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
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.
Table 1: App icon and short description
Quick overview and access to all the settings and properties for signal generation and demodulation.
The lock-in tab provides controls for all demodulators in the
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
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 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
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
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
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.
Table 2: Lock-in MF tab
Switch between RF and Baseband frequency range.
Center frequency of the detection band at the input/output of the instrument.
Defines the gain of the analog input amplifier. The range should exceed the incoming signal by roughly a factor two including a potential DC offset.
The instrument selects the next higher available range relative to a value inserted by the user. A suitable choice of this setting optimizes the accuracy and signal-to-noise ratio by ensuring that the full dynamic range of the input ADC is used.
Automatic adjustment of the Range to about two times the maximum signal input amplitude measured over about 100 ms. It will be implemented in a future release.
OFF: DC coupling
Defines the input coupling for the Signal Inputs. AC coupling inserts a high-pass filter.
ON: AC coupling
Indicates how the frequency of the corresponding oscillator is controlled (manual, external reference, PLL, PID). Read only flag.
The user setting defines the oscillator frequency.
An external reference is mapped onto the oscillator frequency.
Frequency control for each oscillator.
ON / OFF
Oscillator locked to external reference when turned on.
Select the reference mode (manual or external reference) or indicate the unit that uses the demodulator (e.g. PLL).
Default lock-in operating mode with manually set reference frequency.
The demodulator is used for external reference mode and tracks the frequency of the selected reference input. The demodulator bandwidth is set automatically to adapt to the signal properties.
Connects the selected oscillator with the demodulator corresponding to this line. Number of available oscillators depends on the installed options.
1 to 1023
Multiplies the demodulator's reference frequency with the integer factor defined by this field.
Demod Freq (Hz)
Indicates the frequency used for demodulation and for output generation.
-180° to 180°
Phase shift applied to the reference input of the demodulator.
Adjust the phase of the demodulator reference automatically in order to read zero degrees at the demodulator output.
This action maximizes the X output, zeros the Y output, zeros the Θ output, and leaves the R output unchanged.
Selects the signal source to be associated to the demodulator.
Sig In 2
Signal Input 2 is connected to the corresponding demodulator.
Sig In 1
Signal Input 1 is connected to the corresponding demodulator.
Selects the filter roll off between 6 dB/oct and 48 dB/oct.
1st order filter 6 dB/oct
2nd order filter 12 dB/oct
3rd order filter 18 dB/oct
4th order filter 24 dB/oct
Defines the display unit of the low-pass filters: time constant (TC) in seconds, noise equivalent power bandwidth (BW NEP) in Hz, 3 dB bandwidth (BW 3 dB) in Hz.
Defines the low-pass filter characteristic using time constant (s) of the filter.
Defines the low-pass filter characteristic using the noise equivalent power bandwidth (Hz) of the filter.
BW 3 dB
Defines the low-pass filter characteristic using the 3 dB cut-off frequency (Hz) of the filter.
Defines the low-pass filter characteristic in the unit defined above.
ON / OFF
Enables the sinc filter.
When the filter bandwidth is comparable to or larger than the demodulation frequency, the demodulator output may contain frequency components at the frequency of demodulation and its higher harmonics. The sinc is an additional filter that attenuates these unwanted components in the demodulator output.
Makes all demodulator filter settings equal (order, time constant, bandwidth).
Enabling the lock copies the settings from demodulator 1 to all other demodulators. With locked filters, any modification to a filter setting is applied to all other filters, too. Releasing the lock does not change any setting.
ON / OFF
Enables the data acquisition and streaming of demodulated samples to the host computer for the corresponding demodulator. The streaming rate is defined in the field on the right hand side. Enabling a stream activates a corresponding element in the numeric tab and allows for demodulated samples to be visualized and analyzed in any of the LabOne measurement tools. Note: increasing number of active demodulators increases load on physical connection to the host computer.
Defines the demodulator sampling rate, the number of samples that are sent to the host computer per second. A rate of about 7-10 higher as compared to the filter bandwidth usually provides sufficient aliasing suppression.
This is also the rate of data received by LabOne Data Server and saved to the computer hard disk. This setting has no impact on the sample rate on the auxiliary outputs connectors. Note: the value inserted by the user may be approximated to the nearest value supported by the instrument.
Demodulator Sampling Rate Lock
Makes all demodulator sampling rates equal.
Enabling the lock copies the settings from demodulator 1 to all other demodulators. With locked sampling rates, any modification to a sampling rate is applied to all other sampling rate fields, too. Releasing the lock does not change any setting.
Select the unit of the displayed amplitude value.
ON / OFF
Enables individual output signal amplitude.
-range to range
Defines the output amplitude for each demodulator frequency as rms or peak-to-peak value.
A negative amplitude value is equivalent to a phase change of 180 degree. Linear combination of multiple amplitude settings on the same output are clipped to the range setting. Note: the value inserted by the user may be approximated to the nearest value supported by the Instrument.
Selects the most suited output range automatically. It will be implemented in a future release.
Indicates that the specified output amplitude(s) exceeds the range setting. Signal clipping occurs and the output signal quality is degraded. Adjustment of the range or the output amplitudes is required.
-range to range
Defines the DC voltage that is added to the dynamic part of the output signal.
ON / OFF
Main switch for the Signal Output corresponding to the blue LED indicator on the instrument front panel.
Defines the maximum output voltage that is generated by the corresponding Signal Output. This includes the potential multiple Signal Amplitudes and Offsets summed up. Select the smallest range possible to optimize signal quality.
This setting ensures that no levels or peaks above the setting are generated, and therefore it limits the values that can be entered as output amplitudes. Therefore selected output amplitudes are clipped to the defined range and the clipping indicator turns on. If 50 Ω target source or differential output is enabled the possible maximal output range will be half.