Patent Application
20090086106
1. Field of the Invention
The present invention relates to a video signal processing circuit which uses voltages that are provided from a DC-DC converter or the like, and relates to an electronic device in which the same is mounted.
2. Description of the Related Art
In an electronic circuit dealing with video signal (hereinafter referred to as “video signal processing circuit”), a plurality of different voltages used in the video signal processing circuit are sometimes required, not one type of power supply voltage. In such cases, a measure can be considered to provide a plurality of power supply voltages from an outside power supply circuit. Instead of providing a plurality of power supply voltages from outside, there is also a measure to provide one type of power supply voltage and to obtain a plurality of voltages using a charge pump circuit functioning to convert one type of the power supply voltage into different voltages.
It generally follows from the operating principle of a charge pump circuit that an output voltage is not ideal due to a noise occurring in a rising edge or a trailing edge of the clock and the ripple components of the clock frequency remaining in the output voltage. For example, Patent document 1 discloses an uneven display caused by the ripple occurring in the drive voltage.
Patent Document 1: JP Patent Application Laid-open No. 2001-92402
When a voltage generated in such a charge pump circuit is used in a video signal processing circuit, a circuit element of the video signal processing circuit can be affected because the video signal processing circuit operates after being provided with the voltage in which noises are superimposed. In particular, when a video signal processing circuit and a charge pump circuit are both mounted in the same IC chip of a semiconductor IC or the like, it becomes a more serious problem because a clock frequency of the charge pump circuit interferes directly in the video signal processing circuit. In images played back in such a video signal processing circuit, an image noise such as a stripe line occurs due to the noise component from the charge pump circuit, which makes the image quality lower.
In view of these situations, the present invention has been made, and a general purpose of the present invention is to provide a video signal processing circuit that can reduce the influence of the image quality deterioration in a circuit configuration provided with voltage from a DC-DC converter or the like, and to provide an electronic device in which the video processing circuit is mounted.
The video signal processing circuit according to an embodiment of the invention includes: a video signal processing unit which subjects a video signal to a given process; a circuit which generates the other voltages from a given fixed voltage to provide the video signal processing unit with a plurality of mutually different power supply voltages; and a clock generating circuit which provides the circuit which generates the other voltages with a clock frequency, wherein the clock frequency is selected so that the clock generating circuit visually reduces quality deterioration caused by an image noise occurring in an image that is generated from the video signal processed by the video signal processing unit into which a noise caused by the clock frequency of the circuit which generates the other voltages is introduced. “A given fixed voltage” may be a power supply voltage. “A clock generating circuit” may be an oscillating circuit or a circuit generating a new clock by converting a given clock.
According to this embodiment, by adjusting a clock frequency of a DC-DC converter or the like, it is possible to visually adjust the influence that an image noise caused by a noise occurring with switching actions of a DC-DC converter or the like, exerts on the image quality.
The clock generating circuit may have the clock frequency set so that a line made from a collection of image noises occurring in an image runs obliquely. Further, the clock generating circuit may have the clock frequency set so that the line moves at a given speed or higher. Furthermore, the clock generating circuit may have the clock frequency set so that a plurality of lines occur. The clock frequency may be set within the range of 90 kHz to 230 kHz. According to this embodiment, an image noise can be adjusted to one that is difficult to notice for the human eye.
The clock generating circuit may have the clock frequency set so that the clock frequency and the frequency of the horizontal synchronizing signal of the video signal satisfy a given relationship. The clock generating circuit may have the clock frequency set so that the clock frequency is not an integral multiple or an approximate integral multiple of the frequency of the horizontal synchronizing signal of the video signal. As the clock frequency approaches an integral multiple of the horizontal synchronizing signal of the video signal, an occurring image noise becomes a motionless vertical line in shape. According to this embodiment, such an image noise can be prevented from occurring.
The video signal processing unit may include an operational amplifier for amplifying input signal with a given gain. The operational amplifier may operate with a plurality of power supply voltages and may receive provision of at least one of the power supply voltages from the circuit which generates the other voltages. The circuit which generates the other voltages may be a DC-DC converter, which may generate the negative voltage by stepping down a given fixed voltage, and the operational amplifier may operate with the given fixed voltage being provided from a positive power supply terminal and with the negative voltage being provided from a negative power supply terminal. By using the operational amplifier of the positive and negative power supplies, it is possible to adjust the output voltage level of the operational amplifier and to simplify the circuit element in a subsequent stage.
At least, the video signal processing unit and the circuit which generates the other voltages may be integrated on the same semiconductor substrate. The clock generating circuit may also be integrated on the same substrate.
Another embodiment of the present invention is an electric device. This electric device includes a video signal processing circuit and a battery providing the video signal processing circuit with a given fixed voltage. According to this embodiment, it is possible to configure a video signal processing circuit having a plurality of power supplies with a small-scale circuit, and also possible to reduce the influence of the image quality deterioration caused by the use of a DC-DC converter.
It is to be noted that any arbitrary combination or rearrangement of the above-described structural components and so forth are all effective as and encompassed by the present embodiments.
Moreover, this summary of the invention does not necessarily describe all necessary features so that the invention may also be sub-combination of these described features.
Embodiments will now be described, by way of example only, with reference to the accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several Figures, in which:
The present invention will be explained below with reference to the accompanying drawings. The same or equivalent component parts, members and processes shown in each drawing shall be denoted by the same reference symbols, and duplicated explanations are omitted appropriately. In addition, embodiments do not limit the invention, only describe exemplifications, and not all of the features and combinations thereof described in the embodiments are essential to the present invention.
At first as premise, a video signal that is input into a video signal processing circuit according to the embodiment of the invention will be explained. The video signal includes the horizontal synchronizing signal besides image information, and images are played back on the display of the TV screen or the like, based on the horizontal synchronizing signal. In the horizontal synchronizing signal, the frequency of 15.734 kHZ is adopted for NTSC method, and the frequency of 15.625 kHz for PAL method.
Here, if the frequency of the noise introduced into from the charge pump circuit described later is the same as that of the horizontal synchronizing signal, a noise of vertical line n appears on the screen. This occurs because if both frequencies are the same, the noises n occur in the same position for each scanning line h, and each noise n is in a vertical line on the screen. In addition, the occurrence of the noise in the same position makes the line seem motionless. If the frequency of the noise introduced into from the above charge pump circuit is twice that of the horizontal synchronizing signal, two motionless vertical lines n occur based on the same principle. Further, the same phenomena will continue as the frequency of the noise increases, and when the ratio between the frequency of the noise and that of the horizontal synchronizing signal is an integral ratio, as many vertical lines n as the ratio occur.
On the other hand, as the frequency of the noise introduced into from the charge pump circuit is getting higher than that of the horizontal synchronizing signal, the vertical lines run obliquely then laterally, which makes the noise difficult to notice for the human eye. As described above, the vertical lines n are very noticeable because they are motionless on the screen. Conversely, when the relationship between the both frequencies is set so as not to make the vertical lines n occur, it is possible to reduce the influence of the image quality deterioration by the noise introduced into from the charge pump circuit. Using this knowledge, the video signal processing circuit of which the clock frequency is set so that the clock frequency is not an integral multiple of the frequency of the horizontal synchronizing signal, will be explained below.
The video amplifying circuit 10, the oscillating circuit 20 and the charge pump circuit 30 are provided with the power supply voltage Vcc. The video amplifying circuit 10 is connected to a first capacitance C10 to be provided with the negative power supply. The first capacitance C10 maintains the output voltage of the charge pump circuit 30.
The video amplifying circuit 10 is configured using an operational amplifier or the like, and amplifies the input video signal with a given gain. According to this embodiment, the operational amplifier uses two power supplies, that is, the positive and the negative power supplies, not a single power supply. Employing the operational amplifier using two power supplies can make it possible to set the direct current component to 0V level, and therefore, connection of a greater capacitance to the output of the operational amplifier is not required, which contributes to reduction in the size of the entire circuit.
As described above, the charge pump circuit 30 generates the negative voltage using the power supply voltage Vcc to provide the video amplifying circuit 10 with the negative voltage. That is, the charge pump circuit 30 includes a capacitance and a switch functioning to change the pathways of capacitance between a first pathway of the power supply voltage Vcc through the ground and a second pathway of power supply voltage Vcc through the capacitance serving as maintaining the output voltage, as a basic configuration. The charge pump circuit 30 reverses the power supply voltage Vcc in such a process. In addition, the charge pump circuit 30 is an example of a DC-DC converter, and it may be a switching regulator or the like.
The oscillating circuit 20 forms a clock functioning to carry out on/off control of the switch in the charge pump circuit 30. In this embodiment, the frequency of the clock is adjusted so as not to be an integral multiple of the frequency of horizontal synchronizing signal of the above video signal. With respect to the clock frequency of the charge pump circuit 30, from the viewpoint of the image quality generated from the video signal, making the clock frequency of the charge pump circuit 30 lower can curb the noise occurring in images. Further, as the frequency is higher, the noise is more unnoticeable for the human eye because the noise in images runs faster. A sensitivity evaluation may indicate that the more stripe lines there are, the less noticeable they are. Opposing to this, the appropriate frequency range of the charge pump circuit 30 exists in accordance with its specification, in order to exert the performance of the charge pump circuit 30 sufficiently. In view of these aspects, for example, the frequency range of the clock frequency of the charge pump circuit 30 is set within about 90 kHz to about 230 kHz, and also set so as not to be an integral multiple of the horizontal synchronizing signal.
Making the oscillating frequency of the oscillating circuit 20 that specifies the clock frequency of the charge pump circuit 30 higher, decreases the ripple rejection ratio of the video amplifying circuit 10.
On the other hand, since the ripple voltage occurring in the power supply decreases proportionately to the oscillating frequency fosc, the decrease of the ripple voltage is offset by the increase of the ripple rejection ratio and then, the ripple voltage level appearing in the output of the video amplifying circuit 10 is unrelated to the oscillating frequency fosc. The effect of lowering the oscillating frequency fosc levels out because the ripple rejection ratio is no longer increased beyond a certain limit.
On the other hand, to control interference fringes occurring on the screen, precise control at the interval of an integral multiple of about 15 kHz of the horizontal synchronizing signal, that is, at the interval of about 15 kHz, is required. Making the oscillating frequency fosc of the oscillating circuit 20 higher, decreases the stability of the oscillating frequency fosc since the ratio between 15 kHz and the oscillating frequency fosc is severe. In view of these situations, this embodiment sets the clock frequency of the charge pump circuit 30 to the range of about 90 kHz to about 230 kHz.
The configuration of the oscillating circuit 20 to adjust the clock frequency of the charge pump circuit 30 will be explained below.
A first switch SW22 is provided between the power supply voltage Vcc and the first constant current source 24, and a second switch SW24 is provided between the second constant current source 26 and a connection point of the first constant current source 24 and the second constant current source 26. The first switch SW22 is subject to on/off control by the output signal of the flip-flop 28, and the second switch SW24 is subject to on/off control by its inverting signal. In addition, a voltage-current conversion circuit 22 is provided for providing the above first constant current source 24 with current. The voltage-current conversion circuit 22 generates the current provided to the first constant current source 24, based on the voltage generated from a third reference voltage Vref.
The first comparator CP22 and the second comparator CP24 output a high level signal or a low level signal after comparing the reference voltages generated by each resistant string with the above triangular-wave-shaped input voltage. The output signal of the first comparator CP22 is input to the reset terminal of the flip-flop 28, and the output signal of the second comparator CP24 is input to the set terminal of the flip-flop 28. In the first comparator CP22 and the second comparator CP24, since the input terminals are opposite to each other in respect of their connections, the phases of the output signals are opposite to each other. The flip-flop 28 latches signals input from the first comparator CP22 and the second comparator CP24 for a given period, and outputs them to meet a given timing, respectively.
In a configuration like the oscillating circuit 20, a designer adjusts a resistance value or a capacitance value that determines the frequency of the output signal of the oscillating circuit 20 using laser trimming or diode zapping or the like. Therefore, the clock frequency used in the charge pump circuit 30 can be set to the desired value.
For example, as shown in
Next, in case the voltage-current conversion circuit 22 is configured with an operational amplifier, the output current can be adjusted by adjusting the value of the feedback resistance or the value of the resistance for generating its reference voltage. Like this, adjustment of a resistance value for adjusting the ratio between the input voltage and the output current can be achieved, using the resistance strings including the ninth resistance R30, the tenth resistance R32 and the eleventh resistance R3; and the third fuse F30 and the fourth fuse F32 that are connected in parallel with the ninth resistance R30 and the tenth resistance R32, respectively.
In addition, six resistances from the twelfth resistance R40 through the seventeenth resistance R49 are connected in series between the power supply voltage Vcc and the ground. The seventh fuse F40, the eighth fuse F42, the ninth fuse F46, and the tenth fuse F48 are connected in parallel with the twelfth resistance R40, the thirteenth resistance R42, the fifteenth resistance R46, and the sixteenth resistance R48, respectively. The reference voltage provided to the first comparator CP22 is obtained from the connection point between the fourteenth resistance R44 and the fifteenth resistance R46. The second comparator CP24 may be the same circuit configuration, using the eighteenth resistance R50, the nineteenth resistance R52, the twentieth resistance R54, the twenty-first resistance R56, the twenty-second resistance R58, the twenty-third resistance R59, the eleventh fuse F50, the twelfth fuse F52, the thirteenth fuse F56, and the fourteenth fuse F58.
Further, the capacitance value of the second capacitance may be adjusted. A designer may employ one way for adjustment, or two or more ways cumulatively. Furthermore, a diode may be employed in place of a fuse. In the case, the diode may be short-circuited by causing a current beyond the break down voltage to flow in the diode.
As described above, according to the embodiment, when providing the video amplifying circuit amplifying the video signal with the power supply from the charge pump circuit, the influence of the image quality deterioration played back from the above video signal may be reduced by setting the clock frequency of the charge pump circuit not to make a certain relationship between the noise frequency introduced into from the charge pump circuit, and the frequency of the horizontal synchronizing signal of the above video signal.
More specifically, at first, the influence of the image quality deterioration by a noise introduced into the negative power supply terminal of the operational amplifier included in the above video amplifying circuit, from the charge pump circuit may be reduced. In addition, current changes corresponding to switching actions occur in the power supply terminal of the charge pump circuit. As shown in
Further, it is possible that the noise occurring in the charge pump circuit is introduced into the preceding circuit to cause the noise to be mixed in the video signal in the preceding circuit.
Next, an electronic device 400 in which the video signal processing circuit 100 is mounted in accordance with the above embodiment, will be explained.
As described above, the present invention is an effective technology when it is difficult to be provided with a plurality of power supply voltages from outside. It can be said that a portable apparatus is just in such a situation. The video signal processing circuit 100 according to the above embodiment can reduce the influence of the quality deterioration of the image generated from the video signal, without decreasing the noise occurring from the charge pump circuit by using a ripple filter and so on, which leads to consist reduction in the size of a circuit with measurement for image noise.
The present invention has been described based on embodiments. It is understood to a person skilled in the art that the embodiments are only exemplary, and various modifications are possible in combinations of each configuration element and each processing process, and those modifications are also within the scope of the present invention.
In the above embodiments, an example in which the clock frequency of the charge pump circuit 30 is provided from an oscillating circuit 20 in the same IC chip has been described. With respect to this, if a desired clock frequency can be obtained from outside, the clock may be the clock frequency of the charge pump circuit 30. In the case, reduction in the size of the IC chip commensurate with the absence of the oscillating circuit 20 is achieved.
The present invention has been described according to the embodiments, but it goes without saying that the embodiments only show the principles and applications of the present invention, and that many examples of variation or modifications of arrangement are possible in the embodiments without departing from the spirit of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-189353 | Jun 2005 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2006/312805 | 6/27/2006 | WO | 00 | 12/27/2007 |
