Two-tone Input Research Articles

A High-Frequency Transconductor Using a Robust Nonlinearity Cancellation

This brief deals with the design of a linear operational transconductance amplifier (OTA) intended for high-frequency continuous-time filters. Three source-degenerated differential pairs are used to reduce the third-order distortion components regardless of process parameter tolerances and bias current. Experimental results for an OTA fabricated in the TSMC 0.35-mum CMOS process are presented and compared with recently reported topologies. Draining 2.8 mA from a single supply voltage of 3.3 V, the transconductor achieves IM3<-70 dB for a two-tone input signal of 1.3 Vpp measured at 70 MHz. The input referred noise density is only 7 nV/radicHz, leading to an SNR of 75 dB

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-mum CMOS process; filter's area is 0.84 mm2

Large signal performance of micromachined silicon condenser microphones

A mathematical model for the open-circuit output voltage of a micromachined silicon condenser microphone with a single deeply corrugated diaphragm as a function of the applied acoustic pressure is presented. The model, basically a sine-series function, can easily yield closed-form expressions for the amplitudes of the output components resulting from a multisinusoidal input acoustic pressure. The special case of an equal-amplitude two-tone acoustic pressure input is considered in detail. The results show that the microphone generates only odd-order harmonic and intermodulation products. The results also show that the amplitudes of these components are strongly dependent on the microphone parameters, the corrugation depth and the ratio between the half-length of the diaphragm and its thickness. Moreover, the results show that the acoustic pressure required to produce a pre-specified output open-circuit voltage is strongly dependent on these parameters.

A CMOS 140-mW fourth-order continuous-time low-pass filter stabilized with a class AB common-mode feedback operating at 550 MHz

A 550-MHz linear-phase low-pass continuous-time filter is described. The operational transconductance amplifier (OTA) is based on complementary differential pairs in order to achieve high-frequency operation. A common-mode feedback (CMFB) based on a Class AB amplifier with improved stability at high frequencies is introduced. Results for the stand alone OTA show a unity gain frequency of 1 GHz while the excess phase is less than 5/spl deg/. The filter is based on G/sub m/-C biquads and achieves IM3 <-40 dB for a two-tone input signal of -10 dBm each. The power consumption of the fourth-order filter is 140 mW from supply voltages of /spl plusmn/1.65 V. The chip was fabricated in a standard 0.35-/spl mu/m CMOS technology.

Evaluation of ACPR in mixers based on a parametric harmonic-balance approach

This paper reports an extension of parametric harmonic balance (PHB) to efficiently analyze mixers excited by communications signals. In the case of digitally modulated signals, PHB is demonstrated in this paper, exhibiting reduced simulation times and memory resources. For validation purposes, a high electron-mobility transistor mixer has been constructed and characterized with single- and two-tone 2-GHz input RF signals, and also the output spectra under Universal Mobile Telecommunications System-wide-band code-division multiple-access signal excitations above the 1-dB compression point have been obtained. In addition to its fast convergence properties, the presented simulations demonstrate a very good agreement with experimental results. The close correspondence between calculated and measured spectral regrowth permitted a reliable prediction of adjacent channel power rejection

Ku-band subsampling track-and-hold amplifier with 8 ENOB resolution

A wideband subsampling track-and-hold amplifier has been designed for input frequencies up to Ku-band and clock rates up to 2.5 GS/s. Circuits were fabricated in 1 µm InP SHBT technology. Spur-free dynamic range measured with two-tone input frequencies of 12.6 and 12.602 GHz and a 2.5 GS/s clock rate ranges from 53–69 dB at an input level of −1 dBFS for each tone. Signal-to-noise ratio (SNR) test results show that the master/slave (M/S) track-and-hold design provides 59 dB of SNR in a 1 GHz bandwidth at input frequencies up to at least 2.6 GHz. A single track-and-hold dissipates 1.5 W while the M/S configuration dissipates 2.5 W.

Multitone phase and amplitude measurement for nonlinear device characterization

This paper presents a new setup for nonlinear device characterization. The presented measuring bench allows the characterization of phase and amplitude of correlated and uncorrelated multitone signals. The method presents a simple hardware implementation using only an ordinary scope as the main device. The validity of the technique is confirmed by an experimental test using a two-tone uncorrelated input signal. The experimental values agree with the theoretical results assuring the validity of the proposed technique. Moreover, they confirm the fact that despite the lower and upper intermodulation distortion can have the same amplitude; they could present different relative phases.

Microwave intermodulation distortion of MgB2 thin films

The two-tone intermodulation arising in MgB2 thin films deposited in situ by planar magnetron sputtering on sapphire substrates is studied. Samples are characterized using an open-ended dielectric puck resonator operating at 8.8 GHz. The experimental results show that the third-order products increase with the two-tone input power with a slope ranging between 1.5 and 2.3. The behavior can be understood introducing a mechanism of vortex penetration in grain boundaries as the most plausible source of nonlinearities in these films. This assumption is confirmed by the analysis of the field dependence of the surface resistance, that show a linear behavior at all temperatures under test.

Power-amplifier characterization using a two-tone measurement technique

An accurate nonlinear model is necessary to optimize the tradeoff between efficiency and linearity in power amplifiers. Gain compression (AM/AM) and amplitude-phase (AM/PM) distortion are the two primary model inputs used to characterize the nonlinearity. The amplifier's AM/AM and AM/PM characteristics are typically measured statically using a vector network analyzer. Since the input is typically a modulated signal, it is desirable to characterize the amplifier dynamically. This paper describes and demonstrates a dynamic AM/AM and AM/PM measurement and modeling technique involving a spectrum analyzer and two-tone input signals. A complete analysis of the measurement technique is presented, along with the data processing needed for the identification of a new three-box model. The test configuration and procedure are presented with special precautions to minimize measurement error. Results for a solid-state amplifier are used to accurately predict intermodulation distortion, while those for a traveling-wave tube amplifier show good agreement with that obtained dynamically using a 16 quadrature-amplitude-modulation signal.

Harmonic and intermodulation performance of analogue-to-digital converters with multibit errors and additive dither

This paper presents a simple approach for mathematical modelling of real analogue-to-digital converters (ADCs) with multibit errors and dither. Using this model, expressions are obtained for the harmonic and intermodulation performance of a real ADC excited by a multisinusoidal signal. While these expressions involve infinite summations, they always converge. The special case of a two-tone half-scale equal-amplitude input signal to a real ADC is considered in detail and it is shown that the infinite summations can be converted into finite ones in this special case. Numerical results obtained from a 5-bit ADC are presented and discussed. The results show that while all forms of dither will linearise the staircase characteristic of the ADC, thus improving its intermodulation performance, they may degrade its harmonic and intermodulation performance resulting from the multibit errors. The feasibility of cancellation of output harmonic and intermodulation products is discussed.

Digitally linearized wide-band photonic link

A photonic analog-to-digital (A/D) link with third-order distortion suppression is proposed and demonstrated. Experimental results with single-and two-tone analog input signals and a one giga-sample per second (GSPS) photonic A/D system with 500-MHz instantaneous bandwidth are presented. The application of a simple time-domain linearization scheme results in distortion suppression approaching 30 dB and allows optical modulation depths over 80%.

Bandpass delta-sigma class-S amplifier

A class-S amplifier with a bandpass delta-sigma modulated input is demonstrated using CMOS devices at 10 MHz. With a two-tone modulated input, third-order intermodulation products below –40 dBc were measured, with an output power of 26 dBm and a drain efficiency of 33%. This new amplifier topology demonstrates promising performance for simultaneously achieving high linearity and efficiency.

Power-dependent microwave properties of superconducting YBa2Cu3O7−x films on buffered polycrystalline substrates

We have studied the microwave properties of 0.4 μm thick YBa2Cu3O7−x (YBCO) films on polycrystalline substrates with ion-beam-assisted-deposited yttria-stabilized zirconia buffer layers using a parallel-plate resonator technique at 10 GHz. The YBCO films with similar in-plane texture grown on both forsterite and Ni-based alloy substrates show similar microwave properties. We measure low-power surface resistance Rs values of about 0.5 mΩ at 76 K and 0.15 mΩ at 4 K for films with an in-plane mosaic spread of about 7°. Single-tone power-dependence measurements show that the surface resistance and the surface reactance increase linearly and by the same amount with increasing microwave field level. At intermediate power levels, the intermodulation measurements show odd-order intermodulation products that increase quadratically with two-tone input power. These results indicate a hysteretic vortex penetration mechanism in the weak links as the most plausible source of the observed nonlinearities in these films.

Low-frequency modulation of inner hair cell and organ of Corti responses in the guinea pig cochlea

Low-frequency tones are used to study changes in responsiveness as a function of phase in inner hair cell (IHC) and organ of Corti (OC) responses recorded from second turn of the guinea pig cochlea. In these experiments a 40 Hz stimulus is combined with a variable frequency probe to determine the degree to which tones at and below best frequency (BF) are modulated. Changes in responsiveness produced by the low-frequency input are quantified and related to position of the basilar membrane which is estimated using the phase of the cochlear microphonic measured in the OC fluid space. Results obtained when 40 Hz is presented at its lowest effective level demonstrate that ac responses to low-level BF probes are reduced for basilar membrane displacements to scala tympani while probe tones well below BF are modulated in the opposite direction. The transition between these two response patterns occurs when the overall DC produced in the OC by the two-tone input changes from positive to negative. Because of this association, the frequency dependence exhibited in the bias results may be linked to mechanisms responsible for generating the two polarities of the summating potential and the DC receptor potentials that it reflects. An attempt is also made to relate bias-induced changes in hair cell receptor potentials to modulations in single-unit rate responses. In other words, to address variations in the temporal relationships between excitation and suppression measured in the auditory nerve.

Simulating the response of coupled channel and interferometric modulator designs

An algorithm is developed that enables the response of a large class of electrooptic modulator designs to be calculated quickly and accurately. Using this algorithm, a computer program can be developed that allows the following responses to be accurately calculated and displayed in real-time: intensity versus voltage, optical phase versus voltage, the output spectrum for any one or two-tone input, the dynamic response of the nonlinear distortion products, and the frequency response of the fundamental and nonlinear signals. By properly time sampling the modulator output in response to a one or two-tone input, an accurate modulator simulation can be accomplished with a minimal number of calculations. Such a program is useful in the development of novel modulator designs and in evaluating the tolerance of various aspects of modulator performance to variations in fabrication and passive bias control. Furthermore, the ability to determine the frequency response of the nonlinear distortion is significant in itself. In this paper, a detailed description of the algorithm is presented which includes an optimized sampling technique for both the one and two-tone tests. Several new results obtained with this method are also presented. >

Nonlinear distortion prediction of active filters

The represention of circuit variables in frequency-domain complex matrix and nonlinearities by power series gives rise to a nonlinear distortion prediction technique, the intermodulation-balance method. This operates entirely in the frequency domain. The technique is verified by a single-amplifier filter with a two-tone input signal.

A 10.7-MHz 68-dB SNR CMOS continuous-time filter with on-chip automatic 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/sub p-p/). The complete system operates with supply voltages of +or-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- mu m n-well CMOS process.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The effect of acoustic diffraction and acoustic attenuation on the dynamic range of acoustooptic Bragg cells

A three-dimensional model for the propagation of finite acoustic waves in nonlinear media is developed. This model implicitly includes the effects of acoustic attenuation and divergence due to diffraction. The generation of intermodulation products in the case of a two-tone input signal is numerically analyzed. It is found that acoustic diffraction can have a significant effect on the dynamic range of a Bragg cell if the acoustic field extends well into the Fraunhofer region. Inclusion of the effect of diffraction in the model predicts a dynamic range that can be considerably larger than the value obtained by using the infinite plane wave assumption. It is shown that acoustic attenuation significantly reduces the level of the acoustic intermodulation products relative to the level of the fundamental modes. This also increases the dynamic range. The influence of these effects on design considerations for Bragg cells is discussed.

Nonlinear circuit analysis of harmonic and intermodulation distortions in laser diodes under microwave direct modulation

A microwave nonlinear circuit analysis technique which can account for all known steady-state responses has been developed and applied to the large-signal characterization of directly modulation laser diodes. An equivalent circuit derived from the rate equations is used to model the laser diode. The proposed technique is based on a harmonic balance algorithm which represents two-tone inputs by describing frequencies. Second-harmonic and third-order intermodulation distortion results for a single-mode GaAlAs diode have been compared with corresponding measured data to validate the method. Aperiodic responses are detected by means of bifurcation theory prior to the harmonic balance analysis and are simulated in the time domain. Simulated results are shown to agree well with published measurements, and indicate the capability of using this approach for the computer-aided design of microwave fiber-optic transmitters. >

Generalized Power Series Analysis of Intermodulation Distortion in a MESFET Amplifier: Simulation and Experiment

The design of microwave integrated circuits requires accurate simulation tools capable of predicting a variety of nonlinear distortion effects, including gain compression and intermodulation distortion. This paper uses the recently developed generalized power series analysis to simulate a MESFET amplifier. The simulations are in agreement with experimental results for single-tone and two-tone inputs, thereby validating the analysis method. Tlds analysis is suited to nonlinear microwave circuits having arbitrarily spaced input frequencies.