Search Results (12)

This brief proposes a signal-independent background calibration in pipeline-SAR analog-to-digital converters (ADCs) with a convergence-accelerated technique. To achieve signal independence, an auxiliary capacitor array C_A is introduced to pre-inject a pseudo-random noise (PN) in the sampling phase to cancel out the opposite PN injection of the calibrated capacitor in the conversion phase, and C_A is also used to realize the D/A function of the calibrated capacitor in the conversion phase. In this way, no matter what the signal is, the residue headroom remains unchanged even with PN injection. Moreover, the first sub-ADC is designed with extended conversion bits to quantize its own residue after delivering the conversion bits required by the first stage. Afterwards, this result is provided to the calibration algorithm to reduce the signal component and accelerate the convergence. Based on the simulation, the signal-to-noise and distortion ratio (SNDR) and spur-free dynamic range (SFDR) improve from 45.3 dB and 56.4 dB to 68.2 dB and 88.4 dB, respectively, after calibration. In addition, with the acceleration technique, convergence cycles decrease from 1.7 × 10⁸ to 5.8 × 10⁶. Moreover, no matter whether the input signal is DC, sine wave or band-limited white noise, the calibration all works normally. Full article

This paper presents an electrochemical impedance spectroscopy (EIS) system-on-chip in 0.18-$\mathsf{\mu }\mathrm{m}$ CMOS, achieving a wide scan frequency range of 1.25 MHz. An on-chip direct digital frequency synthesizer generates a digital sine wave as well as in-phase and quadrature-phase clocks that are synchronized to the sinewave. A chopped sampling mixer realizes lock-in detection without requiring quadrature sinewaves while suppressing low-frequency noise and offset. The receive utilizes a 12-bit pipelined SAR ADC operating in 5 MS/s in combination with a digital averaging filter to maximize the dynamic range. The measured performance shows that the prototype EIS chip achieves the highest frequency scan range with a comparable dynamic range of 108 dB and power consumption of 14 mW when compared with the previous state-of-the-art prototypes. Full article

This paper presents a pipelined noise-shaping SAR (PLNS-SAR) ADC for high SNDR, wide bandwidth, and low power consumption. The proposed design achieves a sharp second-order NTF of an error feedback structure, without a multi-input comparator and additional residue amplifier. Additionally, the SNDR is improved via zero optimization. Additionally, the speed is enhanced via prediction logic and alternately using the passive switched capacitor FIR filter. This consequently achieves the high-power efficiency of the ADC. The simulated SNDR is 79.97 dB; it achieves a 12.5-MHz BW at a 175-MHz sampling rate, with OSR of 7. The total power consumption of the ADC is 4.27 mW at a 1.1-V supply. The ${\mathrm{FoM}}_{\mathrm{S},\mathrm{SNDR}}$ is 174.6 dB. The proposed structure achieves high resolution and wide bandwidth with good energy efficiency. Full article

This paper presents a calibration-free, 16-channel, 14-bit, 50-MS/s, pipelined successive approximation register (pipelined-SAR) analog-to-digital converter (ADC) for ultrasound imaging systems. A reference sharing scheme with reduced buffers is proposed to improve area-and-power efficiency, which is essential for multi-channel systems. Based on this, a three-stage, pipelined-SAR ADC architecture with reference/op-amp sharing and optimized stage resolution distribution is proposed. The prototype ADC is designed in a 0.18-μm process with peripheral circuits integrated, including low-voltage differential signaling (LVDS), bandgap, etc. It achieves a robust and calibration-free performance with 68.25-dB signal to noise and distortion ratio (SNDR) and 82.19-dB spurious-free dynamic range (SFDR), translating into a competitive figure of merit (FoM) of 0.47 pJ/conversion-step among other high-resolution ADCs used in ultrasound applications. Full article

As traditional ultrasonic imaging systems (UIS) are expensive, bulky, and power-consuming, miniaturized and portable UIS have been developed and widely utilized in the biomedical field. The performance of integrated circuits (ICs) in portable UIS obviously affects the effectiveness and quality of ultrasonic imaging. In the ICs for UIS, the analog-to-digital converter (ADC) is used to complete the conversion of the analog echo signal received by the analog front end into digital for further processing by a digital signal processing (DSP) or microcontroller unit (MCU). The accuracy and speed of the ADC determine the precision and efficiency of UIS. Therefore, it is necessary to systematically review and summarize the characteristics of different types of ADCs for UIS, which can provide valuable guidance to design and fabricate high-performance ADC for miniaturized high resolution UIS. In this paper, the architecture and performance of ADC for UIS, including successive approximation register (SAR) ADC, sigma-delta (Σ-∆) ADC, pipelined ADC, and hybrid ADC, have been systematically introduced. In addition, comparisons and discussions of different types of ADCs are presented. Finally, this paper is summarized, and presents the challenges and prospects of ADC ICs for miniaturized high resolution UIS. Full article

A 2.5-GS/s 12-bit four-way time-interleaved pipelined-SAR ADC is presented in 28-nm CMOS. A bias-enhanced ring amplifier is utilized as the residue amplifier to achieve high bandwidth and excellent power efficiency compared with a traditional operational amplifier. A high linearity front-end is proposed to alleviate the non-linearity of the diode for ESD protection in the input PAD. The embedded input buffer can suppress the kickback noise at high input frequencies. A blind background calibration based on digital-mixing is used to correct the mismatches between channels. Additionally, an optional neural network calibration is also provided. The prototype ADC achieves a low-frequency SNDR/SFDR of 51.0/68.0 dB, translating a competitive ${\mathrm{FoM}}_{\mathrm{w}}$ of 0.48 pJ/conv.-step at 250 MHz input running at 2.5 GS/s. Full article

This paper presents a 9-bit 1 GS/s successive approximation register (SAR) analog-to-digital converter (ADC). In this hybrid architecture, the pseudo-pipeline operation is realized, which increases the sampling rate effectively. The ADC adopts two key technologies: the variable gain voltage-to-time converter (VTC), which ensures the linearity is not sacrificed; the segmented time-to-digital converter (STDC), which further improves the linearity of time domain quantization. The prototype ADC is simulated in a standard 65-nm CMOS process with an active area of 0.038 mm². The simulated SNDR and SFDR are 44.3 and 58 dB with a sampling rate of 1 GS/s. The FoMW and FoMS are 24.7 fJ/conv-step and 150.7 dB, respectively. Full article

In this study, a pipelined noise-shaping successive-approximation register analog-to-digital converter (PLNS-SAR ADC) structure was proposed to achieve high resolution and to be free from comparator design requirements. The inter-stage amplifier and integrator of the PLNS-SAR ADC were implemented through a ring amplifier with high gain and speed. The ring amplifier was designed to improve power efficiency and be tolerant to process–voltage–temperature (PVT) variation, and uses a single loop common-mode feedback (CMFB) circuit. By processing residual signals with a single ring amplifier, power efficiency can be maximized, and a low-power system with 30% lower power consumption than that of a conventional PLNS-SAR ADC is implemented. With a high-gain ring amplifier, noise leakage is greatly suppressed, and a structure can be implemented that is tolerant of mismatches between the analog loop and digital correction filters. The measured signal to noise distortion ratio (SNDR) is 70 dB for a 5.15 MHz bandwidth (BW) at a 72 MS/s sampling rate (Fs) with an oversampling ratio (OSR) of 7, and the power consumption is 2.4 mW. The ${\mathrm{FoM}}_{\mathrm{S},\mathrm{SNDR}}$ (= SNDR + ${10\log }_{10}$BW/Power) is 163.5 dB. The proposed structure in this study can achieve high resolution and wide BW with good power efficiency, without a filter calibration process, through the use of a ring amplifier in the PLNS-SAR ADC. Full article

This work presents a 12 bit 200 MS/s dual-residue pipelined successive approximation registers (SAR) analog-to-digital converter (ADC) with a single open-loop residue amplifier (RA). By using the inherent characteristics of the SAR conversion scheme, the proposed ADC sequentially generates two residue levels from the single RA, which eliminates the need for inter-stage gain-matching calibration. To convert the sequentially generated the two residues, a capacitive interpolating SAR ADC (I-SAR ADC) is also proposed. The I-SAR ADC is very compact because it consists of the one comparator, a CDAC, and control logic like a conventional SAR ADC. In addition, the I-SAR ADC needs no static power dissipation for the residue interpolation. A prototype ADC fabricated in a 40 nm CMOS technology occupies an active area of 0.026 mm². At a 200 MS/s sampling-rate with the Nyquist input, the ADC achieves an SNDR (Signal-to-Noise distortion ratio) of 62.1 dB and 67.1 dB SFDR (Spurious-Free Dynamic Range), respectively. The total power consumed is 3.9 mW under a 0.9 V supply. Without any inter-stage mismatch calibration, the ADC achieve Walden Figure-of-Merit (FoM) of 19.0 fJ/conversion-step. Full article

A 12-bit 200 MS/s pipelined successive-approximation-register (SAR) analogue-to-digital-converter (ADC) implemented in 40 nm CMOS is presented. Such an ADC consists of two asynchronous SAR ADCs and a dynamic amplifier, which consumes a static power of 1.2 mW (the total power is 8 mW) and occupies an area of 0.046 mm². The inter-stage gain is affected by the parasitic capacitance in SAR ADCs as well as the gain of the dynamic amplifier, which is variable with respect to process-voltage-temperature (PVT). A background calibration of the inter-stage gain is proposed to adjust the inter-stage gain and to track the PVT variables. The measurement results show that, with calibration, the spurious-free-dynamic-range (SFDR) and signal-to-noise-and-distortion-ratio (SINAD) can be improved from 68 dB and 61 dB to 78 dB and 63 dB, respectively. The dynamic performance was stable under different VT conditions. Full article

A 1 GS/s 12-bit pipelined/successive-approximation-register (pipelined/SAR) hybrid analog-to-digital converter (ADC) is presented in this paper, where the five most significant bits are resolved by two cascading 2.5-bit multiplying digital-to-analog converters, and the eight least significant bits are determined by a two-channel time-interleaved successive-approximation-register (TI-SAR) quantizer. An integrated input buffer and an operational amplifier with improved voltage efficiency at 1.8 V are adopted to achieve high-linearity stably in wide band for 1 GS/s. By designing a 500 MS/s 8-bit SAR quantizer at 1 V, the number of required interleaved channels is minimized to simplify the complexity and an adaptive power/ground is used to compensate the common-mode mismatch between the blocks in different power supply voltages. The offset and gain mismatches due to the TI-SAR quantizer are compensated by a calibration scheme based on virtually-interleaved channels. This ADC is fabricated in a 40 nm complementary metal-oxide-semiconductor (CMOS) technology, and it achieves a signal-to-noise-and-distortion ratio (SNDR) of 58.2 dB and a spurious free dynamic range (SFDR) of 72 dB with a 69 MHz input tone. When the input frequency increases to 1814 MHz in the fourth Nyquist zone, it can maintain an SNDR of 55.3 dB and an SFDR of 64 dB. The differential and integral nonlinearities are −0.94/+0.85 least significant bit (LSB) and −3.4/+3.9 LSB, respectively. The core ADC consumes 94 mW, occupies an active area of 0.47 mm × 0.25 mm. The Walden figure of merit reaches 0.14 pJ/step with a Nyquist input. Full article

The features of high-resolution and high-bandwidth are in an increasing demand considering to the wide range application fields based on high performance data converters. In this paper, a modeling of high-resolution hybrid analog-to-digital converter (ADC) is proposed to meet those requirements, and a 16-bit two-step pipelined successive approximation register (SAR) analog-to-digital converter (ADC) with first-order continuous-time incremental sigma-delta modulator (ISDM) assisted is presented to verify this modeling. The combination of high-bandwidth two-step pipelined-SAR ADC with low noise ISDM and background comparator offset calibration can achieve higher signal-to-noise ratio (SNR) without sacrificing the speed and plenty of hardware. The usage of a sub-ranging scheme consists of a coarse SAR ADC followed by an fine ISDM, can not only provide better suppression of the noise added in 2nd stage during conversion but also alleviate the demands of comparator’s resolution in both stages for a given power budget, compared with a conventional Pipelined-SAR ADC. At 1.2 V/1.8 V supply, 33.3 MS/s and 16 MHz input sinusoidal signal in the 40 nm complementary metal oxide semiconductor (CMOS) process, the post-layout simulation results show that the proposed hybrid ADC achieves a signal-to-noise distortion ratio (SNDR) and a spurious free dynamic range (SFDR) of 86.3 dB and 102.5 dBc respectively with a total power consumption of 19.2 mW. Full article