Hamed Gheidi

All-Digital Cancellation Technique to Mitigate Receiver Desensitization in Uplink Carrier Aggregation in Cellular Handsets

Future handsets will employ uplink carrier aggregation to increase transmit data rates. This can lead to significant receiver desensitization for a number of LTE band combinations, because of the cross-modulation products created by the nonlinearity of antenna switches and duplexers in the RF front end. To mitigate this effect, an all-digital cancellation algorithm is proposed that relies solely on the digital representation of the signals, a peak covariance search for time alignment, and an adaptive distortion canceller. The recursive least squares (RLS) algorithm is used to find the optimal coefficients for the adaptive filter. Employing the distortion canceller improved the signal-to-interference-plus-noise ratio (SINR) and error-vector-magnitude (EVM) of the desired received signal by up to 20 dB.

Phase-Noise Measurement of Microwave Oscillators Using Phase-Shifterless Delay-Line Discriminator

In this paper, a modified method based on the frequency discriminator technique for measuring phase noise of microwave oscillators is presented. In the proposed method, the phase shifter is omitted. In contrast, a 90° hybrid with one more channel containing a phase detector, and a low-noise amplifier is added to the measurement setup. It can be said that an in-phase/quadrature phase-noise detection has been developed. With the proposed method, tuning of the variable phase shifter is not needed anymore. Therefore, the measurement is done automatically, and as a result, the measurement time is decreased. Another considerable advantage of this method is that the method is theoretically self-calibrated. For verifying the accuracy of the method, a measurement setup based on the proposed method was established. Two relatively low phase-noise phase-locked oscillators at frequencies of 2.8 and 4.9 GHz were designed. Their phase noise was measured by the proposed method, the conventional delay-line method, and the two-oscillator technique. Comparison of the measured data of the three methods shows the validity of the proposed method.

Characterization of Intermodulation and Memory Effects Using Offset Multisine Excitation

This paper proposes a new class of multisine excitations that allows efficient characterization of nonlinear circuits. By offsetting the frequency of tones, one can distinguish between different intermodulation products in a multisine response. This property leads to many applications for nonlinear circuit characterization, such as in-band distortion measurements, memory effects characterization, and model performance assessment. Some applications are highlighted in this paper, focusing especially on the characterization of memory effects. The effectiveness of the approach is demonstrated with a series of measurement results.

All-digital cancellation technique to mitigate self-jamming in uplink carrier aggregation in cellular handsets

Future handsets employing uplink carrier aggregation to increase transmit data rates will experience severe degradation in receiver sensitivity due to intermodulation products created by the nonlinearity of switches and duplexers in the RF front end for a number of LTE band combinations. To maintain the same receiver sensitivity an all-digital cancellation algorithm is proposed that relies solely on the digital representation of the signals, a peak covariance search for time alignment, and a recursive least squares (RLS) adaptive filter. This technique provides up to 20 dB improvement of signal-to-interference-plus-noise ratio (SINR), for 5-MHz LTE signals.

An Ultra-Broadband Direct Demodulator for Microwave FM Receivers

A new broadband frequency discriminator is introduced for demodulating the frequency modulated signals in the microwave frequency range. Direct demodulation with no need for tuning the center frequency of the resonance circuits is the most important advantage of the proposed technique. This technique uses the in-phase/quadrature demodulation, in some manner, without using any additional local oscillator for down conversion. Simulation of the proposed demodulator has been done with Advanced Design System software to evaluate and predict the system behavior. A setup based on the proposed method was designed and implemented in order to verify the accuracy of the theory. We tested the proposed frequency discriminator for FM signals at different microwave frequencies with various waveforms of the modulating signal. We also measured the bit error rate of the demodulator when the modulating signal is pseudorandom binary sequences for some data rates. To the best of our knowledge, this structure demonstrates the widest bandwidth direct demodulator without any tuning circuits among published FM demodulators to date.

Digital cancellation technique to mitigate receiver desensitization in cellular handsets operating in carrier aggregation mode with multiple uplinks and multiple downlinks

Recent explosive growth in uplink and downlink carrier aggregation in cellular networks is leading to severe desense in receivers for deployment of certain band combinations. In this paper, we studied receiver desense caused by 2nd order nonlinearity of components in the signal chain. A practical case of two (bands 3 and 8) uplink aggregation and three (bands 3, 8 and 26) downlink carrier aggregation was considered to demonstrate greater than 20dB desense in band 26 receiver despite using state of the art frontend components including linear diplexer with IIP2 greater than +90dBm. We developed a digital cancellation technique that is capable of achieving greater than 20dB improvement in signal-to-interference-plus-noise ratio for 10MHz LTE signals.

A Watt-Class, High-Efficiency, Digitally-Modulated Polar Power Amplifier in SOI CMOS

This paper presents a digitally-controlled polar power amplifier implemented in 0.18 um SOI CMOS technology. The output amplitude is determined by a 10 bit Amplitude Control Word (ACW) which controls 31 unary cells and 5 binary-weighted cells. Each unit cell is designed as a 4-stacked FET amplifier to achieve high power. The Digital Power Amplifier (digital PA) achieves peak power of 31.6 dBm at >65% drain efficiency at 900 MHz. Peak power and efficiency are both the highest reported to date for CMOS digital PAs. For 5 MHz WCDMA uplink signals, the digital PA gives 28.3 dBm average output power at 49.5% average drain efficiency while meeting ACPR requirements.

Modeling of Deterministic Output Emissions of Power Amplifiers Into Adjacent Receive Bands

This paper discusses the measurement and modeling of the deterministic components of power amplifier (PA) emissions into neighboring receive (Rx) bands caused by PA nonlinearity, and proposes ways to distinguish these components from stochastic components. A method is presented to determine the orders of nonlinearity that are the principal contributors to the Rx band emissions. A Volterra-based model for their estimation is proposed, along with considerations for estimation accuracy. A criterion based on the matrix condition number for efficient pruning of the Volterra-based models is also presented. The proposed techniques are verified with measurements. The proposed model can be used to gain a deeper understanding of the nonlinearity mechanisms responsible for PA spurious emissions, and offers the possibility of canceling the deterministic components to improve receiver sensitivity.

A New Phase Shifter-less Delay Line Method for Phase Noise Measurement of Microwave Oscillators

In this paper a new method for measuring phase noise of microwave oscillators based on delay line frequency discriminator is proposed. Elimination of phase shifter is the major advantage of this technique over the traditional delay line technique. By using this new technique, manual or electronic tuning of phase shifter to reach phase quadrature at the phase detector input ports is not needed anymore. A 90-degree hybrid is used in this technique and another path including a phase detector and LNA is added. Finally by using a dual channel FFT analyzer and performing some processing over the sampled data of the two channels, the phase noise of the oscillator will be extracted. A setup based on the proposed method was constructed and the phase noise of a 3 GHz phase locked oscillator was measured via three methods; the traditional delay line method, the phase shifter-less method and direct spectrum reading from spectrum analyzer. Comparison of the measured data of the three methods shows the validity of the proposed method.

Signal generation algorithm for digital polar transmitters with reduced receive band noise

Digital polar transmitters are under development for multiband handset applications, but typically lead to excess Rx band noise (RxBN). In this paper, a technique to improve the RxBN of a digital polar transmitter is demonstrated. Linear phase FIR filters are applied to both envelope and phase signals, so that the RxBN becomes relatively insensitive to transmitter non-idealities. At the same time, there is only small degradation of ACLR and EVM. Noise shaping algorithms are also applied to reduce the envelope quantization noise. For a WCDMA signal at 1.75 GHz, with a corresponding Rx band at 1.845 GHz, we demonstrate RxBN of -142 dBm/Hz in simulation and -125 dBm/Hz in experimental measurements.