Waveform Generation Options - Metrix GX1010 Notice De Fonctionnement

4.2.3. Waveform Generation Options

A number of parameters are, by default, switched automatically either when the frequency
is set above 30kHz or when the operating mode is changed such that the best overall
performance is achieved across the whole generator frequency range; see the DDS
Principles section for further details of the 30kHz changeover. In addition, triangle, ramp,
staircase and arbitrary waveforms can be inhibited from being set above 100kHz, to ensure
that they are not used accidentally at frequencies where the waveshape is noticeably
deteriorating. In all cases, however the default choice can be overridden by the user by
changing the setting on the OPTions menu.
The OPTions edit menu shown above is selected by pressing the blue EDIT key followed
by OPTN (the shifted function of 1). The following descriptions, grouped together in this
section for reference convenience, should be read in conjunction with the main
explanations of the appropriate parameter elsewhere in this manual. Each parameter is
altered by moving the edit cursor to the appropriate field with the FIELD keys and using the
DIGIT keys or rotary control to change the setting.
4.2.3.1. Squarewave Generation
In LOW FREQency mode the squarewave and pulse waves are generated digitally; in this
way precision squarewaves can be generated down to very low frequencies without the
edge uncertainty that would be associated with conventional ramp-and-comparator
techniques. Above approximately 27kHz (clock frequency, 27·487MHz, ÷1024) the
waveforms are sampled and the 1 clock (36ns) uncertainty introduces edge jitter which
becomes increasingly significant at higher frequencies. In HIGH FREQuency mode the
squarewave and pulses are derived from the output of a comparator driven by the DDS
generated sinewave. The sinewave is, by default, filtered and jitter-free; the high frequency
squareware and pulse waveforms are thus jitter free too.
In AUTO mode (the default) the generation of squarewave and pulse waveforms is
automatically switched from low to high frequency mode when the frequency exceeds
30kHz. However, when these waveforms are used in sweep and FSK modes, over a
frequency range which includes the 30kHz changeover point, the generation mode will not
change even though AUTO is selected. Instead, the mode in use before sweep or FSK are
turned on is maintained across the frequency range; this can of course be overridden by
selecting either high or low frequency mode on the Options menu, as described above.
4.2.3.2. Filter
The generator contains a 7-stage elliptical filter which exhibits a sharp cut-off beyond the
maximum generator frequency, reducing intermodulation spurii and clock harmonics to a
very low level. With the default condition of FILTER=AUTO set on the Option menu, the
filter is switched in automatically for sine, triangle, high frequency squarewave and high
frequency pulse waveforms (although the squarewave and pulse waveforms themselves do
not pass through the filter); the filter is automatically switched out for low frequency
squarewave and pulses, ramp, staircase and arbitrary waveforms because of the
degrading effect it has on fast transitions in the waveform. However, for all these
waveforms the filter can be set to be always on (FILTER=ON) or always off
(FILTER=OFF); this has the advantage that, for example, an arbitrary waveform with an
essentially sinusoidal content can be output with the filter on.
20 - II
SQWAVE GEN=AUTO
FILTER=AUTO
AUX=AUTO FSTOP=ON
SWEEP TGEN OUT=AUTO
GX1010