| 摘要 |
PROBLEM TO BE SOLVED: To provide a delta sigma type analog/digital converter that causes no increase in the circuit scale and has an optimum frequency characteristic to both FM and AM broadcast programs. SOLUTION: An input analog signal in a 1st stage of the delta sigma type analog/digital converter is outputted to a post-stage arithmetic unit 107 via a coefficient buffer, an arithmetic unit, a delay unit and a coefficient buffer. In this case, the arithmetic unit 102 sums a feedback signal from a 2nd stage analog/digital conversion section 114 and subtracts a feedback signal resulting from multiplying a coefficientαwith an output of a delay unit 103 by the coefficient buffer and a feedback signal from a delay unit 105 respectively from the sum. Further, a 2nd stage arithmetic unit of the delta sigma type analog/digital converter is similarly configured, but a coefficientβdifferent from the coefficientαis used for the feedback. The frequency characteristic of a quantized noise Q (Z) has a transmission zero above and under a center frequency of the input analog signal by properly selecting the coefficientsα,βso as to attenuate the quantized noise over a wide band.
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