Lock-in Tab (GHF-MF option)¶
This tab is the main lock-in amplifier control panel for GHFLI Instruments with the GHF-MF Multi-frequency option installed. Users with instruments without this option installed are kindly referred to Lock-in Tab.
Features¶
- Parameter table with main input, output and demodulator controls
- Controls for 8 individually configurable demodulators
- Control for 8 oscillators
- Settings for main signal inputs and signal outputs
Description¶
The Lock-in tab is the main control center of the instrument and open after start up by default. Whenever the tab is closed or an additional one of the same type is needed, clicking the following icon will open a new instance of the tab.
The lock-in tab provides controls for all demodulators in the instrument.
The lock-in tab for Multi-frequency GHFLI instruments`` (see Figure 1) consists of 5 vertical sections: Signal Inputs, Oscillators, Demodulators, Output 1 and Output 2. The Demodulator section contains 8 rows, each of them providing access to the settings of one dual phase demodulator. Every demodulator can be connected to any of the possible inputs, outputs and oscillators. Signal Input 1 and 2 are identical in all aspects, but each can be set to a different center frequency; the same holds for Signal Outputs 1 and 2. Each input and output pair constitutes a signal channel with a specific center frequency.
The Signal Inputs section allows the user to define all relevant settings specific to the signal at the input such as input coupling, amplitude range, etc. On the right-hand side of the Lock-in tab the two Output sections allow to define the individual tones amplitudes and the output range value.
The "Freq Range" button toggles the input between baseband, in which no analog mixing occurs and the signal is digitized directly, and RF, in which the analog up- and down-mixing path is selected. The AC/DC button sets the coupling type: AC coupling has a high-pass cutoff frequency that can be used to block large DC signal components to prevent input signal saturation during amplification. This button is only active when in baseband (BB) mode, because RF mode is AC coupled by design.
The Oscillator section controls the frequencies of all 8 internal oscillators. Where the Mode indicator shows Manual the user can define the oscillator frequency manually defined by typing a frequency value in the field.
The next section contains the Demodulators settings. The block diagram displayed in Figure 2 indicates the main demodulator components and their interconnection. The understanding of the wiring is essential for successfully operating the instrument.
Every line in the Demodulators section represents one demodulator. It is possible to demodulate the input signals with up to 8 demodulators simultaneously at up to 8 independent frequencies and using different filter settings.
In the Input Signal column one defines the signal that is taken as input for the demodulator. Currently Input 1 and Input 2 can be selected, but in the future more sources will be made available, such as Auxiliary Inputs and Outputs.
Demodulation of frequencies that are at integer multiples of any of the oscillator frequencies is achieved by entering the desired factor in the "n" column; the demodulation frequency is then the oscillator frequency times the factor n plus the channel center frequency. The result of the demodulation, the amplitude and phase can be read, for instance, using the Numeric tab which is described in Numeric Tab.
In the center of the Lock-in tab is the Low-Pass Filters section where the filter order for each demodulator can be selected in the drop-down list and the filter bandwidth (BW 3dB) can be chosen by typing a numerical value. Alternatively the time constant of the filter (TC) or the noise equivalent power filter bandwidth (BW NEP) can be chosen from the drop-down menu in the column’s header. Each unit of the filter order correspond to a 6 dB/oct increase in the filter steepness; for example, setting the filter order to 4 corresponds to a roll off of 24 dB/oct or 80 dB/dec i.e. an attenuation of 104 for a tenfold frequency increase. If the Low-Pass Filter bandwidth is comparable to or larger than the oscillator frequency (not the full demodulator frequency), the demodulator output may contain frequency components at the frequency of demodulation and its higher harmonics, when operating in baseband, or the component at the center of the measurement window (i.e. oscillator frequency =0). In this case, a smaller low-pass filter bandwidth is recommended, and the additional Sinc Filter should be enabled. The Sinc Filter is useful when measuring at low oscillator frequencies, since it allows one to apply a Low-Pass Filter bandwidth closer to the oscillator frequency, thus speeding up the measurement time
The data transfer of demodulator outputs is activated by the Enable button in the Data Transfer section where also the sampling rate (Rate) for each demodulator can be defined.
The 2 Output sections are only available on Instruments with the GHFLI-MF option installed. They allow for the flexible adjustment of output amplitudes of different demodulators and their summation on either Signal Output 1 or Signal Output 2. In order to avoid signal clipping the sum of the amplitudes of each signal output needs to be smaller than the range defined in the the corresponding Output section. At the top of each Output section one can select the format in which amplitudes are displayed in that section between root mean square values or peak-to-peak values.
In the top right-hand-side corner of each Output section the On button turns on or off the corresponding physical output. Even when the Output panel is collapsed, the On button remains available. The Range drop down list is used to select the proper output range setting for each channel.
Functional Elements¶
Note
Please note that some elements will be implemented in a future LabOne release. This is reflected in the description of these elements in the table below and also in the LabOne tooltips.