UWB Transmitter Design

Abstract

In this chapter, we present the design of a sub-nanosecond tunable monocycle pulse transmitter for low-power short-range UWB applications. The transmitter is made up of a clock driving circuit, a SRD coupling circuit, a backward decoupling circuit and two distributed delay-lines. The clock driving and SRD coupling circuits improve the output power and transition speed. Using opamp and buffer IC’s for the clock driving circuithas greatly simplified the circuit design. In the SRD coupling circuit, a simple RC filter structure is used to achieve near optimal bias condition for the SRD without external, complicated bias control circuit. A backward decoupling circuit is designed to reduce ringing in the output monocycle pulse. Tuning of the output monocycle pulse duration is achieved by alternately switching on and off the p-i-n-diode pairs spatially located along the delay lines. The employed tuning method is easy to implement and results in a compact circuit structure. The developed tunable monocycle pulse transmitter achieves varying pulse duration from 0.4-1.2 ns, corresponding approximately to the operating frequency range of 0.15-3.7 GHz, and 200-400 mW of peak power. These results show that the designed monocycle transmitter with advanced tuning capability can be used for most short-range UWB applications, even for high-resolution radar applications such as UXO and land-mine detection. The impulse generator, developed along with the tunable monocycle pulse transmitter, exhibits a performance of 160-ps FWHM and 8-V peak amplitude and can also be used for UWB systems. Comparison between the tunable impulse generators employing p-i-n diodes and MESFETs as the switching elements shows the MESFET impulse generator produces relatively less distorted and more symmetric pulses than its p-i-n-diode counterpart. The MESFET tunable impulse generator also does not require DC blocking capacitors and is thus simpler.