A Vector Signal Analyzer (VSA) combines traditional superheterodyne technology with modern high speed Analog to Digital Converters (ADCs) and Digital Signal Processors (DSPs) to perform spectrum measurements, demodulation and time-domain analysis on time-varying and complex modulated signals. These capabilities make the VSA an ideal instrument for communications, radar/sonar, video, and many other applications.
The common sub-systems include:
After amplification or attenuation and filtering, the RF input signal goes through one or more frequency translation stages to downconvert the signal to the Intermediate Frequency (IF). Key specifications include phase noise and jitter.
The commercial availability of very high-speed ADCs played a key role in the emergence of the Vector Signal Analyzer class of instruments. Bandwidth, dynamic range and signal to noise ratio are key specifications for these ADCs.
Digital Signal Processing
The bulk of the signal analysis functions are implemented in software running on the DSP. The software enables a VSA to characterize complex modulated, time varying signals in terms of spectrum, modulation and waveform analysis. The input to the DSP based software is sampled I/Q vector modulated signals generated by different wireless and wireline communication standards. The receive chain is implemented in the DSP, which includes modulation/demodulation, channel decoding, MIMO processing, equalization, multipath fading compensation etc. Typical analysis functions include swept spectrum analysis, wideband FFT signal analysis, high speed continuous measurements including CCDF, power spectral density, auto-correlation and coherence measurements etc. Optionally it enables standards-based modulation analysis, vector signal generation, and Burst Error Rate (BER) measurement. Software implementation provides the inherent advantage of quick and easy implementation of new features, modifications to existing features and supporting multiple standards and technologies. The TI DSP architecture lends itself to very power and code efficient and fast execution of math intensive signal processing algorithms, which are common to all complex communication standards. Along with very high speed C64x+ cores, TI DSPs have other performance enhancing features such as large amounts of internal memory, multiple high speed I/O and high speed external memory interfaces to process the large amounts of sampled data.
Power Management and Conversion
Vector Signal Analyzers exist in various form factors such as bench, portable, and modular (or backplane based). The form factor plays a large role in determining the power management requirements of the instrument. For example, many bench VSAs are based on a computer architecture, leveraging display, interface, and power management functions from the high-volume PC market. Other VSAs operate from batteries for use in field service applications. Texas Instruments offers power management solutions for each of the available instrument form factors.