| 摘要 |
<p>Tone receiver comprising a switched capacitor zero crossing detector (10). The zero crossing detector is arranged for compensating the input offset voltage by causing during a first capacitor switching phase this offset voltage to be present across a capacitor (34) which is connected in parallel with the input of the comparator. At the same time it appears that with this operation any DC voltage component in the input signal can be blocked. With the aid of a voltage step source (46) a voltage step is realised on the input capacitor (34), which step functions as a threshold in the comparator phase. Once the threshold voltage has been exceeded, the comparator is reversed and the processor changes the control of the voltage step source, so that this source produces a threshold voltage of opposite sign. This achieves an effect of hysteresis which counteracts the constant reversing of the comparator.</p> |
