Gated Mode - Metrix GX1010 Notice De Fonctionnement

4.4.3.3. Start/Stop Phase
The start and stop phase of the triggered burst is set in the PHASE field. The PHASE field
actually sets the phase of the Auxiliary Output and it is from this output that control of the
start and stop point of the main generator is derived; the rising edge of the AUX OUT
signal, which can be phase shifted with respect to the MAIN OUT, determines the start and
stop point of the main waveform burst. Consequently, the conditions under which the
Auxiliary Output phase shift is constrained, and which are fully explained in that section, all
apply to start/stop phase. For example, the start/stop phase of sine and triangle waveforms
cannot be adjusted for main output frequencies above 30kHz unless the AUX OUTPUT
field on the Options menu is set to LOW FREQuency generation mode because only in this
mode does the AUX OUT continue to be phase shifted with respect to MAIN OUT.
Because the phase control signal is derived from the Auxiliary Output waveform further
considerations apply as the main generator frequency is increased. With AUX OUTPUT=
LOW FREQ on the Options menu phase shift control is still available above 30kHz but real
hardware delays become increasingly significant such that the start/stop phase increases
for no change in phase setting; this shift is caused by the delay between AUX OUT and
MAIN OUT becoming more significant and by the delays in the burst count and phase
control circuit themselves. These delays can be equivalent to say a +45° phase shift at
1MHz; however, by 'backing off' the required phase shift by -45° the desired condition can
still be achieved. At the same time, howver, the fewer samples making up each cycle of the
waveform means that the start/stop point becomes an uncertain 'band' which is 1 clock
wide.
Note that these effects apply even when the phase is set to 0°; at frequencies approaching
10MHz the phase shift can be 90° or more and the uncertainty band becomes wide.
Because this effect is seen at 0° phase it is also evident when AUX OUTPUT is in HIGH
FREQuency mode, i.e. when there is no phase control. In fact, because the AUX OUT
signal is derived from the filtered DDS sinewave in this mode the filter adds further phase
delay, creating even longer phase shifts at a given frequency than are evident with AUX
OUTPUT in LOW FREQuency mode.
In summary, phase errors and uncertainty will increase as the main frequency is increased
above 30kHz, even with 0° phase set. However, stop/start phase control can be used, with
care, to much higher frequencies by 'backing-off' the phase to compensate for the
hardware delays.

4.4.4. Gated Mode

Gated mode is turned on and off with alternate presses of the GATE key; the lamp beside
the key lights when gate mode is on. The selection of the gate source signal is made from
the gate edit menu which is selected by pressing the blue EDIT key followed by the GATE
key. when gate edit is selected the lamp beside the GATE key flashes to show edit mode
regardless of whether gate operation is currently selected to be on or off.
4.4.4.1. Gate Source
With the edit cursor in the SOURCE field of the gate edit menu, the digit keys or rotary
control can be used to select EXTernal, MAN/REMOTE, or Trigger GENerator as the gate
source. In all cases, when the gate condition is true, the main generator signal is gated
through to the MAIN OUT socket. Since the main generator is free-running and not
synchronised with the gate source the start and stop phase of the waveform is entirely
26 - II
SOURCE=EXT
TGEN=1·00ms 1·000kHz
GX1010