Patent Document

TECHNICAL FIELD 
       [0001]    The invention relates to the field of electronic circuits and more particularly to an interfacing circuit comprising a First In First Out (FIFO) storage. 
       BACKGROUND ART 
       [0002]    FIFO storages are well known in the art of electronic circuits and computers and are widely used for embodying interfacing circuits in many different applications. 
         [0003]    They are particularly widely used, but not exclusively, in the field of image and video processing. 
         [0004]      FIG. 1  reminds the general architecture of an interfacing circuit based on a FIFO memory which allows the transfer of data (such as audio samples or picture elements) FROM a “data producer device”  100  (such as audio or image sensor) via a lead  99  or we can consider that data are already available in a memory  150 , TO, a “data consumer device”  299  (like a signal processor device for audio, video or image). The circuit comprises an interface  120  receiving data from memory  150  via a data bus  151 . The interface  120  is used for proper formatting operation of the data before it is forwarded to a FIFO  100  through a data bus  101 . The reading of the FIFO is controlled by the “data consumer device”  299  represented by an external circuit (image or audio signal processor) by means of a ENABLE lead  113  and a CLK_RD clock signal lead  112 . On the other side, the writing of the FIFO by the “data producer”  100  is controlled by a (inverted) WR signal  103  under the clocking of a WR signal conveyed by a lead  102 . Two additional FIFO_FULL and FIFO_empty signals, respectively on leads  121  and  122 , are used for respectively reporting a situation of full storage and empty storage to the “data producer”  100  and “data consumer devices”  299 . 
         [0005]    The circuit which is represented in  FIG. 1  is a typical example of a set of well known circuits and, therefore, does not need to elaborate any further introduction nor development to a skilled man. 
         [0006]    Briefly, it suffices to recall that such circuit is widely used for achieving many different interfaces, such as image and video interface such as camera interface circuits. 
         [0007]    However, one may recall the general trend to an increase of the resolution of image sensors which lead to a significant volume of data to be transferred between the sensors/memory to the video or image interface circuits. 
         [0008]    This drastic increase in the volume of data clearly generates a significant pressure on the FIFO circuits which have to operate at very high speed clocks. 
         [0009]    The continuous trend to higher speeds might result the designer to proceed with a new redesign of the analog interface and therefore the interfacing circuits comprising the FIFO. Such redesign would inevitably results in higher manufacturing costs which is not desirable. 
         [0010]    Alternatively, one may wish to improve the design of the conventional FIFO based interfacing card so as to increase the efficiency even without increasing the frequency of the clocking circuits. 
         [0011]    Such is the technical problem to be solved by the present invention. 
       SUMMARY OF THE INVENTION 
       [0012]    It is an object of the present invention to provide a new architecture for an interfacing circuit, based on a FIFO storage, which provides increased data rate in the transfer of data. 
         [0013]    It is another object of the present invention to provide an enhanced architecture for a interfacing circuit which limits the size of the FIFO storage required for interfacing two circuits. 
         [0014]    It is still a further object of the present invention to provide a new interface circuit for an image and video system of a 2G/3G mobile terminal baseband circuit. 
         [0015]    These and other objects are achieved by means of a interfacing circuit comprising a First In First Out (FIFO) memory for exchanging data between a first system (known as &lt;&lt;data producer&gt;&gt;) and a second system (known as &lt;&lt;data consumer&gt;&gt;). The FIFO memory is controlled by first write control signals (WR, CLK_WR) and second read control signals (ENABLE, Clk_Rd). 
         [0016]    The interfacing circuit further includes:
       a redundancy filter for receiving a sequence of N data (such as audio or image luminance samples Y 0 , Y 1 , Y 2  . . . Y n-1 ) to be stored within said FIFO, and for generating a redundancy control word representative of the presence of consecutive identical data within said sequence;   means for controlling said first and said second control signals of said FIFO for the purpose of preventing the storage into said FIFO of multiple consecutive identical data (redundant samples).       
 
         [0019]    Therefore, the redundant data are simply not written in the FIFO during the WRITE operation and, conversely, during the READ operation, the ENABLE control lead is not activated what results in the fact that the same output data (assumed to be a redundant data) is represented again at the output interface of the FIFO. 
         [0020]    This results in the fact that the conventional FIFO may be used with a READ clock interface which is much higher depending on the redundancy of the information which is stored within the memory or sensed by the sensor. 
         [0021]    In the case of audio samples or picture elements (pel), the redundancy may be particularly significant, thus resulting in a significant increase of the performance of the FIFO. 
         [0022]    In one embodiment, redundancy filter generates said redundancy control word in addition to a filtered sequence of data Y 0 , Y* 1 , Y* 2  . . . Y* n-1  to be stored into the FIFO. 
         [0023]    In one embodiment, the control unit comprises two WRITE and READ state machines for the purpose of generating the control signals of the FIFO. 
         [0024]    The invention also achieves a 2G/3G mobile terminal baseband circuit comprising a First In First Out (FIFO) memory for transferring data between a &lt;&lt;data producer device&gt;&gt;and a &lt;&lt;data consumer device&gt;&gt;. The FIFO memory is controlled in first case by write control signals (WR, CLK_WR) and by read control signals (ENABLE, Clk_Rd) in the second case. 
         [0025]    The interfacing circuit further includes:
       a redundancy filter for receiving a sequence of N data (Y 0 , Y 1 , Y 2  . . . Y n-1 ) to be stored within said FIFO, and for generating a redundancy control word representative of the presence of consecutive identical data within said sequence (then called redundant data);   means for controlling said first and said second control signals of said FIFO for the purpose of preventing the storage into said FIFO of multiple consecutive identical data.       
 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0028]    Other features of one or more embodiments of the invention will best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings. 
           [0029]      FIG. 1  illustrates a known architecture of an interfacing circuit based on a conventional FIFO circuit. 
           [0030]      FIG. 2  illustrates the principle of the redundancy filter used in the interface circuit shown in  FIG. 3 . 
           [0031]      FIG. 3  illustrates on embodiment of an interfacing circuit comprising a redundancy filter. 
           [0032]      FIG. 4  illustrates the principle of the write state machine. 
           [0033]      FIG. 5  illustrates the principle of the read state machine 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0034]    There will now be described one particular embodiment of the invention which consists in an interfacing circuit for providing high speed data rate for an image processor contained in the imaging and video sub-system of a 2G/3G terminal baseband circuit. 
         [0035]    Indeed such embedded image processor requires (to fulfill state of the art video support), both big image resolutions and large frame rates resulting in a very high speed data flux from the image sensor to the image signal processor. 
         [0036]    Such application requires for example in the case of a parallel interface, reception of data clock, video synchronization signals (vertical+horizontal) and data on a parallel bus that will be called here “Camera Interface Bus”. In a real product, an external device called an image sensor is connected to this bus, delivering a pixel clock, vertical and horizontal video synchronization depending on data format and pixel data (on 8 or 10 bits) as processed by the image sensor optics and sensor embedded signal processor. 
         [0037]    Clearly, in view of the high resolution and high frame rate of the image and video captures, the interface between the sensor (or the memory storing the images and video files) requires a very high rate of transfer and such high rate significantly stresses the intermediate storage circuit, such as the FIFO. 
         [0038]      FIG. 3  illustrates one embodiment of an interfacing circuit which achieves high speed transfer of the data generated by a data producer device  100  providing data into a memory  150 ) or, alternatively by a memory  150  and an external (data consumer device  299 ) video processing interface receiving a high speed flux of pixel data via a bus  211 . By using memory  150  in lieu of a real sensor, the interfacing circuit becomes able to continuously produce loop images. 
         [0039]    It should be noticed that, generally speaking, the particular realization of the interfacing circuit of  FIG. 3  depends on the data format used for representing the image and video: (YUV 422-BT601, YUV 422-BT656, Raw Bayer-BT601, Raw Bayer-BT656, Data mode). In particular, the processing of pixel data being represented in colors components will result in the use of three FIFO circuits , one dedicated to each particular color component (R, G, B or Y, U, V). 
         [0040]    For clarity&#39;s sake, the interfacing circuit of  FIG. 3  only shows one FIFO storage but it is clear to the skilled man that the circuit of  FIG. 3  may be adapted and arranged so as to include multiple FIFO circuits, each dedicated to one color component. 
         [0041]    Furthermore, the conventional address and control bus are being arranged so as to allow the interface between memory  150  and circuit  120 . All those buses being simply illustrated by bus  151 . 
         [0042]    Interface  120  achieves a physical interfacing between the particular format of the data stored into memory  150  (e.g. a 32 bit format) and the format of the subsequent FIFO storage. For instance, in the preferred embodiment, interface  120 , will performs successive reading operation into memory  150  so as to generate on a bus  101  a 192 bits vector (for instance) which is representative of a sequence of picture elements or more generally data to be processed. 
         [0043]    In one particular embodiment, the interface  120  produces a serie of picture elements (pel) belonging to a group of N pels. 
         [0044]    Y 0 , Y 1 , Y 2  . . . Y n-1    
         [0045]    The interfacing circuit further comprises a redundancy filter  230  which receives the pixel data Y 0 , Y 1 , Y 2  . . . Y n-1  which is carried by bus  101  and which forward to FIFO  201  via a lead  201  a corresponding sequence of filtered values Y 0 , Y* 1 , Y* 2  . . . Y n-1 . Furthermore, redundancy filter  230  generates a control word on a bus  231  consisting in a vector of n+1 bits, where each &lt;&lt;0 &gt;&gt; represents a redundancy present in the corresponding pels. 
         [0046]    Practically, if one particular pel Yk is identical to pel Yk−1, the control word will be such that: 
         [0047]    CW [k]=0, otherwise it is equal to 1. 
         [0048]      FIG. 2  particularly illustrates one example of 16 consecutive pels Y 0 , Y 1 , Y 2 , . . . Y 15 , which are such that: 
         [0049]    Y 0 =Y 1 =Y 2 ; 
         [0050]    Y 4 =Y 5 ; 
         [0051]    Y 9 =Y 10 =Y 11 =Y 12 ; 
         [0052]    Y 13 =Y 14 =Y 15   
         [0053]    In that case, redundancy filter  230  generates the following control word: 
         [0054]    CW=(1, 0, 0, 1, 1, 0, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0) 
         [0055]    Representative of the redundancy of the pels in the group of N. 
         [0056]    It can be seen that a &lt;&lt;1 &gt;&gt; in the control word is representative of a pel Y[i] (i=1 to N−1) which is considered to be significant (since it provides a new information), while a &lt;&lt;0 &gt;&gt; is representative of a non significant (or redundant) pel because it carries a value which was already carried by the previous one. 
         [0057]    While the example which was described above is based on a &lt;&lt;strict&gt;&gt; mathematical comparison of the two consecutive pels—0 being reported only when strict mathematical equality—many embodiments may be considered for the purpose of generating a redundancy filtering based on the measurement of &lt;&lt;distance&gt;&gt;between two consecutive pels. 
         [0058]    Alternatively, one may consider a more complex redundancy filtering reporting, for instance, a close proximity of two subsequency pels. For instance, one may decide that the redundancy vector will report a &lt;&lt;0&gt;&gt; when the difference between two consecutive pels is inferior to a predetermined threshold. 
         [0059]    It can be seen in the  FIG. 3  that the control word CW which is generated by redundancy filter  230  is forwarded to a control unit  250  which achieves the generation of write control signals, and particular the WR (inverted) and CLK_WRITE signals, respectively on leads  203  and  202 ) controlling the FIFO memory  200  which, on the other side, receives from the data consumer (such as audio or image processor) the conventional ENABLE signal on a lead  213  and the CLK_RD clock signal on a lead  212 . 
         [0060]    Control Unit  250  generates the WR (inverted) and CL WR control signals so as to reduce the writing operations within FIFO  200  when the considered pels Y[i] carries a non significant data (CW[i]=0). Conversely, when the pels Y[i] carries a is significant data (CW[i]=1), then an effective WRITE operation is performed within the FIFO so as to keep in the storage such data. 
         [0061]    By only writing the significant pels (corresponding (CW[i]=1)), one can avoid a write operation in FIFO  200  and thus reduce both the amount of data written in FIFO and the average speed on the write clock. 
         [0062]    But what is even more interesting is that the interfacing circuit of  FIG. 3  allows to significantly increase the average READ clock of the &lt;&lt;data consumer device&gt;&gt; (without any need of an increase in the speed of access in memory  150 , which can hence be a low cost slow memory). This gain is obtained at redundancy occurence instants by just repeating redundant data on lead  211  towards data consumer device. What happens is that during periods of high redundancy pels, while the same redundant data is repeated at lead  211  to consumer device, the FIFO have time to refill from the slow memory. This significantly reduces the probability for a FIFO_EMPTY signal to occur later on, It is important to notice that in case of a slow memory  150 , the rate of activity of FIFO_EMPTY signal is directly correlated to the slow down of the average data flux going to the &lt;&lt;data consumer device&gt;&gt; through lead  211 . 
         [0063]    In other words, it can be seen that the new architecture of the interfacing circuit which is shown in  FIG. 3 , allows to increase the &lt;&lt;clk_read&gt;&gt; while requiring any change in the fondamental structure of the FIFO. By using the arrangement shown in  FIG. 3 , a conventional FIFO may be operated at a higher read clock. 
         [0064]    Alternatively, a given FIFO storage, having predetermining clocking requirements, can be used at an extended high rate. 
         [0065]    With respect to  FIGS. 4 and 5 , there will now be described the two state machines embodying the control unit  250 . 
         [0066]      FIG. 4  shows the state machine of the WRITE operation of FIFO  200 . 
         [0067]    State  310  consists in an IDLE state which the state machine remains as long as the value of the current index &lt;&lt;i&gt;&gt; of the control word CW(i) (with i=1 to N−1) is equal to &lt;&lt;0&gt;&gt;. (arrow  311 ), that is to say as long as the pixel data is representative of a non significant (or redundant) data. 
         [0068]    When the value of the current index CW(i) is equal to a &lt;&lt;1&gt;&gt;, which is representative of a significant pixel data (giving a new information also named &lt;&lt;innovation&gt;&gt; in signal processing theory), then the state machine proceeds to a state  320  (Write) where the following actions (arrow  321 ) are taken:
       activating the WR control signal of the FIFO by switching the (inverted) WR control signal to a &lt;&lt;0&gt;&gt;; and   present the redundancy filter value Y*(i) on bus  201         
 
         [0071]    The state machine then waits until a rising edge of the Clk_write signal, in which case it proceeds to a control state  330 , where the WR control signal is disactivated by switching the (inverted) WR signal to &lt;&lt;0&gt;&gt;, thus controlling the end of the write operation. 
         [0072]    The state machine remains at that state  330  when the FIFO_FULL condition is present, representative of a full condition of the FIFO. 
         [0073]    Conversely, if the FIFO does not show to be full, then the state machine proceeds again to the IDLE state  310 . 
         [0074]      FIG. 5  shows the state machine of the READ operation of FIFO  200 . 
         [0075]    State  410  consists in an IDLE state which the state machine remains as long as the value of the current index &lt;&lt;i&gt;&gt; of the control word CW(i) (with i=1 to N−1) is equal to &lt;&lt;0&gt;&gt; (arrow  411 ), but also when the FIFO_empty condition is present. This causes the non significant data to remain at the physical output interface of 
         [0076]    FIFO  200  which can thus generate the same data to the video system during multiplex periods of the clock rd signals. In that case, FIFO  200  behaves as if it was operated at a high speed receive clock. 
         [0077]    When the value of the current index CW(i) is equal to a &lt;&lt;1&gt;&gt;, which is representative of a significant pixel data, then the state machine proceeds to a state  420  (READ) where the ENABLE control lead of the FIFO  200  is activated, by means of switching the (inverted) ENABLE control lead to a &lt;&lt;0&gt;&gt;. 
         [0078]    The state machine then waits until a rising edge of the Clk_rd signal, in which case it proceeds to a control state  430 , where the ENABLE is disactivated, by means of switching the (inverted) ENABLE control lead to a &lt;&lt;1&gt;&gt;, thus controlling the end of the READ operation. 
         [0079]    The state machine then loops back again to IDLE state  410 . 
         [0080]    It can be seen that, thanks to those two state machines, the significant pixel data are effectively stored and retrieved from FIFO storage  200 , while the non significant pixel data remain at the input interface of the FIFO or are simply repeated at the output interface.

Technology Category: 5