Patent Application
20110241560
The present invention relates to the field of generating drive signals, especially for lamp devices, such as LED spots.
The adjustment of the brightness of an LED (light emitting diode) lightning device, such as an LED spot (for example, with a plurality of LEDs) is realized by a fast off and on switching of the LEDs. The higher the ratio between an on-state and an off-state of the LED is, the brighter the LED seems to light. If the frequency of the on and off switching is above 100 Hz, the human eye does not recognize the pulsing (the on and off switching) of the LEDs.
For cameras, especially for the new HDTV cameras, this on and off switching of the LEDs poses a problem. The pulsing of the LEDs leads to interferences with shutter-times and refresh-rates of the HDTV cameras. This can be recognized by a pulsing of the light in the camera.
A modulation signal for the on/off switching of LEDs is typically based on pulse-width modulation (PWM). To dim the LEDs, i.e. to adjust the brightness without visible jumps in the lightning curve, a high PWM ratio is desired. Typically, a ratio of 1:4096 is used. This relates to a resolution of 12 Bits.
If an LED spot (for example, with a plurality of LEDs) shall be applicable for modern TV cameras, like HDTV cameras, it is desired to have a PWM frequency as high as possible. Furthermore, this PWM frequency should be an integer multiple of 50 Hz and 60 Hz, otherwise, the LED spot cannot be used world-wide. As mentioned before, in the case of the TV cameras, not only the refresh rate, but also the shutter time is of importance. The shutter time of a TV camera defines how long a shutter of the TV camera is opened to acquire one picture. If this mentioned shutter time is very short, then a very high PWM frequency is desired. It has been found that a PWM frequency of 600 Hz is sufficient, but a PWM frequency of 1200 Hz or 2400 Hz offers a safety distance to obtain a picture without pulsing and jittering also in ambient lightning conditions.
This leads to a shortest pulse length ton min of a PWM signal for an LED or an LED spot based on the following equation:
For a typical microcontroller with a typical instruction time of 100 ns (which corresponds to a frequency of 10 Mz), this time is much too short to output impulses of this length. Furthermore, one microcontroller should be used to control a plurality of LEDs to save costs and effort. Therefore, a typical microcontroller cannot be used for providing a signal to drive an LED or a plurality of LEDs of an LED spot, which fulfils all the above-mentioned requirements for modern HDTV cameras. One possibility would be to use high-sophisticated digital signal processing processors, but which would result in a dramatically increase of costs and effort.
An object of the present invention is to provide a concept allowing to drive an LED or an LED spot for an HDTV camera with lower requirements to a drive signal generator for the LED or the LED spot than in the prior art.
This object is attained in accordance with an apparatus according to claim 1, an apparatus according to claim 12, a method according to claim 19, a method according to claim 20 and a computer program according to claim 21.
It is the central idea of the invention that a first drive signal for a first brightness for a lamp device differs from a second drive signal for a second brightness for the lamp device by a frequency or, in other words, by a number of pulses the drive signals contain in a certain amount of time. It has been found that by changing the frequency of the drive signals for a change in brightness, instead of keeping the frequency constant and changing the length of the pulses of the drive signals for changing the brightness, as this is done in PWM, the individual pulses of the drive signals can be made longer than in the conventional PWM. Therefore, a conventional microcontroller and especially a low-cost microcontroller can be used for generating a drive signal for a lamp device, such as an LED or an LED spot.
An advantage of the present invention is, therefore, that by changing the frequency to adjust the brightness of a light device, instead of changing the length of pulses and keeping the frequency constant, cheaper and easier devices for generating a drive signal for a lamp device or an LED or an LED spot can be used as this is known in the prior art.
Some embodiments of the present invention provide an apparatus for generating a drive signal for a lamp device. The apparatus comprises a pulse generator for generating a first pulse train in response to a first brightness request for a first brightness and for generating a second pulse train in response to a second brightness request for a second brightness. The first pulse train has a first frequency and the second pulse train has a second frequency, wherein the first frequency is different from the second frequency. The second pulse train comprises two neighboring pulses of the first pulse train and a further pulse between the two neighboring pulses, the further pulse not being comprised in the first pulse train.
According to some embodiments, the pulse generator may be configured to generate the first and the second pulse trains such that a pulse length of the two neighboring pulses and of the further pulse is identical. In other words, the pulse generator may be configured to change a brightness of the lamp device by adding or removing pulses of an equidistant length. In a conventional PWM system, the frequency of the drive signal is constant and a change of brightness is attained by changing the on/off ratio of the pulses. In other words, in a conventional PWM system, different drive signals for different degrees of brightness differ only by the on/off ratio of the pulses (and therefore by the length of the pulses) and not by the frequency of the drive signal itself.
According to some embodiments, the second brightness may be brighter than the first brightness, for example, if a pulse is a current pulse provided to the lamp device.
According to some further embodiments, the apparatus may further comprise a brightness request generator, which is configured to provide at least a first and a second brightness request to an input terminal of the pulse generator. The pulse generator may, for example, receive the first and the second brightness request at the input terminal and may output a drive signal with a corresponding pulse train, for example, depending on an internal look-up table.
Other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.
Embodiments of the present invention will be explained below in more detail with reference to the accompanying Figs., wherein:
a shows an apparatus according to an embodiment of the present invention coupled to a lamp device;
b shows two diagrams of pulse trains generated by a pulse generator of the apparatus shown in
a shows a block diagram of an apparatus according to an embodiment of the present invention coupled to a lamp device;
b shows two diagrams of pulse trains generated by a pulse generator of the apparatus shown in
a to 6d show diagrams of pulse trains generated by pulse generators of apparatuses according to embodiments of the present invention;
Before embodiments of the present invention will be explained in greater detail in the following on the basis of the Figs., it is to be pointed out that the same or functionally equal elements are provided with the same reference numerals in the Figs. and that a repeated description of these elements shall be omitted. Hence, the description of the elements provided with the same reference numerals is mutually interchangeable and/or applicable in the various embodiments.
A pulse length may in the following also be called as a pulse time or as a temporal extension of the pulse.
a shows a block diagram of an apparatus 100 according to an embodiment of the present invention coupled to a lamp device 110. The apparatus 100 for generating a drive signal 120 for the lamp device 110 comprises a pulse generator 130. The pulse generator 130 is configured to generate a first pulse train 140 (shown in
b shows a schematic diagram 150 of the first pulse train 140 and a schematic diagram 170 of the second pulse train 160 The first pulse train 140 comprises at least a first pulse 142a and a second pulse 142b. The first pulse 142a and the second pulse 142b are neighboring pulses, which means the second pulse 142b follows the first pulse 142a in time and no other pulse is arranged between these two neighboring pulses 142a, 142b. Therefore, the period of the pulse train 140 may be a time t140 between the first pulse 142a and the second pulse 142b. The frequency f140 may then be f140=1/t140.
The second pulse train 160 comprises the two neighboring pulses 142a, 142b of the first pulse train 140 and a further pulse 162a between the two neighboring pulses 142a and 142b. The further pulse 162a is not comprised nor contained in the first pulse train 140. Because of the temporal arrangement of the further pulse 162a between the two neighboring pulses 142a, 142b a second time t160 between two temporally-subsequent pulses of the second pulse train 160 is shorter than the first time t140 (between the two neighboring pulses 142a, 142b) of the first pulse train 140. In other words, a first time t160 between a rising edge of the first neighboring pulse 142a and a rising edge of the temporally-following further pulse 162a is shorter than the first time t140 between the rising edge of the first neighboring pulse 142a and the rising edge of the second neighboring pulse 142b of the first pulse train 140. Therefore, a frequency f160 of the second pulse train 160 is higher than a frequency f140 of the first pulse train 140. In addition, the further pulse 162a is temporally arranged between the two neighboring pulses 142a, 142b such that a time between the rising edge of the first neighboring pulse 142a and the rising edge of the further pulse 162a is the same, like a time between the rising edge of the further pulse 162a and a rising edge of the second neighboring pulse 142b. In further embodiments, the further pulse 162a could also be arranged in a temporally-arbitrary position between the two neighboring pulses 142a, 142b. In the concrete embodiment shown in
According to some embodiments, a pulse length tpulse or of the two neighboring pulses 142a, 142b and the further pulse 162a may be identical. Furthermore, the first time t140 and the second time t160 may be a multiple of the pulse length tpulse.
According to some embodiments, a temporal extension of the first pulse train 140 and a temporal extension of the second pulse train 160 may be identical, as is shown in
According to further embodiments, the drive signal 120 may comprise a plurality of first pulse trains 140 or second pulse trains 160. For the first brightness, the drive signal 120 would, for example, be a continuous stream of pulse trains 140 and for the second brightness, the drive signal 120 would be a continuous stream of the pulse trains 160. In a drive signal 120 based on the first pulse trains 140, a time between two rising edges of two temporally subsequent pulses would be the first time t140. In a drive signal 120 based on the second pulse trains 160, a time between two rising edges of two temporally subsequent pulses would be the second time t160.
According to further embodiments a time between two rising edges of subsequent following pulses of a pulse train may vary within in the pulse train, therefore a time between two rising edges of pulses of the pulse train may be different for different subsequent following pulses of the pulse train.
According to further embodiments, the pulse generator 130 may be further configured to generate a plurality of pulse trains in response to a plurality of different brightness requests, such that a pulse train out of the plurality of pulse trains corresponds to a brightness request out of the plurality of brightness requests. Different pulse trains may differ from each other by the number of pulses they comprise. As mentioned before, a temporal extension of the different pulse trains may be identical for all pulse trains.
According to further embodiments, the pulse train generator 130 may comprise a microcontroller, which is configured to provide the drive signal 120 or a plurality of drive signals 120 at an output terminal or at a plurality of output terminals. An output terminal of the microcontroller may, for example, be an I/O pin of the microcontroller. The I/O pin of the microcontroller may be coupled to the lamp device 110, by directly connecting the lamp device 110 to the I/O pin, or with a lamp device driver, which provides a drive current for the lamp device 110, between the I/O pin and the lamp device 110.
According to further embodiments, the lamp device 110 may comprise an LED or a plurality of LEDs or any other lightning devices. A lamp device 110 comprising a plurality of lightning devices or LEDs may therefore comprise a plurality of input terminals for the plurality of drive signals 120, such that degrees of brightness of the different LEDs or lightning devices of the lamp device 110 can differ from each other. In particular, the different LEDs or lightning devices of the lamp device 110 may comprise different colors, for example, an LED or a lightning device for red, an LED or a lightning device for green and an LED or a lightning device for blue. In other words, the lamp device 110 may be an RGB lamp device.
The first PWM signal 210 comprises four pulses 222a, 222b, 222c, 222d in the time interval t140 between the two neighboring pulses 142a and 142b of the first pulse train 140. A time interval tPWM between two rising edges of neighboring pulses of the second PWM signal 220 is a quarter of t140 (t140/4). A frequency fPWM of the first PWM signal 220 is, therefore, four times higher than the frequency f140 of the first pulse train 140. A drawback of the conventional PWM is that the frequency for a conventional PWM drive signal stays constant for every brightness request. Therefore, a minimum pulse duration of a PWM signal has to be much shorter than in embodiments of the present invention, wherein drive signals 120 for different brightness requests differ by frequency. In the concrete embodiment shown in
As mentioned before, in an embodiment of the present invention, a brightness of the lamp device 110 is raised by raising the frequency of the drive signal 120. Therefore, the frequency f160 of the second pulse train 160 is higher than the frequency f140 of the first pulse train 140 and, therefore, the frequency of the drive signal 120 is higher when the drive signal 120 is based on the second pulse train 160 than on the first pulse train 140. In contrast to this, the second PWM signal 240, which corresponds to the second pulse train 160, has the same frequency fPWM as the first PWM signal 220. This is a typical property of conventional PWM signals, wherein different degrees of brightness would be obtained by different lengths of the pulses of the PWM signal, while the frequency of the PWM signal would be kept constant. As mentioned before, a drawback of these conventional PWM signals is that, therefore, pulse lengths of the pulses of the conventional PWM signal have to be kept much shorter than in embodiments of the present invention, wherein different degrees of brightness correspond to different frequencies of the drive signal 120.
In
For a further increase in the brightness of the lamp device 110, a further pulse may be added between the two neighboring pulses 142a, 142b, wherein with each increase of brightness of the lamp device 110, the frequency of the drive signal 120 would be increased, too. Therefore, a drive signal 120 generated by the pulse generator 130 may have the same or even a higher frequency than a corresponding PWM signal for the same brightness of the lamp device 110. The pulse generator 130 may be configured such that a frequency of the drive signal 120 is the highest, when a sensitivity of a TV camera used in conjunction with a lamp device 110 is the highest in regards of a pulsing of the lamp device 110. In particular, the pulse generator 130 may be a conventional microcontroller with a comparatively low instruction cycle time compared to a pulse generator needed for generating a drive signal based on a conventional PWM signal and fulfilling the requirements of a TV camera used in conjunction with the lamp device 110. As it can be seen from
a shows a schematic block diagram of an apparatus 300 for generating a drive signal 320 for a lamp device 110. The apparatus 300 comprises a pulse generator 330 for generating a first pulse train 340 in response to a first brightness request for a first brightness and for generating a second pulse train 360 in response to a second brightness request for a second brightness. The first pulse train 340 (shown in
The pulse generator may, for example, be a microcontroller (for example, directly connected or with a lamp driver in-between) coupled to the lamp device 110. The drive signal 320 may be based on a continuous stream of first pulse trains 340 or on a continuous stream of second pulse trains 360, dependent on a brightness request. A drive signal 320, which is based on the first pulse train 340 may lead to a different brightness of the lamp device 110 than a drive signal 320 based on the second pulse train 360. For example, a brightness of the lamp device 110 may be higher or larger when a drive signal 320 based on the second pulse train 360 is applied to the lamp device 110 than when a drive signal 320 based on the first pulse train 340 is applied to the lamp device 110. Therefore, the second brightness may be higher than the first brightness.
b shows a schematic diagram 350 of the first pulse train 340 and a schematic diagram 370 of the second pulse train 360. The first pulse train 340 comprises a first pulse 342a, a second pulse 342b and a third pulse 342c. A temporal extension t342a of the first pulse train 342a is twice the temporal extension tpulse of the pulse 342b and the pulse 342c. The three individual pulses 342a, 342b, 342c are individual, because the first pulse train 340 not comprises any pulses between two neighboring pulses of the three individual pulses 342a, 342b, 342c. In other words, if an amplitude of the three individual pulses 342, 342b, 342c is a current flowing into the lamp device 110 between the three individual pulses 342a, 342b, 342c, i.e. between a falling edge of one of the three individual pulses 342a, 342b, 342c and a rising edge of a temporally-following pulse of the three individual pulses 342a, 342b, 342c, no current flows into the lamp device 110.
The second pulse train 360 comprises three individual pulses 342a, 342b, 362c (from the first pulse train 340). A temporal extension t362c or a pulse length of the third pulse 362c of the three individual pulses 342a, 342b, 362a of the second pulse train 360 differs from the pulse length tpulse of its corresponding pulse 342c of the first pulse train 340. The pulse length of the other two individual pulses 342a, 342b of the second pulse train 360 is identical to the pulse length of the corresponding individual pulses in the first pulse train 340. In the concrete embodiment shown in
According to further embodiments, the time tpulse may be the smallest possible pulse length, wherein pulse lengths of all pulses of pulse trains generated by the pulse generator 330 may be at least the smallest pulse length tpulse or a multiple of the smallest pulse length tpulse.
According to further embodiments, the pulse length of a pulse of a pulse train may differ to a pulse length of another pulse of the same pulse train at maximum by the smallest pulse length tpulse.
According to further embodiments, the time between two rising edges of pulses of a pulse train may be a multiple of the smallest pulse length tpulse.
As it can be seen in
Analogously to the first pulse train 340 and the first PWM signal 420, the second PWM signal 440 corresponds to the second pulse train 360, because a brightness of the lamp device 110 generated by a drive signal 320 based on the second pulse train 360 is the same as the brightness generated by a drive signal based on the second PWM signal 440. As mentioned before, the second pulse train 360 differs from the first pulse train 340 by the pulse 362c, which length differs from its corresponding pulse 342c in the first pulse train 340. In the concrete embodiment shown in
An advantage of the pulse generator 330 for generating the first pulse train 340 and the second pulse train 360 compared to a conventional pulse generator for generating the first PWM signal 420 and the second PWM signal 440 is, that for a change of brightness, only a length of one pulse of a pulse train has to be changed by a certain time interval (for example, by the pulse length tpulse) instead of changing the time of all pulses of the pulse train by a much smaller pulse length (tpulse/3). A pulse generator 330 according to an embodiment of the present invention may, therefore, comprise a conventional microcontroller with a significantly lower instruction cycle time than a pulse generator for generating the conventional PWM signal. This leads to a significant cost reduction of the apparatus 300 compared to conventional apparatuses driving a lamp device with a conventional PWM signal.
Although amplitudes of the pulses of the pulse trains 140, 160 generated by the pulse generator 130 according to
a shows schematic diagrams of pulse trains, for example, generated by the pulse generator 130 according to
The concept of changing a frequency by adding pulses to pulse trains instead of keeping the frequency constant and extending a length of all pulses of the pulse trains reduces a frequency by a factor (for example, by a factor of 2 . . . 256). In the concrete embodiment shown in
At the maximum frequency (value 8 in
If the brightness of the lamp device 110 should be further increased above half of the maximum brightness of the lamp device 110, further pulses are added and, therefore, a frequency of the drive signal 120 is lowered, but which does not have negative consequences, because HDTV cameras, as mentioned above, react most critically at half of the maximum brightness of the lamp device 110.
By choosing the frequency and by having longer pulse lengths than conventional PWM signals, a pulse generator 130 and, therefore, an apparatus 100 can be less sophisticated than a pulse generator needed for generating a conventional PWM signal for driving the lamp device 110 fulfilling the same requirements, like the pulse generator 130.
b shows the schematic diagrams of
c shows schematic diagrams of drive signals with different pulse trains for different degrees of brightness for a lamp device 110. The pulse trains shown in
The concept shown in
For example, if a first pulse of the first pulse train has a pulse length of 1 ms, after fifteen further pulses have been added for a factor of 16 (in the concrete embodiment shown in
d shows a schematic diagram from
The four concepts shown of the
In contrast to this, the concepts or methods described herein have a changeable frequency and/or pulses are added in discrete length. Within the drive signals based on pulse trains shown in
Furthermore, the method 700 comprises a step 720 of generating a second pulse train in response to a second brightness request for a second brightness. The second pulse train has a second frequency, wherein the first frequency of the first pulse train is different from the second frequency of the second pulse train. The second pulse train further comprises two neighboring pulses of the first pulse train and comprises a further pulse between the two neighboring pulses. The further pulse of the second pulse train is not comprised in the first pulse train.
According to further embodiments, the method 700 may comprise a step of receiving a first brightness request before the step 710 of generating the first pulse train. Furthermore, the method 700 may comprise a step of receiving the second brightness request before the step 720 of generating the second pulse train.
Furthermore, the method 800 comprises a step 820 of generating a second pulse train for a second brightness. The second pulse train comprises at least the three individual pulses of the first pulse train. Less than all of the at least three individual pulses of the second pulse train have the same length as in the first pulse train and at least one of the at least three individual pulses of the second pulse train has a different length compared to its corresponding individual pulse in the first pulse train.
According to further embodiments, the method 800 may comprise a step of receiving the first brightness request before the step 810 of generating the first pulse train. Furthermore, the method 800 may comprise a step of receiving the second brightness request before the step 820 of generating the second pulse train.
The methods 700 and 800 may be supplemented by any features or functions of the apparatus as described before.
The concept described herein of providing a drive signal for a lamp device has several advantageous features compared to conventional PWM concepts.
Although some aspects have been described in the context of an apparatus, it is clear that these aspects also represent a description of the corresponding method, where a block or device corresponds to a method step or a feature of a method step. Analogously, aspects described in the context of a method step also represent a description of a corresponding block or item or feature of a corresponding apparatus.
Depending on certain implementation requirements, embodiments of the invention can be implemented in hardware or in software. The implementation can be performed using a digital storage medium, for example a floppy disk, a DVD, a Blue-Ray, a CD, a ROM, a PROM, an EPROM, an EEPROM or a FLASH memory, having electronically readable control signals stored thereon, which cooperate (or are capable of cooperating) with a programmable computer system such that the respective method is performed. Therefore, the digital storage medium may be computer readable.
Some embodiments according to the invention comprise a data carrier having electronically readable control signals, which are capable of cooperating with a programmable computer system, such that one of the methods described herein is performed.
Generally, embodiments of the present invention can be implemented as a computer program product with a program code, the program code being operative for performing one of the methods when the computer program product runs on a computer. The program code may for example be stored on a machine readable carrier.
Other embodiments comprise the computer program for performing one of the methods described herein, stored on a machine readable carrier.
In other words, an embodiment of the inventive method is, therefore, a computer program having a program code for performing one of the methods described herein, when the computer program runs on a computer.
A further embodiment of the inventive methods is, therefore, a data carrier (or a digital storage medium, or a computer-readable medium) comprising, recorded thereon, the computer program for performing one of the methods described herein.
A further embodiment of the inventive method is, therefore, a data stream or a sequence of signals representing the computer program for performing one of the methods described herein. The data stream or the sequence of signals may for example be configured to be transferred via a data communication connection, for example via the Internet.
A further embodiment comprises a processing means, for example a computer, or a programmable logic device, configured to or adapted to perform one of the methods described herein.
A further embodiment comprises a computer having installed thereon the computer program for performing one of the methods described herein.
In some embodiments, a programmable logic device (for example a field programmable gate array) may be used to perform some or all of the functionalities of the methods described herein. In some embodiments, a field programmable gate array may cooperate with a microprocessor in order to perform one of the methods described herein. Generally, the methods are preferably performed by any hardware apparatus.
The above described embodiments are merely illustrative for the principles of the present invention. It is understood that modifications and variations of the arrangements and the details described herein will be apparent to others skilled in the art. It is the intent, therefore, to be limited only by the scope of the impending patent claims and not by the specific details presented by way of description and explanation of the embodiments herein.
