Conferences

A Novel Formulation for Defining Linearising Baseband Injection Signals for RF Power Amplifier Devices Under Arbitrary Modulation

It is possible to linearise RF power amplifiers by signal injection, at the output port, using a time varying baseband voltage waveform.  The key is the formulation and optimisation of this time varying baseband voltage. 

This paper will demonstrate that an envelope domain formulation is ideal.  In this formulation, ‘engineering’ the optimised time varying baseband voltage requires the determination of only a small number of constant coefficients. These coefficients should be invariant to changes in the complexity and bandwidth of the RF modulation signal applied.

A large signal waveform measurement system (LSWMS),  modified to enable the measurement of modulated RF signals and provide for the ‘engineering’ of injected baseband voltage waveforms has been used to experimentally investigate and validate this approach.

The investigation and validation experiment was performed on a 10W Cree GaN HEMT device, using a 3-tone modulated RF excitation signal with RF fundamental and all harmonic frequencies terminated into a passive 50ohms.

IM3 and IM5 distortions were successfully suppressed by this approach for an optimum case by the determination of these coefficients, only two coefficients in this case. For the optimum case, the observed level of IM3 and IM5 distortion were reduced to less than -56dBc whilst driving into 1.5 dB of compression.

The advantage of this technique is that it is simple and its implementation is compatible with envelope tracking architectures.

An FMCW MIMO Radar Sensor

There are a number of potential applications for low cost short range phased array radar sensors: ship bumpers, large vehicle sensors and level crossing obstacle detection for example.  Phased arrays have the benefit of reduced size and the elimination of moving parts compared with more traditional rotating antenna systems.  Another potential benefit is that the image update rate can be orders of magnitude faster than that for mechanically steered radars.   Phased array radars have been developed for many years but the high cost has traditionally limited their use to high performance military radars.  Co-located Multiple-In Multiple-Out (MIMO) systems have the potential to mimic the performance of more expensive traditional systems but with substantially lower cost.  Such an example system is presented here using 4 transmit elements and 16 receivers to synthesize a 64 virtual element phased array. An integrated 24GHz sensor has been made and field trials performed which confirm the range and angle resolution performance.

Enabling Technology for Ultra-low-cost RF MEMS Switches on LTCC

Screen printing and laser machining are standard processes for the development of RF circuits on many substrates including ceramics (e.g. LTCC), having low losses from 2 to 10 GHz and low material and processing costs. However, the integration of functional components provides a challenge as semiconductor-based devices are generally very expensive.
In this work we propose a novel idea, which allows the integration of RF MEMS switches on LTCC using low cost materials and assembly techniques. Shunt switches and varactors can be realized using aluminium foil cantilevers, which can be controlled by applying suitable electrostatic actuation.
Basic prototype components have been produced and preliminary tests suggest good mechanical behaviour. It is believed that the enabling technologies developed can be applied to create ultralow-cost RF MEMS switches and varactors.
 

From mm-wave to THz, Scalable Filter Design for Ultra-low Cost Applications

This paper shows simulated and measured results of ultra-low cost filters in the mm-wave and THz bands. It provides a broad overview of the filters currently available and their suitability for ultra-low cost applications. We demonstrate scalable conventional metal mesh filters on standard 525 um quartz and high resistivity silicon substrates. In additional, trapped mode excitation is used to improve out-of-band rejection at higher frequencies. The measured results shows that these filters are scalable in the THz range using cost-effective micromachining manufacturing. This potentially opens up the possibility of using metal mesh filters for ultra-low cost applications.

MMIC Futures

Today the great majority of RF/microwave systems implement various classes of MMICs. There is a vast range of implementations from high-volume smartphones through to AESA radars. Various products are commercially available operating across frequency bands ranging from hundreds of MHz to beyond 100 GHz. This paper focuses on the current state of the MMICs side of the industry, identifies influential trends and developments – and then takes a look at the future. Leading fabricators and fabless concerns are identified and commented upon. The shift from dominantly GaAs-based to increasingly GaN and SiGe-based is considered in some detail – including near-future implications. Estimated market shares are presented.

The description of a balancing act: Envelope Tracking and Digital Pre-Distortion in Handset Transmitters

Envelope tracking requires the addition of another connector to the RF power amplifier. Providing this 'supply modulation'  input  leads to many possibilities for improving the performance of the device, such as substantial improvements in linearity and a reduction in the heat dissipated in the RF PA. If the modulating power supply if efficient, you can reduce energy consumption from the battery. However, it’s not a journey into a land of completely alloyed pleasures for the designer. Having recovered from the shock of being told all the decoupling capacitors worth being called such,  are to be removed, the RF engineer comes back to his design to find while it doesn’t burn his fingers, nasty things can happen to the broadband noise floor. This paper takes a practical look at measuring what happens when you apply ET and DPD, using kit you already have, or can easily get.

Understanding the 3 Level Doherty

The Doherty amplifier is a well known technique for improving efficiency of a power amplifier in a backed off condition. The standard 2 way Doherty amplifier with a peak in efficiency at 6dB back off and full power is commonly used and well understood.  With the use of increasingly complex signals comes the requirement to move the peak in efficiency to higher levels of back off whilst maintaining efficiency up to full power output.  This can be achieved with asymmetrical Doherty amplifiers or by utilising N-Way Doherty techniques. In this paper we will explain from first principles the operation of the 3 Level Doherty architecture based on an NXP design that uses three LDMOS transistors of equal size. Design challenges faced with this type of amplifier are presented and compared against conventional 3-Way Doherty and asymmetrical architectures. Test results are presented which demonstrate a drain efficiency of greater than 40% at 10dB back off.