Bandpass Sigma-delta Modulator Research Articles

Simultaneous wireless mm-wave transmission of both SC-modulated and OFDM-modulated high-order QAM signals enabled by bandpass delta-sigma modulation

The application of dual vector millimeter-wave (mm-wave) signals in radio-over-fiber (RoF) systems represents a significant opportunity to enhance spectrum efficiency, transmission capacity, and access flexibility. In addition, facing the increasingly intricate application scenarios, the comprehensive exploitation of high-order quadrature-amplitude-modulation (QAM) signals with hybrid single-carrier (SC) and orthogonal-frequency-division-multiplexing (OFDM) modulation is also vital to rich systematic connotation. Based on bandpass delta-sigma modulation (BP-DSM) and heterodyne detection, we propose what we believe to be a novel scheme for the simultaneous wireless mm-wave transmission of both SC-modulated and OFDM-modulated high-order QAM signals. The innovation lies in the modulation-agnostic nature, accommodating both SC-modulated and OFDM-modulated vector radio-frequency (RF) signals. The BP-DSM is utilized to digitize two independent SC-modulated and OFDM-modulated high-order QAM signals into relatively simple sequences at the transmitter side. With the aid of an optical I/Q modulator, we can integrate both signals after BP-DSM to generate the desired optical quadrature-phase-shift keying (QPSK) signal carrying both information of two original high-order QAM signals. Facilitated by heterodyne detection and a single photodetector (PD), our scheme attains prowess in the detection of both SC-modulated and OFDM-modulated high-order signals. Based on our proposed scheme, we experimentally demonstrate the simultaneous wireless mm-wave transmission of both SC-modulated and OFDM-modulated 512QAM signals at 30-GHz mm-wave band, demonstrating bit-error-rates (BERs) below the hard decision forward error correction (HD-FEC) threshold of 3.8 × 10−3 after transmission over 10-km single-mode fiber (SMF) link and 1-m wireless link. In addition, we further investigate the performance impact between SC-modulated and OFDM-modulated high-order QAM signals, and experiment results indicate that the impact is virtually negligible. Moreover, the performance of the generated QPSK mm-wave signal is transparent to the QAM modulation formats of both SC-modulated and OFDM-modulated signals in our proposed scheme.

Dual high-order QAM-modulated mm-wave signal transmission in the Q-band enabled by simple IM/DD architecture and bandpass delta-sigma modulation.

The intensity-modulation (IM)/direct-detection (DD) systems have been proven effective and low-cost due to their simple system architecture. However, the Mach-Zehnder modulator (MZM) of the IM/DD systems only reserves its driving signal intensity. Therefore, the IM/DD systems are generally unable to transmit vector signals and have a restricted spectrum efficiency and channel capacity. Similarly, the radio-over-fiber (RoF) transmission systems based on IM/DD are limited by their simple architecture and generally cannot transmit high-order quadrature amplitude modulation (QAM) signals, which hinders the improvement of their spectrum efficiency. To address the challenges, we propose a novel, to the best of our knowledge, scheme to simultaneously transmit the dual independent high-order QAM-modulated millimeter-wave (mm-wave) signals in the RoF system with a simple IM/DD architecture, enabled by precoding-based optical carrier suppression (OCS) modulation and bandpass delta-sigma modulation (BP-DSM). The dual independent signals can carry different information, which increases channel capacity and improves spectrum efficiency and system flexibility. Based on our proposed scheme, we experimentally demonstrate the dual 512-QAM mm-wave signal transmission in the Q-band (33-50 GHz) under three different scenarios: 1) dual single-carrier (SC) signal transmission, 2) dual orthogonal-frequency-division-multiplexing (OFDM) signal transmission, and 3) hybrid SC and OFDM signal transmission. We achieve high-fidelity transmission of dual 512-QAM vector signals over a 5 km single-mode fiber (SMF) and a 1-m single-input single-output (SISO) wireless link operating in the Q-band, with the bit error rates (BERs) of all three scenarios below the hard decision forward error correction (HD-FEC) threshold of 3.8 × 10-3. To the best of our knowledge, this is the first time dual high-order QAM-modulated mm-wave signal transmission has been achieved in a RoF system with a simple IM/DD architecture.

SC and OFDM hybrid coherent optical transmission scheme based on 1-bit bandpass delta-sigma modulation.

High-order quadrature amplitude modulation (QAM) can effectively improve the capacity and spectral efficiency of coherent optical transmission systems. However, as the modulation order increases, the signal becomes less tolerant to noise and nonlinear effects during transmission, and the implementation cost also increases. We propose a single carrier (SC) and orthogonal frequency division multiplexing (OFDM) hybrid coherent optical transmission scheme based on a 1-bit bandpass (BP) delta-sigma modulation (DSM). The driving I-channel and Q-channel signals for the optical in-phase/quadrature (I/Q) modulator carry SC-modulated and OFDM-modulated transmitter data, respectively. Optical quadrature-phase-shift-keying (QPSK) modulation is realized by the 1-bit DSM quantizer and I/Q modulator, which can effectively suppress quantization noise and reduce the complexity of digital signal processing (DSP) and the performance requirements of optoelectronic devices. In addition, the hybrid transmission of SC and OFDM can balance the advantages of both to meet the variable channel conditions and complex application scenarios. High-fidelity transmission of SC 512QAM and OFDM 512QAM hybrid signals, in the form of a 60 Gbaud optical QPSK signal, over 60 km single-mode fiber-28 (SMF-28) is verified by offline experiments, and the bit error rates (BERs) of both SC 512QAM and OFDM 512QAM are below the hard-decision forward-error correction (HD-FEC) threshold of 3.8e-3.

Flexible mm-Wave Sigma-Delta-Over-Fiber MIMO Link

Millimeter-wave and multiple-input-multiple-output (MIMO) technologies combine broad bandwidth with spatial diversity to offer a greater data rate. This paper investigates a flexible millimeter-wave sigma-delta-over-fiber based transmitter solution with digital beamforming MISO and MIMO functionality. Those functions are controlled by a central unit connecting a remote radio head with a standardized QSFP28 fiber link. The central unit generates binary encoded intermediate frequency signals using bandpass sigma-delta modulation. The QSFP28 based fiber link transmits the intermediate frequency bitstreams to the remote radio head. The remote radio head consists of a QSFP28 module, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$90^{\circ }$</tex-math></inline-formula> hybrids, and upconverters. The remote radio head feeds four parallel, independent, coherent, and central-unit controlled 28 GHz signals to a linear array transmitting antenna. The transmitter performance is experimentally verified, demonstrating up to 800 Msym/s at an EVM/NMSE of 6.7%/-23.5 dB when tested with a 64 quadrature amplitude modulation (64-QAM) modulation scheme. Digital over-the-air beamforming MISO functionality is demonstrated up to 700 Msym/s across 1 m wireless distance. MIMO communication capabilities is demonstrated by over-the-air transmission of two independent 500 Msym/s to two spatially separated receivers. The results show that the proposed link can be used for realization of scalable, low-cost and flexible transmitter solution for emerging distributed antenna systems.

Photonic-aided W-band dual-vector RF signal generation and detection enabled by bandpass delta-sigma modulation and heterodyne detection.

We propose a photonic-aided dual-vector radio-frequency (RF) signal generation and detection scheme enabled by bandpass delta-sigma modulation and heterodyne detection. With the aid of the bandpass delta-sigma modulation, our proposed scheme is transparent to the modulation format of the dual-vector RF signals and can support the generation, wireless transmission, and detection of both single-carrier (SC) and orthogonal-frequency-division-multiplexing (OFDM) vector RF signals with high-level quadrature-amplitude-modulation (QAM) modulation. With the aid of the heterodyne detection, our proposed scheme can support up to W-band (75-110 GHz) dual-vector RF signal generation and detection. For the validation of our proposed scheme, we experimentally demonstrate the simultaneous generation of a SC-64QAM signal at 94.5 GHz and a SC-128QAM signal at 93.5 GHz and their error-free high-fidelity transmission over a 20-km single-mode fiber 28 (SMF-28) and a 1-m single-input single-output (SISO) wireless link at the W-band. To the best of our knowledge, this is the first time that delta-sigma modulation has been introduced into a W-band photonic-aided fiber-wireless integration system to achieve flexible and high-fidelity dual-vector RF signal generation and detection.

Real-Time Experimental Demonstration of Hybrid FSO/Wireless Transmission Based on Coherent Detection and Delta-Sigma Modulation

For the fronthaul link in the fifth-generation (5G) wireless networks, optical fiber is one of the most widely used medium, owing to its large bandwidth and low transmission loss. However, in some scenarios, especially the dense urban areas, the installation of fiber optic cables is costly and difficult to establish. Alternatively, the free space optical (FSO) link can be installed easily and spans complex terrain. In this context, we propose and experimentally demonstrate a hybrid FSO/Wireless transmission system based on bandpass delta-sigma modulator and real-time coherent transponder. Advantage of the proposed technique is twofold. Firstly, coherent detection is applied to improve the system sensitivity compared to conventional direct detection. Secondly, delta-sigma modulation (DSM) is utilized to greatly simplify the wireless transmitters and to enhance the bandwidth flexibility. Over a 50-m FSO and 1-m wireless link, a 64-QAM wireless signal at 1 GHz with 500 MHz bandwidth is successfully transmitted. With 16 wavelength division multiplexing channels, the total throughput of the system is up to 24 Gb/s. Meanwhile, the error vector magnitude (EVM) of all channels is around 2.68% and 6.51%, which are demonstrated after FSO and FSO/Wireless transmission, respectively. The results meet the requirement of the third-generation partnership project release 15 with EVM value of 8% for 64-QAM. Moreover, sensitivity of the real-time coherent receiver is lower than −48 dBm under the 7% forward error correction limit with bit error rate of 3.8e-3.

A Novel Structure Optimizer Based on Heuristic Search for Delta-Sigma Modulator in Mobile Fronthaul

In this letter, a novel delta-sigma modulator structure design method based on the genetic algorithm is proposed. Compared to the widely adopted R.Schreier’s method, the proposed approach can significantly reduce the in-band quantization noise. Performance comparisons are carried out on 4th-order baseband delta-sigma modulators (DSMs) and 6th-order bandpass DSMs with center frequency at 2GHz. OSR of these delta-sigma modulators are set at 8. Numerical simulations, as well as experimental demonstrations, are conducted to show a 10-Gbaud intensity modulation direct detection transmission with the 64-QAM signal. Experimental results show that compared to R. Schreier’s method, the proposed GA method can improve the SNR by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 5$ </tex-math></inline-formula> dB and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 3$ </tex-math></inline-formula> dB for baseband DSM and bandpass DSM, respectively.

Digital mobile fronthaul based on delta-sigma modulation employing a simple self-coherent receiver

The coherent digital radio-over-fiber (DRoF) system is a promising candidate for future mobile fronthaul networks (MFNs) due to its high receiver sensitivity and excellent robustness against nonlinearities. However, conventional coherent receivers with complicated structure and heavy algorithms are too expensive and power-hungry for cost-sensitive MFN applications. In addition, currently deployed digital MFNs based on common public radio interface (CPRI) suffer from low spectral efficiency and high data rate. Towards these issues we propose a novel DRoF downlink scheme employing a simple self-coherent receiver. In baseband unit (BBU), the radio signal is converted to a digital bit stream by a band-pass delta-sigma modulator (BP-DSM), which can be simply recovered with the utilization of a band-pass filter at the receiver. In remote radio unit (RRU), an electro-absorption modulated laser (EML) acts as a low-cost coherent homodyne receiver in virtue of injection locking technique. In the experiment, the injection-locked operation of the DSM signal is successfully achieved, and two modified schemes are proposed for the DSM signal to increase the locking range with a tolerable sensitivity penalty. The experimental results demonstrate the superiority of our approach in two aspects: 1) the EML-based coherent receiver outperforms a PIN photodiode in terms of receiver sensitivity; 2) compared to the analog RoF system, a 5-dB improvement in loss budget is obtained when DSM is employed with the aid of a simple equalizer.

Pre-filtered and post-filtered 1-bit delta sigma modulator for fronthaul downlinks

The fifth generation (5G) mobile fronthaul transmission system is being investigated, and one potential solution is to use 1-bit bandpass delta–sigma modulation, thus a bandpass filter (BPF) can be used to convert a digital 1-bit signal back to original analog RF signal at remote radio units. It is inevitable that this bandpass filter can induce phase and amplitude distortion to the signal, which may severely distort the signal integrity. In this work, two novel delta sigma modulators (DSM), called pre-filtered and post-filtered DSM, are proposed to compensate for the above both phase and amplitude distortion. The two designs are verified by using both simulation and experimentation with radio-over-fiber (RoF) links up to 20 km. The 5G signal used in the simulation and experimentation is a 200 MHz 64-QAM orthogonal frequency-division multiplexing signal centered at 2.5 GHz. An error vector magnitude is improved by up to ∼19 dB using the above two DSMs.

Wideband 1-Bit Bandpass Delta Sigma Modulator Using Elliptic Filter in Noise Transfer Function

A 1-bit band-pass delta-sigma modulator (BP-DSM), which utilizes oversampling technology, allows a modulated signal to be directly output by using a high-speed 1-bit digital pulse train, thus realizing miniaturization of transmitters. For 1-bit BP-DSM, the noise transfer function (NTF) is used to suppress quantization noise power in the transmission band and a guideline of out-of-band gain of |NTF|&#x003C; 1.5 is used to prevent oscillation. However, in previous studies, such as Butterworth and inverse Chebyshev filters, the out-of-band gain was designed indirectly by tuning the zeros and poles in the transmission band and thus, was not stabilized sufficiently. Furthermore, even though the zeros of the NTF are identical to the poles of the loop filter, there are still widely used designs in which the zeros are set on the unit circle, making stabilization quite difficult. Therefore, in this paper, we propose a feasible implementation of the NTF for 1-bit BP-DSM with an elliptic filter that can be used to set not only in-band but also out-of-band gain, in which both the zeros and poles are set inside the unit circle. As a design result, a modulation bandwidth of 400 MHz as a relative bandwidth of 11%, a noise suppression bandwidth of 800 MHz, and an adjacent channel leakage power ratio of 50 dB were achieved at a center frequency of 3.6 GHz, enabling a wider bandwidth and higher SNR than before by improving the stability.

Multi-Band Transmission Using Reconfigurable Complex Multi-Band Delta Sigma Polar Modulator

This brief presents a new reconfigurable complex multi-band delta sigma polar modulator (CMB-DSPM) architecture for multi-band transmission. In this brief, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6^{\mathrm{ th}}$ </tex-math></inline-formula> order band-pass delta sigma modulator (DSM) is designed and implemented for reconfigurable triple-band transmission. The proposed DSM architecture utilizes the advantage of a complex DSM structure to reduce the required processing block and polar quantizer to reduce the quantization noise. The proposed CMB-DSPM architecture improves the in-band and out-of-band performance in terms of signal-to-noise distortion ratio (SNDR) and coding efficiency (CE), respectively. The proposed scheme is validated in MATLAB/SIMULINK-based digital signal processing platform using three 5 MHz long-term evolution (LTE) signals. The results show up to 12.4 dB improvement in SNDR and 12.3% improvement in CE compared to the standard cartesian DSM architecture. The measured EVM is below 3%, which shows the good in-band performance of the proposed scheme.

An 8 bits, RF UHF-Band DAC based on interleaved bandpass delta sigma modulator assisted by background digital calibration

A multimode 8 to 4 bits delta sigma digital-to-analog converter (DAC) comprises a digital band-pass time interleaved delta sigma modulator (BP-TIDSM) with 2 interleaved channels in 5 frequency modes accompanied by a 4-bit analog DAC with a large SVR bandgap presented. As this interleaved modulator operates in narrow frequency channels around Fs/5, it leads to a low DCE design and there is no severe compulsion to calibrate which it leads to save power, area and hardware. Fully digital modulator design is modelled in MATLAB®/SIMULINK® and results in SNDR = 57 dB in 380, 420, 440, 460 MHz and 55 dB in 400 MHz with 1v supply voltage. In order to verify the results, this BP-TIDSM is synthesized by a behavioral VHDL code in ISE software and also Design compiler. Results are shown and compared in both MATLAB and ISE software. After noise shaping through the modulation and before multiplexing, a digital background calibration by a digital FIR filter applied to the modulator and all of them implemented by Cadence Virtuoso tool. A 4-bit analog DAC assigned to the multiplexer output to deliver a smooth analog signal. BP-TIDSM and calibration filters and also DAC circuits are implemented using Cadence in 180 nm technology. The proposed design used 52 mW of power with 1.6v output voltage swing and occupied an area of 0.121 mm2.

A 38.6-fJ/Conv.-Step Inverter-Based Continuous-Time Bandpass ΔΣ ADC in 28 nm Using Asynchronous SAR Quantizer

We propose a self-biased inverter-based amplifier for realizing a high-speed low-power second-order single-loop continuous-time bandpass delta-sigma modulator (CT-BP- ΔΣM). The design is amenable to nanoscale CMOS and exploits a single self-biased pseudo-differential inverter with a positive feedback to replace conventional op-amps used in an integrator configuration. The modulator also uses a 5-bit asynchronous successive approximation register (ASAR) quantizer. With a 30 MHz bandwidth at 400 MS/s sampling rate and 100 MHz intermediate frequency (IF), the modulator achieves 61 dB dynamic range (DR) and 58 dB SNDR while consuming 2.5 mW from a 1V supply. The core area in 28 nm LP CMOS is 0.04 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . A 38.6 fJ/conv.-step figure of merit is achieved.

A Digital-Analog Hybrid System-on-Chip for Capacitive Sensor Measurement and Control.

Sensors based on capacitance detection are common in the field of inertial measurement and have the potential for miniaturization and low power consumption. In order to control and process such sensors, a novel digital-analog hybrid system-on-chip (SoC) is designed and implemented. The system includes a capacitor to voltage (C/V) conversion circuit and a band-pass sigma-delta modulator (BPSDM) as the analog-to-digital converter (ADC). The digital signal is processed by the dedicated circuit module based on the least mean square error demodulation (LMSD) algorithm on the chip. The low-power Cortex-M3 processor supports software implementation of control algorithms and circuit parameter configuration. The control signal is output through a digital BPSDM. The chip was taped out under SMIC 180 nm Complementary Metal Oxide Semiconductor (CMOS) technology and tested for performance. The result shows that the maximum operating frequency of the chip is 105 MHz. The total area is 77.43 mm2. When the system clock is set to 51.2 MHz, the static power consumption and dynamic power consumption of the digital system are 18 mW and 54 mW respectively.

A 0.032-mm2 43.3-fJ/Step 100–200-MHz IF 2-MHz Bandwidth Bandpass DSM Based on Passive N-Path Filters

In this article, we demonstrate a bandpass (BP) delta–sigma modulator (DSM) using passive $N$ -path filters to implement resonators for high power efficiency, wide intermediate-frequency (IF) tuning range, and small area. The fourth-order modulator loop requires only one active element: an open-loop amplifier. The input magnitude of the amplifier is small due to the modulator’s global negative feedback and the passive $N$ -path filter preceding it. This lowers the power consumption of the amplifier and relaxes the design constraints of the switches in the $N$ -path filter. A system model of the linear periodically time-variant structure of the proposed modulator is developed, and its nonidealities are analyzed. A BP DSM prototype realized in a 65-nm CMOS with an active area of 0.032 mm2 features an IF tunable from 100 to 200 MHz with a sampling frequency ranging from 400 to 800 MHz. Over a fixed 2-MHz bandwidth, the modulator achieves a signal to noise and distortion ratio (SNDR) greater than 55.5 dB over the entire IF range. A maximal SNDR of 60.5 dB is achieved at 175-MHz IF while consuming 150 $\mu \text{W}$ , which corresponds to a Walden’s and Schreier’s figure of merits of 43.3 fJ/conv-step and 164.4 dB, respectively.

An Auto-Tuning Continuous-Time Bandpass Sigma-Delta Modulator with Signal Observation for MEMS Gyroscope Readout Systems.

This paper presents the design and implementation of an auto-tuning continuous-time bandpass sigma-delta (ΣΔ) modulator for micro-electromechchanical systems (MEMS) gyroscope readout systems. Its notch frequency can well match the input signal frequency by adding a signal observation to the traditional ΣΔ modulator. The filter of the observation adopts the same architecture as that of the traditional ΣΔ modulator, allowing the two filters to have the same response to input signal change, which is converted into a control voltage on metal-oxide semiconductor (MOS) resistance in the filters. The automatic tuning not only works to solve the mismatch problem caused by process error and temperature variation, but can also be applied to the interface circuit of gyroscopes with different resonant frequencies. The circuit is implemented in a 0.18-μm complementary metal-oxide semiconductor (CMOS) process with a core area of 2.4 mm2. The improved modulator achieves a dynamic range of 106 dB, a noise floor below 120 dB and a maximum signal-to-noise and distortion ratio (SNDR) of 86.4 dB. The tuning capability of the chip is relatively stable under input signals from 6 to 15 kHz at temperatures ranging from −45 to 60 °C.

Research on digital silicon gyroscope interface circuit based on bandpass sigma-delta modulator

This paper presents a novel digital silicon gyroscope interface circuit, designed by 0.35 [Formula: see text]m BCD process, and the chip area is 4.8 mm ∗ 5.0 mm. The traditional noise model of charge amplifier decomposes the noise into voltage noise and current noise. But the test results show that current noise accounts for a large proportion, which is not consistent with the theoretical model. Through the analysis of experimental data and the study of operational amplifier’s working principle in charge amplifier, a new noise model is established, which makes the experimental data closer to the theoretical model. The design makes use of the bandpass characteristics of the bandpass sigma–delta modulator consistent with the sensitive structure of the silicon gyroscope, and optimizes the digital principle of the silicon gyroscope. The digital demodulation of bandpass sigma–delta modulator (BP SDM) can directly separate the in-phase component from the orthogonal component, which eliminates the tedious design of carrier signal digitization and multi-digital filtering, simplifies the frame structure of the whole digital silicon gyroscope system and reduces the design difficulty and physical cost. The ASIC of silicon gyroscope digital interface circuit is tested in combination with the sensitive structure. The noise density of 0.0014[Formula: see text]/s/Hz[Formula: see text], zero stability of 1[Formula: see text]/[Formula: see text]h (1[Formula: see text]) and 0.2[Formula: see text]/[Formula: see text]h (Allen variation). The test of ASIC and the whole machine proves the correctness of the theoretical model, which reflects the correctness of the performance of the digital interface circuit of silicon gyroscope.

A 1-GHz 16-Element Four-Beam True-Time-Delay Digital Beamformer

Phased arrays are widely used due to their low power and small area usage. However, phased arrays depend on the narrowband assumption and, therefore, are not suitable for high-bandwidth applications. Emerging communication standards require increasingly higher bandwidths for improved data rates, which results in a need for timed arrays. However, high power consumption and large area requirements are drawbacks of radio frequency (RF) timed arrays. To resolve these issues, we introduce the first true-time-delay digital beamforming IC, which eliminates beam squinting error by adopting a baseband true-time-delay technique. Furthermore, we present a constant output impedance current-steering digital-to-analog converter (DAC), which improves the spurious-free dynamic range (SFDR) of a bandpass delta–sigma modulator by 7 dB. Due to the new DAC architecture, the 16-element beamformer improves SFDR by 13.7 dB from the array. Measured error vector magnitudes (EVMs) are better than 37 dB for 5-MBd quadratic-amplitude modulation (QAM)-64, QAM-256, and QAM-512. The prototype beamformer achieves nearly ideal beam patterns for both conventional and adaptive beamforming (i.e., adaptive nulling and tapering). The difference between normalized measured beam patterns and normalized simulated beam patterns is less than 1 dB within the 3-dB beamwidth. The beamformer, including 16 bandpass analog-to-digital converters (ADCs) occupies 0.29 mm2 and consumes 453 mW in total power.

A 1-MHz-Bandwidth Gm-C-Based Quadrature Bandpass Sigma-Delta Modulator Achieving −153.7-dBFS/Hz NSD With Background Calibration

This paper presents a fifth-order continuous-time Gm-C-based quadrature bandpass sigma-delta ( $\Delta \Sigma$ ) modulator for Internet-of-Things applications. In the presented $\Delta \Sigma $ modulator, a reconfigurable full-scale input amplitude assists the $\Delta \Sigma $ modulator, achieving a wide dynamic range (DR) and a low-noise floor. A following system-level supply voltage and temperature background tracking technique stabilizes the frequency response of the Gm-C-based quadrature bandpass $\Delta \Sigma $ modulator. Furthermore, the 1.5-bit feedback current DAC employs a PN-based semi-self-swapping logic to relax the matching requirement. The prototype $\Delta \Sigma $ modulator was fabricated in a 180-nm CMOS process with an active area of 0.28 mm2. The $\Delta \Sigma $ modulator achieves a total DR of 93.7 dB with the reconfigurable full-scale input amplitude, resulting in a noise spectral density of −153.7 dBFS/Hz with a bandwidth of 1 MHz. The presented $\Delta \Sigma $ modulator consumes 2.0 mW with a power supply of 1.8 V and a sampling frequency of 32 MHz.

A 16-bit 12-GS/s Single-/Dual-Rate DAC With a Successive Bandpass Delta-Sigma Modulator Achieving &lt;−67-dBc IM3 Within DC to 6-GHz Tunable Passbands

This paper presents a hybrid digital-to-analog converter (DAC) architecture with a tunable bandpass delta-sigma modulator (DSM) to synthesize channelized signals over a wide frequency range with high linearity and a low in-band noise floor. Due to the mostly digital architecture, this DAC topology favors technology scaling. The DSM uses a successive pipeline structure with time-interleaving techniques to achieve a 12-GS/s data rate and overall 16-bit DAC resolution. To improve the linearity at high frequencies, an inverse-sinc-shaped digital pre-distortion (DPD) scheme is used to better approximate and compensate the timing errors. The DAC can be configured for single- or dual-rate operation modes to tradeoff different input data rates with DAC linearity and spectral images. The prototype was fabricated in 65-nm CMOS technology with an analog area of 0.1 mm2 and 60 dBc up to a 4.2-GHz signal frequency at 12 GS/s in the single-rate mode thanks to the hybrid structure and proposed DPD techniques.