Output Tab

The Output tab can be used to configure the center frequency and maximum output power of the generated signals. It is available on all SHFSG instruments.

Features Overview

  • Enable/disable output

  • Define the Center Frequency of the modulation band

  • Define the output power range

  • Switch between RF and LF paths

Description

Table 1. App icon and short description
Control/Tool Option/Range Description

Output

btn mnu inout um

Quick overview and access to all the settings for configuring the analog upconversion path.

The SHFSG uses the double super-heterodyne frequency upconversion technique to generate its RF output frequencies, and each Output Channel has its own frequency upconversion chain. Each Output Channel has two available Output paths: the RF path for generating signals with center frequencies from 0.6 GHz to 8 GHz, and the LF path for generating signals with center frequencies from 0 GHz to 2 GHz. When using the RF path, center frequencies determine the frequency of an analog synthesizer and can be set with a resolution of 0.1 GHz. Both variants of the SHFSG contain 4 synthesizers. In the 4-channel variant, each Output Channel therefore has its own synthesizer, whereas in the 8-channel variant, there is 1 synthesizer per Output Channel pair. This means that Output Channels 1 and 2 must share the same RF center frequency in the 8-channel variant of the SHFSG Instrument when using the RF path. To achieve different output frequencies on Output Channels 1 and 2 in the 8-channel variant, digital modulation must be employed (see the Modulation Tab). When using the LF path, the center frequencies of each channel can be set independently of the other channels in both variants of the SHFSG Instrument.

shfsg analog output
Figure 1. Analog Signal Output Stage

When using the Signal Output of the RF path, the digital 1-GHz-wide modulation band centered around DC is first interpolated by a factor of 3, then digitally upconverted to 2 GHz (light blue elements) before it is passed to the 14-bit DAC. The resulting 2 GHz analog signal (dark blue elements) is then converted to 12 GHz by means of a local oscillator at 10 GHz. To remove all unwanted spurious signals, the signal is strongly filtered before it is down-converted in a second mixing process with a variable local oscillator. Depending on its software-controllable frequency value, the final output frequency band has a center frequency between 0.6-8 GHz and a width of ±0.5 GHz. Several amplifiers, attenuators, and filters in the up-conversion chain ensure that the different elements are not saturated and that the DAC range is faithfully mapped to the selected Output Range.

When using the LF path, the digital 1-GHz-wide modulation signal is still interpolated by a factor of 3 and passed to the 14-bit DAC, but the analog upconversion chain is bypassed. The center frequency is determined by setting the frequency of the oscillator used in the digital upconversion (fixed at 2 GHz when using the RF path). In this way, signals with center frequencies between 0 and 2 GHz can be generated with the LF path.

The advantages of this up-conversion scheme compared to IQ-mixer-based frequency conversion are that it is calibration-free, wide-band, and stable, in addition to having superior spurious tone performance. The optimal selection of the different gains, attenuators, and filters in the frequency conversion chains are taken over by the SHFSG, such that only a few settings need to be set in the Output band parameters of the SHFSG: Center Frequency, Output Range, and Output On.

Output Tab in the LabOne GUI

The Output settings can be accessed through the Output tab output icon of the SHFSG’s LabOne general user interface. After clicking on the tab, an overview subtab opens that displays all settings for all available Output Channels.

output tab overview
Figure 2. The Overview Output Tab of the GUI

With the selectors at the left side of the Output tab, the detailed view of the up-conversion chain for the different Output Channels can be displayed. Each detailed view shows the available settings in the first, leftmost panel. In the second panel, a graphical representation of the currently selected parameters of the up-conversion chain is displayed.

output tab detail
Figure 3. A detailed Output Tab of the GUI

Functional Elements

Table 2. Output tab
Control/Tool Option/Range Description

Center Frequency

Center frequency of the output band at the output of the instrument. A copy of the displayed value is also contained in the read-only node '/{device}/sgchannels/{n}/centerfreq'.

Center Frequency

Set center frequency of digital mixer.

Center Frequency

Center frequency of the detection band at the input/output of the instrument.

Variable Local Oscillator Frequency

This local oscillator converts between the fixed signal band around 12 GHz and the variable readout band at the In/Out connector. Shared between the Signal Input/Output modules of the same channel, its value is given by the user-determined Center Frequency value + 12 GHz.

Variable Local Oscillator Frequency

This local oscillator converts between the fixed signal band around 12 GHz and the variable output band at the Out connector. Its value is given by the user-determined Center Frequency value + 12 GHz.

Range

Maximal power at the input of the instrument.

Range

Maximal power at the output of the instrument.

Selectable RF Output Filter

The filter value is selected according to the Center Frequency value and ensures that higher signal harmonics are removed at the Signal Output.

Output Path

LF path is used.

Switch between RF and LF output path.

RF path is used.

Delay (s)

This value adds a delay to both the signal and trigger/marker outputs.

Channel Select

Select which channel is to be cleared.

Reset All

Reset all the channels.

Reset Channel

Reset only the selected channel.

Mode

In manual mode the instrument does not automatically reset NCOs when switching a channel from LF to RF mode.

Configure the NCO reset mode.

In automatic mode the instrument automatically resets the NCOs of all channels whenever a channel is switched from LF to RF, in order to restore alignment.