Risto Kaunisto

A 2.14-GHz Chireix outphasing transmitter

A Chireix outphasing system for 2.14 GHz including two saturated class-B pseudomorphic high electron-mobility transistor power amplifiers (PAs) and a Chireix power-combining circuit is reported in this paper. In an outphasing system, an arbitrary input signal is divided into two constant envelope branches. The phase-only modulated branches are then amplified with high-efficiency nonlinear PAs. By controlling the phases of these branches, the original signal waveform can be reconstructed, ideally with high efficiency and perfect linearity. In this paper, the design and implementation of an experimental Chireix outphasing system for a wide-band code division multiple access 2.11-2.17-GHz downlink band is presented. The measured system efficiency for 7-dB backed-off quadrature phase-shift keying signal was 42.2% with a channel power of 31.2 dBm.

A low-power HBT MMIC filter based on tunable active inductors

An integrated active microwave filter employing high-Q active inductance simulating circuits is presented in this paper. Heterojunction bipolar transistor (HBT) technology is best-suited for this specific application facilitating the design and giving optimum performance with low power consumption. The prototype triple-resonator filter operates at 2.32 GHz with a 300 MHz -3-dB bandwidth. The power consumption is only 25 mW drawn from a 3-V supply.

A linear-control wide-band CMOS attenuator

A fully-CMOS controllable attenuator with a multi-octave bandwidth is presented. The linearity of the attenuation control is ensured by a constant-current reference device in a feedback loop, and another self-adjusting control loop is adopted for matching. Realized with a standard 0.8-/spl mu/m CMOS process, the circuit has a bandwidth of DC-900 MHz with an attenuation tuning range of >28 dB. The measured attenuation compression point is +5 dBm, and the total DC power consumption is 12 mW.

Active inductors for GaAs and bipolar technologies

Integrated high performance gallium arsenide and silicon active inductor configurations for microwave frequencies are examined in this article. The existing topologies are considered and a new aspect of comparing the performance of different topologies based on a more complete analysis is utilised. Drawbacks of GaAs technology in this particular case are recognised, while benefits attained by using bipolar technology are presented. A theoretical basis for designing bipolar inductors is examined. On the basis of these studies a new method for raising the Q-factor of an active inductor is found and applied to two novel GaAs Q-enhanced active inductors. New applications for active high-Q resonators are found and their realisation aspects are considered. Integrated test circuits have been designed, and the simulated and experimental results are presented.

Q-enhancing technique for high speed active inductors

Integrated active inductor configurations for RF frequencies are examined in this paper. A new aspect of comparing the performance of different topologies is used, and consequent differences between technologies are recognised. On the basis of these studies a new method for raising the Q-factor is presented and its applications considered.<<ETX>>

Monolithic active resonators for wireless applications

In this paper new tunable, monolithic active resonator topologies are presented. The circuits, based on the advances in GaAs MMIC active inductors, show stable, high-Q performance with large tunability and compact layout. The simulated results exceed significantly the properties of conventional varactor-tuned circuits. The new circuits are applied to active filters and proposed active resonator oscillators (ARO), which show great potential for wireless applications at the 2 GHz band.<<ETX>>

Monolithic tunable capacitors for RF applications

Passive and active tunable capacitors for RF applications are discussed and compared in this paper. In silicon IC technologies passive tunable capacitors are either based on the p-n junction or the metal-semiconductor junction, i.e. the MOS-structure. Active capacitors discussed in this paper are based on the Miller effect or on the current steering principle (Gilbert cell). Modeling issues are discussed and measurement results presented for the passive structures. For active circuits the comparison is based on simulations and experimental results obtained from VCO circuits.

A high frequency harmonic VCO with an artificial varactor

A tunable LC-oscillator utilising an artificial varactor is presented in this paper. The proposed variable capacitor is based on the well-known Miller effect. A theoretical model is developed to study the capacitance tuning range and the corresponding Q-value. Most radio frequency harmonic voltage-controlled oscillators are tuned by changing the capacitance of a pn-junction diode. The inadequate capacitance tuning range of the pn-junction diode severely limits the achievable frequency tuning range of the oscillator. By using an artificial varactor based on the Miller capacitance, the frequency tuning range is enhanced significantly. The proposed LC-VCO has a tuning range of 1.7-2.2 GHz.

A configurable sampling rate converter for all-digital 4G transmitters

This paper presents a digital interpolation chain for non-integer variable-ratio sampling rate conversion, targeted to 4G mobile applications. Such a system is needed in all-digital transmitters, where the sampling rate of the digital input to the RF front-end must be an integer fraction of the carrier frequency. A highly configurable architecture is proposed to cope with the flexibility needed in 4G applications. The system achieves excellent ACLR of 75 dB, EVM degradation of 0.05%, and RX-band noise below -160 dBc/Hz. Digital synthesis of the circuit in a 40nm low-power CMOS process results in a core area of only 0.073 mm2. The estimated power consumption is between 6 and 29 mW, depending on channel bandwidth and transmission band.

A 3 GHz silicon-BJT active resonator and filter

A tunable active resonator for filtering applications is presented in this paper. The resonator consists of a fully differential high-Q active inductor with resonating passive capacitors. The realisation of the active inductor has no critical passive components, which reduces size and sensitivity, and extends the number of possible process technologies. On the other hand, the inherently poor noise properties of active inductors are discussed. The tuning range of the resonator is 2.5-3 GHz with freely adjustable quality factor. A second-order filter with the same tuning range and -3 dB bandwidth of 50 MHz is also described.