Bandpass Sigma-delta Modulator Research Articles

Digital Channelizing Radio Frequency Receiver

HYPRES is developing a class of digital receivers featuring direct digitization at radio frequency (RF). Such a receiver consists of a wideband analog-to-digital converter (ADC) modulator and multiple digital channelizer units to extract different frequency bands-of-interest within the broad digitized spectrum. The single-bit oversampled data, from either a lowpass delta or bandpass delta-sigma modulator, are applied to one or more channelizers, each comprising digital in-phase and quadrature mixers and a pair of digital decimation filters. We perform channelization in two steps, the first at full ADC sampling clock frequency with rapid single flux quantum (RSFQ) digital circuits and the second at reduced (decimated) clock frequency with commercial field programmable gate array (FPGA) chips at room temperature. We have demonstrated lowpass and bandpass digital receivers by integrating an ADC modulator and a channelizer unit on the same chip at clock frequencies up to 20 GHz. These 1-cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> single-chip digital-RF receivers contain over 10,000 Josephson junctions. The channelizing receiver approach can be extended to include multiple ADC modulators and multiple channelizer units on a multi-chip module.

An Injection-Locked Frequency-Tracking &lt;formula formulatype="inline"&gt; &lt;tex&gt;$\Sigma \Delta$&lt;/tex&gt;&lt;/formula&gt; Direct Digital Frequency Synthesizer

A bandpass (BP) sigma-delta modulator (SigmaDeltaM)-based direct digital frequency synthesizer (DDS) architecture is presented. The DDS output is passed through a single-bit, second-order BPSigmaDeltaM, shaping quantization noise out of the signal band. The single-bit BPSigmaDeltaM is then injection locked to an LC-tank oscillator, which provides a tracking BP filter response within its locking range, suppressing the BPSigmaDeltaM out of band quantization noise. The instantaneous digital frequency control word input of the DDS is used to tune the noise shaper center frequency, achieving up to 20% tuning range around the fundamental. The BPSigmaDeltaM-based synthesizer is fabricated in a 0.25-mum digital CMOS process with four layers of metal. With a second-order BP noise shaper and a 44-MHz LC tank oscillator, an SFDR of 73 dB at a 2-MHz bandwidth and phase noise lower than -105 dBc/Hz at a 10-kHz offset is achieved

Bandpass Sigma&amp;ndash;Delta Modulator Employing SAW Resonator as Loop Filter

Continuous-time bandpass (BP) sigma-delta modulators (SigmaDeltaMs) employing surface acoustic wave (SAW) resonators as loop filters are presented. Compared with the loop filters realized with Gm-C and LC resonators, the SAW resonator has the advantage of high-Q factor, wide resonant frequency range and accurate resonant frequency without the need for automatic tuning. With the proposed anti-resonance cancellation and loop filter phase compensation techniques, a second- and a fourth-order BP SigmaDeltaMs are demonstrated in a 0.35-mum CMOS technology. Both modulators are tested with 47.3-MHz off-chip SAW resonators. The second-order modulator attains a dynamic range of 57 dB and peak signal-to-noise distortion ratio (SNDR) of 54 dB and the fourth-order one achieves a dynamic range of 69 dB and peak SNDR of 66 dB, both in a 200-kHz signal bandwidth. The fourth-order modulator is also measured in a 3.84-MHz signal bandwidth and achieves a dynamic range of 52.5 dB and peak SNDR of 50 dB, an effective 8-bit resolution

CMOS RF class-D power amplifier with bandpass sigma–delta modulation

A 0.5μm CMOS radio frequency class-D amplifier is analysed and simulated with a bandpass ΣΔ modulated drive signal. The design includes a five stage driver and operates from 3.3V. The simulated power efficiency at 181MHz is 40.1% for a two tone source, and 16.6% for a 8.7dB peak-to-average wideband code-division multiple access source signal. Equations are derived which demonstrate the relationship between amplifier load power, power efficiency, and modulator parameters called coding efficiency and average transition frequency.

An &lt;emphasis emphasistype="italic"&gt;I/Q&lt;/emphasis&gt;-Channel Time-Interleaved Bandpass Sigma&amp;ndash;Delta Modulator for a Low-IF Receiver

This brief proposes a multiplexing scheme to realize an I/Q-channel time-interleaved (TI) bandpass sigma-delta modulator that shares operational transconductance amplifiers to minimize power consumption and silicon area for a low-intermediate-frequency (IF) wireless receiver. The test chip was fabricated for a 10.7-MHz IF system with a 0.35-mum CMOS process. The measured peak signal-to-noise distortion ratio for a 200-kHz bandwidth is approximately 73 dB. The power consumption of the fabricated chip is 61 mW with a 3.3-V supply, and the silicon area is 1.78 mm2. The measured channel crosstalk is about -48 dB

Manchester encoded bandpass sigma–delta modulation for RF class D amplifiers

An analysis of a continuous-time bandpass sigma–delta modulator in a configuration with an upconverter is given for a RF class D amplifier application. The upconverter multiplies the modulator pulse train with a synchronised clock signal and maps each modulator bit to an integer multiple k of a (+1, −1) or (−1, +1) pattern depending on the sign of the modulator bit. The upconversion is equivalent to an extension of Manchester encoding, which is usually defined for k=1. The analysis focuses on evaluating the impact of upconversion on the modulator coding efficiency and the average pulse period. A design equation is derived, which shows that coding efficiency is dependent only on the upconversion frequency ratio, while the average pulse period depends only on k. The equations provide a designer with a way of evaluating the trade-offs in the amplifier system and show that encoding with k=1 is the most efficient configuration for maximising coding efficiency and minimising switching power loss.

Micromachined Vibratory Gyroscopes Controlled by a High-Order Bandpass Sigma-Delta Modulator

This work reports on the design of novel closed-loop control systems for the sense mode of a vibratory-rate gyroscope based on a high-order sigma-delta modulator (SigmaDeltaM). A low-pass and two distinctive bandpass topologies are derived, and their advantages discussed. So far, most closed-loop force-feedback control systems for these sensors were based on low-pass SigmaDeltaM's. Usually, the sensing element of a vibratory gyroscope is designed with a high quality factor Q to increase the sensitivity and, hence, can be treated as a mechanical resonator. Furthermore, the output characteristic of vibratory rate gyroscopes is narrowband amplitude-modulated signal. Therefore, a bandpass SigmaDeltaM is a more appropriate control strategy for a vibratory gyroscope than a low-pass SigmaDeltaM. Using a high-order bandpass SigmaDeltaM, the control system can adopt a much lower sampling frequency compared with a low-pass SigmaDeltaM while achieving a similar noise floor for a given oversampling ratio (OSR). In addition, a control system based on a high-order bandpass SigmaDeltaM is superior as it not only greatly shapes the quantization noise, but also alleviates tonal behavior, as is often seen in low-order SigmaDeltaM control systems, and has good immunities to fabrication tolerances and parameter mismatch. These properties are investigated in this study at system level

RF Class-D Amplification With Bandpass Sigma&amp;amp;ndash;Delta Modulator Drive Signals

The power efficiency of a RF Class-D amplifier with a bandpass sigma-delta (SigmaDeltaM) modulator is analyzed for a complementary voltage-switched configuration. The modulator broadens the application of the amplifier to include signals with time varying envelopes such as W-CDMA. The addition of a modulator introduces new design variables which affect amplifier power efficiency including coding efficiency and the average transition frequency of the pulse train. Design equations are derived for the optimum load impedance, output power, conduction losses, capacitive switching losses, and drain efficiency. The general design equations are consistent with both periodic and aperiodic drive signals. Analytic and simulated results are compared for an example design with pseudomorphic high-electron mobility transistor and metal-semiconductor field-effect transistor switches with a fourth-order bandpass SigmaDeltaM. The results show a drain efficiency of 52% with a 10-dB peak-to-average power ratio W-CDMA source signal at a frequency of 500 MHz

Can a second order bandpass sigma delta modulator achieve high signal-to-noise ratio for lowpass inputs?

In this letter, it is found that a second order interpolative bandpass sigma delta modulator can achieve high signal-to-noise ratio even if input signals have lowpass characteristics.

Nonlinear Behaviors of Bandpass Sigma&amp;amp;ndash;Delta Modulators With Stable System Matrices

It has been established that a class of bandpass sigma-delta modulators may exhibit state space dynamics which are represented by elliptical or fractal patterns confined within trapezoidal regions when the system matrices are marginally stable. In this brief, it is found that fractal or irregular chaotic patterns may also be exhibited in the phase plane when the system matrices are strictly stable

An automatic coefficient design methodology for high-order bandpass sigma-delta modulator with single-stage structure

An automatic coefficient design method for synthesis of bandpass sigma-delta modulators (BPSDMs) is presented in this brief. Single-stage BPSDM structures, cascade-of-resonator with distributed feedback, cascade-of-resonator with distributed feedforward, and a new structure with lower coefficient spread, are all used to fit the synthesized coefficients. The automatic coefficient design method is realized in an easy-to-use computer program. Even for inexperienced designers, reliable and high-tolerance BPSDM coefficients for various applications can be automatically and efficiently generated. The methodology covers many design concerns including BPSDM coefficient tolerance for circuit component mismatch, design tradeoffs among in-band noise suppression, oversampling ratio, modulator order and quantizer bit number. Finally, design examples with orders of 6 and 8, and quantizer bit number of 1-bit and 3-bit, respectively, are used for the verification of the proposed automatic coefficient design method.

A Design of Continuous-Time Delta-Sigma Modulators Using a Fully-Differential Resonant-Tunneling Comparator

Ultrahigh-speed continuous-tine delta-sigma modulators (DSMs) have been designed by using a fully-differential comparator consisting of resonant-tunneling diodes (RTDs) and HEMTs. Continuous-time lowpass and bandpass filters using HEMTs have also been incorporated to obtain lowpass- and bandpass-type DSMs, respectively. Circuit simulation assuming 0.1-μm InP-based HEMT and RTD technology has revealed a successful operation of the 2nd-order lowpass DSM at a sampling frequency of 20 GHz. The clock frequency was 10 GHz because of the double sampling function of the present comparator. The 2nd-order bandpass DSM has also been designed with a center frequency of 3 GHz. These results clearly show high potential of the present delta-sigma modulators.

A 1.8 V CMOS fourth-order Gm-C bandpass sigma-delta modulator dedicated to front-end ultrasonic receivers

A 4th order bandpass sigma-delta modulator for ultrasound applications is presented. By cascading two second-order identical Gm-C bandpass filters, a 4th-order modulator was designed with high powe...

Study of stability of a bandpass sigma delta modulator with sinusoidal input

Bandpass sigma delta modulators (SDMs) have applications in areas such as digital radio demodulation. Stability issues of bandpass SDMs have been widely studied. Usually, zero or step inputs are considered. In this paper, we study the stability and non-linear phenomena of a bandpass SDM with sinusoidal input. In particular, the effects of the amplitude and frequency of the sinusoidal input signal will be investigated.

Study of nonlinear phenomena in a multi-bit bandpass sigma delta modulator

Bandpass sigma delta modulators (SDMs) have applications in areas such as digital radio demodulation. It is well known that bandpass SDMs with single bit quantizers can exhibit nonlinear and complex state space dynamics like elliptical fractal patterns. These fractal patterns are usually confined in trapezoidal regions. In this paper, we consider bandpass SDMs with multi-bit quantizers. Their nonlinear dynamics is studied.

A new switched capacitor resonator and its research

In bandpass sigma delta modulator, resonator is the key block. This paper proposed a new resonator which can simplify the circuit implementation when designing bandpass modulator with lowpass prototype. The effect of finite gain, finite bandwidth, and path mismatch on the resonator is analyzed. The function of the proposed resonator and the devired equations about path mismatch have been verified by switched capacitor software SWITCAP.

Stability of sinusoidal responses of marginally stable bandpass sigma delta modulators

SUMMARY In this paper, we analyse the stability of the sinusoidal responses of second-order interpolative marginally stable bandpass sigma delta modulators (SDMs) with the sum of the numerator and denominator polynomials equal to one and explore new results on the more general second-order interpolative marginally stable bandpass SDMs. These results can be further extended to the high-order interpolative marginally stable bandpass SDMs. Copyright q 2006 John Wiley & Sons, Ltd.

A Novel$Sigma$–$Delta$Pulsed Digital Oscillator (PDO) for MEMS

A novel digital oscillator topology for microelectromechanical systems (MEMS) based on bandpass sigma–delta modulation is presented. Short pulses of force of the same amplitude maintain the oscillation and the associated bit-stream output serves to know the oscillation frequency which, for low mechanical losses, is very close to the natural frequency of the MEMS resonator. Position-sensing requirements are extremely simplified because, at each sampling time, it is only necessary to know whether the resonator position is above or below the steady-state position. Continuous-time simulations are presented showing the behavior of the oscillator for different sampling frequencies and mechanical damping losses. Experimental results from an oscillator using a MEMS resonator with thermoelectric actuation and piezoresitive position sensing are presented. It is concluded that the quality of the oscillator response depends on the resonator damping losses and on the sampling frequency. The experimental results agree with the analytical and simulation results.

Quadrature /spl Sigma//spl Delta/ modulators with a dynamic element matching scheme

This paper presents a new topology of a multibit quadrature bandpass sigma-delta modulator which employs a simple dynamic element matching (DEM) technique in order to reduce the effects of path mismatch, namely aliasing in the signal band of the mirror images of the signal and of the quantization noise. The DEM scheme results in a reduction of the aliasing of the quantization noise mirror image while it reduces the input signal mirror image alias problem to a self-image problem. It is shown that the self-image can be completely removed in switched-capacitor implementations by using the same capacitors to sample the input and the reference of the feedback digital-analog converters (DACs). Moreover, a simple method for extending low-pass mismatch noise shaping techniques to the complex bandpass case is proposed for the case of multibit feedback DACs.

OCCURRENCE OF ELLIPTICAL FRACTAL PATTERNS IN MULTI-BIT BANDPASS SIGMA DELTA MODULATORS

It has been established that the class of bandpass sigma delta modulators (SDMs) with single bit quantizers could exhibit state space dynamics represented by elliptic or fractal patterns confined within trapezoidal regions. In this letter, we find that elliptical fractal patterns may also occur in bandpass SDMs with multibit quantizers, even for the case when the saturation regions of the multibit quantizers are not activated and a large number of bits are used for the implementation of the quantizers. Moreover, the fractal pattern may occur for low bit quantizers, and the visual appearance of the phase portraits between the infinite state machine and the finite state machine with high bit quantizers is different. These phenomena are different from those previously reported for the digital filter with two's complement arithmetic. Furthermore, some interesting phenomena are found. A bit change of the quantizer can result in a dramatic change in the fractal patterns. When the trajectories of the corresponding linear systems converge to a fixed point, the regions of the elliptical fractal patterns diminish in size as the number of bits of the quantizers increases.