Measure and Generate Periodic Microwave Signals: The GHFLI and SHFLI Launch Event
This blog post accompanies the online launch event of the GHFLI and SHFLI Lock-in Amplifiers, the trailblazers that bring state-of-the-art signal generation, analysis, and control to microwaves.
On the 6th of October, we started the event with an overview of the history of Zurich Instruments lock-in amplifiers and their impact on research and development. This was followed by a presentation of the GHFLI and SHFLI Lock-in Amplifiers during which we introduced the innovations brought by these new instruments and how they can help researchers and engineers.
After the first Q&A session, Kivanç showed how to easily perform the characterization of a pillbox resonator using the SHFLI and extract the parameters of one of its resonances thanks to the automation features of the LabOne® Sweeper tool. In particular, we showed:
- How to set up a driving signal and how to read out the resulting signal;
- How to use the Scope tool on the input signal;
- How the Sweeper automates a broad-frequency scan, spanning multiple 1 GHz measurement windows; and
- How to extract the resonance parameters from a narrower-frequency scan of amplitude and phase.
If you were unable to attend the event, or if you would like to watch it again, you can find the recording here.
We enjoyed your virtual participation and engagement with many questions during the event. We tried our best to cover all of them, but this was not possible in a limited time. In this blog post, we will answer all of them. The recording does not contain the live Q&A sessions, as the questions are answered below.
Get in touch with us to ask more questions and to discuss your application in detail and how these new instruments can help you.
Questions and Answers
When can we get the new microwave Lock-in Amplifiers?
We will start shipping the GHFLI and SHFLI between the end of February and the beginning of March 2023.
Do you provide training for these instruments?
Yes, and not only for the GHFLI and SHFLI, but we offer training and support for all our products. Every Zurich Instruments product comes with a premium customer care package. Please reach out if you need additional training or are in need of support; we are always happy to help.
Do you also plan to sell cheaper (GHFLI) units with fewer demodulators?
The GHFLI base unit has 8 demodulators grouped in 2 groups of 4, one per channel. They can be used for harmonics analysis and to set up measurements with different time constants. The multi-frequency option will add 6 more oscillators, for a total of 8, giving the possibility of measuring up to 8 independent frequency components. We don’t have a GHFLI version with fewer demodulators in the roadmap.
I'm using a lock-in amplifier with an external mixer to measure in the GHz. How are the microwave lock-in amplifiers better?
The GHFLI is a direct-digitization lock-in amplifier, so it does not use any frequency mixing scheme to reach up to 1.8 GHz and it operates very similarly to our other lock-in amplifiers without any added complexity. The SHFLI, on the other hand, does employ frequency up- and down-conversion schemes to address the frequency range from DC to 8.5 GHz, but all the complexity of an external mixing scheme is taken care of by the instrument itself. For instance, there is no need for periodic calibrations of the mixer, common in IQ mixing schemes, and the input and output mixers are constantly synchronized without the need for external intervention.
Could you please comment on comparing the microwave lock-in amplifiers with a Vector Network Analyzer (VNA)?
It is difficult to directly compare VNAs and lock-in amplifiers because the results depend heavily on the VNA considered, and even more importantly on the application and its needs. VNAs are great tools for the task they are designed to do: measure network properties accurately. Lock-in amplifiers, on the other hand, have a broader range of applications and more flexibility in the choice of measurement parameters, such as the measurement time constant, which can lead to faster measurements. Zurich Instruments lock-in amplifiers, in addition, are equipped with multiple demodulators for parallel measurement and tracking of different frequency harmonics. Through the multi-frequency option, they can also measure up to 8 arbitrary frequencies, such as different resonant modes, and the PID option allows tracking resonances and operating in closed-loop mode.
Do you have a detailed SNR comparison of your new lock-in amplifiers to VNAs?
Similar to the previous answer, in this case too, it depends on the situation and the VNA to which our instruments are compared. Both the GHFLI and SHFLI have extremely low input noise, with a noise floor as low as 3.5 nV/√Hz for the GHFLI and the SHFLI in its baseband, and down to 2.5 nV/√Hz for the SHFLI in RF mode, above 800 MHz. Of course, input noise is not the only element when it comes to measuring SNR with lock-in amplifiers, and the GHFLI and SHFLI provide a minimum low pass filter bandwidth of 3.2 mHz for very high noise rejection. The maximum bandwidth, instead, is 11 MHz, corresponding to 14 ns, for when noise is not an issue and very high measurement speed is of the essence.
What are the trade-offs between the two microwave instruments? Are there performance penalties that much be paid to reach 8.5 GHz?
The main difference between the GHFLI and the SHFLI Lock-in Amplifiers is how they digitize the signal: the GHFLI is a direct-digitization instrument, similar to all other Zurich Instruments lock-in amplifiers, while the SHFLI first performs a frequency down-conversion in the analog domain, and then digitizes the signal. As a consequence, the GHFLI provides direct access to its entire 1.8 GHz input range at all times. The SHFLI, instead, has a 1 GHz wide moving measurement window that can span its 8.5 GHz range. The window position is determined by its center frequency, which can be set manually by the user or automatically by tools like the sweeper. Each one of the two channels of the SHFLI can have fully independent center frequencies. There are no performance penalties from the use of a frequency-mixing frontend except for the smaller measurement window.
Is it possible to do a PDH lock?
Yes, it will be possible when the feedback controllers are available. This is planned for Q3 2023.
Are both the GHFLI and SHFLI available for Laser Voltage Imaging LVI applications?
Yes. Laser Voltage Probing and Imaging benefit from fast measurement at high frequencies. Additionally, the multi-frequency option that will be available also for these two lock-in amplifiers allows imaging at different frequencies and harmonics, significantly reducing the measurement time. Additional upgrade options that benefit this application, such as the boxcar averager and the arbitrary waveform generator are in our development roadmap.
How about precision for microwave Q-factor measurements?
The Q-factor and other resonance parameters can be easily extracted by the sweeper tool as shown in the SHFLI demonstration during the launch event. Measurement precision depends on the device being measured and to some extent on the environment, but also, importantly, on the frequency resolution. In terms of frequency resolution, the GHFLI and SHFLI have minimum frequency steps of only a few tens of µHz, allowing for the characterization of even very narrow resonance peaks. Additionally, they also provide very good measurement reproducibility, which is another important factor. The sweeper also provides a baseline function with which you can characterize and remove the effects of the cables and the setup.
Do the new instruments have PLL options?
Yes, PID controllers and PLLs will be upgrade options for GHFLI and SHFLI. This option is planned for Q3 2023.
Do the new models have arbitrary waveform generators?
The arbitrary waveform generator upgrade option is in our roadmap.
Is it possible to recover a modulated signal?
Yes. A simple modulated signal can be easily measured. The AM/FM modulation upgrade option also provides the functionality to extract all the parameters of amplitude- and frequency-modulated signals directly, without the need for tandem demodulation.
What does the SHFLI measure with a 1 GHz measurement window?
The SHFLI has an integrated frequency conversion that allows it to measure from DC to 8.5 GHz in 1 GHz blocks. This window can be positioned anywhere up to a center frequency of 8 GHz and all components within the window can be accessed by the demodulators, the scope and all other integrated tools.
How can you have negative frequencies in the oscillators? Why is the FFT centered at 0 Hz?
These two questions can be answered together as they both relate to the frequency down-mixing: since the measurement window is defined by its center frequency, it spans a range from -500 MHz to +500 MHz, so the oscillators can take positive and negative values. The center frequency, after conversion, acquires a value of 0 Hz
What is the noise figure of the lock-in amplifiers? What is the lowest signal level to be measured by the lock-in amplifier?
The GHFLI has an input noise floor of around ≤3.5 nV/√Hz between 100 kHz and 0.8 GHz and ≤6 nV/√Hz above 0.8 GHz. The SHFLI has an input noise floor of ≤3.5 nV/√Hz from 100 kHz to 0.8 GHz, and ≤2.5 nV/√Hz above 0.8 GHz. Both instruments can measure down to the nV range.
By saying DC, how much is the minimum frequency?
The GHFLI and SHFLI can measure down to 0 Hz. The lowest frequency above 0 Hz is determined by their frequency resolution, which is a few tens of µHz.
About DIO (1,0): is it possible to set a DIO as input and another DIO as output for square signal, and what is the frequency range for DIO ports?
Yes, we provide input and output digital ports that can be used to acquire a signal and output a square waveforms. We will provide more detail on the frequency range of the DIO ports a bit later.
Do the demodulators of these lock-in amplifiers use sine or square waves?
They use sine waves. Historically, some lock-in amplifiers used square waves, which measure odd harmonics of the signal of interest and could introduce systematic measurement errors. Zurich Instruments Lock-in Amplifiers are digital instruments with precise numerical oscillators to generate the sine waves for demodulation. You can read more about how the demodulation works in our white paper Principles of Lock-in Detection.
Is the sweeper implemented at the software level in LabOne as in the UHFLI Lock-in Amplifier, or is it implemented at the FPGA level, making fast sweeping possible?
Currently, the sweeper works at the software level. The sweep duration depends on many parameters, including the range of the parameter swept, the number of data points, and the required precision; hence it can take from sub-seconds to minutes or longer. For a software sweeper, the data transfer to the computer also adds up to this duration. We are working on a sweeper that runs directly on the instrument to eliminate these additional delays for fast device characterization. This feature will become available in the coming months.