Referring to FIG. 17A, a capacitance sensing system 1700 is shown. Capacitance sensing system 1700 includes capacitance elements 1702-1 to -n, sense channels 1704-1 to -n, a multiplexer (MUX) 1706, and an analog-to-digital converter (ADC) 1708. Capacitance elements (1702-1 to -n) are formed by a mutual capacitance between a transmit electrode (Tx) and receive electrodes (Rx1 to Rxn). Such a capacitance can vary in response to an object touching, or being proximate to, a surface containing the electrodes. Sense channels (1704-1 to -n) each include a low noise amplifier (LNA) (one shown as 1708), a mixer (one shown as 1710), and an integrator (one shown as 1712). Each sense channel (1704-1 to -n) generates a voltage corresponding to a sensed capacitance. A MUX 1706 sequentially connects an output of each sense channel (1704-1 to -n) to ADC 1708. ADC 1708 converts analog outputs from integrators (e.g., 1710) into digital output values DOUT.
Referring to FIG. 17B, a capacitance sensing operation for system 1700 is shown in a timing diagram. Waveform CHs shows operations of sense channels in a system. Waveform ADC shows an operation of an ADC 1708.
At about time t0, signals can be generated corresponding to the Rx electrodes.
At about time t1, once sufficient time has passed for sense channels (1704-1 to -n) to acquire analog values, a MUX 1706 starts to sequentially connect each channel to the ADC 1708. The analog value from channel CH1 (1704-0) is the first value converted by ADC 1708. One-by-one, each channel is connected to the ADC 1708, and the analog value generated by the sense channel is converted into a digital value.
At time t2, MUX 1706 can switch a next channel to ADC 1708, which can generate a digital value for a next channel of the row (in this case channel CH2). This can continue until all channels of ROW I are sensed.
At about time t3, signals can be generated corresponding to a next row (ROW II) of Rx electrodes. Sensing can continue for the next row in the same fashion.
As understood from above, in the approach shown, generating signals for one row (i.e., ROW II) does not start until the ADC 1708 has finished converting values for a previous row (i.e., ROW I).