Aleksandar Tasic

Design of Adaptive Multimode RF Front-End Circuits

Migration towards higher data rates and higher capacities for multimedia applications, and provision of various services (text, audio, video) from different wireless standards with the same device require integrated designs that work across multiple standards, can easily be reused, and achieve maximum hardware share at minimum power consumption. This can be achieved by using adaptive circuits that are able to trade off power consumption for performance. The design of an adaptive multimode image-reject downconverter (oscillator and two mixers) is presented in this paper. In the highest performance mode, the image-reject downconverter (the quadrature mixers) has an IIP3 of +5.5 dBm, a single-side band noise figure of 13.9dB and a conversion gain of 1.4 dB, while drawing 10mA from a 3 V supply. The adaptive oscillator achieves -123 dBc/Hz phase noise at 1MHz offset from a 2.1 GHz carrier with a bias current of 6 mA in the highest performance mode. Adaptivity in the downconverter is achieved by trading off RF performance for current consumption, ranging from 10 mA for the relaxed mode (e.g., DECT) to 20 mA in the highest performance mode (e.g., DCS1800) of operation

Adaptive multi-standard circuits and systems for wireless communications

Telecom trends such as smooth migration towards higher data rates and higher capacities for multimedia applications, and provision of various services (text, audio, video) from different standards with the same wireless device require integrated designs that work across multiple standards, can easily be reused and achieve maximum hardware share at minimum power consumption. This can be achieved by using adaptive circuits that are able to trade off power consumption for performance on the fly. Realization of the adaptivity function requires scaling of parameters such as current consumption to the demands of the signal-processing task. This paper describes adaptivity design concepts and application of design for adaptivity to multi-standard circuits and systems for wireless communications. An exploratory multi-standard RF front-end is discussed with phase-noise tuning, noise-figure tuning, and input-intercept point tuning requirements of 21 dB, 12 dB, and 7 dB, respectively.

Design of multistandard adaptive voltage-controlled oscillators

A multistandard/multiband adaptive voltage-controlled oscillator (VCO) satisfying the phase-noise requirements of both second- and third-generation wireless standards is described in this paper (1.8-GHz DCS1800, 2.1-GHz wide-band code division multiple access, and 2.4-GHz wireless local area network, Bluetooth, and digital enhanced cordless telecommunications standards). The design procedure for the VCO is based on an adaptive phase-noise model. A factor of 12 reduction in power consumption with a phase-noise tuning range of 20 dB is demonstrated by adapting the VCO bias to the desired application. The VCO achieves -123-, -110-, and -103-dBc/Hz phase noise at 1-MHz offset in a 2.1-GHz band at supply currents of 6, 1.2, and 0.5 mA, respectively

Adaptivity of voltage-controlled oscillators - theory and design

Analog RF front-end circuits are typically designed to perform one specific task, while key parameters such as dynamic range, bandwidth and selectivity are fixed by the hardware design and not by the communication system in an adaptive way. As a result, todays receiver topologies are designed to function under the most stringent conditions, which increases circuit complexity and power consumption. However, the conditions under which the RF circuits operate are not fixed but vary widely and depend upon a multitude of factors. Therefore, a concept of design for adaptivity is introduced in this paper. It establishes a trajectory for an all-round performance characterization of adaptive oscillators with an explicit qualitative and quantitative description of all the existing relations and tradeoffs among the oscillator performance parameters. As a proof of concept, an 800-MHz adaptive voltage-controlled oscillator is designed with phase-noise tuning range of 7 dB and more than a factor 3 saving in power consumption, suitable for unobtrusive mobile equipment, foreseen to operate in this band.

Concept of phase-noise tuning of bipolar voltage-controlled oscillators

So far, oscillators have been designed to perform a specific task while the key parameters such as phase-noise and power consumption are set by the hardware design and not by the communication system in an adaptive way. As the communication channel is often subject to changes, the conditions under which the oscillator operates should be changed as well. Therefore, the concept of design for adaptivity must be considered as a cornerstone in the design of todays telecommunication systems. Accordingly, the concept of phase-noise tuning, introduced in this paper, shows how oscillators can trade performance for power consumption in an adaptive way. The presented model of a quasi-tapped bipolar VCO reveals the resulting trade-offs between phase-noise and power consumption imposed by the design for adaptivity.

A multi-standard adaptive image-reject downconverter

A multi-standard adaptive image-reject downconverter (oscillator and dual mixers) that satisfies the basic requirements of 2/sup nd/ and 3/sup rd/ generation wireless standards (i.e., DCS1800, W-CDMA, 802.11b, Bluetooth and DECT) is presented. The adaptivity between the standards is achieved by trading RF performance for current consumption, ranging from 9.9 mA for the relaxed mode (2.4 GHz DECT) to 20.2 mA for the highest performance mode (1.8 GHz DCS1800) of operation. The adaptive oscillator achieves -123 dBc/Hz and -103 dBc/Hz phase noise at 1 MHz offset in a 2.1 GHz band for bias current levels of 6 mA and 0.5 mA, respectively. In the highest performance mode, the image-reject downconverter (quadrature mixers) has an IIP3 of +5.5 dBm, single-side band NF of 13.9 dB (50 /spl Omega/) and conversion gain of 1.4 dB, while drawing 10 mA from a 3 V supply.

Circuits and Systems for Future Generations of Wireless Communications

The explosive demand in wireless-capable devices, especially with the proliferation of multiple standards, indicates a great opportunity for adoption of wireless technology at a mass-market level. The communication devices of both today and the future will have not only to allow for a variety of applications, supporting the transfer of characters, audio, graphics, and video data, but they will also have to maintain connection with many other devices rather than with a single base station, in a variety of environments. Moreover, to provide various services from different wireless communication standards with higher capacities and higher data-rates, fully integrated and multifunctional wireless devices will be required. In Circuits and Systems for Future Generations of Wireless Communications circuit and system solutions for multiple communication standards and future generations of wireless communications are discussed.

Optimal distribution of the RF front-end system specifications to the RF front-end circuit blocks

Rather delicate, distribution of the system specifications to the individual receiver blocks has not gained any exactness for the last decades. When distributing the system specifications to each of the blocks in receive chain, it is rather common practice to consider each performance parameter separately. However, as both the noise and the linearity performance depend on the gain of the corresponding circuit blocks, the noise figure (NF) and the third order intercept point (IP3) optimization procedure are not mutually exclusive. Therefore, a procedure for the optimal allocation of the performance parameters to the individual RF front-end circuit blocks is introduced in this paper. Optimizing the system performance with respect to the ratio NF/IP3/sup 2/, the maximum dynamic range design point can be found, satisfying both the noise and the linearity requirements.

Matching of low-noise amplifiers at high frequencies

Higher transistor transition frequencies, lower supply voltages and smaller physical dimensions are, nowadays, general trends in the semiconductor industry. Operating at lower supply voltages often results in a low-power design, smaller dimensions allow the use of a large number of transistors and a high transition frequency (f/sub T/) opens the way to design of amplifiers with ever-higher gains and lower noise figures. However, such trends make the use of some circuit topologies questionable. Take the inductively-degenerated low-noise amplifier, arguably the most-widely used RF amplifier topology, requiring an impractical inductance in the order of pH for a simultaneous input-power match at high f/sub T/s. Therefore, a conceptual change in a design approach has resulted in transformer-feedback degenerated low-noise amplifier, presented in this paper. By controlling the coupling coefficient, the power match is possible even for the highest values of f/sub T/, with practical values of primary inductance for the transformer. The analysis gives full insight into the performance of the newly introduced transformer-feedback degenerated low-noise amplifier scheme.

Concept of frequency-transconductance tuning of bipolar voltage-controlled oscillators

Due to technology limitations as well as stringent operating conditions that are imposed, the design of fully integrated analog RF front-end circuits is aimed at the edge of the required performances. Such an approach implies that each dB of power or noise is of high importance, as it directly determines the range of operation of a system. Accordingly, a design trajectory that offers certain power savings, while still keeping the system within the required range of operation, appears to be a promising candidate for nowadays highly stringent low-power RF front-end circuit design. The concept of frequency-transconductance tuning, introduced in this paper, offers the possibility for voltage-controlled oscillators to trade power consumption for loop-gain and phase-noise. Detailed analysis shows how this concept is employed to achieve full control over the operation of the oscillator that is being changed as a result of a frequency tuning.