BioSemi ActiveThree: Now Shipping!


BioSemi introduces the ActiveThree biopotential measurement system for electrophysiological research. The new system is the latest iteration if the successful line of Biosemi active electrode biopotential measurement systems.

The world’s first and most advanced active electrode EEG system breaks new ground, again.

BioSemi introduces the ActiveThree biopotential measurement system for scientific research in the field of electrophysiology. The new system is the third iteration of the successful line of BioSemi active electrode biopotential measurement systems. In this summary, we explain the reasons for developing a new system, and we highlight the improvements and advantages with respect to the previous systems.

All BioSemi systems use the same basic setup with active electrodes: preamplifier integrated in the electrode, a compact battery powered AD-box, and data transfer to the acquisition computer via a single optical fiber. This setup offers optimal reduction of interference and maximal subject safety. In 2000, BioSemi introduced the ActiveOne, the first commercially available biopotential measurement system with active electrodes. In 2002, this system was succeeded by the 24–bit ActiveTwo, which became the de facto standard workhorse for electrophysiological research with more than 2000 systems in use leading to over 10,000 scientific publications: 


However, recent advances in semiconductor and battery technology offered opportunities to develop a significantly improved successor. A first important upgrade is a change of Analog-to-Digital Converter (ADC) technology, which offers a cleaner frequency spectrum. A second change is the use of novel low-voltage components, allowing the AD-box to run on half the supply voltage when compared to its `predecessors. As a result, a much smaller battery could be used, leading to decreased size and weight. The setup of the auxiliary sensors (response switches, respiration, temperature, etc.) was completely revised. Finally, the CMS/DRL circuitry was redesigned for improved interference suppression. The sum of these changes offers improved signal quality coupled with much easier handling and operation of the hardware and software.

ActiveThree / ActiveTwo Points of Comparison

  • ADC type – ActiveThree uses a 24 bit SAR ADC, while ActiveTwo uses a 24 bit Delta-Sigma ADC. This SAR ADC provides a cleaner frequency response without spurious tones that can occur with Delta-Sigma ADCs and may impact one’s ability to distinguish signal from noise at certain frequencies in FFR paradigms.
  • Number of channels — ActiveThree has a maximum of 136 biopotential channels plus six auxiliary sensors. ActiveTwo has a maximum of 264 biopotential channels plus four auxiliary sensors.
  • High frequency response – ActiveThree has a low-pass antialiasing filter at 5.4 kHz, while ActiveTwo has a low-pass antialiasing filter at 3.2 kHz.
  • Battery type / size – ActiveThree uses a single Li-ion battery cell, while ActiveTwo uses a multi-cell Lead-acid battery unit. This new battery type supports the use of modern low voltage components and greater power efficiency.
  • Auxiliary sensors for ActiveThree require no installation of new internal components — all that is needed is already built-in. All you need to do is purchase the sensor and plug it in. The software automatically detects what is plugged in and displays/saves the sensors being used. ActiveTwo requires internal sensor couplers to be installed inside the AD box, and the user needs to select the desired sensors on the Sensors tab.
  • ActiveThree’s CMS/DRL circuitry was redesigned for improved suppression of interference from a wide range of ubiquitous high-frequency interference sources.
  • Weight – ActiveThree’s AD box weighs 1.76 lbs with the battery, and ActiveTwo weighs 2.4 lbs with the battery.
  • Size – ActiveThree’s AD box measures about 6.4 X 5.9 X 2.4 in with battery, and ActiveTwo’s AD box measures about 4.7 X 5.9 X 7.5 in with battery.

Visit the ActiveThree product pages to learn more!

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ActiveThree EEG System