Introduction - Linear CMOS RF Power Amplifiers for Wireless Applications - page 2

amplifier must comply with both IEEE 802.11a and 802.11g standards, for instance,
it should be able to operate in both the 2.4 and 5.2 GHz bands. In this topic, we call
this feature the frequency-tunable capability.
Both issues make up part of the scenario of present and future local and personal
area networks. Increased comfort and more liberty to the user can be achieved when
these issues are addressed.
Units
The units of the SystèmeInternational (SI) are used throughout this document.
The power gain is always expressed in dB, whereas the primary unit for power
is dBm and the secondary is W—always given in parentheses after dBm.
1.2 Objectives
1.2.1 Efficienc Enhancement
One of the objectives is to develop a Complementary Metal-Oxide-Semiconductor
(CMOS) RF PA in which the linearity-efficiency trade-off is mitigated, so that it can
be used in a system employing a variable envelope modulation scheme. To achieve
this, the dynamic supply technique is used. It combines a high-efficiency, fast modu-
lator operating in switched-mode and a linear PA. The effectiveness of this principle
had already been demonstrated in a previous work [ 4 ] by Schlumpf. In his the-
sis, Schlumpf used a discrete power amplifier based on silicon bipolar transistors
for Code-Division Multiple Access (CDMA) applications at 1.9 GHz. This topic
presents a system designed in a 0.11 µm CMOS technology, in which both the mod-
ulator and the PA are integrated on the same chip.
The interest of an implementation in CMOS of an existing solution in bipolar
technology resides mainly on the pursuit of the so-called single chip radio. Such
an integrated circuit (IC) would allow increased functionality to be added to mobile
devices since more room is freed by the integration of all the parts of a transceiver on
the same die. The integration of a whole transceiver implies its realization in CMOS
technology which is undoubtedly the most appropriate for the required digital signal
processing circuitry due to its high level of integration, low cost, and high yield.
Nevertheless, the design of an RF PA in CMOS technology has two major hur-
dles: first, the lower breakdown voltage due to scaling down in technology that re-
stricts the maximum output power; and second, the reduced transconductance of
MOS transistors leading to inferior power gain and poorer efficiency.
1.2.1.1 Specification
The target frequency of operation is 5.2 GHz and the desired maximum output
power is 16 dBm (40 mW)—maximum output power defined for the Unlicensed