Abstract:
A method and system for converting a digital code. A digital signal is encoded to have a digital code having multiple binary bits. Substantially one half of the binary bits of the digital code is inverted to produce a modified digital code to reduce digital noise associated with the digital code.

Description:
BACKGROUND 
   1. Field of Invention 
   The teachings presented herein relate to electronic circuitry. More specifically, the teachings relate to methods and systems for digital data coding and electronic circuits incorporating the same. 
   2. Discussion of Related Art 
   A/D and D/A converters are widely used in the industry of electronics. In converting an analog signal to a digital signal, the analog signal is sampled at discrete points according to a certain frequency. Voltages of the analog signal at such sampled points are measured. Each measured voltage at a sampling point is then coded using a digital code having a plurality of binary bits. Such a digital code can be used to represent the sampled analog value and can be transmitted in a digital means to a destination. Once the digital code representing an analog value is received by a receiver, the digital code can be decoded by a D/A converter to derive an estimated voltage that is similar to the original voltage being coded.  FIG. 1(   a ) shows a typical A/D and D/A processing flow. In  FIG. 1(   a ), an A/D converter  110  takes an analog signal A as input and generates a digital code B as an output. The digital code B is often processed by a digital signal processor  115  to generate a digital signal C. When digital signal C is transmitted and received by a receiver  120 , which may then apply a D/A process at a D/A converter  130  and produces a recovered analog signal C′ based on digital signal C. 
   A digital code representing a particular sampled voltage of the analog signal is conventionally determined, by the A/D converter  110  based on a look-up table in accordance with the voltage level of the sample. For example,  FIG. 1(   b )(Prior Art) depicts a typical A/D converter  110 . An analog signal A is sampled first by an analog sampling unit  140  to produce individual analog voltages as an output. For each such analog voltage, an A/D look-up unit  150  determines a digital code representing the analog voltage based on a look-up table  160 . 
   A D/A converter reverses the process to convert a digital code to generate an analog voltage represented by the digital code. This is shown in  FIG. 1(   c ) (Prior Art), where a D/A look-up unit  170  in a D/A converter  130  consults with the look-up table  160  based on a received digital code C to produce an analog voltage. The represented analog voltage is then sent to an analog signal generator  180 , which may utilize different analog voltages to produce an estimated analog signal C′. 
     FIG. 1(   d ) (Prior Art) shows an exemplary look-up table  160  in which the left column  190  lists various ranges of analog voltages and, correspondingly, the right column  195  provides 14-bit digital codes for different voltage ranges. For instance, for a zero voltage, the digital code is “00 0000 0000 0000”. For a voltage between +0.000122 v and +0.000244 v, the corresponding digital code is “00 0000 0000 0001”. For a voltage between −0.000122 v and −0.000244, the corresponding digital code is “11 1111 1111 1111”, etc. 
   In accordance with the conventional look-up table, as shown in  FIG. 1(   d ) (Prior Art), when an analog signal crosses 0V in a negative direction, all the binary bits of the digital code change state from 0 to 1. When a large number of digital outputs change at the same time in the same direction (from 1&#39;s to 0&#39;s or from 0&#39;s to 1s), noise current on the circuit board is induced because the output load capacitances are charged and discharged. In various applications such as communications, it is common to have an analog signal centered at 0 v and such an analog signal may also have frequent deviations from 0V. Consequently, all binary bits of a digital code will frequently change states which make the problem worse. 
   A previous solution for reducing digital noise is Gray Coding, as disclosed in U.S. Pat. No. 2,632,058 issued to F. Gray. This method solves the problem by allowing only one bit changing state between any two adjacent codes. Although such a solution solves the problem, a disadvantage of this approach is that its implementation requires complex circuitry for coding and decoding data. Therefore, a solution that both reduces digital noise and is cost effective is needed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The inventions claimed and/or described herein are further described in terms of exemplary embodiments. These exemplary embodiments are described in detail with reference to the drawings. These embodiments are non-limiting exemplary embodiments, in which like reference numerals represent similar structures throughout the several views of the drawings, and wherein: 
       FIG. 1(   a )-( d ) (Prior Art) illustrate a conventional A/D and D/A flow and how analog information is digitally coded and decoded; 
       FIG. 2  depicts a high level block diagram for bit polarization format coding, according to an embodiment of the present teaching; 
       FIG. 3  shows a conversion table facilitating transformations from an analog voltage to a digital code and from a digital code to a modified digital code using bit polarization format, according to an embodiment of the present teaching; 
       FIG. 4  depicts a block diagram  400  incorporating BPF coding in the context of A/D and D/A flow, according to an embodiment of the present teaching; and 
       FIG. 5(   a )-( e ) show different exemplary implementations of bit polarization coding according to embodiments of the present teaching. 
   

   DETAILED DESCRIPTION 
   The present teaching discloses methods and systems for realizing bit polarization format and application thereof.  FIG. 2  depicts a high level block diagram  200  for bit polarization format coding, according to an embodiment of the present teaching. A digital code  205  is a binary code having a plurality of binary bits. For example, a digital code can have 14 binary bits, each of which has a state of either 0 or 1. Such a binary code may be an output from an A/D converter (not shown). According to the present teaching, when a digital code  205  is received, it is modified by a bit polarization format (BPF) unit  210  to produce a modified digital code  215 . Compared with the digital code  205 , the modified digital code  215  is derived by inverting a certain portion of the bit state of the digital code  205 . For example, substantially one half of the bits in the digital code  205  may be inverted. When the present teaching is deployed in connection with an A/D converter, employment of the bit polarization format is for the purpose of balancing the number of bits that change from 0s to is and the number of bits that change from 1s to 0s, especially when the analog signal is a small signal. 
   On the receiver side (not shown), when the modified digital code  215  is received, a BPF decoder  220  performs a reverse operation to recover the digital code  205  based on the modified digital code  215 . When the BPF coder  210  inverts a certain number of bits, the BPF decoder  220  applies inversion to the same bits that have been inverted by the BPF coder  210 . An exemplary BPF coding scheme is to alternate the bits to be inverted, namely alternate bit polarization format or ABPF. This ensures that one half of the bits are inverted when the total number of bits is an even number and a substantially one half of the total number of bits are inverted when the number of bits is an odd number.  FIG. 3  illustrates an ABPF conversion table for the BPF coder  210  and BPF decoder  220 . 
   In  FIG. 3 , a conversion table facilitates transformations from an analog voltage to a digital code and from a digital code to a modified digital code using bit polarization format, according to an embodiment of the present teaching. The left column  190  and the middle column  195  correspond to the left column  190  and right column  195  in  FIG. 1(   d ). The right column  310  in  FIG. 3  corresponds to the BPF coding. For each digital code in the table (one row), the modified digital code can be derived by inverting every other bit in the given digital code. For instance, for a digital code with all zeros corresponding to analog voltage 0V, the modified digital code is “10 1010 1010 1010”. Similarly, for digital code “11 1111 1111 1111” corresponding to a small deviation from 0V, i.e., −0.000122V, the modified digital code is “01 0101 0101 0101”. As can be seen, from 0V to −0.000122V, the digital codes change from all zeros to all ones, which has the problem discussed herein. With the modified digital codes, about one half of such changes are avoided and, hence, to reduce the digital noise associated with the original digital code. 
     FIG. 4  depicts a block diagram  400  incorporating BPF coding in the context of A/D and D/A flow, according to an embodiment of the present teaching. The block diagram structure illustrated in  FIG. 4  is largely similar to what is shown in  FIG. 1  except for the incorporation of the BPF coder  210  and the BPF decoder  220 . In this depicted embodiment, a digital code generated by the A/D converter  110  is modified by the BPF coder  210  to generate a modified digital code according to a pre-determined coding scheme. Such a pre-determined scheme may correspond to what is illustrated in  FIG. 3  or can be any coding scheme (some are shown in  FIG. 5(   a )-( e )) that is appropriate. 
   A receiver  410  in  FIG. 4  decodes first, upon receiving the modified digital code, to recover the digital code that has been modified. Such produced digital code is then sent to the D/A converter to produce an estimate A′ for the original analog voltage A. 
     FIG. 5(   a )-( e ) show different exemplary bit polarization formats according to embodiments of the present teaching.  FIG. 5(   a ) shows an exemplary scheme in which alternate bits are inverted to achieve bit polarization, according to an embodiment of the present teaching. In  FIG. 5(   a ), the left circuitry  510  represents an exemplary implementation of a BPF coder, having inverters arranged in alternate to achieve alternate bit inversion. The outputs of the circuit  510  collectively represent the modified digital code. The right circuitry  515  represents an exemplary implementation of a BPF decoder, having inverters arranged in the same configuration as in the BPF coder  510  to recover the original digital code. The outputs of the circuitry  515  collectively represent the decoded digital code. 
     FIG. 5(   b ) shows a different exemplary scheme in which about one half of the bits are inverted to achieve bit polarization, according to an embodiment of the present teaching. In  FIG. 5(   b ), the left circuitry  520  represents an exemplary implementation of a BPF coder, having inverters arranged in the top end portion of the circuitry to invert the first one half of the bits. Such first one half may correspond to the least significant bits or most significant bits of a digital code. The right circuitry  525  represents an exemplary implementation of a BPF decoder, having inverters arranged in the same configuration as in the BPF coder  520  to recover the original digital code. 
     FIG. 5(   c ) shows another different exemplary scheme in which about one half of the bits are inverted to achieve bit polarization, according to an embodiment of the present teaching. In  FIG. 5(   c ), the left circuitry  530  represents an exemplary implementation of a BPF coder, having inverters arranged in bottom end portion of the circuitry to invert the bottom one half of the bits. Such bottom one half may correspond to the most significant bits or least significant bits of a digital code. The right circuitry  535  represents an exemplary implementation of a BPF decoder, having inverters arranged in the same configuration as in the BPF coder  530  to recover the original digital code. 
     FIG. 5(   d ) shows yet another different exemplary scheme in which about one half of the bits are inverted to achieve bit polarization, according to an embodiment of the present teaching. In  FIG. 5(   d ), the left circuitry  540  represents an exemplary implementation of a BPF coder, having inverters corresponding to about one half of the total number of bits of a digital code and arranged in a consecutive manner in any middle portion of the of the circuitry to invert corresponding one half of the bits. By middle portion, it can be anywhere as long as it does not include the least and most significant bits. The right circuitry  545  represents an exemplary implementation of a BPF decoder, having inverters arranged in the same configuration as in the BPF coder  540  to recover the original digital code. 
     FIG. 5(   e ) shows another different exemplary scheme in which about one half of the bits are inverted to achieve bit polarization, according to an embodiment of the present teaching. In  FIG. 5(   e ), the left circuitry  550  represents an exemplary implementation of a BPF coder, having inverters corresponding to about one half of the total number of bits of a digital code and arranged in a plurality of clusters, each may have a different number of inverters and scattered in non-adjacent portions of the circuitry to invert corresponding one half of the bits. The right circuitry  555  represents an exemplary implementation of a BPF decoder, having inverters arranged in the same configuration as in the BPF coder  550  to recover the original digital code. 
   All embodiments disclosed have simple and cost effective implementations, yet can achieve the goal of avoiding having all bits changing states at the same time and, hence, reduce the digital noise. 
   While the inventions have been described with reference to the certain illustrated embodiments, the words that have been used herein are words of description, rather than words of limitation. Changes may be made, within the purview of the appended claims, without departing from the scope and spirit of the invention in its aspects. Although the inventions have been described herein with reference to particular structures, acts, and materials, the invention is not to be limited to the particulars disclosed, but rather can be embodied in a wide variety of forms, some of which may be quite different from those of the disclosed embodiments, and extends to all equivalent structures, acts, and, materials, such as are within the scope of the appended claims.