Fully integrated CMOS impulse UWB transmitter front-ends with BPSK modulation

Abstract

We present the development of a miniaturized broadband Wilkinson power divider on a multilayer organic substrate with integrated thin film resistors. The VSWR for all port for both dividers is better than 1.6:1, the excess insertion loss is less than 1.6 dB up to 18 GHz, and 12 dB of isolation is realized. A size reduction of 43% is achieved. The proposed divider has the widest bandwidth ratio, 9:1, and the most compact size, 9.3 mm by 6 mm. In previous work, researchers have fabricated Wilkinson power dividers on liquid crystal polymer (LCP) with integrated resistors operating in the V-band and the W-band [5], with bandwidth ratios of 1.6:1 and 1.5:1, respectively. Their designs are compact and broadband simply because the fractional bandwidth is higher at higher operating frequencies. Many applications, such as UWB (3.1-10.6 GHz), require a wide bandwidth at lower operating frequencies. Wide bandwidth Wilkinson power combiners/dividers can be realized by cascading multiple sections, which can lead to large sizes. A folded Wilkinson power divider proposed in [6] was implemented on a GaAs substrate with a bandwidth ratio of 3:1, from 15 to 45 GHz.In this article, we report a folded compact Wilkinson divider (see Fig. 1) that achieves a measured VSWR of better than 1.6:1 with a bandwidth ratio of 9:1 and a size reduction of 43%. This is the most compact Wilkinson divider with the highest bandwidth ratio to date. The Wilkinson power divider is implemented on a multilayer LCP substrate. DESIGN CONSIDERATIONSIn this article, a multiple cascading stage technique [4] is used to enhance the bandwidth. A binomial multisection matching transformer is used to ensure a maximally flat passband. An odd-mode and even-mode half circuit is the conventional model used for analysis. In the odd mode, the half circuit is essentially a multisection quarter-wavelength impedance transformer. In this case, a binomial matching transformer is used, defined by the function [7] where C is the reflection coefficient, N is the number of cascaded sections, andUsing the binomial expansion on [1] and equating it to the reflection coefficients derived from the small reflections approximations, one is left with the following results to derive for the impedance of each quarter-wavelength section.where the binomial coefficient is defined asCascading of quarter wavelength sections can increase the bandwidth dramatically and a seven-stage Wilkinson was chosen for our design. CIRCUIT DESIGNIn the frequency band of 2-18 GHz, the length of a quarter wavelength transmission line at the center frequency of 10 GHz is 30 mm. We have used both the folding and circular [8] section techniques to miniaturize the Wilkinson divider. As shown in Figure 1, four circular sections of quarter wavelength transmission lines are printed on top of the LCP substrate and the other three sections on the bottom side. A metal sheet is inserted in the center of the LCP board to provide a ground plane for the top and bottom circular sections. We used Ansoft's high ...