A Fully-Dynamic Capacitive Touch Sensor with Tri-Level Energy Recycling and Compressive Sensing Technique Achieving 1513 Hz Framerate and 10.66 pJ/Step Energy Efficiency

Capacitive touch sensing systems are widely adopted in portable devices such as tablets [1]–[6]. To properly respond to the rapid movements of fingers and styluses, a sensing IC with a high framerate is necessary, e.g. 380 Hz for smartphones. However, high framerate demands high driving power in the transmitter circuit (TX) (Fig. 1, top-left), especially in the presence of large load capacitance, e.g. 0.39 nF in the case of a flexible OLED display [1]. To accommodate the high framerate, additional readout channels and a faster scanning speed are required at the receiver (RX) end (Fig. 1, bottom-left), leading to more die area and power consumption. The increased power consumption leads to a shorter battery lifetime, which is highly undesirable for portable applications. To mitigate the issue, a charge-recycling driving technique is proposed in [6] (Fig. 1, top-middle), which reduces the driving power by 64%. However, the technology in [6] requires additional off-chip capacitors and complex timing control, increasing the overall hardware cost. A two-step sensing approach (Fig. 1, bottom-middle) has been introduced in [7] to address the issue at the RX end, achieving a 322 Hz framerate at the expense of limited signal-to-noise ratio (SNR) (41 dB for finger).