| 摘要 |
<p>The Hall sensor circuit includes a Hall element (10) that is preferably followed by a Hall-voltage amplifier (11), and a pole end of a magnet is preferably fixed adjacent to the Hall element. The amplifier output is connected directly to one of a pair of differential inputs of a Schmitt trigger circuit (29) and is also connected, via a single or a dual-polarity track and hold circuit (18,19,20), to the other of the differential Schmitt inputs. The dual-polarity track and hold circuit (18,19,20) causes the voltage across a capacitor (20) to track positive and negative Hall voltage slopes, and to hold the positive-going peaks and negative-going peaks of the Hall voltage presented to the fore-mentioned other Schmitt input so that when the difference voltage between the Hall voltage and the held voltage of the capacitor (20) exceeds a positive or negative threshold of the Schmitt circuit, the Schmitt circuit (29) output changes binary state indicating the approach or the receding of a ferrous-gear tooth. The dual-polarity track and hold circuit is made up of two complementary plus and a minus peak detector circuits (Fig.11), each including a bipolar transistor (53,83) having an emitter connected to the voltage-holding capacitor (54), an operational amplifier (52,80) with an output connected to the base of the transistor (53,83), the amplifier having a negative input connected to the transistor emitter and a positive input serving as the input of the each Hall voltage tracking and holding circuit. <IMAGE></p> |
