Compensated chirp fourier transformer

Abstract

A method and circuit for compensating a chirp Fourier transformer wherein alignment tones of known frequency are provided in the input signal, and the transforms of the alignment tones in the output signal are measured. The output signal is converted to baseband and digitized at intervals defined by a clock signal which is generated at a rate proportional to the spacing of the transformed alignment tones. As the temperature varies, displacement of the transformed alignment tones is detected and the clock is slued such that each sample of the baseband-converted output corresponds to a fixed bandwidth segment of the input signal. In one construction, an identical SAW element generates a delayed replica which is used as a baseband conversion reference to convert the output to baseband. In a preferred embodiment, all reference frequencies are synthesized from a common clock synchronized to the input frame, and phase and frequency compensating loops adjust the output sampling clock and the baseband conversion reference waveform.