Variable gain amplifiers (VGA) with temperature-independent linear-in-dB gain characteristics for wireless communication

Abstract

This thesis describes the design and implementation of variable gain amplifier (VGA) circuits for WCDMA, DSRC, and UWB applications. The focus is on the development of a design methodology for a VGA design in CMOS and BiCMOS technologies with temperature-independent linear-in-dB gain control characteristics. Research approach to design a VGA is different according to a process technology and its communication system. Therefore, we design each VGA cell suitable for its process technology and VGA requirements for WCDMA, DSRC, and UWB applications. Prior to VGA design, we propose a control signal conversion circuit, as it is called a voltage-to-current converter (VIC), including a temperature and supply-voltage compensation method for applying to three VGAs. At first, we describe a SiGe BiCMOS transmitter IC for WCDMA applications. It consists of an up-conversion mixer and a variable gain driver amplifier (RF VGA). To satisfy the VGA requirements with RF performance and VGA performance, we propose and demonstrate a current steering structure VGA. The mixer (UP-MIX), based on the MICROMIXER, utilized an IF transconductance stage with a cross-coupled type to improve the balancing property and linearity and uses a double balanced-type switching stage to isolate LO and IF signals at the output. The proposed Tx IC is achieved greater than 30 dB of a gain control range and has a highly linear characteristic with an output IP3 of 25 dBm, successfully operates in an accurate linear-in-dB up to the maximum gain and achieves a gain error less than ±1.2 dB over 25 ~ 80 ℃ and 2.7 ~ 3.3 V supply voltage using the temperature and supply voltage compensation techniques for gain variations. Next, we present a transmitter IC for 5.8-GHz DSRC applications. It consists of a baseband variable gain amplifier, an ASK modulator, and a LO signal source. To satisfy the VGA requirements with high linearity, we propose and demonstrate a triode transconductor with an exponential curren...