Methods and devices for controlling access to an optical disc

A device for controlling access to an optical disc includes a control word calculator and a numerically controlled oscillator (NCO). The control word calculator is arranged to calculate a control word corresponding to a radius where the optical disc is accessed. In addition, the NCO is arranged to generate an output frequency according to the control word, wherein the output frequency is utilized for accessing the optical disc. An associated method for controlling access to an optical disc includes: calculating a control word corresponding to a radius where the optical disc is accessed; and generating an output frequency according to the control word, wherein the output frequency is utilized for accessing the optical disc.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to optical disc access control, and more particularly, to methods and devices for controlling access to an optical disc.

2. Description of the Related Art

A conventional optical disc device typically comprises a closed loop generating a channel bit clock for accessing an optical disc. According to the related art, the closed loop is implemented as a phase locked loop (PLL). For example, in a reading procedure of the optical disc device, the PLL receives a data signal derived from the optical disc, and utilizes the data signal as a reference signal for the operation of the PLL. As the data signal is read from the optical disc and the PLL generates the channel bit clock by utilizing the data signal as the reference signal, and as the optical disc device reads the data signal from the optical disc based on the channel bit clock, it is indeed a closed loop and the control thereof requires many high accuracy components. As a result, a tradeoff between reducing the costs of the conventional optical disc device and preventing the closed loop control from being degraded is introduced.

In another example, when the optical disc is a Rewritable disc with wobbles pre-grooved on the optical disc, the wobbles typically carry certain disc information and address information. The PLL receives a wobble signal derived from the optical disc in accordance with the wobbles, and utilizes the wobble signal as the reference signal for the operation of the PLL. As the wobble signal is read from the optical disc and the PLL generates the channel bit clock by utilizing the wobble signal as the reference signal, and as the optical disc device utilizes the channel bit clock to access the optical disc, it is indeed a closed loop and the control thereof also requires many high accuracy components. Similarly, the above-mentioned tradeoff is again introduced.

In order to reduce the costs of the conventional optical disc device, a novel method is therefore required for reducing the costs of the products without lowering the performance, in order to benefit both the end users and the manufacturers.

SUMMARY

It is therefore an objective of the claimed invention to provide methods and devices for controlling access to an optical disc, in order to solve the above-mentioned problem.

It is another objective of the claimed invention to provide methods and devices for controlling access to an optical disc, in order to reduce costs of products (e.g. optical storage devices implemented according to the present invention, and associated control circuits) without lowering the performance thereof. As a result, the end users and the manufacturers can benefit.

An exemplary embodiment of a device for controlling access to an optical disc comprises a control word calculator and a numerically controlled oscillator (NCO). The control word calculator is arranged to calculate a control word corresponding to a radius where the optical disc is accessed. In addition, the NCO is arranged to generate an output frequency according to the control word, wherein the output frequency is utilized for accessing the optical disc.

An exemplary embodiment of a method for controlling access to an optical disc comprises: calculating a control word corresponding to a radius where the optical disc is accessed; and generating an output frequency according to the control word, wherein the output frequency is utilized for accessing the optical disc.

DETAILED DESCRIPTION

Please refer toFIG. 1, which illustrates a diagram of a device for controlling access of an optical disc according to a first embodiment of the present invention. The device of this embodiment is a device100for controlling access to an optical disc, wherein the device100can be seen as a part of an optical storage device. This is for illustrative purposes only, and is not meant to be a limitation of the present invention. According to a variation of this embodiment, the device represented by the numeral shown inFIG. 1can be a portion of the optical storage device, such as a control circuit within the optical storage device. According to another variation of this embodiment, the device mentioned above can be at least a portion of the optical storage device, such as the whole of the optical storage device.

As shown inFIG. 1, the device comprises a control word calculator110(labeled “CW calculator”) and a numerically controlled oscillator (NCO)120. The control word calculator110is arranged to calculate a control word CW corresponding to a radius where the optical disc is accessed (i.e. the radius where an optical pickup unit (OPU) of the device100accesses the optical disc). In addition, the numeral101labeled at an input of the control word calculator110represents a radius indicator corresponding to the radius where the optical disc is accessed.

For example, the radius indicator101can be a counter value related to revolutions of the optical disc, for example, the counter value is derived from a hall sensor of the device100, and the control word calculator110calculates the control word CW according to the counter value. In another example, the radius indicator101can be an elapsed time representing a number of elapsed revolutions of the optical disc (e.g. the elapsed revolutions are proportional to the number of elapsed revolutions), and the control word calculator110calculates the control word CW according to the elapsed time. In another example, the radius indicator101can be a coding address such as an encoding address or a decoding address for accessing the optical disc (e.g. an encoding address for writing the optical disc, or a decoding address for reading the optical disc), and the control word calculator110calculates the control word CW according to the encoding address or the decoding address.

According to this embodiment, the NCO120is arranged to generate an output frequency according to the control word CW, where the control word CW may represent a frequency control word (FCW) value or a period control word (PCW) value. In practice, the NCO120can be implemented with a specific circuit comprising a voltage controlled oscillator (VCO) (not shown) controlled by a digital-to-analog converter (DAC) (not shown), where the control word CW represents an FCW value, and the control word calculator110can be referred to as the FCW calculator. Thus, the NCO120generates the output frequency by controlling a frequency of the output of the VCO according to the FCW value represented by the control word CW. This is for illustrative purposes only, and is not meant to be a limitation of the present invention.

According to a variation of this embodiment, the NCO120can be implemented with the specific circuit equipped with a voltage mapping circuitry, where the control word CW represents a PCW value, and the control word calculator110can be referred to as the PCW calculator. Thus, the NCO120generates the output frequency by controlling a period of the output of the VCO according to the PCW value represented by the control word CW. According to another variation of this embodiment, the NCO120can be implemented with an oscillator of another type.

In addition, the output frequency is utilized for accessing the optical disc. For example, the output frequency is utilized as a clock signal, and can be utilized for writing or reading the optical disc, such as utilized for encoding or decoding, wherein the clock signal can be referred to as a channel bit clock. In another example, the output frequency is utilized for performing spindle control during a writing procedure or a reading procedure.

According to a special case of this embodiment, the device100operates in a constant angular velocity (CAV) mode, and the output frequency is utilized as a clock, which is described as the channel bit clock later. In this special case, the linear velocity is proportional to the radius while the OPU is moving from inner tracks to outer tracks of the optical disc. The control word calculator110is arranged to calculate the control word CW according to this relationship and according to characteristics of the control word calculator110mentioned above. As a result of the calculations of the control word calculator110in this special case, the output frequency has a properly increased frequency while the OPU is moving from the inner tracks to the outer tracks of the optical disc, and therefore can be utilized as a channel bit clock.

According to another special case of this embodiment, the device100operates in a constant linear velocity (CLV) mode, and the output frequency is utilized for further operation, such as performing spindle control. In the CLV mode, the angular velocity is inversely proportional to the radius while the OPU is moving from the inner tracks to the outer tracks of the optical disc. The control word calculator110is arranged to calculate the control word CW according to this relationship and according to characteristics of the control word calculator110mentioned above. As a result of the calculations of the control word calculator110in this special case, the output frequency has a properly decreased frequency while the OPU is moving from the inner tracks to the outer tracks of the optical disc, and therefore can be utilized for performing spindle control.

In contrast to the related art, the present invention devices such as the device shown inFIG. 1and the associated methods mentioned above help end users and the manufacturers to get benefit from the reduction in related costs.

It is another advantage of the present invention that, in a situation where the optical disc is a wobbleless disc, the present invention methods and devices can be utilized for controlling access to the optical disc without difficulties that will be encountered by the closed loop control of the related art. When access the wobbleless disc, the encoding or decoding address used to obtain the radius indicator101described above is derived from data address.

FIG. 2is a diagram of a device for controlling access to an optical disc according to a second embodiment of the present invention, where this embodiment is a variation of the first embodiment. The numeral100is replaced by another numeral200since a counter205is inserted between the radius indicator101and the control word calculator110. This is for illustrative purposes only, and is not meant to be a limitation of the present invention. According to a variation of this embodiment, the device mentioned above can be a portion of the optical storage device of the second embodiment, such as a control circuit within the optical storage device. According to another variation of this embodiment, the device mentioned above can be at least a portion of the optical storage device of the second embodiment, such as the whole of the optical storage device.

In this embodiment, the counter205is arranged to generate a counter value corresponding to the radius where the optical disc is accessed. For example, the counter205counts the radius indicator101mentioned above to generate a counter value, where the counter value is utilized as a representative of the radius indicator101, and is therefore input into the control word calculator110.

In addition, the output frequency is utilized as a channel bit clock. This is for illustrative purposes only, and is not meant to be a limitation of the present invention. According to a variation of this embodiment, the output frequency is utilized for performing spindle control. Similar descriptions for this embodiment or for associated variations thereof are not repeated in detail here.

FIG. 3is a diagram of a device for controlling access to an optical disc according to a third embodiment of the present invention. The device of this embodiment is a device300for controlling access to an optical disc. This is for illustrative purposes only, and is not meant to be a limitation of the present invention. According to a variation of this embodiment, the device represented by the numeral300shown inFIG. 3can be a portion of the optical storage device of the third embodiment, such as a control circuit within the optical storage device. According to another variation of this embodiment, the device mentioned above can be at least a portion of the optical storage device of the third embodiment, such as the whole of the optical storage device.

As shown inFIG. 3, the device comprises a control word calculator310(labeled “CW calculator”), a NCO320and a spindle control circuit350(labeled “Spindle control”), where the NCO320of this embodiment comprises a multiplexer322(labeled “MUX”) and a frequency divider324. In addition, the device further comprises a frequency multiplier and/or a frequency divider, such as a frequency multiplier342and a frequency divider344.

The control word calculator310is arranged to calculate a control word ZCAV_DIV[15:0] corresponding to a radius where the optical disc is accessed (i.e. the radius where an OPU of the device300accesses the optical disc). More particularly, the control word calculator310generates the control word ZCAV_DIV[15:0] according to the radius indicator101mentioned above.

In addition, a selection signal ZCAV_EN is utilized for enabling the NCO320to receive the control word ZCAV_DIV[15:0]. When the selection signal ZCAV_EN is in a state “0”, the NCO320receives a fixed value (such as a fixed value ‘2048’) through an input terminal “0” of the multiplexer322. As a result, the NCO320is arranged to generate an output frequency spin_pd_ref according to the fixed value. When the selection signal ZCAV_EN is in a state “1”, the NCO320receives the control word ZCAV_DIV[15:0] through an input terminal “1” of the multiplexer322. As a result, the NCO320is arranged to generate the output frequency spin_pd_ref according to the control word ZCAV_DIV[15:0], where the output frequency is utilized for accessing the optical disc. Please note that the frequency divider324is arranged to convert a reference frequency Fr into the output frequency spin_pd_ref according to a divisor corresponding to the control word ZCAV_DIV[15:0], where the frequency divider324performs a frequency dividing operation on the reference frequency Fr to generate the output frequency spin_pd_ref.

In this embodiment, the frequency multiplier342and the frequency divider344are arranged to convert a hall sensor output frequency FG into a frequency spin_pd_in. It is noted that the frequency spin_pd_in is derived from a hall sensor which detects the operation of a spindle (not shown), and the frequency spin_pd_in can be taken as a feedback frequency. In addition, the spindle control circuit350is arranged to perform spindle control according to the output frequency spin_pd_ref and the feedback frequency spin_pd_in. More particularly, the spindle control circuit350comprises a frequency detector (FD) (not shown) or a phase detector (PD) (not shown), arranged to detect a difference between the output frequency spin_pd_ref and the feedback frequency spin_pd_in.

As mentioned, the NCO320of this embodiment comprises the frequency divider324arranged to convert the reference frequency Fr into the output frequency spin_pd_ref according to the divisor corresponding to the control word ZCAV_DIV[15:0]. This is for illustrative purposes only, and is not meant to be a limitation of the present invention. According to a variation of this embodiment, the NCO320comprises a frequency multiplier (not shown) arranged to convert the reference frequency Fr into the output frequency spin_pd_ref according to a multiplicator corresponding to the control word ZCAV_DIV[15:0]. According to another variation of this embodiment, the NCO320comprises a frequency multiplier (not shown) and/or a frequency divider, arranged to convert the reference frequency Fr into the output frequency spin_pd_ref according to at least one multiplicator/divisor corresponding to the control word ZCAV_DIV[15:0].

FIG. 4illustrates implementation details of the control word calculator310shown inFIG. 3according to one embodiment of the present invention, where the radius indicator101of this embodiment is derived from the hall sensor output frequency FG mentioned above. The control word calculator310comprises a counter310c, a step control unit312, a plurality of multiplexers314-1and314-2(labeled “MUX”), a register316and an adder318. Please note that the multiplexers314-1and314-2are two copies of the multiplexer322shown inFIG. 3. As a result, operations of the multiplexers314-1and314-2are similar to the above-mentioned operations of the multiplexer322.

According to this embodiment, the counter310ccounts revolutions of the optical disc based on the hall sensor output frequency FG to generate a counter value CV corresponding to a number of elapsed revolutions of the optical disc, where the selection signal ZCAV_EN is utilized for enabling the counting operation of the counter310c. When the selection signal ZCAV_EN changes from the state “0” to the state “1”, the counter310cstarts to count the counter value CV with an initial value to make the counter value CV start from zero. When the counter310cstarts to count the counter value CV, it is suggested that the control word calculator310should apply a setting signal ZCAV_DIV_SET_VAL carrying an initial value of the control word ZCAV_DIV[15:0] to the multiplexer314-2, and the initial value of the control word ZCAV_DIV[15:0] is stored into the register316.

Most of the time, another two selection signals ZCAV_DIV_SET and ZCAV_DIV_INC are typically in the state “0” to keep the control word ZCAV_DIV[15:0] from being changed. The control word calculator310sets the selection signal ZCAV_DIV_SET to be in the state “1” when applying the setting signal ZCAV_DIV_SET_VAL to the multiplexer314-2is required. In addition, the step control unit312sets the selection signal ZCAV_DIV_INC to be in the state “1” when increasing the control word ZCAV_DIV[15:0] with an increment is required. More particularly, when the counter value CV is equal to a threshold value ZCAV_DIV_INC_THRE or a multiple of the threshold value ZCAV_DIV_INC_THRE, the step control unit312sets the selection signal ZCAV_DIV_INC to be in the state “1”. As a result, the control word calculator310increases the control word ZCAV_DIV[15:0] with the increment every ZCAV_DIV_INC_THRE counts of the counter value CV.

In this embodiment, increasing the control word ZCAV_DIV[15:0] with the increment is implemented with the adder318arranged to receive an increment step ZCAV_DIV_INC_STEP representing the increment. This is for illustrative purposes only, and is not meant to be a limitation of the present invention. According to a variation of this embodiment, in a situation where decreasing the control word ZCAV_DIV[15:0] with a decrement is required, the adder318can be replaced with a subtractor arranged to receive a decrement step ZCAV_DIV_DEC_STEP (not shown) representing the decrement.

According to this variation, the selection signal ZCAV_DIV_INC and the threshold value ZCAV_DIV_INC_THRE can be renamed as generalized names, for example, the selection signal ZCAV_DIV_INC_DEC and the threshold value ZCAV_DIV_INC_DEC_THRE, respectively. As a result, the control word calculator310increases the control word ZCAV_DIV[15:0] with the increment every ZCAV_DIV_INC_DEC_THRE counts of the counter value CV in an increasing mode, and decreases the control word ZCAV_DIV[15:0] with the decrement every ZCAV_DIV_INC_DEC_THRE counts of the counter value CV in a decreasing mode.

FIG. 5illustrates practical design values that the control word calculator310shown inFIG. 3utilizes for calculations according to the embodiment shown inFIG. 4. The inclined line on the top is extracted from a portion of a design curve with the horizontal and the vertical axes respectively representing an accessed track (e.g. the track where the OPU accesses the optical disc) and a divisor (e.g. the divisor corresponding to the control word ZCAV_DIV[15:0]).

As shown inFIG. 5, the divisor changes from 2048 to 4916 while the OPU is moving from the inner tracks to the outer tracks of the optical disc, where 4916/2048=2.4 approximately, while 2.4 represents a ratio of the maximal radius to the minimal radius of the tracks. As the number of tracks is around 40000, and as the total increment of the divisor is equal to 2868, the slope of the inclined line is around 2686/40000=7/100 approximately. Therefore, the setting signal ZCAV_DIV_SET_VAL can be set as 2048, and the increment step ZCAV_DIV_INC_STEP and the threshold value ZCAV_DIV_INC_THRE can be set as 7 and 100, respectively.

Please note that, according to the architecture shown inFIG. 3, the spindle control circuit350typically performs the spindle control to maintain the feedback frequency spin_pd_in and the output frequency spin_pd_ref at the same frequency. The feedback frequency spin_pd_in can be expressed according to the following equation:
spin_pd_in=FG*(Mf)/(Df);
where Mf and Df respectively represent the multiplicator of the frequency multiplier342and the divisor of the frequency divider344on the feedback path (i.e. the path from FG to the spindle control circuit350).

In addition, the output frequency spin_pd_ref can be expressed according to the following equation:
spin_pd_ref=Fr/(Dr);
where Dr represents the divisor of the frequency divider324on the reference path (i.e. the path from Fr to the spindle control circuit350).

In order to maintain the feedback frequency spin_pd_in and the output frequency spin_pd_ref the same, let spin_pd_in=spin_pd_ref, which means
FG*(Mf)/(Df)=Fr/(Dr);

In the third embodiment, by changing the divisor Dr (e.g. the divisor Dr is proportional to the radius), the frequency divider324is utilized for implementing the NCO320of this embodiment. This is for illustrative purposes only, and is not meant to be a limitation of the present invention.

Therefore, the spindle control circuit350of the device300is arranged to control the disc to operate in several CAV modes with different angular velocities, wherein the different angular velocities are inversely proportional to the radius, and the angular velocities reduce from the inner tracks to the outer tracks of the optical disc based on the equation: FG*(Mf)/(Df)=Fr/(Dr). By utilizing this device300a, when the difference between the angular velocities is small enough, the optical disc can operate in a CLV mode approximately.

According to a variation of the third embodiment, such as the variation shown inFIG. 6, by changing the multiplicator Mf (e.g. the multiplicator Mf is proportional to the radius), the frequency multiplier342can be utilized for implementing the NCO320of this variation, where the output of the multiplexer322is redirected to the frequency multiplier342in order to control the multiplicator Mf with the control word ZCAV_DIV[15:0]. Therefore, the spindle control circuit350aof the device300ais arranged to control the disc to operate in a CLV mode approximately. Similar descriptions for this variation are not repeated in detail here.

According to another variation of the third embodiment, such as the variation shown inFIG. 7, by changing the divisor Df (e.g. the divisor Df is inversely proportional to the radius), the frequency divider344can be utilized for implementing the NCO320of this variation, where the output of the multiplexer322is redirected to the frequency divider344in order to control the divisor Df with the control word ZCAV_DIV[15:0]. Therefore, the spindle control circuit350bof the device300bis arranged to control the disc to operate in a CLV mode approximately. Similar descriptions for this variation are not repeated in detail here.