Baseband vector signal analyzer hardware design - HP 89410A electronic test device - Technical

Hewlett-Packard Journal, Dec, 1993 by Manfred Bartz, Keith A. Bayern, Joseph R. Diederichs, David F. Kelley

The HP 89410A combines superior front-end linearity and high-speed data conversion with powerful digital signal processing to provide advanced measurement capabilities. Extensive calibration, flexible triggering, and arbitrary source types provide the accuracy and versatility needed to make the sophisticated measurements required for complex signal analysis at RF information bandwidths.

The HP 89410A vector signal analyzer provides an array of new capabilities to meet the emerging measurement requirements of complex signals that require simultaneous analysis in the time, frequency, and modulation domains. It makes measurements with resolution bandwidths as low as one millihertz and frequency spans as wide as 10 MHz to accommodate the wide information bandwidths of complex and frequency-agile communications signals. Its user interface is familiar to users of traditional swept spectrum analyzers, making it easy to use. With an optional second channel, a versatile source with arbitrary source types, flexible triggering, a built-in disk drive, and a variety of software and hardware options, the HP 89410A provides the upgrade paths necessary to accommodate the most sophisticated user needs.

The HP 89410A measurement engine is based upon powerful digital signal processing technologies that provide its speed and flexibility. The key elements of the hardware that support the HP 89410A's high performance include:

* An exceptionally linear front end with high input impedance capability, input protection, autoranging, and anti-alias protection.

* A high-speed, 25.6-MSa/s (million samples per second), wide-dynamic-range analog-to-digital converter (ADC) that employs a proprietary implementation of large-scale dithering to provide superior linearity

* A custom 25.6-MSa/s digital local oscillator and decimating filter chipset that provide up to 23 bits of effective resolution

* Powerful floating-point signal processing using the Motorola DSP96002, which delivers up to 48-MFLOP (million floatingpoint operations per second) peak performance

* Dedicated display processing using the Texas Instruments TMS34020 graphics system processor, providing up to 60 display updates per second to a color display

* A versatile signal source that provides sine, chirp, random noise, and arbitrary signal types

* Full calibration to provide superior accuracy and signal fidelity

* Flexible triggering with both pretrigger and post-trigger delay and arm delay

* A backplane with slots to accommodate hardware upgrade options.

The block diagram, Fig. 1, depicts the data flow path of the HP 89410A baseband vector signal analyzer. (Note that the HP 89410A and the HP 89440A IF section are identical. All further discussion will refer to the HP 89410A but applies equally to the HP 89440A IF section.) The signal input at the analog front end is amplified and alias protected. Following the analog signal conditioning, the signal undergoes analogto-digital conversion. The digital data, which is sampled at 25.6 MSa/s, is routed to a digital switch assembly and on to a proprietary digital LO and digital decimating filter chipset. The digital LO and decimating filters perform frequency selective band translation. The translated data is then stored in a sample RAM with a capacity of 32K samples per channel, which can be optionally increased to 512K. From the sample RAM, the captured data is bused to the DSP96002 processor and subjected to corrections, windows, FFT algorithms, and other math operations. The DSP also formats the data for viewing and writes the data to the display system. In the final step of the data path, the display processor, the TMS34020 GSP, constructs a trace from the formatted data and presents it to the user on an internal 7.5-inch color CRT. By using the high-speed components in the data path, the HP 89410A's signal processing hardware can process approximately 300 512-point complex spectra per second with display update rates reaching 60 per second.

The data flow path for the source follows a similar sequence leading from the digital processing to the output of the analog source. In contrast to the receiver path, the digital LO and filters operate in the reverse mode in the source path, performing the necessary operations of data interpolation and frequency translation. The interpolated data is converted by the source digital-to-analog converter (DAC) at 25.6 MSa/s. A reconstruction filter and further conditioning circuitry prepare the analog signal to be output on the HP 89410A's front panel. The digital switch assembly between the front-end ADC and the digital local oscillator (LO) and decimating filters allows the digital source to be connected to the receiver data path for diagnostic purposes. Full analog calibration is accomplished by placing the internal calibration source path between the analog source and the two input channels.

Analog Input

The analog input provides the interface between the signal to be measured and the instrument's analog-to-digital converter. Impedance matching, ranging, and anti-alias filtering must be accomplished without compromising signal fidelity. The input must be robust in the face of real-world signals and inadvertent abuse. One input channel is standard, and a second is optional.