Two-stage digital down-conversion of rf pulses

Abstract

A two-stage digital down-conversion device for optimal detection of varying RF pulses incorporates a front end analog to digital converter (ADC), which samples an input RF signal and performs a first stage digital down conversion in wide bandwidth by means of two digital local oscillator multipliers, low pass filters and decimators. A stream of first stage quadrature I and Q samples is analyzed by a first stage I/Q processor. The I/Q processor generates an RF pulse trigger based on a first-stage envelope signal, center frequency and frequency span data which are used for a second stage narrow band digital down-conversion. The second stage digital down-conversion is based on mixing the first stage I and Q data samples with a second stage local oscillator, further low pass filtering and decimation using a second bandwidth. A stream of second stage I/Q quadrature samples has an optimal signal to noise ratio and allows accurate estimation of RF pulse parameters (magnitude, phase and frequency) by means of a second I/Q signal processor and/or by storing second I/Q data for subsequent processing and analysis.