| 摘要 |
PURPOSE: A 64-quadrature amplitude modulation(QAM) branch metric circuit for a trellis coded modulator(TCM) decoder is provided to implement an in-phase(I) branch metric circuit so as to find the first to the fourth branch metrics. CONSTITUTION: An in-phase(I) branch metric circuit comprises as follows. A first adder(210) adds each of I signals of a 64-QAM and each of 64-quadrature amplitude modulation(QAM) constellation values. An absolute value circuit(220) makes each of the added first to eighth values absolute values. A comparison selector(230) reciprocally compares the first to the eighth values, and selects a first and a second minimal value. First/second registers(240,250) store the first and the second minimal value. A second adder(260) reciprocally adds the first/the second minimal values from the comparison selector(230) to the first/the second minimal values from the first/the second registers(240,250). A multiplexer(270) responds to a control signal from an exterior, and selects four signals among ninth to twelfth added values and the first/the second minimal values from the second adder(260), then generates first to fourth I branch metrics.
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