PLL FM demodulator performance under Gaussian modulation

A widespread test of the phase-locked loop (PLL) FM demodulator under Gaussian modulation is simulated using the Monte Carlo method. Unified noise-free and noise performance analyses of the PLL FM demodulator are presented. Substantial reduction of the modulation limit by the input bandpass filter is reported in the region of the input bandwidth of practical interest. Bessel bandpass filters of order greater than two are shown to compare favorably with Butterworth filters in front of the PLL FM demodulator relative to the intermodulation (IM) distortion. A lower bound on the loop noise bandwidth is found by minimizing the output click rate for given IM distortion specifications. FM threshold of 4 and 7 dB for the root-mean-square (RMS) frequency deviation-to-message bandwidth ratio 0.1 and 1.0, respectively, is reported on the worst-case IM distortion of 45 dB     

Integrated selectivity for narrow-band FM IF systems

An 18th-order all-pole continuous-time bandpass filter for IF (intermediate frequency) filtering purposes has been designed and integrated in a 3-μm CMOS process. Implemented using nine fully balanced, transconductor-capacitor coupled resonators, the filter features a 20-kHz bandwidth at 200-kHz center frequency and 54-dB dynamic range (IM3<-40 dB) and consumes 300 μA from a single 4-V supply. With the use of conventional phase-locked loop techniques for automatic tuning, the accuracy of the filter response is comparable to that of ceramic filters. As expected, the fundamental limitations of such an active implementation compared to a passive realization are noise and distortion     

A highly linear CMOS Gm-C bandpass filter with on-chipfrequency tuning

A fourteenth-order CMOS transconductance-C (G_m-C) bandpass filter with on-chip automatic frequency tuning is described. By using highly linear G_m-C integrators, the filter achieves 75 dB dynamic range over 700 kHz noise bandwidth. The measured intermodulation distortion (IM3) @ 600 kHz for a 4 V_pp input signal is only -61 dB. On-chip automatic frequency tuning provides more than 300% center frequency range (i.e., 165-505 kHz) of the filter with ±1% frequency accuracy. The 0.7-μm CMOS filter measures 4.8 mm ² and consumes 70 mW from a single 5 V power supply     

A 10.7-MHz sixth-order SC ladder filter in 0.35-/spl mu/m CMOS technology

A sixth-order 10.7-MHz bandpass switched-capacitor filter based on a double terminated ladder filter is presented. The filter uses a multipath operational transconductance amplifier (OTA) that presents both better accuracy and higher slew rate than previously reported Class-A OTA topologies. Design techniques based on charge cancellation and slower clocks are used to reduce the overall capacitance from 782 down to 219 unity capacitors. The filter's center frequency and bandwidth are 10.7 MHz and 400 kHz, respectively, and a passband ripple of 1 dB in the entire passband. The quality factor of the resonators used as filter terminations is around 32. The measured (filter + buffer) third-intermodulation (IM3) distortion is less than -40 dB for a two-tone input signal of +3-dBm power level each. The signal-to-noise ratio is roughly 58 dB while the IM3 is -45 dB; the power consumption for the standalone filter is 42 mW. The chip was fabricated in a 0.35-/spl mu/m CMOS process; filter's area is 0.84 mm/sup 2/.     

Direct digital-to-RF converter employing semi-digital FIR voltage-mode RF DAC

A direct digital-to-RF converter (DRFC) is presented in this work. Due to its digital-in-nature design, the DRFC benefits from technology scaling and can be monolithically integrated into advance digital VLSI systems. A fourth-order single-bit quantizer bandpass digital ΣΔ modulator is used preceding the DRFC, resulting in a high in-band signal-to-noise ratio (SNR). The out-of-band spectrally-shaped quantization noise is attenuated by an embedded semi-digital FIR filter (SDFIR). The RF output frequencies are synthesized by a novel configurable voltage-mode RF DAC solution with a high linearity performance. The configurable RF DAC is directly synthesizing RF signals up to 10 GHz in first or second Nyquist zone. The proposed DRFC is designed in 22 nm FDSOI CMOS process and with the aid of Monte-Carlo simulation, shows 78.6 dBc and 63.2 dBc worse case third intermodulation distortion (IM3) under process mismatch in 2.5 GHz and 7.5 GHz output frequency respectively.     

A 1-V 10.7-MHz fourth-order bandpass /spl Delta//spl Sigma/ modulators using two switched op amps

A 1-V 10.7-MHz fourth-order bandpass delta-sigma modulator using two switched opamps (SOPs) is presented. The 3/4 sampling frequency and the double-sampling techniques are adapted for this modulator to relax the required clocking rate. The presented modulator can not only reduce the number of SOPs, but also the number of capacitors. It has been implemented in 0.25-/spl mu/m 1P5M CMOS process with MIM capacitors. The modulator can receive 10.7-MHz IF signals by using a clock frequency of 7.13 MHz. A dynamic range of 62 dB within bandwidth of 200 kHz is achieved and the power consumption of 8.45 mW is measured at 1-V supply voltage. The image tone can be suppressed by 44 dB with respect to the carrier. The in-band third-order intermodulation (IM3) distortion is -65 dBc below the desired signal.     

A 10.7-MHz 68-dB SNR CMOS continuous-time filter with on-chipautomatic tuning

A maximally flat 10.7-MHz fourth-order bandpass filter with an on-chip automatic tuning system is presented. The signal-to-in-band integrated noise ratio (SNR) of the automatically tuned filter is around 68 dB. The third intermodulation distortion (IM3) is lower than -40 dB for a two-tone input signal of 3.2 V peak to peak (V_p-p). The complete system operates with supply voltages of ±2.5 V. The power consumption of the system is 220 mW. All this has been achieved due to the use of a low-distortion transconductor, the development of a high-frequency CMOS resistor, and the realization of an advanced on-chip automatic tuning system for both frequency and bandwidth control. The chip has been fabricated in a standard 1.5-μm n-well CMOS process     

Distortion Mechanisms in Varactor Diode-Tuned Microwave Filters

This paper examines the broadband distortion behavior in flexible filters employing varactor-diode tuning elements. Series- and parallel-resonant varactor-loaded transmission-lines, both commonly used in bandpass and bandstop microwave filters, are analyzed. Nonlinear Volterra-series analysis is employed to determine the second- and third-order distortion ratios dependent on the frequencies of the incident signals. It is shown that in a bandpass filter (employing parallel tuned resonators), maximum distortion occurs in the passband, while in a bandstop filter (employing series tuned resonators), minimum distortion occurs at the minimum-loss passband. The analysis is verified by practical measurement of filters employing the two modes of resonators.     

A compensation method for dispersion-induced third-orderintermodulation distortion using an etalon

A method to compensate dispersion-induced third-order intermodulation distortion (IM3_CD) in subcarrier multiplexing (SCM) optical transmission systems is proposed. It is confirmed theoretically and experimentally that IM3_CD can be compensated by interference-induced third-order intermodulation distortion (IM3_IN). Simple analytic expressions of IM3_CD and IM3_IN are derived from the same expression of optical electric field which includes exact phase term taking into account the phase of laser chirp. From the theoretical analyses, we clarified the conditions of IM3_CD-compensation. IM3_IN can be easily generated by an etalon which is a kind of interferometer and a optical glass plate. More than 30 dB of IM3_CD -compensation was achieved, and IM3_CD-compensation was achieved regardless of the transmission distance by adjusting tilt angle of the etalon. Using this method, high quality signal transmission can be realized even though the wavelength of laser diode (LD) is not coincident with the fiber zero dispersion wavelength     

A distortion control technique for achieving high power efficiency in an HPA array

This paper proposes a new technique for reducing the intermodulation (IM) distortion products in a high-power amplifier (HPA) array. The proposed technique dissolves the relations between carriers and IMs by applying IM phase control. As a result, IMs are distributed to all the output ports in the array, and the carrier power to intermodulation power ratio (C/IM) of the HPA array can be increased. The improvement in CI/M is as high as 10log N dB, where N is the number of HPAs. Newly developed even-order distortion implemented intermodulation distortion controllers (EODICs) are used to achieve the IM phase control. A test carried out using a four-parallel HPA array with EODICs confirms that the technique noticeably improves C/IM and demonstrates its validity.     

Zolotarev bandpass filters

Zolotarev rational functions may be used in certain bandpass filter applications for which two narrower passbands are required. Coupled-resonator low-pass prototypes for narrow bandpass filters based on even- and odd-degree Zolotarev functions are synthesized using a transformed variable. Compared to other filters, those with Zolotarev responses have sharper skirt selectivity, resulting in lower passband distortion     

FM and IM intermodulation distortions in directly modulatedsingle-mode semiconductor lasers

Intermodulation distortion in directly-modulated semiconductor lasers is described with the aid of a nonlinear differential equation for the photon density. Both frequency modulation (FM) and intensity modulation (IM) have been investigated. Curves are presented of the magnitudes of the intermodulation products relative to the carriers intensity. Second order distortions are also reported. The comparison of the Bessel function analysis and the perturbation method is quite successful. Finally, laser's FM and IM modulation characteristics are compared, and these theoretical results show that distortion levels would be stronger in FM than in direct IM, when the same operating conditions are adopted     

A 44-MHz wideband switched-capacitor bandpass filter using double-sampling pseudo-two-path techniques

A fully differential wideband sixth-order switched-capacitor bandpass filter is designed for channel selection in cable TV applications. A modified double-sampling pseudo-two-path technique is proposed to achieve a second-order wideband bandpass filter with a single opamp. Implemented in a standard double-poly four-metal 0.35-/spl mu/m CMOS process and operated at 176-MHz sampling frequency, the filter achieves a measured center frequency of 44 MHz with a bandwidth of 6.28 MHz and a dynamic range of 58.3 dB at 3% IM3. The filter consumes 92.5mW at a single 3.0-V supply and occupies a chip area of 0.52 mm /sup 2/.     

Chromatic dispersion induced distortion of modulated monochromatic light employing direct detection

The spectrum of an intensity modulated (IM) and a combined intensity-frequency modulated (IM-FM) monochromatic light source has been generated. The amplitudes of the modulated carrier and the first three pairs of sidebands are plotted showing the influence of IM on an FM signal. The effects of first order chromatic dispersion on the baseband amplitude response and harmonic distortion are determined. The manner in which modulation type and depth, modulating frequency, wavelength, and fiber length alter harmonic distortion is presented. Numerical examples giving the amplitude response of a single-mode fiber system as well as the magnitude of the second- and third-harmonic distortion caused by chromatic dispersion are presented. Based on this material, the limits placed on analog transmission due to chromatic dispersion may be assessed.     

Optimization of Third-Order Intermodulation Product and Output Power from an X-Band MESFET Amplifier Using Volterra Series Analysis

A third-order analysis for accurately predicting large-signal power and intermodulation distortion performance for GaAs MESFET amplifiers is presented. The analysis is carried out for both single- and two-tone input signals using the Volterra series representation and is based only on small-signal measurements. Simple expressions for the nonlinear power gain frequency response, the output power, the gain compression factor, and the third-order intermodulation (IM/sub 3/) power are presented. The major sources of gain compression and intermodulation distortion are identified. Based on the developed nonlinear analysis in conjunction with the device nonlinear model, a systematic procedure for designing a MESFET amplifier under large-signal conditions for optimum output power and IM/sub 3/ performance is proposed. The method utilizes out of band computed matching compensation through a nonlinear model of the amplifier. The accuracy of the device large-signal and IM/sub 3/ distortion characterization and the practicability of the proposed method are illustrated through comparison between measured and predicted results.     

Design of low distortion active inductor and its applications

This paper proposes a novel distortion reduction technique for active inductors. A bias current of a MOSFET, which acts as transconductor in an active inductor, is controlled to reduce a distortion of a active inductor. When an input voltage increases, the bias current is decreased by a control circuit. As a result of this control, transconductance of the MOSFET remains constant. An active inductor using this technique is free from distortion caused by a transconductance variation of a MOSFET. The proposed technique is applied to two different conventional active inductors and novel low distortion active inductors are derived. Computer simulations show that distortion of the proposed active inductor is very low. The proposed low distortion active inductors are applied to a second order bandpass filter and a voltage controlled oscillator. Thanks to the proposed technique, distortion of these circuits are reduced and their performance is improved.     

Using an MRI distortion transfer function to characterize the ghosts in motion-corrupted images

Motion artefact suppression remains an active topic in MRI. In this paper, we suggest that certain nonrigid, or spatially variant, characteristics of motion of an object can be represented by extending the work of Mitsa et al. This empirical extension uses a ghost distortion transfer function (GTDF) applied to the k-space (frequency domain) data. We demonstrate the variety of ghost characteristics that can be generated from various two-dimensional (2-D) GTDF's. The distortion transfer function for periodic motion along the Z-axis can be determined from the nonoverlapped portions of the ghost and central image. It required a GDTF with the shape of a belt bandpass filter to produce an image corresponding to the ghosts of a volunteer's abdomen image corrupted by unknown respiratory motion artefacts. The preliminary results of a composite method of motion artefact suppression are presented. The artefact suppression was successful for ghost images described by a GDTF have a low-pass nature, but less successful with ghosts have a GDTF of a bandpass nature.     

Bandpass filtering of high-speed forwarded clocks

Bandpass channel filtering is shown to attenuate both random and determinstic jitter components in high frequency clock signals. A fully differential, tunable LC bandpass filter is developed and employed to reduce Gaussian and sinusoidal distributed jitter and duty cycle distortion.     

Three-tone intermodulation distortion generated by superconducting bandpass filters

Microwave bandpass filters constructed from materials exhibiting some nonlinearity, such as superconductors, will generate intermodulation distortion (IMD) when subjected to signals at more than one frequency. In commercial applications of superconductive receive filters, it is possible for IMD to be generated when a weak receive signal mixes with very strong out-of-band signals, such as those coming from the transmitter. A measurement procedure was developed and data were taken on several different types of superconducting bandpass filters, all developed for commercial application. It was found that in certain interference situations, the three-tone mixing can produce a spur that is noticeable by the receiver, but that there are simple preventative design solutions.     

All-Optical Demultiplexing of WLAN and Cellular CDMA Radio Signals

Subcarrier multiplexed transmission of multimedia radio signals over fiber is often done to deliver broadband services cost effectively. These signals need to be demultiplexed, preferably in the optical domain, to avoid loss and noise due to optical-to-electrical conversion. However, it is challenging to optically isolate signals at subgigahertz range due to the need for very narrow optical bandpass filters with high selectivity and low insertion loss and distortion. We developed such a novel subpicometer all-optical bandpass filter by creating a resonance cavity using two closely matched fiber Bragg gratings. This filter has a bandwidth of 120 MHz at -3 dB, 360 MHz at -10 dB, and 1.5 GHz at -20 dB. Experimental results show that this filter optically separates two RF signals spaced as close as 50 MHz without significant distortion. This paper analytically and experimentally investigates the scenario when this filter was used with 2.4-GHz (wireless local area network) and 900-MHz (cellular wireless) radio signals. The bit-error rate of the underlying baseband data is related to the linearity and isolation of the filter.