Linearized microring-loaded Mach-Zehnder modulator with RF gain

A linearized modulator based on the Mach-Zehnder interferometer (MZI) loaded with a second-order allpass microring resonator is proposed and analyzed. The device is shown to exhibit much smaller intermodulation distortion than standard Mach-Zehnder modulators, thus greatly enhancing the device dynamic range. Gain effect associated with the microring resonance results in a modulator transfer function with high slope efficiency and large RF gain. Moreover, combined with the use of a highly electrooptic polymer, the high slope efficiency allows for the possibility of realizing modulators with subvolt drive voltage. The detrimental effect of loss in the microring resonators on device performance is also investigated and a design approach to mitigate its effect is presented. The proposed modulator can be linearized to any arbitrary nth order by loading the MZI with a higher order allpass microring resonator.     

Large Signal Analysis of the Michelson Interferometer with Gires-Tournois Interferometers in its Arms

A mathematical model for the transfer function of the Michelson interferometer with Gires-Tournois interferometers in its arms is presented. The model, basically a sine-series function, can easily yield closed-form expressions for the amplitudes of the harmonic and intermodulation components of the output when the input is formed of large-amplitude multisinusoidal voltage. The special case of two-tone equal-amplitude input voltage is considered in detail. The results show that the third-order intermodulation component is always higher than the third-harmonic component. The results also show that the linearity of the Michelson interferometer with Gires-Tournois interferometers in its arms improves with the increase of the front mirror reflectivity. Moreover, the results show that the third-order intermodulation exhibits a minimum for relatively large values of the front mirror reflectivity. Furthermore, compared with the traditional Mach-Zehnder interferometer, the results show that a reduction of 15 dB in the third-order intermodulation can be achieved even for relatively small values of the front mirror reflectivity.     

Harmonic and Intermodulation Performance of Quantum-Well Mach-Zehnder Electro-Optic Modulators with Electrical Biasing

A mathematical model for the transfer function of the Mach-Zehnder interferometers based on the quantum-confined Stark effect (QCSE) is presented. The model, basically a cosine-series function, can easily yield closed-form expressions for the amplitudes of the harmonic and intermodulation components of the output when the input is formed of any scenario of large-amplitude multisinusoidal voltages. The special case of three-tone equal-amplitude input voltage is considered in detail. The results show the strong dependence of the harmonic and intermodulation performance on the electrical biasing. The results also show that for a proper selection of the electrical biasing the third-order intermodulation or the second-order intermodulation can be minimized. While the results obtained are in excellent agreement with previously published results, the present analysis is applicable to multisinusoidal input voltages with different scenarios and is not restricted to small-amplitude two-tone inputs only.     

Harmonic and Intermodulation Performance of Metallic Carbon Nanotube (MCNT) and Complementary Carbon Nantube Field Effect Transistor (CNTFET) Amplifier

This paper presents a simple mathematical model for the output-voltage (current)/ input-voltage characteristic of the carbon nanotube field effect transistor (CNTFET) complementary inverting amplifier and the metallic carbon nanotube (MCNT) interconnect. The model, basically a Fourier series, yields closed-form expressions for the amplitudes of the harmonic and intermodulation components of the output voltage (current) resulting from a multisinusoidal input voltage. The special case of a two-tone equal-amplitude input voltage is considered in detail. The results show that the harmonic and intermodulation performance of the complementary CNTFET-based inverting amplifier and the MCNT interconnect is strongly dependent on the values of the amplitudes of the input tones with the third-order intermodulation component dominating over a wide range of the input voltage amplitudes. The results also show that while the harmonics may exhibit minima, the intermodulation products are almost monotonically increasing with the increase in the input voltage amplitude and exhibit no minima.     

Harmonic and Intermodulation Performance of the Semiconductor Bolometer

A mathematical model for the temperature dependence of the bolometer semiconductor resistance is presented. The model, basically a sine-series function, can easily yield closed-form expressions for the harmonic and intermodulation performance of the acquired interferogram voltage with large-amplitude multisinusoidal variations in the incident radiation. The special case of two-tone equal-amplitude incident radiation is considered in detail. The results show that the intermodulation components are always higher than the harmonic components of the same order. The results also show that the second-order intermodulation is always dominant and is higher than the second-harmonic component by about 6 dB. Moreover, the results show that for relatively small incident amplitudes of the incident radiation the ratio between the second- and third-harmonic components is almost equal to the ratio between the second-harmonic component and the fundamental. The results also show that the ratio between the amplitudes of the second- and third-order intermodulation components is almost equal to the ratio between the amplitudes of the second-order intermodulation component and the fundamental.     

Harmonic and intermodulation performance of MoS2FET- and GFET-based amplifiers

This paper presents a simple mathematical model for the output–input voltage characteristic of the graphene field effect transistor (GFET)- and the molybdenum disulfide field effect transistor (MoS₂FET)-based inverting amplifiers. The model, basically a Fourier series, yields closed-form expressions for the amplitudes of the harmonic and intermodulation components of the output voltage resulting from a multisinusoidal input voltage. The special case of a two-tone equal-amplitude input voltage is considered in detail. The results show that the harmonic and intermodulation performance of the complementary GFET- and the MoS₂FET-based inverting amplifiers is strongly dependent on the bias voltage and the amplitudes of the input tones with the third-order intermodulation component dominating over a wide range of the input voltage amplitudes.     

双音调制星间微波光子链路信号噪声失真比优化

建立了包括光源、马赫曾德尔调制器、掺铒光纤放大器和光电探测器的双音调制星间微波光子链路模型。利用贝塞尔函数展开、傅里叶变换/反变换和Graf加法定理,推导出探测器输出信号的严格通用解析解,考虑三阶交调失真的影响,得出信号噪声失真比（SNDR）的表达式。着重分析了在不同调制方式下SNDR、基波和三阶交调信号功率随射频输入功率的变化情况。数值计算结果表明:SNDR、基波和三阶交调信号功率随射频输入功率的增大先增大后减小,存在最优的射频输入信号功率使SNDR达到最大。相同射频输入功率条件下,双边带调制SNDR大于单边带调制,适合星间微波光子链路应用。     

Large Signal Analysis of the Infrared Semiconductor Mercury-Cadmium-Telluride Detectors

A mathematical model for the relationship between the output voltage and incident radiation of the infrared semiconductor mercury-cadmium-telluride (MCT) detector is presented. The model, basically a sine-series function, can easily yield closed-form expressions for the harmonic and intermodulation performance of the MCT detector with large-amplitude multisinusoidal incident radiation. The special case of two-tone equal-amplitude incident radiation is considered in detail. The results show that the second-order harmonic and intermodulation products are always higher than the third-order components. Moreover, the results show that the second-order intermodulation is always dominant.     

Varactor Tuning Diodes as a Source of Intermodulation in RF Amplifiers

In RF amplifiers used in the front ends of VHF receivers which are to be tuned over a wide frequency range, varactor diodes are often used to accomplish the necessary change in tuning capacitance. nce. The variation of capacitance with dc voltage which enables the tuning function to be accomplished results in a nonlinear characteristic stic which, in turn, introduces harmonic and intermodulation dtion.storon. This paper is concerned with the determination of tef12f 1-J2) intermodulation distortion product generated by the varactor diodes and modified by the characteristics of the input tuned circuit. Both third-order and "distortion-on-distortion" second-order intermodulation mechanisms are included in the calculation. An expression is presented for the magnitude of the (2f1-f2) intermodulation intercept which includes the effects of the characteristics of the tuned circuit and the various parameters used to characterize the varactor diode. Design considerations combining both the linear and the intermodulation ation performance of the input circuit are discussed, including design tradeoffs and interrelationships among the circuit parameters and performance variables. Illustrative calculations are given based on the characteristics of the MV3102 varactor diode.     

Harmonic and intermodulation performance of double-gate CMOS inverting voltage amplifier

This paper presents a simple mathematical model for the transfer characteristic of the double gate (DG) CMOS inverting voltage amplifier. The model yields closed-form expressions for the amplitudes of the fundamental and distortion components of the output voltage resulting from a multisinusoidal input voltage for different scenarios and values of the bottom gates voltages. The special case of a two-tone equal-amplitude input voltage is considered in detail. The results show that the distortion performance of the DG-CMOS inverting voltage amplifier is strongly dependent on the bottom gates voltages and the amplitudes of the input sinusoids with the third-order intermodulation component dominating over the whole range of the input voltage amplitudes and different bottom gates voltages.     

Theoretical Analysis of the Intermodulation Performance of Mach-Zehnder Modulators with Difference Frequency Injection

Large signal analysis of Mach-Zehnder electro-optic modulators excited by three tone signals is presented. The special case of two equal-amplitude sinusoids plus a difference-frequency injection is considered in detail. The results show that even under large signal conditions it is possible, at least in theory, to totally eliminate the third-order intermodulation when the amplitudes of the equal-amplitudes input sinusoids and the difference-frequency injection are equal. This would be a promising technique for achieving highly linear Mach-Zehnder electro-optic modulators.     

Cancellation of second-order intermodulation distortion and enhancement of IIP2 in common-source and common-emitter RF transconductors

In this paper, a biasing technique for cancelling second-order intermodulation (IM2) distortion and enhancing second-order intercept point (IIP2) in common-source and common-emitter RF transconductors is presented. The proposed circuit can be utilized as an RF input transconductor in double-balanced downconversion mixers. By applying the presented technique, the achievable IIP2 of the mixer is limited by the linearity of the switching devices, component mismatches, and offsets. The proposed circuit has properties similar to the conventional differential pair transconductor in that it ideally displays no IM2 distortion. However, the presented circuit is more suitable for operation at low supply voltages because it has only one device stacked between the transconductor input and output. In the conventional differential pair, two devices consume the voltage headroom. The noise performance of the proposed transconductor is similar to the noise performance of the traditional common-source (emitter) and differential pair transconductors at given bias and device dimensions. On the other hand, the third-order intercept point (IIP3) of the presented transconductor is slightly higher than the IIP3 of the differential pair transconductor at given bias. Finally, the proposed circuit can also be employed as a current mirror, the ratio of which is very insensitive to the voltage swings at the gate or base of the current mirrored transistor.     

一种用于射频功率放大器的新型预失真器的设计

预失真技术是功率放大器线性化的主要技术之一。分析了传统预失真器不能消除其输出端所产生双音基频分量的特点,提出一种新的预失真器,并利用它改善射频功率放大器的非线性失真。仿真结果表明,该方法可以明显改善射频功率放大器的三阶交调非线性失真。     

Performance analysis and comparison of multi-level hard limiters

A general formula, using a Fourier sine-series representation, is derived for the input–output characteristic of multilevel hard limiters (MHLs) with unequal output jumps occurring at unequally spaced inputs. Using this formula, closed-form expressions involving ordinary Bessel functions are obtained for the harmonic and intermodulation performance of MHLs excited by multisinusoidal inputs with arbitrary amplitudes. The results show that, compared to the ideal hard limiter, MHLs can result in a reduction in the relative third harmonic distortion of about 40 dB, and a reduction in relative third-order intermodulation distortion of about 19 dB depending on the amplitude of the input sinusoids and the shape of the MHL characteristic. Using the proposed model it is possible to generate a database for the harmonic and intermodulation performance of any MHL with arbitrary values of jumps and their locations. Simulation results obtained using the harmonic balance simulator controller in the advanced design system design automation software confirm the accuracy of the proposed technique.     

Improved direct-modulation characteristics of a semiconductor laserby FM/IM conversion through an interferometer

The behavior of the light signal converted by means of a Mach-Zehnder interferometer is analyzed under the assumption of a three-tone modulation of the emitting laser source. Illustrations are given of the signal at the interferometer output, showing the frequency response, the second- and third-order intermodulation distortions (IMDs), with a direct comparison between intensity modulation (IM) and optical frequency modulation (FM). The FM characteristics are plotted for the different cases where the spurious IM component and the term of chirp formula involving the gain compression factor are taken into account or not. Successful results are obtained in agreement with previous studies. In addition, this work shows that the FM-to-IM signal would exhibit lower distortion levels than the conventional direct IM, placing less stringent requirements on the laser linearity     

一种新颖的复合环形谐振腔的理论分析

文章基于环形谐振腔所具有的非线性相位传输特性,提出了一种新型的动态光谱滤波器结构,它将全通环形谐振腔调相器接入平衡马赫-曾德干涉仪,实现复合结构的动态滤波特性.与传统的马赫-曾德干涉仪相比,此复合滤波结构可利用远小于π的相移调整实现输入光信号的开关,因此,在提高开关速度、降低调相器功耗等方面具有重要的应用价值.     

基于ADS平台不对称Doherty功率放大器的仿真设计

为在高线性的前提下提高WCDMA基站系统中功率放大器的效率,仿真设计了一款工作于2.14 GHz频段不对称功率驱动的Doherty功率放大器。基于ADS平台,采用MRF6S21140H LDMOS晶体管,通过优化载波放大器和峰值放大器的栅极偏置电压改善三阶互调失真(IMD3),同时通过调节输入功率分配比例改善由于峰值放大器对载波放大器牵引不足导致的失配问题,从而改善不对称Doherty功率放大器的输出性能。仿真结果表明,当载波放大器的栅极偏置电压为2.84 V,峰值放大器的栅极偏置电压为0.85 V并且输入功率比例为1:2.3,输出功率为44 dBm时其功率附加效率(PAE)为24.21%,IMD3为-44.46 dBc,和传统AB类平衡功率放大器相比PAE提高了8.58%,IMD3改善了6.98 dBc。     

Nonlinear models for the intermodulation analysis of FET mixers

An accurate, detailed analysis program has been developed for intermodulation distortion (IMD) simulation of FET mixers. This program is very efficient at calculating the IMD from multiple RF inputs. We have proposed a simplified nonlinear model for IMD analysis of FET gate mixers. The accuracy of the simplified model has been verified experimentally using two different MESFET mixers and one HEMT mixer at X band. All the tests show good agreement between measured results and the calculated results for second- and third-order IMD. The simplified model is based on modeling the derivative of the device transconductance by a sum of a Gaussian function and a linear function of the gate voltage. Drain bias dependence is ignored. The advantage of this model is that it can be used for both MESFET and HEMT mixers, and its fitting parameters can be easily determined from a nonlinear characterization of the devices at low frequencies     

Realization of an analog predistortion circuit for RF optical fiber links

This paper presents an analog predistortion circuit for RF optical fiber links. The circuit consists of two source-coupled differential transconductance amplifiers which could provide linear and nonlinear transfer charac-teristics by adjusting the bias voltage and the transistor sizes. The circuit was designed and realized in a standard 0.18-μm CMOS technology of SMIC. The chip occupies 0.48 × 0.24 mm~2. The DC supply is 3.3 V. Using this circuit, the third-order intermodulation distortion (IMD) suppression of a directly modulated RF optical fiber link can be improved by 9-16 dBc at relatively low cost.     

Improved Large Signal Analysis of the Dual-Wavelength Linearization Technique of Optically Phase-Modulated Analog Microwave Signals

This paper presents simple closed-form expressions, in terms of the ordinary Bessel functions, for the amplitudes of the third- and fifth-order intermodulation products of the dual-wavelength linearized phase modulated link for any scenario of the microwave driving voltage. The results obtained for a microwave driving voltage comprising equal-amplitude two- and three-tones show that the third-order intermodulation can be minimized for values of phase modulation depth less than 0.2 over a relatively wide range of the ratio between the powers in the TM and TE waves of the link. Using these results it is possible to adjust the phase modulation depth and/or the ratio between the powers of the TM and TE waves to achieve a dual-wavelength linearized phase modulated link with a predetermined intermodulation performance.