Abstract
In this paper, a high noise immunity, 28 × 16-channel finger touch sensing IC for an orthogonal frequency division multiplexing (OFDM) touch sensing scheme is presented. In order to increase the signal-to-noise ratio (SNR), the OFDM sensing scheme is proposed. The transmitter (TX) transmits the orthogonal signal to each channels of the panel. The receiver (RX) detects the magnitude of the orthogonal frequency to be transmitted from the TX. Due to the orthogonal characteristics, it is robust to narrowband interference and noise. Therefore, the SNR can be improved. In order to reduce the noise effect of low frequencies, a mixer and high-pass filter are proposed as well. After the noise is filtered, the touch SNR attained is 60 dB, from 20 dB before the noise is filtered. The advantage of the proposed OFDM sensing scheme is its ability to detect channels of the panel simultaneously with the use of multiple carriers. To satisfy the linearity of the signal in the OFDM system, a high-linearity mixer and a rail-to-rail amplifier in the TX driver are designed. The proposed design is implemented in 90 nm CMOS process. The SNR is approximately 60 dB. The area is 13.6 mm2, and the power consumption is 62.4 mW.
Highlights
As the demand for the various touch applications has grown, the interest of touch technology has increased [1,2,3,4,5,6,7,8]
In the orthogonal frequency division multiplexing (OFDM) demodulator, the requested frequency can be acquired by the orthogonality and the noise is rejected by the discrete cosine transform (DCT) and the channel estimation
If the linearity is broken in this system, it is difficult for the OFDM modulator to detect the touch point because the carriers are distorted by the analog front-end (AFE)
Summary
As the demand for the various touch applications has grown, the interest of touch technology has increased [1,2,3,4,5,6,7,8]. The mutual capacitance touch panel is adopted to employ multi-touch and to reduce the ghost point [10]. In order to increase very small touch signals and reduce the noise, integrators are implemented in the receiver. To overcome the limit of the AFE, a frequency division sensing scheme is used. The various noises are rejected by orthogonality of frequencies and the OFDM touch sensing scheme can acquire a high SNR in this system. By using the OFDM sensing scheme, it is possible to detect each channel of the panel at the same time. When the touch is generated on the panel, the capacitor of the touch point is varied and the AFE senses the varied touch signal.
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