| 摘要 |
PURPOSE: To attain high speed decoding processing by approximating square operation for finding out the squared value of a subtracted result value between a received sample value and a predicted sample value by a broken line based upon plural linear functions. CONSTITUTION: A subtractor 21 subtracts between a received sample value and a predicted sample value and supplies the subtracted result to a broken line conversion circuit 23. The circuit 23 converts the subtracted result value by a broken line approximate function for square operation to obtain a conversion value as a branchmetric value. When the subtracted result value is defined as X, the broken line approximate function is expressed by linear functions Ya, Yb. Namely Ya=2<i> .|X|provided with|x|<t and Yb=(2<i> .N|X|-a) provided with|X|>=t. When the|X|is smaller than a prescribed value (t), the subtracted result value X is converted into a branchmetric value Y by using the linear function Ya, and when the|X|is more than the prescribed value (t), the value X is converted into the branchmeteric value Y by using the linear function Yb.
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