Ultra wideband AGC and VGA designs for software radio applications

In this paper we discuss a CMOS based wideband VGA configuration designed in 0.18 mum UMC process providing a gain of 21 dB and bandwidth of 360 MHz with control voltage range of 1.0 V to 1.6 V. The results of the design were verified through layout. Further, the design was modified to incorporate it in an AGC for Software radio applications. The design process resulted in two ultra wideband VGA designs. The first VGA has a 3 dB bandwidth of 3.2 GHz (800 MHz to 4 GHz), a maximum gain of 23 dB and an operating range of control voltage from 0.8 V to 1.4 V but larger active area. The second VGA designed using only NMOS transistors has relatively reduced active area, a bandwidth of 2.4 GHz (800 MHZ to 3.2 GHz), a maximum gain of 24 dB and an operating range of control voltage from 1.1 V to 1.6 V. The power consumption of both the VGAs is 6 mW at 1.8 V supply voltage. Compared to existing architectures, these designs provide much higher bandwidth and consume relatively low power. One of the VGA designs was then used to implement a wideband AGC for software radio applications. Based on the results obtained, modifications needed to obtain the complete AGC design are discussed in the end. Both the ultra-wideband VGAs and AGC have been designed and optimized in Mentor Graphics Eldo simulation software with TSMC process technology and the layout was done in Cadence Virtuoso XL Layout Editor.