| 摘要 |
PURPOSE:To accurately decide a clamp level and an input sesitivity by using one of two comparators so as to set a clamp level and using the other to set the input sensitivity thereby avoiding the peak of an input signal from exceeding the clamp level. CONSTITUTION:When an amplitude VIN of a pulse signal impressed to an input terminal 15 exceeds the input sensitivity (VT-VA) set by a comparator 19, a Schmitt circuit comprising a P-channel MOSFET 26 and N-channel MOSFETs 27, 28 is operated. Then the reference voltage VT of the comparator 19 is lowered by nearly 150mV and an output signal subjected to waveform shaping is obtained at an output terminal 17. The amplitude VIN of the input signal gets higher and reaches a clamp level VC being a reference voltage of a comparator 18, then the output voltage of the comparator 18 transits to a high level. As a result, an N-channel MOSFET 25 is turned on to discharge the electric charge in a coupling capacitor 16 thereby clamping a voltage VA after the capacitor couping to the clamp level VC. |
