With the rapid growth in mobile data traffic due to the recent widespread use of smartphones and other mobile devices, there is an urgent need to increase the communication capability of systems used in cellular phone base stations. As a technical solution to this situation, the extension of the radio frequency bandwidth is considered. The bandwidth extension technology has been applied to the LTE-Advanced, the successor of the currently used LTE mobile communication standard, to increase the bandwidth from 20 MHz up to 100 MHz.
However, associated with the upgrade of cellular systems, there is a major problem of increased power consumption of cellular phone base stations due to the increasing data transmission rate and widened bandwidth. Therefore, radical improvement is required for the power efficiency of RF power amplifiers, which consume most of power required in a base station. Currently, the Doherty amplifier*2 is commonly used due to its high efficiency, however, it can cover only low frequency bands of several tens of MHz, which is insufficient in terms of bandwidth and power efficiency to support the LTE-Advanced system.
Under such circumstances, Sumitomo Electric has succeeded in extending the RF bandwidth of the Doherty amplifier by drawing on its RF power amplifier technology and optimizing the fundamental frequency and the high-order harmonics over a wide frequency range inside the amplifier modules incorporated in the Doherty amplifier.
The features and major specifications of the high-efficiency broadband power amplifier are as follows:
- (1) High power efficiency of 53% or more at a wide band of over 100 MHz (see Fig.1)
- (2) Component cost equivalent to that of the conventional Doherty amplifier
- (3) Applicability for broadband wireless communication systems such as LTE and LTE-Advanced
▲Composition of RRH and high-efficiency broadband power amplifier
Table1 Specifications of the high-efficiency broadband power amplifier
|RF power amplifier architecture
|Adjacent channel leakage power ratio
||LTE, 10 MHz × 2 carriers,
PAPR = 6.5 dB
Fig.1 Features of amplification efficiency and gain by frequency
- *1 Remote radio head (RRH):
A system that transmits and receives wireless signals. It consists of a transmitter with a high-power RF amplifier, a receiver that amplifies the radio waves transmitted from cellular phones, and a duplexer that allows bidirectional communication over a single antenna.
- *2 Doherty amplifier:
An RF amplifier that consists of two types of amplifiers: a carrier amplifier that is in continuous operation and a peak amplifier that supports the carrier amplifier when the output power is high. This saves power consumption at low power output, and accordingly, improves the efficiency of radio communication systems, particularly those with a large difference between the maximum and average output power levels, like the LTE system.
- *3 Drain efficiency:
The ratio of output RF power to supply DC power of an amplifier.