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Questions to Ask when Purchasing a 4-quadrant Amplifier System

The testing of automotive electronic systems requires a sophisticated highspeed 4-quadrant amplifier. Many EMC test standards call out highspeed voltage testing that requires such a setup (for example, ISO 16750, ISO 7637, LV148, LV124, LV123, ISO 21498, VW 80300, and many more.) A 4-quadrant supply system consists of both an amplifier and a control system. The amplifiers being 4-quadrant means it is bipolar (+/-) for voltage and can source (deliver) and sink (receive) current in both directions. Control is just as crucial as the amplifier. One does not want to be limited by one or the other devices in the system. There are tests where a DC or bipolar DC supply cannot be used. We will discuss what questions must be asked before purchasing such a system.


What test standards and tests do you want to cover with your system?

Knowing the tests you need is vital to determining what equipment covers each pulse. This is not always easy to understand, which is why one should learn and research the equipment. High voltage fast pulses like ISO pulses 1, 2a, 3a/b, and 5a/b come from transient generators. In contrast, the 4-quadrant amplifier does slower pulses with sine waves and DC transitions. Even though these battery pulses are slower, they require a relatively fast frequency response. The ability to perform in 4 quadrants allows for more complex requirements such as ground ripple.

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The high-speed 4-quadrant amplifier can also apply to High Voltage (HV) testing. The amplifier is coupled onto an HV supply with different methods to produce the required fast test profile HV supplies cannot do. Having a 4-quadrant amplifier that can be used for more requirements helps make your lab more efficient.


What is the amplifier’s frequency range?

The amplifier’s frequency response is critical in determining what can be used for your testing. The 4-quadrant amplifier will have a listed frequency response. This should be listed as a minimum (guaranteed specification). There will be a listing of what is possible for the entire voltage range and a separate listing for small signal frequency response. Many standards can be satisfied with a 150 kHz frequency response, but newer standards push higher and higher frequency requirements. A system capable of at least 300 kHz is needed to meet all requirements. Since testing of ripple sine waves at the top frequency (300 kHz) is usually only a few volts peak to peak, a small signal frequency response is essential. For example, a unit that can do 200 kHz full range and 500 kHz small signal will be an amplifier that will meet present requirements and can grow and be ready for the future.

Another component of frequency response is the ability to make fast voltage transitions while not over and undershooting the intended voltage. Over/undershoots can produce high-frequency immunity transients, causing unwanted DUT (Device Under Test) failures that are not designed parts of the test.   Seeing measurements of how fast a transition can be done and that no over/undershoots are present is a true sign of a high-quality 4-quadrant amplifier. A rise or fall time of <1µs is very fast and will easily meet many applications.


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What is the maximum output?

The 4-quadrant amplifier will have a rating for +/-Voltage output and current output. The voltage will need to fit within the requirements of your automotive testing. -30/+70 V is a good range meeting 12, 24, and 48V testing requirements. The 4-quadrant amplifiers will be offered in different power sizes, and in most cases, you will be concerned with how much current they can do. To select the correct model, you must know your DUT’s steady state current draw and its in-rush current requirements. An inrush current is the maximum short time <500 ms current draw. This typically happens when a unit is switched on. The steady-state current draw is the maximum current the DUT draws for a sustained amount of time >500 ms. Knowing these two values allows you to select the correct amplifier system. The 4-quadrant amplifiers will be rated with a steady current and a short-duration inrush current.


Can the amplifier system be expanded in the future?

Predicting the future and what your testing may need regarding power is difficult. Selecting a system that can be expanded to higher current needs without purchasing a whole new system will protect your investment if the need arises. In contrast, a system that cannot be upgraded and must be replaced will add to your cost. There are different options on the market where more modules can be added, or an additional system can be added and used in parallel. Having this flexibility is a cost savings. Some systems on the market even allow for multiple systems to be used independently for lower current testing and to bring the systems together to allow for testing of larger DUTs.


What are the amplifier’s protection mechanisms?

4-quadrant amplifiers should have protection mechanisms that protect them from misuse and allow for a safe environment for the user. This will consist of at least an interlock system that the user can set up to protect the area from people unknowingly coming up to a LIVE test setup. The use of warning lights or shut-off triggers should be used.


How is the amplifier controlled in the system?

The system needs input control to produce the voltage variation requirements. This control is often an external Arbitrary Waveform Generator (ARB). The ARB allows for programmed pulses/waveforms to be downloaded to it and produce the waveform in a +/-10V output to the amplifier system. The difficulty with an ARB system is that the waveform is stored in its memory as points. And there is a limit to the maximum points it can use. Because of this limitation, longer waveforms of only a few minutes required the ARB to spread out the points in time, causing the output to the amplifier to become stepped between each point.

Many ARBs are also function generators which allow for a frequency response output. This can be continuous sine/triangle waves. This has no point limitation, but it can not do complex waveforms or combine different functions/waveforms as the ARB function does. However, new technology has been developed that takes away the point limitation of the ARB, allowing for continuous testing without loss of pulse clarity for hours or even days of testing. A control system that can produce ANY WAVE is ideal. Be sure to understand the limitations of your system before purchasing.


Is the amplifier software included and is it compatible with your test lab?

Software control is required when performing automotive testing. With such an extensive listing of pulses and standards, software is needed. Different auto manufacturers and international standards committees continually develop new tests and standards. These tests and requirements required the user or the manufacturer to update the library to include the updates. Having easy programming software allows the user to be very reactive. If the system manufacturer can also program and supply the new and updated pulse libraries promptly, it can save the technicians and engineers valuable time.

Some features to be included in the software:

  • Standards Library with existing tests and pulses
  • The ability to edit, update, and save existing pulses (all pulses should be editable)
  • Ability to create pulses from an easy user interface
    • Save, modify, update, copy, paste, etc.
  • Import measured test data from an actual vehicle measurement to run as a test
  • No limit to time and test duration
  • Report/protocol creation contains all required parameters and measured pulses
  • See measured output in real time and compare it to the programmed pulse
  • Pause and continue testing from DUT error and note in the report
  • Macro function to create user-specific test profiles.
  • Easy integration into other software programs and programming languages


How precisely can voltage and current levels be controlled?

Measuring and knowing what the output of the 4-quadrant amplifier system is doing is required. Each pulse needs to be verified and shown in the reporting. This is typically done with an external oscilloscope. But this can also be achieved if the system has measurement capability integrated. In this case, one can see in real time that a pulse has been executed correctly every time, not just when the pulse is being verified.

Another aspect to consider for voltage control is that the ARB or signal source will always have a voltage offset at the output. The slight voltage offset then gets amplified by the 4-quadrant amplifier. This produces errors in the final testing. One needs to compensate for this offset in the pulse creation. A better solution is for the 4-quadrant amplifier system to integrate the control inside. The control and amplifier become 1 unit. The inherent offset can be compensated for in the system design. In this case, the user does not need to take additional steps in the pulse creation.

Can the amplifier simulate specific disturbance waveforms?

The 4-quadrant amplifier must be able to simulate and produce the required waveforms under any loading condition. DUT loading and performance are unknown and complex, so the 4-quadrant amplifier must have a low-impedance output. Having an added variable resistance output to match the requirements listed in the standards is also needed.


Can the amplifier be rack-mounted or integrated into a test system?

It may be necessary to rack the amplifier system and integrate it with other equipment to save on lab space. Having a system that is flexible and can be integrated might be needed. The packing, size, and weight are all things to consider. Will it need to be stationary in the lab, or can it be moved to the test setup? Before purchasing, these are things to know and understand to see what fits best in your lab.


Is training and technical support available?

Understanding your equipment before use and having support throughout its long life span is very important for safety and to reduce user mistakes. Having a training or a learning platform available in person, online, or through an E-learning web portal is very important to having a well-working lab. Make sure this is included in your offer. See if there are costs associated with it and if there are any yearly costs to maintain the software and support. A robust support network is vitally important throughout the product’s life.


What are the maintenance requirements?

Find out if there are any requirements for maintenance and upkeep. Depending on your quality system, there may be requirements for calibration or verification before each use. Be sure to investigate this fully to know what is involved. Know where the unit would be sent for calibration/repair/maintenance.

Having a modular system will help with downtime and diagnosing problems. If a module fails, it can pulled to be replaced or repaired. In some cases, a module might be removed while the rest of the system operates at a lower current output. This allows for less downtime. Flexibility in the lab is essential to maintain a good workflow.


Are there any upgradable features or options available?

There are options available with 4-quadrant amplifier systems that may be needed. Work with your supplier to be educated and understand all that is available. Here are some possible options:

  • An electronic switch to quickly remove voltage is a requirement E10/E13 of LV124/LV148 and other standards to remove voltage from DC and Signal lines quickly
  • Calibration Accessories/loads
  • Rack Integration
  • Isolation amplifier, isolated 4-quadrant supply to be used in series with external HV supply
  • Discover if there is an upgrade path to increase voltage or current.



In the ever-evolving landscape of automotive technology, EMC testing remains a crucial step in ensuring the safety and reliability of vehicles. 4-quadrant amplifiers stand as indispensable tools in this endeavor, offering a multitude of features that enhance the accuracy, versatility, and reliability of EMC testing.

Their bidirectional operation, precise control, high linearity, wide frequency range, high power output, integration with test software, and robust protection mechanisms make them the ideal choice for engineers evaluating the electromagnetic compatibility of automotive electronic systems.

As automotive electronics continue to advance and become more interconnected, the role of 4-quadrant amplifiers in EMC testing becomes even more significant. They empower engineers to simulate real-world electromagnetic scenarios with unparalleled precision, ensuring that the vehicles of tomorrow can navigate the electromagnetic landscape safely and without interference.

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