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Unformatted text preview: IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 32, NO. 5, MAY 1997 745 A 1.5-V, 1.5-GHz CMOS Low Noise Amplifier Derek K. Shaeffer, Student Member, IEEE , and Thomas H. Lee, Member, IEEE Abstract— A 1.5-GHz low noise amplifier (LNA), intended for use in a global positioning system (GPS) receiver, has been implemented in a standard 0.6- " m CMOS process. The amplifier provides a forward gain (S21) of 22 dB with a noise figure of only 3.5 dB while drawing 30 mW from a 1.5 V supply. In this paper, we present a detailed analysis of the LNA architecture, including a discussion on the effects of induced gate noise in MOS devices. Index Terms— Amplifier noise, induced gate noise, low noise amplifier, microwave amplifier, MOSFET amplifier, noise figure, random noise, semiconductor device noise. I. INTRODUCTION R ADIO frequency designs are increasingly taking advan- tage of technology advances in CMOS that make possible the integration of complete communications systems. As an example, global positioning system (GPS) receivers employ extensive digital signal processing to perform acquisition, tracking, and decoding functions. The use of CMOS tech- nologies for implementation of the front end electronics in a GPS system is therefore attractive because of the promise of integrating the whole system on a single chip. The first step in achieving this goal is to test the suitability of present-day CMOS for the task of low noise amplification at multigigahertz frequencies. Received GPS signal power levels at the antenna are around 130 dBm, and this low level degrades further in the presence of physical obstructions such as buildings and trees. Hence, a good amplifier is critical for enabling robust performance in obstructed environments. One possible threat to low noise operation is the well- documented, but relatively unappreciated, excess thermal noise exhibited by submicron CMOS devices [1]–[4]. This noise is believed to arise from hot electron effects in the presence of high electric fields. Despite this excess noise, recent work has demonstrated the viability of CMOS low noise amplifiers (LNA’s) at frequencies around 900 MHz [5]–[7]. As we will show, CMOS is also a suitable medium for implement- ing a GPS receiver, which must receive signals centered at 1.575 42 GHz. To provide some background, Section II presents a re- view of recent LNA work in various technologies in the 900 MHz–2 GHz frequency range. A thorough mathematical treatment of the LNA architecture that we have chosen is presented in Section III. It is our hope that this treatment will be useful as a guide in future design efforts. In pursuing this goal, we will consider the effect of induced gate noise in Manuscript received August 20, 1996; revised November 24, 1996....
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