Conferences

A Broadband LNA Design in Common-Source Configuration for Reconfigurable Multi-standards Multi-bands Communications

The design of broadband low noise amplifiers (LNAs) for reconfigurable and real-time multi-standard multiband RF/microwave transceiver requires a holistic design trade-off for a given active device configuration. The common-source configuration generally yields moderate gain, narrow bandwidth and compensated stability for the lowest noise figure response. This paper presents a novel single-ended LNA topology that achieves high gain, broadband and very low noise in the common-source configuration. The pseudomorphic high electron mobility transistor process technology was utilised over the C- and K-band frequencies. The GaAs-based active device libraries came from two different foundries. The simulation results show that the reported circuit topology yielded gain and noise figure responses of 37.6 dB and 0.5 dB (over 4–8 GHz); and 30 dB and 1.0 dB (over 18–21.6 GHz). The minimum stability factor was higher than 4 at the respective centre-design frequencies and the in-band ripples were 5% (C-band) and 4% (K-band) relative to the 3 dB communication threshold. These results enable the reported broadband LNA to accommodate a wide dynamic range for multi-process technologies. The presented LNA designs can combine multi-band direct-conversion RF transceiver with embedded field programmable gate array processing to provide a multi-standard radio solution for reliable and cost-effective capability-based communication solutions.

A Transmission Line-Based Load Compensation Network for Outphasing Power Amplifiers

The outphasing concept proposed by Chireix in 1935 is an effective method to address the efficiency drop in power amplifiers caused by modulated signals exhibiting high peak-to-average power ratios. In outphasing, the efficiency is preserved by amplifying two constant amplitude signals. Amplitude modulation, now contained as phase offset between input signals, is reconstructed at the combiner stage by performing vector summation of the two constant amplitude signals.

One of the key elements enabling high efficiency in Chireix outphasing is the load compensation network, traditionally realized by a shunt reactance at the output of each saturated amplifier. This paper presents an alternative way of realising this network, which has the advantage of not requiring additional discrete components to provide the aforementioned reactance. Instead, the same effect is achieved using simple transmission lines in series with the output of each amplifier, here named offset transmission lines (OTLs).

At 2 GHz, the fabricated prototype amplifier maintains an efficiency greater than 50% over an output power back-off in excess of 8 dB.  Drain efficiencies higher than 65% and 40% are maintained over 5.5dB and 10dB output power ranges respectively, while achieving a maximum combined output power of 44.5 dBm.

Cost-Effective Hybrid Input-Matched GaN Transistor for S-band Radar Applications

The use of Gallium Nitride (GaN-on-SiC) technology in high performance RF power amplifiers (PAs) is now widespread. Whilst the per-area cost of GaN-on-SiC has dropped significantly in recent years it is still higher than competing technologies, and as active phased-array radars can contain hundreds of amplifiers any cost reduction that can be achieved quickly adds up. At the same time, the RF performance of the system is paramount, and GaN-on-SiC can be used to design power amplifiers that have excellent power and efficiency.

This paper describes the design of the QPD1020 hybrid input-matched GaN transistor, which includes internal input matching for 2.7 – 3.5 GHz realised on a passive GaAs die. This transistor provides the performance of GaN with the convenience of internal input matching at a reduced cost compared to a GaN MMIC. The QPD1020 can be used as an output stage in an active phased-array radar system or as a driver amplifier for a higher power output stage. An accompanying PA reference design with an output matching network tuned for optimum efficiency between 2.7 to 3.1 GHz is also described.

Frequency Selective Surface with Miniaturized Elements: a Different Approach

Recently, many approaches have been proposed to miniaturize the dimensions of frequency selective surface (FSS) array elements. This is usually achieved by increasing the equivalent electrical lengths of array elements. In this paper, a different approach is proposed to realize the miniaturization by making use of the capacitance between adjacent layers of an FSS. Such an FSS will not only have a very small element size, but also have an extremely low profile. The element size is one of the smallest reported so far to the authors’ best knowledge.

Mutual Coupling Impact on GaN Power Amplifiers in Antenna Array Systems

Multiple-input multiple-output (MIMO) technologies have become fundamental for telecommunications. In the fifth-generation (5G) standard, the MIMO system requires multiple independent radio frequency (RF) paths to excite an antenna array. In one possible implementation, each RF path has its own power amplifier (PA), whose performance is compromised due to the mutual electromagnetic coupling between the radiating elements. Consequently, the performance of digital pre-distortion (DPD) techniques can be compromised, negatively impacting the linearity of the PA. This impact on the PA behaviour does, in turn, affect the bit error rate (BER) performance due to the fact that certain digital modulations proposed for 5G, such as quadrature amplitude modulation (QAM), are extremely sensitive to the PA non-linearities.

Although this topic has been actively examined, there are few experimental measurements of the interaction between DPD techniques and PA load impedance mismatch in the literature. Moreover, measurements of GaN PAs, which can be used in multi-user MIMO systems due to their high power capabilities, under mismatched conditions are scarce. As different device technologies may have different behaviours when it comes to their linearity characteristics and load impact, this paper aims to present measured results to show the output impedance variation impact on the performance of a GaN PA. The figures of merit considered for this purpose are the normalized mean-square error (NMSE), for the in-band distortion, the adjacent channel power ratio (ACPR), for the out-of-band distortion, and the power added efficiency (PAE). Two GaN PAs are tested: a Class-A and a Class-AB.

RF Performance Potential of Diamond Field Effect Transistors

Diamond possesses a range of unique properties that make it of interest as a robust semiconductor platform for the production of high power and high frequency RF devices. Such properties include a large bandgap of 5.5 eV, intrinsic electron and hole mobility ~ 3000 cm2/V.s and an extremely high thermal conductivity of 300 W/m.K.

Despite diamond’s semiconductor potential, progress towards the production of mature, high performance diamond electronic components has predominantly been limited by the difficulty associated with doping. Substantial progress has been made in recent years however towards the development of high frequency devices such as field effect transistors.

We will present an overview of progress in the area of diamond RF device performance and show results achieved at the University of Glasgow that demonstrate the highest frequency performance yet achieved for a diamond-based transistor (fT = 53 GHz). These results shed light on the intrinsic high frequency limitations of this technology and highlight areas of research that must be prioritised moving forward to advance its maturity and performance potential.

The Dual-Input Doherty Amplifier

The Doherty Amplifier, since its invention almost 100 years ago, has enjoyed something of a renaissance in the last 20 years. Proliferation of digitally modulated signals, increasingly noise like in their signal statistics, along with semiconductor device technology advancements, have fuelled this rediscovery process.

As Engineers try to squeeze remaining drops of performance out of their Doherty designs, there's an increasing awareness that there are significant gains to be made departing from the industry standard 3dB/90deg. fixed RF input split network.

By measuring the Doherty amplifier as a dual-path/dual-input device, and stimulating those two inputs with a range of different signals, it is possible to identify best performance and to understand the performance trade-offs and sensitivities.

Armed with that information, the Engineer is then empowered to make the best design decision. The presentation will be accompanied by a live, automated, measurement demonstration.