Auto Scale Button
Press Auto Scale on the N1000A front panel or click FlexDCA's Auto Scale button to automatically scale the waveform vertically and horizontally and to adjust the trigger level in Oscilloscope, Eye/Mask, or Jitter Mode. Before using Auto Scale, turn on at least one channel and ensure a valid signal and trigger source is connected. After an Auto Scale is performed, you can adjust the waveform settings to your liking. On FlexDCA, you can click Setup > Auto Scale to undo a previous Auto Scale.
During an Auto Scale, the following three tasks are performed:
- Sets the vertical scale and offset of all the input channels that are turned on.
- Sets the trigger level and bandwidth.
- Sets the horizontal scale and position of the lowest numbered channel turned on.
If multiple eye diagrams are displayed, software delay can be applied to align the eye diagrams.
Auto Scale and Triggering
The Auto Scale function sets the trigger level, so a required trigger signal must be provided in addition to the input signal. You can connect a trigger signal to the front panel trigger input or use clock recovery. The trigger level is set to the mean value of the trigger input. For example, if the input trigger is 0 to 0.6V, Auto Scale sets the trigger level to 0.3V. Auto Scale also resets the trigger bandwidth if necessary. If the trigger bandwidth is set to DC–100 MHz, Auto Scale resets the bandwidth to DC–2.5 GHz. Performing an Auto Scale will not affect the trigger bandwidth if either the DC–2.5 GHz or 2.5–12 GHz (option ETR) bandwidth is selected.
If a trigger input is not available or the trigger is in freerun, Auto Scale vertically centers the waveform on the display using scaling and offset.
Auto Scale and Y-axis (Vertical Scale)
The instrument evaluates the maximum and minimum values of all the input channels that are turned on and adjusts the vertical scale and offset to place the waveforms on the display screen. The waveform is moved so that it is centered in the middle of the display screen. The instrument then moves the waveforms so that the maximum value (Vmax) is positioned 2.5 divisions above the center of the display. The minimum value (Vmin) is positioned 2.5 divisions below the center of the display screen.
The instrument places the waveform in the middle of the display screen, within 5 graticule divisions (Vp-p). However, if the input signal is out of the operating range of the plug-in module (large peak-to-peak amplitude or large DC offset), the instrument may not be able to center the waveform. Therefore, an Auto Scale will not be able to produce an optimum waveform display.
Auto Scale and X-axis (Horizontal Scale)
If there is more than one channel turned on, the instrument adjusts the horizontal time-per-division (or UIs-per-screen) for the lowest number channel. For example, if all four channels are turned on, the instrument adjusts the horizontal time-per-division based on channel 1. While the instrument adjusts the horizontal scale based on the trigger source and input selected, the horizontal position of the waveform on the display screen differs for multi-valued and single-valued waveforms.
- Multi-valued waveforms. The centers of the crossing points of the waveform are approximately positioned on the second and eighth horizontal divisions of the display screen.
- Single-valued waveforms. The first two zero-crossings of the waveform are positioned on the first and fourth horizontal divisions to the right of the display's left edge. For clock signals, two cycles are displayed on screen, with a positive pulse centered on the display. When pattern lock is turned on, ten UIs are displayed, and the left edge of the screen is aligned with the center of a symbol.