This article presents a readout integrated circuit (ROIC) for capacitive touch-screen panels (TSPs) employing an amplitude-modulated multiple-frequency excitation (AM-MFE) technique. To prevent charge overflow, which occurs periodically at the beat frequency of the excitation frequencies, the ROIC modulates the amplitude of the excitation voltages at a mixing frequency derived from the excitation frequencies. Thus, the ROIC can sense the charge signal without charge overflow and maximize the signal-to-noise ratio (SNR) by increasing the amplitude of the excitation voltages up to the sensing range of the readout circuit. The proposed ROIC was fabricated in a 0.13- $\mu \text{m}$ standard CMOS process and was measured with a 32-in 104 $\times $ 64 touch-screen panel using 1 and 10 mm metal pillars. It reduces charge overflow up to 33.9 dB compared to operation without AM-MFE. In addition, the ROIC achieves a frame rate of 2.93 kHz, and SNRs of 41.7 and 61.6 dB with 1 and 10 mm metal pillars, respectively.

In this paper, the surveys on the stylus technologies for capacitive-type touch systems (CTSs) are presented. The stylus technologies are classified into the passive and active stylus depending on the battery integration. To explain two types of the stylus, the architecture of CTS with the stylus is firstly explained. Afterward, the operation principles of the passive, which have a capacitive-type (C-type), an electromagnetic resonance type, and an electrically coupled resonance type, and a C-type active type styli are described. Author Keywords

As the demand for high frame rate and SNR increases in capacitive touch systems (CTSs), several driving methods have been reported [1], [5]. However, when excitation circuits simultaneously send excitation signals V_EXTs to multiple TX electrodes in order to increase frame rate, the readout circuit suffers from charge overflow because of the superposition of V_EXTs. To prevent this, driving methods such as time-division [1], [5] and reduced-amplitude excitation [3], and signal omitting and linear interpolation in the digital domain [4] have been adopted in AFE ICs, but they degrade the frame rate, and SNR, and increase the computational load of the CTS, respectively. In this paper, amplitude-modulated multiple-frequency excitation (AM-MFE) is used to prevent charge overflow without degrading the frame rate, SNR, and computational load. In addition, an electric pencil case (EPC) is proposed for wireless power and data transfer to an active stylus, so as to avoid the need to replace the battery of the stylus or charge it via an adapter.

This article presents a fully integrated 64-channel programmable ultrasound transmit beamformer for catheter-based ultrasound probes, designed to interface with a capacitive micro-machined ultrasound transducer (CMUT) array. The chip is equipped with programmable high-voltage (HV) pulsers that can generate ±30-V return-to-zero (RZ) and non-RZ pulses. The pulsers employ a compact back-to-back isolating HV switch topology that employs HV floating-gate drivers with only one HV MOS transistor each. Further die-size reduction is achieved by using the RZ switches also as the transmit/receive (T/R) needed to pass received echo signals to low-voltage receive circuitry. On-chip digital logic clocked at 200 MHz allows the pulse timing to be programmed with a resolution of 5 ns, while supporting pulses of 1 cycle up to 63 cycles. The chip has been implemented in 0.18-μm HV Bipolar-CMOS-DMOS (BCD) technology and occupies an area of 1.8 mm ×16.5 mm, suitable for integration into an 8-F catheter. Each pulser with embedded T/R switch and digital logic occupies only 0.167 mm2. The pulser successfully drives an 18-pF transducer capacitance at pulse frequencies up to 9 MHz. The T/R switch has a measured ON-resistance of ~180Ω. The acoustic results obtained in combination with a 7.5-MHz 64-element CMUT array demonstrate the ability to generate steered and focused acoustic beams.

Miniature ultrasound probes, such as the intra-cardiac echography (ICE) probe shown in Fig. 23.6.1, increasingly employ in-probe ASICs to interface with the elements of an ultrasound transducer array to improve signal quality and reduce cable count [1]-[4]. For each transducer element, such an ASIC contains a pulser that drives the element to generate a pressure wave, a low-noise amplifier (LNA) that amplifies the resulting echo signal, and a time-gain compensation (TGC) circuit that compensates for the time-varying echo-signal amplitude due to propagation attenuation of the acoustic wave. Without TGC, the first echoes, from shallow tissue, are much larger than later echoes from deeper tissue. The TGC circuit corrects for this, ideally by providing a gain that increases exponentially with time, thus reducing the dynamic range (DR) by as much as 40dB and strongly relaxing the requirements of subsequent blocks. In conventional ultrasound systems, TGC is typically performed after the LNA, implying that a power-hungry LNA is required that can handle the full DR of the echo signal [5], [6]. In recent in-probe ASICs, programmable-gain LNAs have been employed that provide a step-wise TGC approximation [1]-[3]. While this saves power, the associated gain-switching transients lead to imaging artefacts. In this paper, we present an LNA with a built-in continuous TGC function that mitigates this problem. The LNA is a transimpedance amplifier (TIA) optimized to amplify the signal current of a capacitive micro-machined ultrasound transducer (CMUT). We demonstrate its integration into a 64-channel ASIC for a CMUT-based ICE probe.

This article presents a low-noise transimpedance amplifier (TIA) designed for miniature ultrasound probes. It provides continuously variable gain to compensate for the time-dependent attenuation of the received echo signal. This time-gain compensation (TGC) compresses the echo-signal dynamic range (DR) while avoiding imaging artifacts associated with discrete gain steps. Embedding the TGC function in the TIA reduces the output DR, saving power compared to prior solutions that apply TGC after the low-noise amplifier. The TIA employs a capacitive ladder feedback network and a current-steering circuit to obtain a linear-in-dB gain range of 37 dB. A variable-gain loop amplifier based on current-reuse stages maintains constant bandwidth in a power-efficient manner. The TIA has been integrated in a 64-channel ultrasound transceiver application-specific integrated circuit (ASIC) in a 180-nm BCDMOS process and occupies a die area of 0.12 mm2. It achieves a gain error below ±1 dB and a 1.7 pA/ √ Hz noise floor and consumes 5.2 mW from a ±0.9 V supply. B-mode images of a tissue-mimicking phantom are presented that show the benefits of the TGC scheme.

This letter presents a compact programmable high-voltage (HV) pulser for ultrasound imaging, designed for driving capacitive micromachined ultrasonic transducers (CMUTs) in miniature ultrasound probes. To enable bipolar return-to-zero (RZ) pulsing and embedded transmit/receive switching, a compact back-to-back isolating HV switch is proposed that employs HV floating-gate drivers with only one HV MOS transistor each. The pulser can be digitally programmed to generate bipolar pulses with and without RZ, with a peak-to-peak swing up to 60 V, as well as negative and positive unipolar pulses. It can generate bursts of up to 63 pulses, with a maximum pulse frequency of 9 MHz for an 18-pF transducer capacitance. Realized in TSMC 0.18-μm HV BCD technology, the pulser occupies only 0.167 mm ². Electrical characterization results of the pulser, as well as acoustic results obtained in the combination with a 7.5-MHz CMUT transducer, are presented.