Alain Barel

Accurate on wafer measurement of phase and amplitude of the spectral components of incident and scattered voltage waves at the signal ports of a nonlinear microwave device

A measurement setup and calibration procedure are described allowing the accurate on wafer measurement of phases and amplitudes of the spectral components of incident and scattered voltage waves at the signal ports of a nonlinear microwave device. A comparison is made between measurements performed with the setup and simulations based on a Root-model.<<ETX>>

OFDM-MIMO WLAN AP front-end gain and phase mismatch calibration

The work presents a front-end gain and phase mismatch calibration scheme for OFDM-MIMO/TDD WLAN systems using transmit-processing, where complete channel reciprocity and calibration of the access point (AP) hardware is needed. Simulation results for a single-user 2/spl times/2 OFDM-MIMO system with QAM-64 modulation show that our calibration method can reduce the implementation loss to as little as 0.2 dB at a coded BER of 10/sup -5/ The calibration scheme has been implemented and demonstrated by IMEC.

A 6.5-kV ESD protected 3-5-GHz ultra-wideband BiCMOS low noise amplifier using interstage gain roll-off compensation

Design and validation of an electrostatic discharge (ESD)-protected ultra-wideband low-noise amplifier (LNA) is presented in this paper. It features an interstage matching network for gain roll-off compensation to achieve a flat gain over its passband. Evaluated with a chip-on-board approach, the amplifier demonstrates a gain of 11.8 /spl plusmn/ 0.3 dB, minimum noise figure of 2.1 dB, and a group delay variation of /spl plusmn/30 ps from 3 to 5 GHz, even though it uses a less advanced 0.35-/spl mu/m BiCMOS technology. The LNA is protected against human body model ESD stress up to 6.5 kV. The measured input third-order intercept point at 4.5 GHz is -5.5 dBm. The core LNA draws 3 mA from a 3-V supply.

Black box modelling of hard nonlinear behavior in the frequency domain

A black box model is proposed to describe nonlinear devices in the frequency domain. The approach is based upon the use of describing functions and allows a better description of hard nonlinearities than an approach based upon the Volterra theory. Simulations and experiments are described illustrating the mathematical theory.

Impact of front-end effects on the performance of downlink OFDM-MIMO transmission

The work presents the impact of analog front-end effects on the BER performance of MIMO/SDMA-OFDM downlink transmission using minimum mean-squared error transmit processing at the access point. The implementation loss due to gain and phase mismatch, analog filtering, clipping and quantization, phase noise, and I/Q mismatch in the front-ends is given.

Broadband high frequency differential coupler

This paper describes the design methodology of a broadband, high frequency differential coupler. The output signal of this differential coupler is proportional to the difference of 2 input ports, i.e. proportional to the differential signal of the 2 inputs. This signal is made using a hybrid structure. The overall performance of this differential coupler and the hybrid structure is characterized by the differential coupling factor and by the common mode rejection ratio. A pair of broadband impedances are used to scale the 2 incoming signals with 2 complex coefficients. A symmetric structure of two identical broadband directional couplers and a symmetric power combiner are used afterwards to obtain the differential signal. The high bandwidth of both the terminations, the directional couplers and the power combiner make it possible to obtain a differential coupling factor and a common mode rejection ratio which is frequency insensitive over several decades. Measurements demonstrate a differential coupler with a bandwidth of more than 3 decades.

A microwave multisine with known phase for the calibration of narrowbanded nonlinear vectorial network analyzer measurements

A method is proposed to generate an RF multi-tone (up to 10 GHz) calibration signal with a very narrow harmonic spacing (down to 100 KHz) and a known phase relation between tones. This signal is requested for the phase calibration of a nonlinear vectorial network analyzer on a dense grid, as occurs when modulated signals are measured. The phase relation is traceable to a nose-to-nose calibrated microwave sampling oscilloscope.

Waveform Measurements on a HEMT Resistive Mixer

Calibrated on-wafer waveform measurements under two-tone stimuli are demonstrated on a HEMT, configured as a resistive mixer. These large-signal measurements allow us not only to determine the conventional performance parameters, but also to analyse the influence of the phase relationship between the two excitation signals on the characteristics. For the considered HEMT resistive mixer, the dependency of the intermodulation products on the phase relationship between the LO-signal and the RF-signal becomes significant at high RF-powers.

Impact and mitigation of multiantenna analog front-end mismatch in transmit maximum ratio combining

Transmit maximum ratio combining (MRC) allows to extend the range of wireless local area networks (WLANs) by exploiting spatial diversity and array gains. These gains, however, depend on the availability of the channel state information (CSI). In this perspective, an open-loop approach in time-division-duplex (TDD) systems relies on channel reciprocity between up- and downlink to acquire the CSI. Although the propagation channel can be assumed to be reciprocal, the radio-frequency (RF) transceivers may exhibit amplitude and phase mismatches between the up- and downlink. In this contribution, we present a statistical analysis to assess the impact of these mismatches on the performance of transmit-MRC. Furthermore, we propose a novel mixed-signal calibration scheme to mitigate these mismatches, which allows to reduce the implementation loss to as little as a few tenths of a dB. Finally, we also demonstrate the feasibility of the proposed calibration scheme in a real-time wireless MIMO-OFDM prototyping platform.

Characterization of substrate noise impact on RF CMOS integrated circuits in lightly doped substrates

Analog and RF circuit performance in single-chip transceivers can severely suffer from coupling of digital switching noise to the silicon substrate. To predict this performance degradation, a deeper understanding of the impact of substrate noise is absolutely necessary. Using measurements, this impact is studied as the cascade of attenuation through the substrate from the source of substrate noise to the RF circuit and the propagation through the RF circuit to its output. This approach has been validated with measurements on a 0.25 /spl mu/m and a 0.18 /spl mu/m CMOS low-noise amplifier (LNA) and reveals insight in the mechanisms of impact of substrate noise on RF circuits. In addition, impact of a real digital circuit is measured on a 0.18 /spl mu/m differential CMOS LNA.