[AK4160]

MS1313-E-01

2011/11

- 9 -

OPERATION OVERVIEW

The touch switch (capacitor) that is connected to the sense input is charged up with direct current during a given period of

time. The switch is connected to ground before the measurement. As a result, the touch switch capacitance is completely

discharged before start being charged. When the touch switch is fully charged, the voltage is inversely proportional to the

capacitance. When the touch switch is touched, this charge voltage decreases because the capacitance value when the

switch is touched is larger than when not touched. The charged voltage is converted to a digital data by ADC. The data is

get through the noise reduction filter, and compared to a touch threshold value. When the measurement value exceeds the

threshold that is corrected environmental drifts, the AK4160 updates the status register to the touch detected state.

SAR

ADC

VDD

VSS

Environmental

Drifts

Correction

Second

Noise Reduction

Filter

First

Noise Reduction

Filter

VSS

Touch Switch

Control Logic

(Touch Detection)

Figure 5. Touch Sensor Block Diagram

The touch switch (capacitance C), that is connected to the sense terminal, is charged with a direct current I during the

period T. The voltage of the sense terminal is V=(I × T)/C, and if the values of I and T are constant, the charged voltage is

inversely proportional to the value of capacitance C. The charge voltage is decreased by V=(I × T)/(C+dC) when the

capacitance C is increased by dC by touching the touch switch comparing with the not touched status. After the voltage is

charged, the AK4160 discharges the sense terminal by a direct current I, during T period. At the same time, the ADC

converts the terminal value. The sense terminal must be connected to ground before the next measurement. The next

measurement should be started when the sense terminal is discharged completely.

Next Measurement

V

T

T

Charge

Discharge

Ground

A/D Convert

Measurement

value

C

T

I

V

×

=

dC

C

T

I

V

+

×

=

(Not Touched)

(Touched)

Figure 6. The Voltage Transaction of a Sense Terminal