Coded data generation or conversion – Digital code to digital code converters – Serial to parallel
Reexamination Certificate
2003-03-17
2004-05-11
Tokar, Michael (Department: 2819)
Coded data generation or conversion
Digital code to digital code converters
Serial to parallel
C341S101000, C341S050000, C341S102000
Reexamination Certificate
active
06734813
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a serial data receiving device in which an input serial bit string distorted due to noise is correctly received according to an over-sampling method.
2. Description of Related Art
In a case where binary digits are sampled from an input serial bit string received in a conventional serial data receiving device, a level change time (hereinafter called a change point) of each binary digit of the bit string is unknown in the conventional serial data receiving device. Therefore, in a case where a binary digit is undesirably sampled in the neighborhood of its change point, there is a probability that a value of the sampled binary digit is incorrect.
To prevent the occurrence of error in the sampling for the input serial bit string, an over-sampling method has been adopted to correctly perform the sampling of binary digits.
In detail, as shown in
FIG. 7
, binary digits are sampled from an input serial bit string at a sampling rate higher than a bit rate of the binary digits. For example, the sampling is performed five times during a time period corresponding to one binary digit to obtain five sampled binary digits for each binary digit. Therefore, an amount of sampled binary digits is five times larger than an amount of binary digits of the input serial bit string. Though there is a probability that data sampled at positions near change points is incorrect, there is a high probability that data sampled at positions far from change points is correct. In the over-sampling method, data correctly sampled at a high probability is selected from five sampled binary digits corresponding to each binary digit of the bit string, and a set of parallel bit strings composed of pieces of data correctly sampled at a high probability are obtained from the input serial bit string.
FIG. 6
is a block diagram showing the configuration of a conventional serial data receiving device. In
FIG. 6
,
101
indicates an over-sampling unit for performing the over-sampling N times (for example, N=5) for each input binary digit of an input serial bit string to obtain a serial bit string of over-sampled binary digits from the input serial bit string.
102
indicates a serial-parallel converting unit for converting a plurality of over-sampled binary digits corresponding to each group of L input binary digits (for example, L=10) successively placed in the input serial bit string to a set of L parallel bit strings respectively composed of N over-sampled binary digits.
103
indicates a data selecting unit for selecting a correctly-sampled binary digit from N over-sampled binary digits of each parallel bit string to obtain a selected bit string composed of L correctly-sampled binary digits and to obtain a plurality of selected bit strings corresponding to the input serial bit string.
104
indicates a word retrieving unit for retrieving a string of words from the correctly-sampled binary digits of the selected bit strings.
Next, an operation of the conventional serial data receiving device will be described below.
FIG. 7
is an explanatory view of the over-sampling method performed in the conventional serial data receiving device for an input serial bit string. In this example, the number of over-sampling operations for each input binary digit is set to five.
When an input serial bit string composed of input binary digits serially arranged is received in the over-sampling unit
101
, the sampling is performed five times for each input binary digit of the input serial bit string to obtain a serial bit string of over-sampled binary digits, and a plurality of over-sampled binary digits corresponding to each group of input binary digits successively placed in the input serial bit string are converted in the serial-parallel converting unit
102
to a set of parallel bit strings respectively composed of five over-sampled binary digits. The number of parallel bit strings is equal to the number of input binary digits corresponding to the conversion, and each parallel bit string corresponds to one input binary digit. In this example, fifty over-sampled binary digits corresponding to each group of ten input binary digits successively arranged in the input serial bit string are converted to a set of ten parallel bit strings composed of fifty over-sampled binary digits (5×10=50). Therefore, an operating frequency of the conventional serial data receiving device can be reduced, each group of ten input binary digits included in the input serial bit string can be estimated at once, and the data selection and the word retrieval can be easily performed later.
Thereafter, in the data selecting unit
103
, ten over-sampled binary digits correctly sampled at a high probability are selected from each set of ten parallel bit strings as a selected bit string of ten correctly-sampled binary digits. In this case, to select one over-sampled binary digit correctly sampled at a high probability from each parallel bit string, a method for finding out two successive over-sampled binary digits having different values at a high probability is often used. For example, a value of the first over-sampled binary digit differs from a value of the second over-sampled binary digit at a high probability in each of four parallel bit strings “10000”, “01111”, “11111” and “01000” shown in FIG.
7
. In this case, it seems reasonable to conclude that the change point of each input binary digit in the input serial bit string is placed between the first over-sampled binary digit and the second over-sampled binary digit of the corresponding parallel bit string. Also, because the fourth over-sampled binary digit has the same value as those of the third and fifth over-sampled binary digits adjacent to the fourth over-sampled binary digit in each parallel bit string at a high probability, it seems that the value of each fourth over-sampled binary digit is stable. Therefore, the fourth over-sampled binary digit in each of ten parallel bit strings is selected as a correctly-sampled binary digit. Because the transmission time period for each input binary digit of the input serial bit string is normally constant, the change point of the input binary digit is placed every five over-sampled binary digits and is placed between the (5M+1)-th over-sampled binary digit and the (5M+2)-th over-sampled binary digit (M denotes zero or a positive integral number), and one (5M+4)-th over-sampled binary digit is to be selected as a correctly-sampled binary digit from each of ten parallel bit strings. In the example shown in
FIG. 7
, the fourth (M=0 in (5M+4)-th) over-sampled binary digit, the ninth (M=1 in (5M+4)-th) over-sampled binary digit,---, the forty-ninth (M=9 in (5M+4)-th) over-sampled binary digit are selected as ten correctly-sampled binary digits of one selected bit string.
However, in the actual operation, the input serial bit string undesirably receives the influence of noises, the change point of an input binary digit is moved, for example, from the position between the (5M+1)-th over-sampled binary digit and the (5M+2)-th over-sampled binary digit to the position between the (5M+2)-th over-sampled binary digit and the (5M+3)-th over-sampled binary digit. In this case, to reliably select correctly-sampled binary digits, one over-sampled binary digit most stable among five over-sampled binary digits in each parallel bit string is selected as one correctly-sampled binary digit.
Thereafter, a plurality of selected bit strings respectively composed of ten correctly-sampled binary digits are successively input to the word retrieving unit
104
. In general, a group of input binary digits preset to a predetermined bit number and expressing a fixed meaning is included many times in the input serial bit string. For example, in case of picture data, red information of one pixel, green information of one pixel and blue information of one pixel are respectively expressed by using a group o
Hirade Takuya
Nakao Hiroomi
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