ANALOG SIGNAL SYNTHESIZERS have been used for years in communications, radar, and general-purpose testing. The output of these synthesizers is usually a carrier with simple amplitude, frequency, or phase modulation. This is adequate for many applications, but more complex waveforms are needed for others. These more complex waveforms are difficult or impossible to generate with currently available commercial equipment. This has led to the development of the HP 8770a Arbitrary Waveform Synthesizer. The HP 8770A has a digital architecture and an analog output of [plus-or-minus] 1 volt into 50 ohms, from dc to 50 MHz.
An example of a complex waveform that is easily synthesized using the HP 8770A is a simulated radar return pulse with all the distortions, overshoots, and noise that occur in actual operation. Another example of an HP 8770A application is as a calibration source for magnetic media certifiers. A test signal with missing bits, extra bits, or amplitude modulation can be precisely provided. For TV applications, the HP 8770A can be used to add distortion or extra modulation to TV test signals, or to try new scrambling and transmission formats. Many other applications have been demonstrated.
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An external computer workstation (HP 9000 Series 200 or 300), running the HP Waveform Generation Language (WGL), creates the desired final waveform. This waveform is quantized into 4096 amplitude sample points and downloaded, via the HP-IB (IEEE 488/IEC 625), to the HP 8770A memory system. The memory is organized into 512K 12-bit words and has an equivalent access time of 8 ns. The RAM now contains an image of the desired output waveform as represented by amplitude samples uniformly spaced in time. The waveform memory is composed of 8 groups of relatively slow 64K-by-12-bit CMOS RAMs. Using ECL multiplexing, the groups are converted into a 12-bit, 8-ns data stream that sources the DAC.
