This paper describes the design of a small-offset 12-bit CMOS charge-redistribution DAC using a weighted-mean flip-around sample-and-hold circuit (S/H). Flip-around S/H topology can realize small-offset characteristics, and it is effective to reduce power dissipation and chip area because independent feedback capacitors are not necessary. In this DAC the small-offset characteristic remains not only in amplification phase but also in sampling phase with the circuit technique. The design of 1.8 V, 50 MS/s fully differential DAC with output swing of 2 Vp-p has very small offset of 100 µV for the reset switch mismatch of 2%. A technique to improve dynamic performance measured by SFDR using damping resistors and switches at the output stage is also presented. The designed 12-bit DAC with 0.25 µm CMOS technology has low-power dissipation of 35 mW at 50 MS/s.

A high-speed high-resolution sample-and-hold amplifier (SHA) is designed for time-interleaved analog-to-digital converter applications. Using the techniques of precharging and output capacitor coupling can mitigate the stringent performance requirements for the opamp, resulting in low power dissipation. Implemented in a standard 0.25 µm CMOS technology, the SHA achieves 80 dB spurious-free dynamic range (SFDR) for a 1.8 Vpp output at 100 MHz Nyquist sampling rate. The SHA occupies a die area of 0.35 mm2 and dissipates 33 mW from a single 2.5 V supply.

This paper describes an MOS current-mode sample-and-hold (S/H) circuit that potentially operates with a sub-1. 5 V supply voltage, 20 MHz clock frequency, and less than 0. 1% linearity. A newly developed voltage-to-current converter suppresses the voltage change at an input terminal and achieves low-voltage operation with superior linearity. Sample switches are differentially placed at the inputs of a differential amplifier so that the feedthrough errors from switches cancel out. The MOS current-mode S/H circuit is designed and simulated using CMOS 0. 6 µm device parameters. Simulation results indicate that an operation with 20 MHz clock frequency, linearity error of less than 0. 1%, and 1 MHz input from a 1. 5 V power supply is achievable.

Our study investigated the realization of a high-precision MOS current-mode circuit. Simple studies have implied that it is difficult to achieve a high signal-to-noise ratio (S/N) in a current-mode circuit. Since the signal voltage at the internal node is suppressed, the circuit is sensitive to various noise sources. To investigate this, we designed and fabricated a current-mode sample-and-hold circuit with a 3V power supply and a 20MHz clock speed, using a standard CMOS 0.6µm device process. The measured S/N reached 57dB and 59dB in sample mode, and 51dB and 54dB in sample-and-hold mode, with 115µA from a 3V power supply and 220µA from a 5V power supply of input currents and a 10MHz noise bandwidth. The S/N analysis based on an actual circuit was done taking device noise sources and the fold-over phenomena of noise in a sampled system into account. The calculation showed 66.9dB of S/N in sample mode and 59.5dB in sample-and-hold-mode with 115µA of input current. Both the analysis and measurement indicated that 60dB of S/N in sample mode with a 10MHz noise bandwidth is an achievable value for this sample-and-hold circuit. It was clear that the current-mode approach limits the S/N performance because of the voltage suppression method. This point should be further studied and discussed.

This paper presents an 8-bit 200M-sample/s (Ms/s) analog-to-digital converter (ADC) applicable to liquid crystal display (LCD) driver systems. The ADC features such circuit techniques as a low-power and high-speed comparator, an open-loop sample-and-hold amplifier with a 3.4-ns acquisition time, a fully differential two step architecture, and a replica circuit. It is fabricated with a 0.8µm BiCMOS process onto an area of only 12mm2 and it dissipates 500mW from a single-5.2V power supply.

This paper describes a segment driver IC for high-quality liquid-crystal-displays (LCDs). Major design issues in the segment driver IC are a wide signal bandwidth and excessive output-offset variation both within a chip and between chips. After clarifying the trade-off relation between the signal bandwidth and the output-offset variation originated from conventional sample-and-hold (S/H) circuits, two wide-band S/H circuits with low output-offset variation have been introduced. The basic ideas for the proposed S/H circuits are to improve timing of the sampling pulses applied to MOS analog switches and to prevent channel charge injection onto a storage capacitor when the switches turn off. The inter-chip offset-cancellation technique has been also introduced by using an additional S/H circuit. Two test chips were implemented using the above S/H circuits for demonstration purposes. The intra-chip output-offset standard deviation of 9.5 mVrms with a 3dB bandwidth of 50 MHz was achieved. The inter-chip output-offset standard deviation was reduced to 5.1 mVrms by using the inter-chip offset-cancellation technique. The evaluation of picture quality of an LCD using the chips shows the applicability of the proposed approaches to displays used for multimedia applications.