| 摘要 |
The amplifier circuit for a high-impedance sensor, for example a piezoelectric sensor (1), exhibits an operational amplifier (7). A positive feedback loop which consists of a first resistor (R1), a second resistor (R3) and a capacitor (C1) is connected between the positive input (5) of the operational amplifier (7) and its output (11). The output (11) of the operational amplifier (7) is connected to the negative input (9). A switch (17) connects the positive feedback loop to earth in dependence on the signal (A) at the output (11) of the operational amplifier (7) and, as a result, renders this loop ineffective. As a criterion for this disconnection of the positive feedback loop, the change in the sign of the slope of the signal (A) at the output (11) can be used, for example. The advantage of the circuit is a very high input impedance whilst at the same time eliminating the risk of unwanted switching processes due to damped slow oscillations at the output (11). The amplifier circuit is preferably used with a touch-sensitive device. <IMAGE>
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