Digitally controlled RF CMOS power amplifier for polar transmitter

Abstract

The demand for wireless technology has dramatically increased in recent years. The cellular telephony throughout the country uses a number of standards including GSM, PCS-1900, and WCDMA. In addition, multiple standards have also emerged for wireless data such as 802.11a, 802.11b, 802.11g, and Bluetooth. Multiple standards have evolved for many reasons and consequently offer a variety of options for the end user. Integrated circuit technology has played a key part in this advancement, as have improvements at both the circuit and the system level. The ability of the technology to deliver high performance, low-cost electronics. The polar transmitter has emerged as a promising system-level approach to realizing efficient transmitter architecture. PAs for polar transmitters can be switching-mode amplifiers, which are much more efficient than linear PAs. The PAs may have constant input power, and the envelope information is loaded through regulators such as low voltage dropouts or dc-dc converters to control their supply voltages. However, those amplitude modulators in analog polar transmitters suffer from low efficiency and limited bandwidth. Digitally controlled PAs (DPAs), which have been proposed recently, can overcome these difficulties. In such a mixed-signal polar transmitter, the number of sub-PAs are activated or deactivated by digital control signals to realize amplitude modulation. Each sub-PA is implemented as an efficient switching PA. After linearity to meet EVM and mask performance, power efficiency is the most important specification for wireless transmitters. In most portable applications the transmitter is the highest power consuming block in the system because of the high power requirements of the PA. Since power levels in wireless transmitters tend to be highly variable, average efficiency tends to be a better metric of performance than maximum efficiency. The DPA has a high power and high efficiency theoretically, however there are some dr...