| 摘要 |
PURPOSE:To obtain directly a differentiation phase characteristic from a digital signal by calculating a phase of outputs of a digital filter passing through a high frequency signal only and obtaining a differentiation gain. CONSTITUTION:A sapling frequency when a composite signal is digitized by a measured circuit is 4f0 being four times of a sinusoidal high frequency signal frequency f0 included in a composite signal and an output signal of a digital filter is a sinusoidal signal shifted by pi/2 each. An input signal section 10 outputs a composite signal where a sinusoidal minute signal in a color subcarrier frequency f0 is superimposed on a step wave or a low frequency signal, the composite signal is inputted to an AD converter of a measured circuit 11 and inputted to a PLL circuit 12. The PLL circuit 12 generates a four times fre quency 4f0 synchronously with a chroma signal in a composite signal and inputs it to the AD converter as a sampling input. An operating section 14 outputs a differentiation phase DP. Thus, the digital signal output is not DA-converted nor converted into an analog signal and the phase information is obtained directly from the digital signal itself.
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