Second-harmonic Distortion Research Articles

Analysis of nonlinearities in MOS floating resistor networks

Expressions for the linearised V/I characteristics of a group of floating resistor structures employing MOS transistors operating in the triode mode are presented. Mobility-degradation effects are accurately modelled and identified as the major residual distortion source in most configurations. The application of common-mode signals to the gate and substrate terminals of a single device is shown to produce a benchmark linearisation performance. Geometrical mismatches are identified as having a potentially dominant influence on the extent to which second-harmonic distortion is suppressed.

A diode mixer with harmonic-distortion suppression

It is shown that terminating the second and third LO harmonics and associated mixing frequencies in a short circuit results in substantial reduction in a diode mixer's harmonic distortion. It was found experimentally that the second-harmonic distortion level dropped a maximum of 28.7 dBm, and the third-harmonic distortion level also dropped a maximum of 16 dBm. The practical possibility of improving IM distortion levels is established. This technique should prove valuable in the lowering of IM distortion levels of diode mixers. >

Effect of azimuth angle and bias field on second harmonic distortion in differentially biased MR heads

Measurement of the azimuth dependence of the second harmonic distortion (SHD) in magnetoresistive (MR) heads is presented. The use of differential biasing and sensing is one method of eliminating SHD by perfect cancellation of distortion signals from two half-elements oppositely biased. However, when some azimuth angle between the MR element and recorded signals is introduced, the SHD rapidly increases due to an imbalance in the input signal strength for each half-element. The effect of bias field and data on single end biased elements is given.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Second-harmonic angular-structure distortion in strongly interacting series-located crystals

Second-harmonic angular-structure distortion in strongly interacting series-located crystals

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. >

On the relationship between the CMRR or PSRR and the second harmonic distortion of differential input amplifiers

The results of a harmonic distortion analysis for a differential pair are presented, including the effects of mismatches and of the finite nonlinear common-mode rejection ratio (CMRR) or power-supply rejection ratio (PSRR). Due to mismatches, a differential pair produces second-harmonic distortion. The presence of a finite common-mode gain limits the amount of feedback which can be usefully applied to suppress the harmonic distortion. When the common-mode gain is nonlinear, additional distortion is generated which is not suppressed by the feedback. When the amplifier has to drive a large load and when the supply line impedance is large, the finite PSRR causes similar effects.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A low-distortion K-band GaAs power FET

A K-band low-distortion GaAs power MESFET was developed by incorporating a pulse-type channel doping profile using molecular-beam-epitaxial technology and a novel 0.3- mu m T-shaped gate. The low-distortion FETs offer about 10 to 15 dBc improvement in second-harmonic distortion compared to devices fabricated on a uniformity doped active layer. Significantly larger power load-pull contours are obtained with the low-distortion devices, indicating the improved linearity of these devices. In an 8-20-GHz single-stage broad-band amplifier, up to 10 dBc improvement in harmonic performance was achieved using the low-distortion device. This low-distortion device exhibits very linear transconductance as a function of the gate bias. A typical 750- mu m-gate-width device is capable of 26 dBm of output power with 6 dB of gain, and power-added efficiency in excess of 35% when measured at 18 GHz. At 25 GHz, the device is capable of 24 dBm of output power with 5 dB associated gain. >

Hemispherical large-area surface-emitting SH GaAlAs LED with very low nonlinear distortion characteristics

A large-area surface-emitting SH GaAlAs LED is fabricated with the aim of reducing optical nonlinear distortion. A drastic reduction of the second-harmonic distortion level due to a compensation effect is confirmed at the position of maximum fiber input power. The developed LED exhibits -61-dB second-harmonic and -57-dB third-harmonic distortion levels under a 100-mA bias current and 50-percent modulation depth.

Envelope detection and correction of SSB

Envelope detection is significantly less complex to implement and use than coherent detection if applied to SSB results in gross distortion unless the carrier component is very large. A method of correcting this distortion is discussed and a variant which achieves partial correction with some hardware simplification is investigated. Computer simulation shows that a reduction of 15 dB in second-harmonic distortion can be achieved, and this is confirmed by tests on a prototype system.

The tidal signal in inverted echo-sounder records

Four IES records of several months duration from the western equatorial Atlantic are analysed with principal interest in their tidal content. Spectral noise level in the tidal bands is some two orders of magnitude higher than in comparable sea-level records, but the main constituents of both diurnal and semi-diurnal tides stand out with usable coherence with the tidal potential. A mid-ocean record, FLAVIA, gives amplitudes and phases that correspond closely with the surface tide, but three other records in a region of disturbed bathymetry near the continental shelf give amplitudes and phases which differ from the expected surface effect, indicating relatively strong coherent internal tides in the region as well as an evident incoherent tidal signal. Two of the latter records also show second-harmonic distortion, which is characteristic of internal tides, in the present case corresponding to a steeppened forward face of the internal wave. Theory, following the analysis of Long (1972 Tellus, 24, 88–89), suggests that this form of wave steepening is due to the steady shear in the surface layer. The physical theory of acoustic time-delay in vertical transmission through long internal waves with and without surface elevation is analysed quantitatively. In the region studied a pure internal tide of amplitude 10 m at 200-m depth would produce the observed changes in tidal signal. Wave amplitudes resulting from tidal flow over a 2.4-km high ridge, computed from the linear theory of Zeilon (1912 Kungliga Svenska Vetenskapsakademiens Handligar, 47, 1–45), are only about 1.2 m maximum, but the theory does suggest a likely mechanism for producing coherent internal tidal motion, possibly by invoking the shelf edge.

Constricted double-heterojunction AlGaAs diode lasers: Structures and electrooptical characteristics

Constricted double-heterojunction (CDH) diode lasers are presented as the class of nonplanar-substrate devices for which the laser cavity is one of the least resistive electrical path between the contact and the substrate. Various types of CDH structures are discussed while treating three general topics: liquid-phase epitaxy (LPE) over channeled substrates, lateral mode control, and current control in nonplanar-substrate devices. `Ridge-guide' CDH lasers have positive-index lateral mode confinement and provide: single-mode CW operation to 7 mW/facet at room temperature and to 3 mW/facet at 150°C, light-current characteristics with second-harmonic distortion as low as -57 dB below to fundamental level, threshold-current temperature coefficients <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> as high as 375° (pulsed) and 310° (CW), constant external differential quantum efficiency to 100°C, lasing operation to 170°C CW and 280°C pulsed. `Semileaky guide CDH lasers have an asymmetric leaky cavity for lateral mode confinement and provide; single-mode operation for 15-20 mW/facet CW, and to 50 mW/facet at 50 percent duty cycle. Modulation characteristics and preliminary reliability data are discussed.

Nonlinear visual responses to flickering sinusoidal gratings.

Over a range of high temporal and low spatial frequencies, counterphase flickering gratings evoke the so-called frequency-doubling illusion, in which the apparent brightness of the grating varies at twice its real spatial frequency. The form of the nonlinearity that causes this second-harmonic distortion of the visual response was determined by a cancellation technique. The harmonic distortion can be measured as a function of amplitude (or contrast) by adding to the flickering grating a real, nonflickering, double-frequency component with the amplitude and phase required to cancel the illusory second harmonic. Harmonic distortion curves obtained in this way imply that the nonlinearity is of the form /s/p, where s is the stimulus pattern (without its dc component) and p is close to 0.6. If p = 1, or if the absolute value is not taken, this expression predicts distortion curves that differ significantly from the experimental results. Hence neither rectification nor compression alone is sufficient to account for the second-harmonic distortion; both are required.

Low-frequency response to AlGaAs double heterojunction LED's

At low frequencies, the optical response of a light emitting diode (LED) to analog intensity modulation is found to decrease, due to the junction-heating effects. This low-frequency response is analyzed using approximated I-P characteristics, and is compared with the experimental results for AlGaAs double heterojunction LED's. The transfer function of the low-frequency response can be expressed by 1 - (1- \phi)/(1+ j\omega\tau_{\sigma}) , where φ and tau σ are the degradation of the fundamental amplitude at lower frequencies normalized to higher frequencies and the thermal time constant with a value of about 10 µs, respectively. It is found that the low-frequency response correlates with the linearity of the I-P characteristics, using the low-frequency degradation factor \psi expressed by -10 \log(1- \phi) in decibels and the linearity coefficient γ defined as {P(1.5 I{o}) - P(I_{o})}/{P(I_{o}) - P(0.5 I_{o})} , where P(1.5 I_{o}) denotes the power at 1.5 times of the basic current I o . Also, the current dependence and modulation degree dependence on both degradation factor \psi and second-harmonic distortion are discussed.

Generation of harmonic distortion at fibre connectors

Harmonic distortion generated by the Fabry-Perot resonator at fibre connectors is described. The maximum second-harmonic distortion is calculated as a function of end separation for GaAlAs lasers. A −42 dB second-harmonic distortion is generated in 100 μm end separation, which is harmful in analogue transmission systems.

Temperature dependence of storage time in silicon p + - n - n + switching diodes and reduction of harmonic distortion

Using the reverse-recovery technique, storage times in p+-n-n+ diodes have been measured as a function of temperature. In all cases the effective lifetime for injected charge increases with increasing temperature within the interval 0 to 180°C. This result was found to reduce second-harmonic distortion in p+-n-n+ switches by as much as 6 dB at 2.5 MHz.

Small-area GaAs-GaAlAs heterostructure light-emitting diode with improved current confinement

A new type of high-radiance GaAs-GaAlAs heterostructure light-emitting diode (l.e.d.) with confinement of the light-emitting area by contact resistance is described. Single heterostructure l.e.d.s of this type with active-region doping of p=3×1018 cm?3 exhibit external quantum efficiency of 1% and a 3 dB modulation cutoff frequency of 66 MHz. Second-harmonic distortion was measured at below 40 dB at a 30 mA peak-peak modulation current and 50 mA direct current (=7.0 kA/cm2).

Frequency offset of a stabilized laser due to modulation distortion

The response of a phase-sensitive detector is examined when its input signal is derived by modulation of a laser-saturated absorption line shape. Neglecting the laser background power curve, it is shown that second-harmonic distortion in the modulation gives rise to the largest laser frequency offset, 0.2% of such distortion yielding approximately 4.5 kHz frequency offset. The distortion effects are also examined when the background power curve is included.

Effects of parasitic elements on the second-harmonic method†

Abstract The second-harmonic distortion in lossy reverse-biased junctions is analysed. It is shown that the doping densities that are derived from measurements of both C-V data and of second-harmonic data depend on the particular equivalent-circuit model if the junction losses are very large. A new technique is described for the measurement of the second-harmonic distortion. The effect of a non-linear parallel conductance on the second-harmonic method is investigated theoretically and experimental data near breakdown support the analysis.

A Study of Asymmetrical Gating for Phase-Controlled Converters

The low power factor of phase-controlled converters when the output voltage is less than the maximum is of-concern in high-power equipment. In a converter consisting of two commutating groups in cascade, the usually low power factor can be improved by firing or gating the thyristors in the two groups asymmetrically. One of the groups is fully advanced (or retarded) to minimize its reactive power, while the other group is controlled to give the desired dc Output. The technique is not recommended for single three-phase bridge converters because of third-hannonic output ripple, second-harmonic line current distortion, and danger of commutation failure. These objections are overcome by combining pairs of three-phase bridges. When regeneration is not required, half of the thyristors can be replaced by diodes, reducing the cost. The method should offer substantial improvement in the power factor of cycloconverter ac motor drives as well as dc motor drives.

Harmonic Generation in the Trumpet

Various possible mechanisms for the generation of harmonics in the tone of the trumpet were investigated. By sounding the trumpet with a mechanical valve utilizing a sinusoidally varying opening, it was shown that nonsinusoidal motion of the player's lips is not an important mechanism for harmonic generation. Nonlinear behavior of the air column of the instrument due to high sound pressures was also shown not to be important by four different methods: (1) by a theoretical estimate of the amount of second-harmonic distortion to be expected; (2) by measuring the input resistance of the trumpet at resonance frequencies and finding that it did not vary significantly with sound pressure in the air column; (3) by measuring the intermodulation distortion produced when the air column was excited at two resonance frequencies simultaneously; and (4) by direct measurement of harmonic distortion produced in the trumpet output by different levels of excitation at the mouthpiece. It was found that the mechanism primarily responsible for harmonic generation is the relationship between the input impedance of the trumpet and the time-varying impedance of the player's lip opening during a cycle. Curves of mouthpiece pressure calculated on this basis showed good agreement with observed waveforms.