Search circuit in decoding unit of low-density parity-check codes and method thereof

A search circuit, used for searching a minimum value and a next minimum value from r input values, where r is an integer greater than 3, comprising:

• a first search circuit, used for performing operations on each pair of input values Vi, Vj of the r input values, respectively, comprising:
• a first comparator, used for comparing if the input value Vi is smaller than the input value Vj, and for producing a first comparison signal;
• and
• a first multiplexing circuit, used for outputting a set of compared valued according to the first comparison signal, outputting the smaller of the input value Vi and the input value Vj as the smaller value of the set of compared values, and outputting the greater of the Vi and Vj as the greater value of the set of compared values according to the first comparison signal;
• a second search circuit, coupled to the first search circuit, used for performing operations on every two sets of compared values Wm, Lm, and Wn, Ln of the s compared values, where s is a positive integer smaller than r, the smaller value Wm being smaller than the greater value Lm, the smaller value Wn being smaller than the greater value Ln, and comprising:
• a second comparator, used for comparing if the smaller value Wm is smaller than the smaller value Wn, and for producing a second comparison signal;
• a second multiplexing circuit, used for outputting the smaller of the smaller value Wm and the smaller value Wn as a smaller value Wo according to the second comparison signal;
• a third multiplexing circuit, used for outputting a set of compared values Wp, Wq according to the second comparison signal, outputting the smaller value Wn and the greater value Lm as the set of compared values Wp, Wq when the second comparison signal represents that the smaller value Wm is smaller than the smaller value Wn, and outputting the smaller value Wm and the greater value Ln as the set of compared values Wp, Wq when the second comparison signal represents that the smaller value Wn is smaller than the smaller value Wm;
• a third comparator, used for comparing if the compared value Wp is smaller than the compared value Wq and for producing a third comparison signal;
• and
• a fourth multiplexing circuit, used for outputting the smaller of the compared value Wp and the compared value Wq as a greater value Lo according to the third comparison signal;
• wherein the second search circuit produces the minimum value and the next minimum value according to the smaller value Wo and the greater value Lo.

A search circuit, used for searching a minimum value and a next minimum value from r input values, where r is an integer greater than 3, comprising:

• a first search circuit, used for performing operations on each pair of input values Vi, Vj of the r input values, respectively, comprising:
• a first comparator, used for comparing if the input value Vi is smaller than the input value Vj, and for producing a first comparison signal;
• and
• a first multiplexing circuit, used for outputting a set of compared valued according to the first comparison signal, outputting the smaller of the input value Vi and the input value Vj as the smaller value of the set of compared values, and outputting the greater of the Vi and Vj as the greater value of the set of compared values according to the first comparison signal;
• and
• a second search circuit, coupled to the first search circuit, used for performing operations on every two sets of compared values Wm, Lm, and Wn, Ln of the s compared values, where s is a positive integer smaller than r, the smaller value Wm being smaller than the greater value Lm, the smaller value Wn being smaller than the greater value Ln, and comprising:
• a second comparator, used for comparing if the smaller value Wm is smaller than the smaller value Wn, and for producing a second comparison signal;
• a second multiplexing circuit, used for outputting the smaller of the smaller value Wm and the smaller value Wn as a smaller value Wo according to the second comparison signal;
• a third comparator, used for comparing if the greater value Lm is smaller than the smaller value Wn and for producing a third comparison signal;
• a third multiplexing circuit, used for outputting the smaller of the greater value Lm and the smaller value Wn as a smaller value Wr;
• a fourth comparator, used for comparing if the smaller value is smaller than the greater value Ln and for producing a fourth comparison signal;
• and
• a fourth multiplexing circuit, used for outputting the smaller of the smaller value Wm and the greater value Ln as a smaller value Wz according to the fourth comparison signal;
• wherein the second multiplexing circuit further outputs the smaller of the smaller value Wr and the smaller value Wz as a greater value Lo according to the second comparison signal, and the second search circuit produces the minimum value and the next minimum value according to the smaller value Wo and the greater value Lo.