Summary Burst‐mode operation of power amplifier (PA) based on multilevel pulse‐width modulation (MPWM) has been frequently discussed as a potential solution to achieve higher efficiency in radio frequency (RF) transmitters. In this paper, a novel multilevel PWM modulator is proposed that utilizes adaptive triangular reference waveforms. As compared with conventional MPWM modulators, the proposed architecture provides significant wider design space such that the efficiency of system can be effectively optimized. A general transmitter architecture based on the proposed concept is analyzed in terms of power efficiency. Efficiency optimization procedures are presented according to input magnitude statistics. Based on the proposed modulator, an optimized 2.4‐GHz RF transmitter is designed in a 0.18‐μm complementary metal‐oxide‐semiconductor (CMOS) process. The circuit‐level simulations show that it delivers 25.8‐dBm peak output power with 46.1% peak efficiency. For a 20‐MHz worldwide interoperability for microwave access (WiMAX) signal with 8.5‐dB peak‐to‐average‐power ratio (PAPR), this transmitter achieves 28.8% (average) efficiency at 17.3‐dBm (average) output power with an error vector magnitude (EVM) of 2.97% rms.

A new architecture for successive-approximation register analog-to-digital converters (SAR ADC) using generalized non-binary search algorithm is proposed to reduce the complexity and power consumption of the digital circuitry. The proposed architecture is based on the split capacitive-array DAC with a simple switching logic as compared to the conventional non-binary SAR ADC architecture. A 10-bit 50-MS/s SAR ADC is designed based on the proposed architecture in a 0.18 lm CMOS technology. Simulation results show that at a supply voltage of 1.2 V, the SAR ADC achieves a peak signal-to-noise-and-distortion ratio of 59.5 dB, and a power consumption of 1.3 mW, resulting in a figure of merit of 33 fJ/conversion-step.

Radio frequency (RF) power amplification based on pulse-width modulation (PWM) has been widely discussed as a potential solution to achieve higher efficiency in RF transmitters. A digitally implemented PWM introduces a large amount of in-band distortion due to spectral aliasing. In this paper, a novel memoryless PWM modulator with a built-in anti-aliasing filter is proposed that effectively reduces the in-band distortion in digital implementation. The spectral characteristics of the proposed PWM modulator as well as the statistical properties of its output PWM signal are analytically studied. The pseudotwo-level output of the proposed modulator provides the capability to compromise between the efficiency, linearity, and complexity of transmitter, based on the given design targets. The proposed PWM method benefits from a simple circuit implementation in both digital and RF sections of the transmitter.Moreover, it preserves the low distortion property at low oversampling ratios of digital baseband. Simulations, as well as measurements, verify the performance of the proposed method. low level of RF input signal, PA consumes no power, while at the high level, PA can be designed to work in saturated output power where it presents the best efficiency performance.Although PA in a PWM-based transmitter operates in its most power-efficient regions, converting RF magnitude into the pulse train generates a significant amount of unwanted frequency components in the output spectrum of PA. 17 As depicted in Figure 2, these spurs are located at integer multiples of PWM frequency ( f PWM ) around the RF carrier frequency ( f c ). The bandpass filter (BPF) in Figure 1 is located at the output of PA to remove these undesired spurs and obtain the amplified version of the RF input. The quality of the signal recovered by BPF highly depends on the amount of distortion around the band of interest in the spectrum of RF PWM signal. The dynamic range (DR) gives a criterion to measure this type of distortion. It is defined as the ratio between the average power of the desired in-band signal and the power of the surrounding distortion, which is given in dB (or dBc). A sufficiently high DR is essential at the output spectrum of PA to satisfy the in-band signal quality and tight spectral requirements imposed by modern wireless standards. This is not feasible unless the RF PWM signal driving the PA itself benefits from excellent spectral characteristics.The spectral characteristics of the analog PWM (APWM) signal have been frequently studied in previous works. [17][18][19][20][21][22] An APWM signal occupies a wide bandwidth with a spectral content that tends to roughly roll-off as ∝ 1= f f PWM with increasing the frequency. By choosing a large enough PWM frequency, f PWM , of the APWM modulator, an arbitrary high DR could be theoretically achieved 19,21 at the cost of a wider output spectral bandwidth. Nevertheless, the practical achievable DR of the modulator is significantly restricted by the accuracy and bandwidth limitation of its analog ...

An ultra-low power successive approximation (SA) analog-to-digital converter (ADC) based on the redundant search algorithm is proposed. The power consumption of the comparator is significantly reduced through gain control of the preamplifier during conversion phase. The number of analog sampling switches is reduced to one by introducing modified clock boosting switch. A single-ended 8-bit SA-ADC is designed in a 0.18 µm CMOS process. Our simulation results show that at a supply voltage of 0.9 V and an output rate of 500 kS/s, the SA-ADC achieves a peak signal-to-noise-and-distortion (SNDR) ratio of 48 dB, and a power consumption of 1.63 µW, resulting in a figure of merit of 15.9 fJ/conversion-step.

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