High Performance and Low Power Consuming MIMO Systems using Adaptive Antenna Combining in the RF Domain
Eickhoff, R¹; Mayer, U¹; Ellinger, F¹; Scheytt, C^2
1Dresden University of Technology; ²IHP Microelectronics

As today's computing is expected to become more and more ubiquitous oriented, decentralized mobile networks will become very important and market analyses predict rapidly growing markets. High speed wireless networks can be realised by exploiting the large bandwidth available at very high frequencies, e.g. at 60 GHz or above. However, the corresponding hardware is expensive, the power consumption is high, and the coverage range and reliability is rather limited. A promising concept mitigating these drawbacks is the multiple-input multiple-output (MIMO) approach, where multiple active antennas and smart control algorithms are applied in the transmitter and/or the receiver. In this paper, a transceiver for high spectral efficient wireless MIMO-system at ultra compact size and low power consumption is proposed.

The transceiver consists of several parallel transmit and receive antennas that allow an improvement in diversity. In contrast to state-of-the-art MIMO, the transceiver performs several signal processing tasks already in the RF domain that relaxes the requirements of the digital signal processing hardware and the receiver and transmitter chains respectively.

For the signal processing in the analogue front-end, signal-combining circuitry in SiGe-BiCMOS technology is developed that is able to control phase and amplitude of the received/transmitted signals independently with low phase and amplitude variations. In the past, such circuits have been designed in III/V technology, which increases the costs, and, therefore, those circuits are not suitable for mass fabrication. With silicon processes, stronger degradations in phase and amplitude variations are expected because of lower Q-factors of the varactors and the variable loads. Consequently, to compensate these impairments, innovative concepts for the amplitude control circuits and the phase shifters are developed.

Phase shifter concepts for low amplitude variations are proposed in this paper, which achieve a linear phase tuning characteristic and where the phase setting is self-calibrating to the input frequency. The amplitude control circuits consist of innovative biasing concepts that prevent bias changes during gain control and, therefore, precise amplitude control with negligible phase variations is achieved. The transceiver is designed for WiFi applications around 5 GHz. However, because of the universal signal processing concept, the approach can also be applied for other communication standards such as WiMAX or UMTS.