A VXI-bus frequency-agile digital filter/analyzer

A significant recent development in ATE design is the virtual instrument. A virtual instrument is usually defined as the use of data acquisition hardware with software executing on a general-purpose computer to emulate such test instruments as oscilloscopes and frequency counters. These instruments are virtual in the sense that software determines their functionality. Applying this idea to filtering, a VXIbus instrument has been developed that provides high-speed, reconfigurable digital filtering. This paper addresses the architecture and applications of this instrument; a frequency-agile Digital Filter/Analyzer (DFA). Combining programmable FIR digital filter processors with a general-purpose DSP, the instrument can act as programmable lowpass, highpass, bandpass, bandstop or variable delay line filters, with cutoff frequencies in the HF region. The instrument's built-in filter design firmware can create Hanning-windowed filter configurations with arbitrary cutoff frequencies. Alternatively, the user can use software on the host computer to compute and upload filter coefficients. Multiple filter configurations from either source can be stored in the instrument's memory and transferred to the digital filter automatically or on command by the DSP and firmware. The instrument's firmware features a filter analysis package. While the filter processors operate in real-time, the DSP performs Fourier analysis on any one of the following: the filter's input spectrum, output spectrum, or its impulse response. This unique feature allows the instrument to analyze its performance.