Sharif Digital Repository

In this paper, we introduce a new bound for the peak of the continuous envelope of an OFDM signal based on the maximum of its corresponding oversampled sequence, that is considerably tighter than the recent results presented in [4]. The proposed bound is then used as the basis of our study in two parts. In the first part, we find an upper bound for the regrowth of the peak of the digitally clipped oversampled sequence after discrete to continuous conversion. We also show that for oversampling rates greater than π/√2, the peak regrowth percentage depends only on oversampling rate, regardless of the number of subcarriers. In the second part, we propose new and tight relative error bounds for... 

It is shown that negative capacitance (NC) circuits can be systematically used to improve the gain-bandwidth product of the operational amplifiers (opamps). The NC circuit moves the nondominant pole of the opamp to higher frequency by decreasing the parasitic capacitance of the critical node. The impedance at the input of the NC circuits is neither purely capacitive nor negative at all frequencies. A design guide is presented by deriving the circuit model for a conventional NC circuit and investigating the extent of the improvement that can be achieved in a circuit by the use of the NC circuit. The model is then used to present the design guide for widebanding the multistage opamps with... 

This paper presents an unilateralization technique for distributed amplifiers (DAs) based on the transformer coupling between the gate and drain lines. Theoretical analysis of the DA indicates that the voltage waves in the gate and drain lines can be described by a system of linear partial differential equations. The transformer coupling between the lines allows for cancellation of the reverse transmission coefficient of the system. There is an optimal value for the coupling coefficient between the lines that unilateralizes the DA. This optimal coupling coefficient is derived in terms of the gate-drain capacitance and capacitances of the gate and drain lines. Using the proposed technique,... 

The transformer-feedback (TRFB) interstage bandwidth enhancement technique for broadband multistage amplifiers is presented. Theory of the TRFB bandwidth enhancement and the design conditions for maximum bandwidth, maximally flat gain, and maximally flat group delay are provided. It is shown that the TRFB bandwidth enhancement can provide higher bandwidth compared to the conventional techniques based on reactive impedance matching networks. A three-stage low-noise amplifier (LNA) monolithic microwave integrated circuit with the TRFB between its consecutive stages is designed and implemented in a 0.1-μ m GaAs pHEMT process. The TRFB is realized by coupling between the drain bias lines of... 

Design techniques to enhance bandwidth and linearity of broadband multistage low-noise amplifiers (LNAs) are presented. A feedback amplifier circuit is proposed to compensate for transistor gain roll-off with frequency in other amplifier stages and extend overall bandwidth. Moreover, a transistor width tapering in a multistage LNA is applied to improve linearity. These techniques are adopted in a three-stage monolithic microwave integrated circuit (MMIC) LNA implemented in a 0.1-μm GaAs pHEMT process. The LNA features 18-43 GHz bandwidth, 21.6 dB average gain, and 1.8-2.7 noise figure (NF). It exhibits output 1-dB compression point of 11.5 dBm at 30 GHz and consumes 70 mA bias current from a... 

In this brief, a design technique for tapered distributed low-noise amplifiers (LNAs) is presented. A circuit model is developed for gain and noise analysis of a nonuniform distributed amplifier (DA). It is shown that by optimal tapering of gate and drain transmission lines and transistors, the tapered distributed LNA can provide lower broadband average noise figure (NF) compared to a uniform DA. A proof-of-concept integrated circuit is implemented using a 0.1-μm GaAs pHEMT process. The amplifier provides average gain of 15.2 dB and 3-dB bandwidth of 43.3 GHz. The average NF of 2.3 dB and minimum NF of 2.0 dB are achieved over 2–40 GHz. The chip consumes 55 mA current from a 2-V supply. IEEE... 

In this brief, a design technique for tapered distributed low-noise amplifiers (LNAs) is presented. A circuit model is developed for gain and noise analysis of a nonuniform distributed amplifier (DA). It is shown that by optimal tapering of gate and drain transmission lines and transistors, the tapered distributed LNA can provide lower broadband average noise figure (NF) compared to a uniform DA. A proof-of-concept integrated circuit is implemented using a 0.1-μm GaAs pHEMT process. The amplifier provides average gain of 15.2 dB and 3-dB bandwidth of 43.3 GHz. The average NF of 2.3 dB and minimum NF of 2.0 dB are achieved over 2-40 GHz. The chip consumes 55 mA current from a 2-V supply. ©... 

A 37 dBm power amplifier (PA) is designed on a 0.25 μm optical T-gate pseudomorphic high electron mobility transistor (pHEMT) technology. The design of this two-stage PA along with a step-by-step design procedure is presented in this paper. This methodology can be used for design of PA in different technologies and frequencies. The PA delivers 5 W output power over the frequency band of 13-19 GHz. It shows average power-added efficiency of 37% and large signal gain of 15 dB in measurements which is consistent with simulation results. The output power and efficiency of the realised amplifier reach maximums of 37.6 dBm and 45%, respectively. Considering output power, bandwidth, chip area and... 

This paper presents a bandwidth enhancement technique for broadband Darlington amplifiers. A detailed analysis of the high-frequency performance of the Darlington amplifier and the effect of bandwidth enhancement is provided. A design procedure is also given for broadband feedback Darlington amplifiers with bandwidth enhancement and gain flattening. A single- and a three-stage feedback amplifier with the proposed improvements are designed and implemented in a 0.25-μm Al-GaAs-InGaAs pHEMT technology. The single-stage amplifier provides 6 ± 0.4 dB of small-signal gain in the frequency band of 1-30 GHz. The three-stage amplifier features 17.8 ± 0.8 dB of small-signal gain in the frequency band... 

Theoretical stability analysis of broadband cascode amplifiers at high frequencies is presented. The stability of the amplifier in the presence of parasitic inductive components is thoroughly investigated. It is shown that the stability can be improved by inserting a series resistance in the gate of common-gate device of the cascode amplifier. To ensure stability, the gate resistance should be selected within specific ranges that are derived analytically. Based on the insights provided by the analyses, several practical design guidelines are given to improve the stability of high-frequency broadband cascode amplifiers. Finally, the derived results are adopted in stabilisation of an X-band... 

A combination of coupled microrings that are coupled to a bus waveguide is proposed as a wide-band microring Raman amplifier. This structure is called one channel coupled microrings (OCCM) Raman amplifier. It is shown analytically that the number of poles in the OCCM transfer function is greater than the square of microrings number (N). The gain bandwidth and gain ripple of the proposed amplifier are increased and decreased, respectively due to increasing the number of poles and zeros in the transfer function. An iterative matrix method is introduced to solve Raman equations in the amplifier with arbitrary number of microrings and Genetic algorithm is employed to maximize the gain flatness  

A side coupled integrated spaced sequence (SCISSOR) of Silicon or Chalcogenide glass microrings of different diameter are considered as a wide-band Raman amplifier. Because the two-photon absorption (TPA) losses in Chalcogenide glass are less than that of Silicon, it is shown that Chalcogenide microrings are suitable for wide-band Raman amplifier in the telecommunication bandwidth (1.5 μm). The Lagrange unknown multiplier method is employed to minimize the gain ripple of the amplifier versus the pump and system parameters. Crown Copyright © 2008  

This paper presents the design and implementation of a bidirectional distributed amplifier (BDDA) in a 0.18- boldsymbol mu ext{m} CMOS process. The performance of the BDDA is theoretically analyzed, and the optimum number of gain stages ( n-{ ext {opt}} ), maximum achievable power gain ( G-{P} ), and circuit bandwidth are formulated. In addition, a new formula for proper choice of the number of DA stages (i.e., n ) is offered where dc-power consumption of the circuit ( P-{ ext {dc}} ) is also considered. This formula optimizes G-{P}/P-{ ext {dc}} , and it is preferred over the conventional n-{ ext {opt}} formula. To validate the theoretical analyses, a 2-12-GHz BDDA with high output 1-dB... 

This article applies a systematic approach based on the normalized determinant function (NDF) theory to analyse stability in multi-loop circuits and to design the required stabilization network. Presenting several provisions, the return ratios are extracted by employing immittance or hybrid matrices (Z, Y, G or H) of active two ports. Using these matrices, instead of the S-parameters, facilitates the selection of an appropriate stabilizer network. As a practical case, a non-uniform distributed amplifier (NDA) is designed and inspected for potential instabilities. The presented procedure detects instability associated with one of the NDA circuit's loops, and an appropriate stabilization... 

This letter presents a Ka-Band 0.1-μm GaAs pHEMT Power Amplifier with broad bandwidth. The isolating backvia wall (IBVW) has been proposed to improve the stability and performance. Over the frequency band of 31-40 GHz, implemented PA delivers 5 W saturated output power, 28% maximum power added efficiency (PAE) and 20 dB maximum small-signal gain. The chip size of the PA is 11.9 mm2. To the best of authors knowledge, the presented PA demonstrates widest bandwidth in Ka-band GaAs PAs while maintaining compact size  

This paper presents a design methodology for class-J monolithic microwave integrated circuit (MMIC) power amplifiers (PAs). Theoretical derivations of optimum load impedances, output power, efficiency, and maximum bandwidth are described in presence of nonlinear drain-source resistance of transistors (RDS). A procedure is developed for ideal transistor sizing where transistors are concurrently stabilized and sized to achieve the maximum power-added efficiency (PAE). A 3.5-7 GHz, 0.5-W class-J PA is implemented in a 0.1-μm AlGaAs-InGaAs pHEMT technology to check the accuracy of the proposed approach. With chip dimensions of 1.57 × 1.29 mm2, the PA achieves 56% average PAE over the frequency... 

This paper presents a methodology for the design of Ka/Q-band monolithic microwave integrated circuit (MMIC) high-power amplifiers (HPAs). Design techniques are introduced to reduce chip area and to improve bandwidth (BW). These techniques are applied to the design of a 31-39-GHz 5-W HPA implemented on a 0.1-μm AlGaAs-InGaAs pseudomorphic HEMT (pHEMT) technology. With chip dimensions of 3.35 × 3.2 mm2, the HPA achieves 24% average power-added efficiency (PAE) over the frequency band, while maintaining an average 22-dB small-signal gain. A balanced high-power amplifier (BPA) is also presented, which combines the power of two 5-W HPA cells to deliver peak 8.5-W output power (Pout) in the...