 605 adds or subtracts the counted pulse count from the counter value based on the output value from comparator 604. When the voltage of the RAMP signal is higher than the pixel output voltage, the output of comparator 604 is low; when the voltage of the RAMP signal is lower than the pixel output voltage, the output of comparator 604 is high. Figure 5 In the example shown, as the output of comparator 604 rises in buffer 606, the pixel value is replaced by a digital value by the counter value of storage counter 605.

[0087] Figure 6 This is a signal diagram in a CDS implemented on a CMOS image sensor. Figure 6In the diagram, the upper solid line shows the RAMP signal used as a reference for the AD conversion, and the dashed line shows the pixel output (analog input) voltage. The lower solid line shows the output of comparator 604. The first slope of the RAMP signal begins at time t0. A reset operation is performed during the reset level period starting from time t0, and counter 605 performs a countdown operation. Next, when the output level of comparator 604 rises, counting stops at time t1, and the counter value is stored in buffer 606. Then, the second slope begins at time t2. A signal output operation is performed during the signal level period starting from time t2, and counter 605 begins counting upwards. Next, when the output level from comparator 604 rises, counting stops at time t3, and the counter value is stored in buffer 606. The digital value of the pixel output is then obtained by calculating the difference between the two counter values ​​stored in buffer 606 and obtaining the difference between the digital values. In this way, CDS is performed, and noise components contained in the pixel output can be removed.

[0088] exist Figure 6 In this process, due to noise derived from the PWM signal used for OIS driving, the pixel output can fluctuate as shown by arrow 502. This fluctuation causes fluctuations in the comparison result of comparator 604, and the rise time of the output signal also fluctuates within the range shown by arrows 504 and 506. The fluctuation in the rise time of comparator 604 further leads to fluctuations in the CDS time interval, thus causing noise.

[0089] Next, refer to Figure 7 and Figure 8 This will describe the limitations of PWM control when executing CDS.

[0090] Figure 7 An example configuration of a lens actuator system is shown. The lens actuator system 800 includes a lens unit 808 and a servo controller 814. The lens unit 808 includes a lens 804, an actuator 806, and a gyroscope sensor 812. The servo controller 814 includes a driver 810, a PWM signal generator 820, and a duty cycle generator 816. In this configuration, when an image is captured using the lens actuator system 800, the image is input from the lens 804 to the imaging unit 802. The imaging unit 802 includes an image sensor, and the image sensor outputs an image signal DATA based on the analog signal from the lens 804. The imaging unit 802 also outputs a control signal Sctrl to the PWM signal generator 820.

[0091] Information regarding the movement of lens 804 is obtained by gyroscope sensor 812. Gyroscope sensor 812 outputs a SENS_OUT signal to duty cycle generator 816. SENS_OUT contains lens movement information (lens acceleration, velocity, and position). Duty cycle generator 816 calculates the duty cycle of the PWM signal to be generated based on the SENS_OUT signal. The calculated duty cycle is sent to PWM signal generator 820. PWM signal generator 820 generates a PWM signal Sdrv0 based on the input duty cycle and control signal Sctrl, and sends the generated PWM signal Sdrv0 to driver 810. Driver 810 generates a drive signal Sdrv based on PWM signal Sdrv0 and outputs it to actuator 806. Actuator 806 moves lens 804 based on drive signal Sdrv to perform OIS control.

[0092] Figure 8 Waveforms of the signals used to perform CDS in the ADC and the PWM signals used for OIS driving are shown. Figure 8 In the diagram, the solid line at the top represents the RAMP signal, and the dashed line represents the pixel output (analog input). The second line shows the comparator output. The third line shows the control signal Sctrl. The fourth through sixth signals represent PWM signals with duty cycles of 10%, 40%, and 90%, respectively. When CDS is executed in the ADC, noise may occur if the PWM signal levels differ at the rise times t1 and t2 of the comparator output. Therefore, when drive control is performed with multiple PWM signals, it is preferable that the multiple PWM signals have the same level at the rise times t1 and t2 of the comparator output during the AD conversion operation cycle t0.

[0093] For four SMA wires using time-division driving, it may be difficult to implement this technology because the maximum pulse width and PWM signal frequency are constrained by the AD conversion cycle.

[0094] This invention provides a method to avoid interference noise generated by a PWM driver without setting a frequency limit between the AD conversion operation and the PWM driver.

[0095] In this embodiment, the waveform modulator generates an output signal for the actuator or other devices by modulating the output PWM signal, thereby driving these devices according to the following rules:

[0096] (1) During the switching disable period defined by the MASK signal, the output PWM signal (H / L) is not switched.

[0097] (2) Outside of the switching disable period, (a) set the output PWM signal to have the same duty cycle as the reference PWM signal, or (b) if the duty cycle of the output is equal to the duty cycle of the reference PWM signal, set the output PWM signal to the reference PWM signal. Here, the switching disable period should include the CDS period (i.e., the CDS period) between the start of reset sampling and the end of signal sampling.

[0098] According to this embodiment, the waveform modulator includes a duty cycle error monitor that measures the duration by which the output H / L state period differs from the H / L state period of the reference PWM signal. The waveform modulator then generates the actual PWM signal by modulating the reference PWM signal based on the output of the duty cycle error monitor and a MASK signal. Here, the MASK signal indicates the inhibit period for preventing switching of the output PWM signal (H / L).

[0099] Figure 9 This is a block diagram of a lens actuator system with a waveform modulator provided in this embodiment. Figure 9 The definition of each signal shown is as follows.

[0100] MASK is a control signal used to define the disable cycle to be switched. SENS_OUT contains lens movement information (lens acceleration, velocity, and position). REF_PWM is a reference PWM signal whose duty cycle is determined by the servo system. ERR is a flag signal indicating whether the actual duty cycle is higher or lower than the target duty cycle. Additionally, ACT_PWM is a pulse train of the actual PWM signal used for the motion actuator.

[0101] The lens actuator system 900 includes a lens unit 902, a servo controller (PWM driver) 904, and an image sensor with a CDS 906. The lens unit 902 includes a lens 908, an actuator 910, and a gyroscope sensor 912. The servo controller (PWM driver) 904 includes a driver 914, a waveform generator 919, and a PWM signal generator 920. The waveform generator 919 includes a waveform modulator 916 and a duty cycle error monitor 918. In this configuration, when an image is captured using a camera including the lens actuator system 900, pixel output is input from the lens 908 to the image sensor with the CDS 906. The image sensor with the CDS 906 performs a conversion process that converts the analog signal of the captured image into a digital output. The image sensor with the CDS 906 performs CDS in the AD conversion for the pixel output (analog input) from the lens 908 and outputs the image signal DATA. In addition, the image sensor with CDS 906 outputs the MASK signal to the waveform modulator 916.

[0102] Information regarding the movement of lens 908 is output to gyroscope sensor 912. Based on the received movement information of lens 908, gyroscope sensor 912 outputs a SENS_OUT signal to PWM signal generator 920. PWM signal generator 920 generates a REF_PWM signal based on the SENS_OUT signal and outputs it to waveform modulator 916 and duty cycle error monitor 918. Duty cycle error monitor 918 counts the number of clock pulses used to control the imaging unit. Furthermore, duty cycle error monitor 918 generates an ERR flag based on the REF_PWM signal and ACT_PWM signal from waveform modulator 916 and outputs the ERR flag to waveform modulator 916. Waveform modulator 916 generates an ACT_PWM signal based on the values ​​of the MASK signal, REF_PWM signal, and ERR flag. ACT_PWM signal is output to driver 914 and duty cycle error monitor 918. Driver 914 outputs the input ACT_PWM signal to actuator 910. Actuator 910 drives lens 908 based on ACT_PWM signal.

[0103] Figure 10 This is a waveform diagram used to explain the waveform operation of a waveform modulator. Figure 10 In the diagram, the first line shows the RAMP signal used for AD conversion. The second signal represents MASK, and the third signal represents REF_PWM. The fourth signal shows the counter value of the counter included in the duty cycle error monitor 918, and the fifth signal shows the value of the ERR flag. Additionally, the last signal shows the ACT_PWM signal.

[0104] The MASK signal indicates the disable period for state H. During the disable period, ACT_PWM is controlled to prevent it from switching. The disable period is set to include the period from the start of the reset operation to the end of the signal output operation within one cycle of the AD conversion.

[0105] The duty cycle of REF_PWM is set based on SENS_OUT from gyroscope sensor 912. In this embodiment, the duty cycle is set to 60%.

[0106] The duty cycle error monitor 918 counts upwards as shown by arrow 1002 (t1 to t2) when the reference PWM signal REF_PWM is L and the waveform modulator 916 outputs H, referencing the counter value CNT. When the reference PWM signal REF_PWM is H and the waveform modulator 916 outputs L, the duty cycle error monitor 918 counts downwards as shown by arrows 1004 (t3 to t4) and 1006 (t5 to t7). The ERR flag is set to –1 when the counter value is positive and set to 1 when the counter value is negative. Therefore, when the counter value CNT is positive (ERR = –1), the H level period of the output signal ACT_PWM is shorter than the H level period of the reference PWM signal REF_PWM. On the other hand, when the counter value CNT is negative (ERR = +1), the L level period of the output signal is less than the L level period of the reference PWM signal REF_PWM. The waveform modulator 916 selects the output level based on the counter value.

[0107] When the ERR flag is -1 (t3), the ACT_PWM signal is in the L state; when the ERR flag is +1 (t7), the ACT_PWM signal is in the H state. Therefore, the ACT_PWM signal is set as follows:

[0108] (1) When CNT is positive, ACT_PWM is L

[0109] (2) When CNT is negative, ACT_PWM is H

[0110] (3) When CNT is “0”, the output signal is the same as the reference PWM signal REF_PWM.

[0111] Based on the above operation, the switching disable period is set so that the actual PWM signal does not switch during the AD conversion process that converts the analog signal of the image captured by the image sensor into a digital output. Therefore, the PWM state changes within one cycle of the CDS, and noise in the AD conversion of the image sensor is suppressed.

[0112] Figure 11 It shows Figure 10 The relationship between the RAMP signal and the ACT_PWM signal used for AD conversion operation during the period (X). Figure 11 In this configuration, the output level of ACT_PWM remains constant during one cycle of the AD conversion operation. Furthermore, as indicated by arrows 1102 and 1104, the average duty cycle is the same as that of REF_PWM. Therefore, waveform modulator 916 can switch the actual PWM signal so that the actual PWM signal approximates the duty cycle of the reference PWM signal.

[0113] Figure 12 This is the state transition diagram for this embodiment. Figure 12The diagram contains six states: 1301, 1302, 1303, 1304, 1305, and 1306. In the three states on the left (1301, 1302, and 1303), ACT_PWM is in the H state. Furthermore, in the three states on the right (1304, 1305, and 1306), ACT_PWM is in the L state. Additionally, the CNT values ​​for the two center states 1302 and 1305 are 0. The two upper states 1301 and 1304 have positive CNT values, and the two lower states 1303 and 1306 also have positive CNT values. This means that the condition is determined regardless of the value of MASK.

[0114] For example, in state 1302, ACT_PWM is in state H and CNT is 0. If REF_PWM = H, the state remains unchanged. Here, when REF_PWM changes to L, if MASK = H, it transitions to state 1301; if MASK = L, it transitions to state 1305. In state 1301, if after CNT decreases, REF_PWM = H, MASK = L, and CNT > 0, it transitions to state 1304. If REF_PWM = L and MASK = L, it also transitions to state 1304. On the other hand, if after CNT decreases, REF_PWM = H, MASK = L, and CNT = 0, it transitions to state 1305.

[0115] According to this embodiment, when the MASK signal is set to high (H), ACT_PWM is not switched. Here, "high" refers to the period of the AD conversion using CDS, which is the period from the start of the reset operation to the end of the signal output operation within one cycle of the AD conversion. This means that fluctuations in the PWM signal edge will not cause noise during the AD conversion process. Therefore, due to the switching of ACT_PWM, the AD conversion operation will not experience noise. Therefore, there is no need to consider the limitation of the relationship between the PWM carrier frequency and the AD conversion period.

[0116] (Second Embodiment)

[0117] In a preferred embodiment of the invention, the counter in the duty cycle error monitor 918 can have the capability to count the number of clock cycles of the PWM signal's duty cycle control clock over a period twice the length of the switching disable cycle. That is, if the number of pulses in a switching disable cycle is T( Figure 13 If the "counting number" is specified in the counter, then the values ​​from –T to +T should be stored in the counter.

[0118] In one embodiment, when a counter overflow is possible, the waveform modulator 916 can be used to switch its output in the event of a counter overflow in the duty cycle error monitor to resolve the data overflow. In this case, the count digit CNT can be switched even during a switching disable cycle. In this case, the actual PWM signal can be switched even during a disable cycle. However, typically, the down-counting for a reset operation begins in the first half of an AD conversion cycle, and the up-counting for a signal output operation begins in the second half of an AD conversion cycle. On the other hand, switching due to down-count overflow may occur in the second half of the disable cycle. Therefore, by controlling the switching as described above, the impact of counter value overflow used to monitor duty cycle error can be reduced.

[0119] Figure 13 This is a schematic diagram showing the operating waveform of the duty cycle error monitor 916 provided in this embodiment in the event of an overflow. Figure 13 In the diagram, the range of countable digits for the counter value CNT is indicated by arrow 1406. On the other hand, the range of actual values ​​is set narrow, as shown by arrow 1408. The upward counting of CNT begins at time t0. Since CNT overflows at time t1, ACT_PWM changes from the L state to the H state even during the disable cycle, as shown by arrow 1404. When CNT does not overflow, ACT_PWM changes to the H state at time t2. Even during the disable cycle, typically, time t1 is located in the latter half of the AD conversion cycle when the comparator responds to a large signal input level. With large signal input levels, the impact of noise on the image signal becomes relatively small.

[0120] Figure 14 This is the state transition diagram for this embodiment. Figure 12 The difference is that when CNT reaches its maximum value (CNT = MAX) in state 1301, the state transitions to state 1304, as shown by arrow 1502. Furthermore, when CNT reaches its minimum value (CNT = MIN) in state 1306, the state moves to state 1303, as shown by arrow 1504.

[0121] According to this embodiment, PWM control can continue to be performed with lower noise while reducing the impact of counter overflow.

[0122] (Third Embodiment)

[0123] Figure 15 This is a block diagram of a lens actuator system with a waveform modulator according to a third embodiment of the present invention. The lens actuator system 1600 has a... Figure 9The configuration shown is essentially the same, except that waveform generator 919 includes a MASK generator 1602. MASK generator 1602 generates a MASK signal based on the horizontal synchronization signal HSYNC output from an image sensor with CDS 906. Since the horizontal synchronization signal HSYNC is a synchronization signal used for AD conversion, the MASK signal can be generated synchronously with the AD conversion process. The effects of this invention can be achieved even when the MASK signal is generated by a servo controller (PWM driver) 904.

[0124] Figure 16 The diagram illustrates the signal waveforms when the lens actuator system 1600 provided in this embodiment is applied to drive four SMAs. The PWM signal ACT_PWM used to drive the four wires, i.e., wires WIRE0, WIRE1, WIRE2, and WIRE3, is switched outside the disable cycle. Comparing the reference PWM signal REF_PWM on each wire with the actual PWM signal ACT_PWM, the duty cycles of the two PWM signals are similar.

[0125] As described above, according to the present invention, the PWM signal is modulated by (1) a MASK signal that is prohibited from switching during one cycle of the AD conversion operation, and (2) a measurement of the duty cycle error caused by the non-switching. The reference PWM signal is switched so that its duty cycle is matched with the target duty cycle of the servo loop based on the error in the duty cycle, taking into account the switching prohibition period defined by the MASK signal.

[0126] Therefore, the influence of noise on pixel output AD conversion can be eliminated, without being limited by the combination of PWM carrier frequency and AD conversion cycle.

[0127] Furthermore, noise can be easily eliminated by monitoring the communication channel between the imaging sensor and the lens driver, as well as the modulated PWM signal used to drive the actuator.

[0128] This invention can be applied to systems with ADCs embedded in various sensors and PWM actuators close to the sensors (e.g., image sensors and lens actuators driven by stepper motors, etc.) to reduce the impact of emission noise generated by actuator driving.

[0129] The summary description is merely a specific implementation of the present invention and is not intended to limit the scope of protection of the present invention. Any variations or substitutions that are readily conceived by those skilled in the art within the scope of the disclosed technology should fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A PWM driver for generating a PWM signal for driving a lens, characterized in that, include: A PWM signal generator is used to generate a reference PWM signal that switches at a predetermined period. A receiving unit is configured to receive a mask signal defining a switching prohibition period, the mask signal being generated based on a control signal used for analog-to-digital conversion of an image captured by an image sensor; A modulation unit is used to generate an actual PWM signal by not switching the reference PWM signal during the switching disable period defined by the mask signal.

2. The PWM driver according to claim 1, characterized in that, The PWM signal generator generates the reference PWM signal based on the movement of the lens.

3. The PWM driver according to claim 2, characterized in that, The PWM signal generator obtains motion information from a gyroscope sensor that detects the movement of the lens.

4. The PWM driver according to claim 1, characterized in that, It also includes a counter, which is used to increase or decrease the counter value of the number of clock pulses according to the H state or L state of the actual PWM signal, wherein the modulation unit is used to switch the actual PWM signal based on the counter value in order to minimize the absolute value of the counter value outside the switching prohibition period.

5. The PWM driver according to claim 4, characterized in that, The range of the counter corresponds to the period of the reference PWM signal for the analog-to-digital conversion.

6. The PWM driver according to claim 5, characterized in that, When the counter value overflows during the switching disable period, the modulation unit switches the actual PWM signal.

7. The PWM driver according to claim 1, characterized in that, The switching disable period is configured such that the actual PWM signal does not switch during the conversion process of converting the analog signal of the image captured by the image sensor into a digital output.

8. The PWM driver according to claim 1, characterized in that, It also includes a monitor for instructing the modulation unit to switch the actual PWM signal based on the reference PWM signal and the actual PWM signal.

9. The PWM driver according to claim 8, characterized in that, The monitor instructs the modulation unit to switch the actual PWM signal so that the actual PWM signal approaches the duty cycle of the reference PWM signal.

10. The PWM driver according to claim 1, characterized in that, It also includes a mask generation unit for generating the mask signal.

11. An actuator system, characterized in that, include: The PWM driver according to any one of claims 1 to 10; A lens unit is used to drive the lens based on the actual PWM signal generated by the PWM driver.

12. A camera module, characterized in that, include: The actuator system according to claim 11; An imaging unit for capturing images using a lens driven by the actuator system.

13. A method for generating a PWM signal for driving a lens, characterized in that, include: Generate a reference PWM signal that switches at a predetermined period; Receive a mask signal that defines a switching prohibition period, the mask signal being generated based on control signals used for analog-to-digital conversion of images captured by an image sensor; The actual PWM signal is generated by not switching the reference PWM signal during the switching disable period defined by the mask signal.

14. The method according to claim 13, characterized in that, The step of generating the reference PWM signal is based on the movement of the lens.

15. The method according to claim 13 or 14, characterized in that, The step of generating the reference PWM signal obtains motion information from a gyroscope sensor that detects the movement of the lens.

16. The method according to claim 13, characterized in that, Also includes: The counter value for increasing or decreasing the number of clock pulses is determined based on the H or L state of the actual PWM signal, wherein the step of generating the reference PWM signal is based on the counter value to minimize the absolute value of the counter value outside the switching disable period.

17. The method according to claim 16, characterized in that, The range of the counter corresponds to the period of the reference PWM signal for the analog-to-digital conversion.

18. The method according to claim 17, characterized in that, When the counter value overflows during the switching disable period, the step of generating the actual PWM signal switches the actual PWM signal.

19. The method according to claim 13, characterized in that, The switching disable period is configured such that the actual PWM signal does not switch during the conversion process of converting the analog signal of the image captured by the image sensor into a digital output.

20. The method according to claim 13, characterized in that, The step of generating the actual PWM signal includes switching the actual PWM signal based on the reference PWM signal and the actual PWM signal.

21. The method according to claim 20, characterized in that, The step of generating the actual PWM signal involves switching the actual PWM signal so that the actual PWM signal has a duty cycle close to that of the reference PWM signal.

22. The method according to claim 13, characterized in that, It also includes the step of generating the mask signal.

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