Patent ID: 8052266

Claim:
A liquid detection device that drives a liquid detecting portion, comprising: a driving portion that supplies a driving signal or a preliminary charging voltage to the liquid detecting portion; a signal detecting portion that receives a detection signal from the liquid detecting portion; a high-pass filter portion that has a capacitor portion and that is arranged between the liquid detecting portion and the signal detecting portion; a first switch that is arranged between the liquid detecting portion and the high-pass filter portion, and that electrically connects or interrupts a line between the liquid detecting portion and the high-pass filter portion; a control portion configured to control the driving portion and the first switch to execute detection of liquid such that the driving portion applies the driving signal to the liquid detecting portion when the first switch is turned off; and a second switch that is arranged between the driving portion and the liquid detecting portion and that is controlled by the control portion to electrically connect or interrupt a line between the driving portion and the liquid detecting portion, wherein the control portion, before the driving signal is applied to the liquid detecting portion, is configured to control the first switch to electrically connect a line between the liquid detecting portion and the high-pass filter portion, to control the second switch to electrically connect a line between the driving portion and the liquid detecting portion, and to control the driving portion to apply the preliminary charging voltage to the liquid detecting portion; the control portion, when liquid is detected, controls the first switch to electrically interrupt a line between the liquid detecting portion and the high-pass filter portion, controls the second switch to electrically connect a line between the driving portion and the liquid detecting portion, and controls the driving portion to apply the driving signal to the liquid detecting portion at a first phase, and the control portion then controls the first switch to electrically connect a line between the liquid detecting portion and the high-pass filter portion, and controls the second switch to electrically interrupt a line between the driving portion and the liquid detecting portion at a next phase after the first phase.