Wide-band CMOS cascode low-noise amplifier design based on source degeneration topology

A design methodology for a wide-band CMOS low noise amplifier (LNA) with source degeneration is presented. By allowing an arbitrary source degeneration and employing a general input matching network, the proposed wide-band CMOS LNA can be shown for any choice of transistor width to achieve the minimum noise figure at all frequencies of interest. The transistor width simply affects the gain of the LNA at the cost of power dissipation. These results apply uniquely to CMOS LNAs, as they are derived from a quasi-static MOSFET model. To validate these design concepts, a wide-band LNA was realized in 0.25-/spl mu/m CMOS technology. The measured noise figure ranges from 2.7 to 3.7 dB over 3.2-4.8 GHz with power consumption of 20 mW. A close agreement with the theoretical results is observed.     

Low-noise amplifier design for ultrawideband radio

A new theoretical approach for designing a low-noise amplifier (LNA) for the ultra-wideband (UWB) radio is presented. Unlike narrow-band systems, the use of the noise figure (NF) performance metric becomes problematic in UWB systems because of the difficulty in defining the signal-to-noise ratio (SNR). By defining the SNR as the matched filter bound (MFB), the NF measures the degree of degradation caused by the LNA in the achievable receiver performance after the digital decoding process. The optimum noise matching network that minimizes the NF as defined above has been solved. When the narrow-band LNA assumption is made, the proposed optimum matching network simplifies to the published optimum narrow-band matching network, and the corresponding NF value also becomes equivalent. Since realizing the optimum matching network is in general difficult, an approach for designing a practical but suboptimum matching network is also presented.     

Noise figure of digital communication receivers-revisited

Noise figure (NF) is a commonly used system parameter that quantifies the degradation in the signal-to-noise ratio (SNR) as the signal passes through a receiving system. Because of the difficulty in defining the SNR, NF depends on how the SNR is computed and the underlying assumptions that are made. Existing NF measures and their shortcomings are explained. A new NF suitable for a digital communication receiver is proposed by redefining the SNR, so that the NF measures the degradation in the achievable performance caused by the receiving system. The proposed NF, which we refer to as the effective NF, can be readily determined based on the existing NF measurement techniques. As an example of the use of the effective NF metric, a direct-conversion receiver with ac coupling in the signal path to remove the dc-offset noise is described.     

Generalized Linear Periodic Time-Varying Analysis for Noise Reduction in an Active Mixer

A simple linear periodic time-varying circuit model is proposed to rigorously analyze the noise behavior in an active mixer. This analysis can be shown to be a generalization of existing LPTV mixer models, which assume that the mixer is a memoryless device and, as a result, is valid for low frequency only. Based on the proposed LPTV circuit model, explicit formulas for noise figure that accounts for the effect of the thermal noise folding and the flicker noise leakage are derived. Our analysis shows that the mixer operating at OFF overlap mode yields a better noise performance. The analysis is validated against simulations and measurements.     

Quasi-two-dimensional transmission line model (QTD-TLM) for planarohmic contact studies

An analytical quasi-two-dimensional transmission tine model (QTD-TLM) has been formulated to more accurately extract the specific contact resistance (ρ_c) of ohmic contacts than the conventional one-dimensional TLM (1D-TLM). Similar to 1D-TLM, the extraction of ρ_c using QTD-TLM is straightforward. By means of the conformal mapping technique, the two-dimensional (2-D) (or lateral) current flow and current crowding, owing to the presence of a gap between the TLM mesa and contacts, are jointly incorporated into our model using a single shunt resistor. QTD-TLM is generalized as it is applicable to a variety of contact dimensions and gap widths, and to both alloyed and nonalloyed contacts. The validity of QTD-TLM has been verified experimentally using two alloyed and two nonalloyed ohmic contacts, and by comparison with results from a 2-D numerical model     

Revisiting spurious-free dynamic range of communication receivers

The spurious free dynamic range (SFDR) is commonly used as a measure of dynamic range for the radio frequency and microwave front-end receivers. Although well defined in narrow-band systems, the definition becomes less clear in wide-band systems, when the nonlinearity is memoryless and the the noise figure is frequency dependent. To generalize the SFDR to wide-band systems, a meaningful physical interpretation of the conventional two-tone test is first developed. Based on this interpretation, the upper bound of the wide-band SFDR is obtained by applying a multitone test, while the lower bound is computed using the effective noise figure. The multitone test in both the memoryless and memory nonlinear Volterra systems is considered. A practical measurement technique to characterize the Volterra kernel is also provided. A realistic example based on a low noise amplifier shows a significant difference between the conventional and wide-band SFDR values. In this example, our results suggest that the use of two tones widely separated in frequency to model the interferers provides sufficiently accurate results compared to a multitone approximation.