D68/4_CHANNEL 3

DESCRIPTION

The ASA is the most advanced signal processor available for PDI applications. It is a Fourier transform-based signal processor with several innovations to ensure optimum performance. The optical signal collected by the PDI optics is converted to a voltage using a PMT/pre-amplification system. The signal is then high-pass filtered and amplified before being fed to the ASA analog section. Within the analog section, the signal is mixed with a software-selectable variable quadrature mixer. The quadrature mixer outputs are low-pass filtered to improve signal SNR. The quadrature outputs of the analog section are sampled and digitized at a software-selectable sampling rate.

The digitized signal is then applied to the phase domain burst detector. The Phase Burst Detector (PBD) output is combined with the analog burst detector output and then used as an input to the adaptive sampling circuitry. The sampled data for each Doppler burst is then packed into a single data packet. The data packets are stamped with other relevant information (time of arrival, transit time and external input data) and transferred to the computer via a high-speed PCI interface card.