| 摘要 |
PROBLEM TO BE SOLVED: To accurately measure the modulation accuracy of aπ/4DQPSK modu lation signal in a circuit for asynchronously sampling symbol identification points of an input signal. SOLUTION:π/4DQPSK-modulated signals to be measured are converted into digital time sequential data Ai for measurement by asynchronously sampling symbol identification points through an A/D converter 10, and from the time sequential data Ai, the symbol point position of the signal to be measured is calculated by a calculating means 12. A deviationΔt between the symbol identification point position of the signal to be measured and sampling timing is calculated by a calculating means 13, phase conversion for theΔt is performed on the time equential data Ai by a means 14, and these data are converted into time sequential data Bi which are sampled at a timing synchronized with the symbol identification point position. The modulation accuracy is calculated by an arithmetic means 15 based on the time sequential data Bi. Through these processes, highly accurate measurement can be made, without being affected by the deviation between the symbol identification point position of the signal to be measured and asynchronous sampling, thus making the circuit configuration simple.
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