| 摘要 |
PURPOSE:To improve SN by providing a filter means removing or reducing noises generated from a precircuit between the precircuit and a post-circuit. CONSTITUTION:A D/A converter converts a received digital signal Di into an analog signal in accordance with an 8kHz sampling pulse phi51 for example. A switched capacitor consists of a switching means SW to be operated by a 128kHz sampling pulse phi52 e.g. a capacitor C1, an operational amplifier OP, and capacitors C2, C3. A resistor R is inserted into a signal line connecting the output terminal of the D/A converter and the switching means SW in series. The insertion of the resistor R constitutes an LPF together with the capacitor C1, etc., reducing noises including comparatively high frequency whisker-like components. Since the switched capacitor itself also constitutes the LPF in said circuit, both switched capacitor and LPF act synergistically and the noises can be removed almost completely. |
