Multifrequency Lockin Amplifier¶
The Multifrequency Lockin Amplifier (MLA™) from Intermodulation Products (also known as the Intermodulation Lockin Analyzer, ImLA™), is a unique measurement system which could be described as a synchronous multifrequency waveform generator, digital oscilloscope, and real-time Fourier analyzing instrument. It is constructed from precision, low distortion, analog components, high speed analog-to-digital (ADC) and digital-to-analog (DAC) converters, and a highly parallel logic circuit called a Field Programmable Gate Array (FPGA). Contact Intermodulation Products <email@example.com> if you need help adapting the MLA with your experiment.
The MLA can run as many as 32 synchronous Lockins, ideal for frequency-domain multiplexing or simultaneous measurement of multifrequency linear response. But the MLA™ is particularly powerful for measuring nonlinear response in the form of intermodulation (response at the mixing products of multiple drive frequencies) or harmonics (response at integer multiples of a single drive frequency). The MLA™ can process 3 input triggers making possible triggered lockin measurement, where amplitude and phase is recorded in relation an external event, while avoiding transient distortions. It can also send three output triggers to initiate external events based on frequency domain response. With two output ports to drive the system under test and 4 input ports to monitor response, all synchronized to the same clock, the MLA™ is a multi-port, multi-frequency and multi-purpose measurement instrument.
This manual provides the basic information you need to use the MLA™. We start with a brief and general description of the ports. Subsequent sections describe how to use the MLA™ through its Graphical User Interface (GUI). Once you are familiar with the GUI you can start to program the instrument, controlling your measurement through a Python script. Full documentation on all functions needed to program the MLA™ is given in the section on MLA programming. For the experts, we have included sections describing Files Folders and Configurations, Calibration, details about the MLA™ Analog interfaces, and a discussion on Advanced Hardware and Software Topics.
When you measure (drive) single-ended, the voltage is between the center pin and the shield of the SMA connector labeled + (e.g. Input 1+ ). When you measure (drive) differential, the voltage is between center pins of two adjacent SMA connectors labeled + and - (e.g. Input 1+ and Input 1-). A complete description of the input and output ports including schematic diagrams is given in the section on Analog interfaces.
TRIGGER OUTPUT and TRIGGER INPUTThe three input and three output triggers all respond to (send) the same voltage level, which can be set to 2.5 V, 3.3 V or 5.0 V with a jumper on the PC-board. The default factory setting is 5.0V unless otherwise specified when ordering.
OUTPUTTwo high speed outputs (500 MSam/sec) with 16 bit resolution. These ports are are always differential. The MLA puts the output voltage between the + port and ground (SMA shield). A voltage of the opposite sign always appears between the - port and ground. If you use these ports differentially, the voltage difference between and + and - ports will be twice the set value. These ports are controlled in the MLA GUI via the analog panel.
INPUTPorts 1 and 2 are high-speed (250 MSam/sec) with 14 bit resolution. Ports 3 and 4 have moderate speed (50 MSam/sec) with 16 bit resolution. All ports have switchable range settings, AC or DC coupling, 50 ohm or 1M ohm input impedance. All ports can measure either differential or single-ended signals. When measuring single-ended the - input sees an open circuit (but the - input amplifier is grounded internally). These ports are controlled in the MLA GUI via the analog panel.
REF CLK OUTand
REF CLK INconnections are used for synchronizing the internal clock of the MLA™ with the clock of some other piece of measurement equipment. These ports are designed to connect to a 50 Ohm matching impedance. REF CLK OUT sends a 10MHz square waveform, AC-coupled, voltage range 2 Vpp. REF CLK IN must be manually locked to an external reference (see
hardware.Hardware.set_clkref_external_10MHz()). Other frequencies and voltage levels can be configured (see Clock Reference).
ETHERNETThe MLA™ communicates with the computer via the Ethernet connection. The MLA™ may be directly connected to the Ethernet connection on the computer, or it may be be put behind an Ethernet router, switch or gateway.
SIGNAL GROUNDgives external access to the grounding point for all input signals. This signal ground is isolated from the shielding enclosure (box) of the MLA™.
POWER GROUNDis connected to the enclosure. With the power supply connected, this will also be connected to the power ground (or protective earth) of the house.
POWER 12 V DCis supplied to the MLA™ via an external power supply. Use only the power supply delivered from Intermodulation Products. Using any other supply voids the warranty.
The MLA-3 has two separate grounds
SIGNAL GROUNDis connected to the outer shield of all SMA connectors.
POWER GROUNDis connected to the enclosure, and via the power supply it is connected to the power ground (or protective earth) in your house.
Both these grounds are exposed as banana connectors on the back side of the MLA-3. The MLA-3 is shipped with a jumper (or busbar) you can use to connect these two grounds.
If the signal ground is left floating, it will not protect against electromagnetic interference. However, if you connected to ground at multiple places, you may get problems with so called ground loops. Therefore, as a rule of thumb, signal ground should be connected to power ground at one, but only one, place. So if your device-under-test is for example a passive device with floating ground, you should usually have the jumper connected on the back side of the MLA-3. However, if the MLA-3 is used together with other instruments, these other instruments will often connect the power ground to the signal ground through their power supply. In theses cases, it is usually best to remove the jumper on the back side of the MLA-3 to avoid ground loops.