Sensing device for detecting approaching object

1. A sensing device for detecting an approaching object comprising:

(a) a sensor section, the sensor section including

(1) a first detection electrode supplied with a detection source signal having a prescribed frequency, and

(2) a second detection electrode disposed in close vicinity to the first detection electrode,

wherein a communication signal is obtained from the detection source signal that is transmitted to the second detection electrode from the first detection electrode and attenuated thereat when an object approaches the sensor section;

(b) a communication signal amplifier amplifying the communication signal and outputting the amplified communication signal as an amplifier output signal;

(c) an integrator integrating the amplifier output signal and outputting a judging signal for judging whether or not an object approaches the sensor section; and

(d) a detection sub-signal switch disposed between an output side of the communication signal amplifier and an input side of the integrator;

wherein the detection sub-signal switch periodically switches on only during a prescribed period in which a peak value of the amplifier output signal is included in response to a detection sub-signal,

wherein a frequency of the detection sub-signal is equal to that of the detection source signal, and

wherein the detection sub-signal maintains specific phase relation with the detection source signal, further

wherein a duty ratio of the detection sub-signal is less than 50%.

2. The sensing device as claimed in claim 1 , wherein the detection sub-signal switch is constituted by a transistor.

3. The sensing device as claimed in claim 1 , wherein the detection sub-signal switch is constituted by a pair of transistors in different polarities.

4. The sensing device as claimed in claim 1 , wherein the detection sub-signal switch is constituted by a field-effect transistor.