| 摘要 |
PURPOSE: A noise shaper for improving a phase noise characteristic in a high offset frequency is provided to improve the capacity of a noise shaper for radio frequency phase locked loop by reducing a phase noise in a high offset frequency. CONSTITUTION: A noise shaper(101) is composed of a sigma-delta modulator(121) and a filter(111). The sigma-delta modulator(121) transfers a phase noise generated from a low frequency band to a high frequency band according to an input signal. The sigma-delta modulator(121) is composed of the first to the third delayed accumulators(A1,A2,A3), the first to the fifth delay devices(D1,D2,D3,D4,D5), and the first and the second adders(S1,S2). The first to the third delayed accumulators(A1,A2,A3) generate the first to the third overflows(N1,N2,N3), respectively. The third overflow(N3) is inputted to the second adder(S2). The second overflow(N2) is inputted to the second adder(S2). The second adder(S2) adds an output of the third delay device(D3) to the third overflow(N3) and subtracts the fifth delay device(D5) from the added result. An output of the second adder(S2) is inputted to the first adder(S1). The first overflow(N1) is inputted to the first adder(S1). The first adder(S1) adds an output of the second delay device(D2) to the output of the second adder(S2) and subtracts an output of the fifth delay device(D4) from the added result.
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