Lock-in Tab¶
This tab is the main lock-in amplifier control panel. Users with instruments with GHFLI-MF Multi-frequency option installed are kindly referred to Lock-in Tab (GHF-MF option)
Features¶
- Parameter table with main input, output and demodulator controls
- Control elements for 8 configurable demodulators
- Control for 2 oscillators
- Settings for main signal inputs and signal outputs
Description¶
The Lock-in tab is the main control center of the instrument and open by default after start up.
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 (see Figure 1) consists of 4 vertical sections: Signal Inputs, Oscillators, Demodulators and Signal Outputs. The Demodulator section is divided horizontally into two identical groups. The upper group is tied to oscillator 1 (f1) and channel 1 (c1), while the lower group is tied to oscillator 2 (f2) and channel 2 (c2). That means demodulators 1 to 4 (5 to 8) demodulate the signals from input 1 (2) at the center frequency of channel 1 (2), plus the frequency of oscillator 1 (2) times a multiplier n. Signal Input 1 and 2 are identical in all aspects, the same holds for the Signal Outputs 1 and 2, but each channel has its own independent center frequency.

The Signal Inputs section allows the user to define all settings relevant to the signal at the input such as input coupling, amplitude range, etc. On the right-hand side of the Lock-in tab the Signal Outputs section allows defining signal amplitudes and range values for the generated sinusoidal signal.
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 both internal oscillators. When the Mode indicator shows Manual, the user can define the oscillator frequency manually by typing a frequency value in the field.
We now discuss the Demodulators settings in more detail. The block diagram displayed in Figure 2 shows 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 and all 4 demodulators in each group can be used to demodulate simultaneously the signal from their signal input, using different filter settings or at different harmonic frequencies of their oscillator within the channel’s measurement window. 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 transfer of demodulator output data is activated with the Enable button in the Data Transfer section where also the sampling rate (Rate) for each demodulator can be defined.
In the Signal Outputs section the On buttons are used to activate the Signal Outputs and remain available even when the Signal Outputs panel is collapsed. This is also the place where the output amplitudes for each of the Signal Outputs can be set in adjustable units (Vpk or Vrms). The Range drop-down list is used to select the proper output range setting.
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.