| 摘要 |
A touch screen includes a transmitter capable of delivering an acoustic signal to the touch screen and a receiver adapted to detect acoustic signals on the touch screen and deliver a first signal representative of the detected acoustic signals. An automatic gain control amplifier has an input, output, and control terminal, and is adapted to receive the first signal on the input terminal and deliver an amplified version of the first signal on the output terminal. The control terminal is adapted to receive a control signal that varies the gain of the amplifier. An analog to digital converter is adapted to receive the amplified first signal and deliver a digital representation thereof. A first circuit is adapted to receive one of the amplified first signal and the digital signal, determine the difference between the received signal and a preselected value, and deliver a control signal to the control input of the amplifier. The control signal has a magnitude responsive to the determined difference. |
