Analog dithering techniques for highly linear and efficient transmitters

The current thesis is about investigation of new methods and techniques to be able to utilize the switched mode amplifiers, for linear and efficient applications. Switched mode amplifiers benefit from low overlap between the current and voltage wave forms in their output terminals, but they seriously suffer from nonlinearity. This makes it impossible to use them to amplify non-constant envelope message signals, where very high linearity is expected. In order to do that, dithering techniques are studied and a full linearity analysis approach is developed, by which the linearity performance of the dithered amplifier can be analyzed, based on the dithering level and frequency. The approach was based on orthogonalization of the equivalent nonlinearity and is capable of prediction of both co-channel and adjacent channel nonlinearity metrics, for a Gaussian complex or real input random signal. Behavioral switched mode amplifier models are studied and new models are developed, which can be utilized to predict the nonlinear performance of the dithered power amplifier, including the nonlinear capacitors effects. For HFD application, self-oscillating and asynchronous sigma delta techniques are currently used, as pulse with modulators (PWM), to encode a generic RF message signal, on the duty cycle of an output pulse train. The proposed models and analysis techniques were applied to this architecture in the first phase, and the method was validated with measurement on a prototype sample, realized in 65 nm TSMC CMOS technology. Afterwards, based on the same dithering phenomenon, a new linearization technique was proposed, which linearizes the switched mode class D amplifier, and at the same time can reduce the reactive power loss of the amplifier. This method is based on the dithering of the switched mode amplifier with frequencies lower than the band-pass message signal and is called low frequency dithering (LFD). To test this new technique, two test circuits were realized and the idea was applied to them. Both of the circuits were of the hard nonlinear type (class D) and are integrated CMOS and discrete LDMOS technologies respectively. The idea was successfully tested on both test circuits and all of the linearity metric predictions for a digitally modulated RF signal and a random signal were compared to the measurements. Moreover a search method to find the optimum dither frequency was proposed and validated. Finally, inspired by averaging interpretation of the dithering phenomenon, three new topologies were proposed, which are namely DLM, RF-ADC and area modulation power combining, which are all nonlinear systems linearized with dithering techniques. A new averaging method was developed and used for analysis of a Gilbert cell mixer topology, which resulted in a closed form relationship for the conversion gain, for long channel devices

Extended modeling for time-encoding converters

Abstract-Amplitude-quantized time-encoding is beneficial in terms of Shannon capacity, a.o. for data converters. In case of asynchronous, it can be used too for power converters and amplifiers, with extra advantages in terms of power efficiency, power control, in-band quantizer distortion, and absence of both clock-induced noise and power dissipation. This paper fills in the lack of analysis and synthesis tools, for random inputs, with special focus on not yet addressed spectral-domain metrics. The strongly-non-linear quantizer function is translated to a weaklynon-linear one; Hermite expansion is used to achieve an analytical expression for the Shannon-defined SNR; and a 3-step insightful and fast synthesis approach, including a tradeoff between SNR and efficiency, is proposed. The approach is universal and can also be applied to synchronous converters

Low frequency dithering technique for linearization of current mode class D amplifiers

Traditionally, dithering has been used to avoid unwanted non-linear effects in transmitter amplifiers. According to conventional understanding, such techniques require a high frequency dithering signal, i.e., dithering frequencies larger than the signal frequency. A problem with this approach is that it results in a reactive power loss that increases with the dithering frequency. In one aspect, the present invention provides an improved transmitter amplifier in a digital communication system. Surprisingly, the transmitter amplifier employs dithering at a frequency lower than the signal frequency. Using this technique, a hard nonlinear characteristic can be linearized using a dither signal component whose main frequency is at least twice the bandwidth of the input band-pass signal. The input and dithering frequencies should be incommensurable. To achieve increased robustness and augmented linearity, the amplifier is preferably implemented with negative feedback

Low frequency dithering technique for high performance transmitters

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A new approach for nonlinear limit cycle amplifiers

Limit Cycle amplifiers are promising solutions to combine high linearity and efficiency, thanks to the efficient switch mode amplifier inside. Therefore an insightful and efficient analysis method is required for these systems. In this paper, a novel Hermite series based statistical approach for nonlinear analysis of the limit cycle amplifier system with real Gaussian excitation is presented. The proposed algorithm gives both in-band and out of band nonlinear distortions through them same approach. The approach is applied to an 802.11 g OFDM signal to calculate nonlinear metrics and power. The method is validated by good agreement between the extracted results and ADS circuit envelope results

A new behavioral model for nonlinear analysis of class D amplifiers for PWM applications

Switch mode PWM amplifiers are good solutions for amplification of. Static behavioral models fail to predict the amplitude and frequency dependent phase-Gain characteristics of Class D Amplifier inside PWM modulator. Nonlinear device models are accurate but very complex and have convergence problems. Therefore there is a need to develop an accurate and time efficient behavioral model suitable for nonlinear analysis of this type of amplifier. In this paper a new behavioral model is presented which is suitable for nonlinear analysis of a Class D used in limit cycle PWM modulator. All the spectral parameters of the output of a single ended Class D are accurately predicted by this model and validated through comparison with a BSIM4 foundry device model

Statistical Analysis of Self-Oscillating Power Amplifiers

Self-oscillating power amplifiers (SOPA) are promising solutions for amplification of high crest factor signals, with good linearity and efficiency, as a result of using a switch mode amplifier inside the oscillating loop. The lack of comprehensive and statistical analysis method complicates the design and analysis procedure. In this paper, a new statistical approach is presented to analyze the nonlinear behavior of SOPA, to predict the required system metrics like EVM and ACPR. The approach is an extension to the describing function concept and is suitable for a general class of complex Gaussian input signals. The approach is validated through comparison with transistor level simulations and measurements performed on a single chip SOPA realized in 65 nm CMOS technology, for three types of input signal

A new approach for nonlinear metric estimation of limit cycle amplifiers

Limit Cycle amplifiers are promising solutions to combine high linearity and efficiency, thanks to the efficient switch mode amplifier inside. Therefore an insightful and efficient analysis method is required for these systems. In this paper, a novel Hermite series based statistical approach for nonlinear analysis of the limit cycle amplifier system with real Gaussian excitation is presented. The proposed algorithm gives both in-band and out of band nonlinear distortions through them same approach. The approach is applied to an 802.11 g OFDM signal to calculate EVM, ACPR and output power. The method is validated by good agreement between the extracted results and ADS circuit envelope results

A new statistical approach for nonlinear analysis of limit cycle amplifiers

Limit cycle loops are becoming popular due to their potential for higher efficiency and linearity, as data convertors and/or amplifiers. Therefore the analysis of this architecture in different aspects is essential. In this paper a statistical orthogonalization based approach for analysis of limit cycle amplifiers, excited by a Gaussian random signal is developed and the advantages over conventional methods are discussed. The validity of the proposed approach is verified by comparison between the circuit envelope simulation and the results achieved from the proposed algorithm. Index Terms — Describing Function, Gaussian Process, Limit Cycle Amplifier, Harmonic Balance, Circuit Envelope Method

A new approach for nonlinear metric estimation of limit cycle amplifiers

Limit Cycle amplifiers are promising solutions to combine high linearity and efficiency, thanks to the efficient switch mode amplifier inside. Therefore an insightful and efficient analysis method is required for these systems. In this paper, a novel Hermite series based statistical approach for nonlinear analysis of the limit cycle amplifier system with real Gaussian excitation is presented. The proposed algorithm gives both in-band and out of band nonlinear distortions through them same approach. The approach is applied to an 802.11 g OFDM signal to calculate EVM, ACPR and output power. The method is validated by good agreement between the extracted results and ADS circuit envelope results.</p