Arbitrary generator
An arbitrary generator , arbitrary function generator or “Arb generator” for short ( English Arbitrary waveform generator, AWG ) is a function generator that can generate output signals of any shape. Arbitrary generators are used in research, development and service for circuit development and optimization, as well as for testing purposes and troubleshooting.
construction
Arbitrary generators work on the principle of direct digital synthesis . The desired signal form is stored in a semiconductor memory, the memory locations of which are called up cyclically by an address generator whose frequency can be changed. A digital-to-analog converter with a subsequent low-pass filter and output amplifier generates the output signal from the numerical values. A central microprocessor controls all functions of the generator and allows programming of the device via keyboard and display, but also via interfaces to computer systems ( e.g. IEC bus or USB ).
The properties of an arbitrary generator are essentially determined by its sampling frequency. According to the sampling theorem , the highest frequency (component) occurring in the output signal can reach a maximum of half the sampling frequency, but in practice a little less due to the finite slope of the anti-aliasing filter. The word length (in bits) of the signal memory and D / A converter determines the achievable signal-to-noise ratio and thus the realizable signal complexity. Good standard devices today offer sampling rates of 50 MHz and signal frequencies of up to 20 MHz with 14 bit resolution and at least 64 K (65536) words memory depth. Top devices achieve signal frequencies of 500 MHz with 15 bit resolution and 16 megasamples memory depth.
Thanks to digital synthesis, very slow signals can also be generated. The signal distortion is essentially determined by the quality of the D / A converter and is therefore generally much lower than with conventional function generators, but the spectral purity of special sine and HF generators is not achieved.
application
Arbitrary generators are used as a universal signal source in development, research, test and service. Thanks to its programmability, an arbitrary generator can replace several separate, specific devices. The basic functions of a function generator (sine, triangle / sawtooth and square / pulse signal) can usually be called up directly with manually operated devices. Also, amplitude or frequency-modulated versions of these signals as well as " bursts " (packets of oscillations with pauses between them) are easy programmable, calculates the desired waveform in either case, the built-in microprocessor and stores it in memory. However, there are also arbitrary generators that are controlled exclusively by external computers and do not offer any manual setting options.
More complex signals can be calculated on the external computer with special programs and loaded into the generator via an interface. For example, it is possible to superimpose defined interference and noise on a useful signal, to simulate fading , etc. Such test signals are used, for example, when testing data transmission equipment ( modems and other). Excerpts from digital signals such as serial data transmission can also be generated in this way.
The signal shapes to be generated can, but need not, be generated synthetically. Real signals recorded by measurement can also be loaded into the arbitrary generator and retrieved at any time in order to work with "real" signals, even if the corresponding test setup or test person is not available, for example for applications in medical technology.
In the industrial environment, for example, a service technician can record the relevant input signal with a transient recorder or storage oscilloscope in the event of a fault in a system and transmit it electronically (e.g. by email) to the system manufacturer, who can then reproduce the situation in the laboratory with the help of an arbitrary generator.