Tero Ranta

Antenna switch linearity requirements for GSM/WCDMA mobile phone front-ends

The design of the RF front-end part in modern cellular phones is becoming increasingly complex and demanding due to increasing number of frequency bands and modes that the phone needs to operate in. One of the main components of the RF front-end is the antenna switch that selects which TX/RX path is connected to the antenna. This paper considers the linearity requirements for antenna switches used to switch full-duplex WCDMA signals. The most demanding linearity requirement for WCDMA is shown to be the RX out-of-band blocking performance. The out-of-band blocking problem is shown to be caused by the three dominating intermodulation distortion (IMD) mechanisms of the switch. The switch IMD performance is also shown to depend on the relative phase shift between switch and duplexer. Two measurement setups are shown with measured results

CMOS based Tunable Matching Networks for cellular handset applications

The explosion in the number of connected cellular devices and ever-increasing data bandwidth requirements has increased the number of bands a modern cellular device must support. This places stringent requirements on cellular handset antennas, as they need to cover more bands than ever before, while meeting increasing Total Radiated Power (TRP) requirements. A potential solution to this problem is achieved by the use of Tunable Matching Networks, which can maximize the transmitted radiated performance and receive sensitivity by optimizing the impedance match between the RF Front End and the Antenna. This paper outlines the challenging requirements placed on tunable components, presents a Tunable Matching Network utilizing Digitally Tunable Capacitors (DTCs), and proposes a method for evaluating the improvement this network brings to the cellular handset.

RF Front-End Tunability for LTE Handset Applications

The deployment of LTE in the frequency range of 700 - 800 MHz is now occurring widely to support increased data application demands. Extending handset operation to lower frequencies in addition to existing bands results in up to 10 dB degradation of the radio link performance due to fixed matching networks. Solutions for tunability of the handset RF Front-End have been slow to develop, mainly attributed to the high operating voltages and wide tuning range requirements of the handset application. This paper outlines the requirements for handset RF Front-End tunability and presents a reconfigurable front-end impedance matching network utilizing digitally tunable capacitors (DTCs). Through the use of this tunable matching network, mismatch loss between the RFFE and the antenna can be reduced by up to 5dB.

The state-of-the-art in silicon-on-sapphire components for antenna tuning

Increased spectrum coverage by mobile wireless devices is dictating the need for active antenna systems. Silicon-on-Sapphire (SOS)-based Digitally Tunable Capacitors (DTCs) and switches enable tunable matching networks and dynamic adjustment of antenna electrical characteristics. Advancements in technology and design techniques have enabled improvements in DTC electrical performance. This paper addresses advancements in DTC and switch capabilities and the resulting improvements in antenna operating bandwidth.

Comparison of substrate effects in sapphire, trap-rich and high resistivity silicon substrates for RF-SOI applications

This paper compares insertion loss, harmonics and Q-factor of sapphire, trap-rich silicon and high-resistivity silicon substrates. The concept of substrate characteristic frequency is shown to be useful metric to evaluate substrate behavior. New methods to evaluate substrate properties are introduced using open CPW stubs and parallel plate capacitors. It is demonstrated that sapphire provides the best RF performance, while trap-rich silicon offers limited but adequate performance with a resistivity around a few kΩ-cm. High-resistivity silicon provides the worst RF performance due to unmitigated parasitic conduction.

High performance 1.8–2.4 GHz phase shifter using silicon-on-sapphire digitally tunable capacitors

This paper introduces the design and implementation of a high performance phase shifter using 5-bit Digitally Tunable Capacitors (DTC) and a miniature surface-mount quadrature 3dB coupler. The phase shifter covers > 85o of phase shift from 1.8-2.4 GHz, with an average insertion loss (IL) of 0.7+/-0.3 dB at mid-band, and 2° phase resolution using two asynchronously tuned DTC over the states with S11 <; -10dB. The measured IP3 is > 58 dBm across all states and the 1 dB power compression point (P1dB) is 10W over the major states. The overall size for the entire circuit is approximately 1 cm2. We believe this hybrid phase shifter represents state-of-art power handling, linearity, insertion loss, phase shift resolution, operational bandwidth and small size for phase-shifter designs using any phase-shifter topologies and fabrication technologies.