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In vivo applications / Electrophysiology / DC amplifier systems
BioAmp Universal Biological Amplifier
BioAmp Universal Biological Amplifier 1-channel
About BioAmp amplifiers
BioAmp is a programmable amplifier, but it has no sampling circuits in the signal path at all. In other words, it is controlled by a built-in microcontroller or a remote computer, but it has got only high-performance, low noise, low distortion analogue amplifier circuits. We keep this traditional construction style, because it provides supreme accuracy and unsurpassable linearity. This full-analog feature is indispensable when you use averaging techniques for processing its output signal. The internal Amplifier Setup Controller and the optional digital port (which offers remote control facility from a PC) are optically isolated from the amplifier stages. This way we could connect all the advantages of high accuracy analogue amplifier circuits and easy usage of digital control.
Although BioAmp is programmable equipment, it does not need a separate computer to work. According to this fact, it can be used as a stand-alone amplifier (while possessing an optional serial port to communicate with a PC). This stand-alone feature is very comfortable, because the computer is always given, but it should be used to collect and to process the experimental data. Every Amplifier Setup Controller on the front panel has got a 3-button keypad and menu-driven internal firmware, so it is very friendly to use.
The internal structure of BioAmp is modular, so the number of the amplifier channels and the number of the Amplifier Setup Controllers built in the equipment can be decided independently. Only the aspects of the application field should be considered when we decide, how many amplifier channels and how many Amplifier Setup Controllers will be placed in the equipment cage (for example it is comfortable to use only one Amplifier Setup Controller to program all the EEG channels together, but another Amplifier Setup Controller should be used if there is a single unit channel in the system, and a third Amplifier Setup Controller is necessary, if there are further channels for ECG). The front plate Amplifier Setup Controller drives an internal serial bus. On this bus the Amplifier Setup Controller is the master and the amplifier boards are the slaves. The slaves cannot be addressed on the bus. All slaves that are connected to the bus receive the commands from the master at the same time. An Amplifier Setup Controller can drive any number of amplifier boards. The slaves are wired on the bus on a fixed way. This is the reason, why usually more than one Controller is located on the front plate. Examples: a 16-channel equipment can be designed with three Amplifier Setup Controllers on the front: Arrangement (1): channels 1 to 8 are connected to the 1st Controller, channels 9 to 12 are connected to the 2nd Controller and channels 13 to 16 are connected to the 3rd Controller. Arrangement (2): channels 1 to 12 are connected to the 1st Controller, channels 13 to 15 are connected to the 2nd Controller and only channel 16 is connected to the 3rd Controller. Other convenient arrangements can be created, too.
Specifications and Technical Data
In the BioAmp system there are 8 positions of gain, 8 positions of high pass filter and 8 position of low pass filter in the menu to choose from. The actual values, what should be realized during the manufacturing process can be ordered with the default parameters, but they can be requested with special values, to meet any special requirements, as well. The default values for the filter and gain sections are listed below. Any combination of the parameters can be selected, even the invalid settings (for instance if the high pass filter is set to higher frequency, than the low pass filter). The invalid settings result no faults in the equipment, only the output voltage will be driven to zero.
| High Pass Filter | Low Pass Filter | Gain |
| DC (0 Hz) | 15 Hz | 500 |
| 0.16 Hz (1 s) | 30 Hz | 1,000 |
| 0.53 Hz (0.3 s) | 70 Hz | 2,000 |
| 1.6 Hz (0.1 s) | 150 Hz | 5,000 |
| 5.3 Hz (0.03 s) | 500 Hz | 10,000 |
| 10 Hz | 2 kHz | 20,000 |
| 30 Hz | 5 kHz | 50,000 |
| 100 Hz | 10 kHz | 100,000 |
There is a possibility to select the full amplifier chain of BioAmp as Inverting or Noninverting characteristics. This selection is also a menu point of the firmware running on the Amplifier Setup Controller.
Offset voltage arisen on the recording electrodes can be corrected on three different ways, depending on the actual amplifier model. All the below mentioned voltages are referring to the input of the preamplifier (in other words referring to the electrode).
Analog offset voltage correction in the Preamplifier:
- Offset voltage correction range: +/- 700 mV
- Control method: 10-turn helical potentiometers
- It can be built into the Monopolar (single-ended) preamplifiers only
Digital offset voltage correction in the Main Amplifier:
- Offset voltage correction range: +/- 200 mV
- Resolution: 100 µV
- Control method: Digital Offset Voltage Controller unit
The above two methods combined together:
- Coarse offset voltage correction in the preamplifier
- Fine digital offset voltage correction in the Main Amplifier
Fields of Applications
- Extracellular recording
- Microelectrode recording (Single-unit activity, Juxtacellular recording, Field Potential, Motor Units, etc.)
- Multi-channel DC recording in epilepsy research
- Evoked Potentials in the brain (EVP)
- Body-surface potentials (ECG, EMG, EEG, ERG, etc.)
- Heart micropotentials (HIS-bundle, Late Potential, etc.)
- Multi-channel applications (EEG Brain Mapping, Cortical Depth Mapping, etc.)
Noise
The noise level of BioAmp was measured under the following conditions. A monopolar (single-ended) headstage was used. The input signal of the headstage was generated by a battery-powered square wave generator. The output impedance of this generator was 470 Ohms. The measured noise voltages were referring to the input of the headstage (in other words, they were measured at the output, but they were calculated to the input, divided by the actual gain). The actual settings of the BioAmp Main Amplifier, except the low pass filter, have negligible effect for the total noise characteristics. The noise level depends mainly on the type of the preamplifier and the low pass filter setting. The results of the noise measurement are:
- If the bandwidth is 10 kHz (the low pass filter is opened to the widest range), the input noise RMS voltage is less than 12 µV (50 µV peak-to-peak).
- If the bandwidth is limited to 2 kHz with the low pass filter, the input noise RMS voltage is less than 4 µV (20 µV peak-to-peak).
- If the bandwidth is limited to 500 Hz with the low pass filter, the input noise RMS voltage is less than 2 µV (10 µV peak-to-peak).
The difference between amplifier models mostly depends on the quality of the design. Such features as hum noise, square wave transient response, phase response, frequency domain characteristics, ability of parasite oscillations, thermal stability, reliability, etc. are responsibility of the designer. But there is no real difference in the signal to noise ratios of biological amplifiers manufactured by different firms. The signal to noise ratio depends on the internal design of the amplifier integrated circuits. The race of the smaller electronic noise is a race of the semiconductor manufacturers. The designer can choose the best amplifier ICs of the leader semiconductor factories.
Ground Topology
There is a general design method in the high gain amplifiers, what is applied in BioAmp, as well. Usually in the biological amplifiers, as in our amplifiers, too (if optical isolators are not used) the Input GND and Output GND points are connected together internally. The resistance between them is less than 0.05 Ohms. However they are signed as different points, because in the interior of the amplifier the ground network forms a linear topology, not a single-point GND (as it is advised in the text-books). The suppression of the hum noise is better if the ground line follows the signal line linearly according to the increasing signal amplitudes from the input to the output. To establish a single-point shielding ground is a good solution at the output end of the signal ground line. Unfortunately the security ground wires are also connected to the metal enclosures of the equipments. The security ground wires are usually hum noise sources for the biological amplifiers (because they usually drive some mains-frequency fault currents from other equipments, from other rooms), but they must not be disconnected, they are compulsory to be used. If you use a mains isolation transformer with symmetrical secondary coil, you can eliminate the disadvantage of the security ground (if in your lab it is allowed to use, please check the local rules). The vibration isolation table, the manipulators, the Faraday-cage, metal parts in the Faraday-cage, the oscilloscope, the PC, the Output GND of the amplifier and the real, separated signal ground line (coming from the earth directly, if it is available) should be connected to this single-point shielding ground. But the ground point of the biological target (the slice chamber or the body of the animal) should be isolated from the shielding ground point (special care should be taken with the metal parts close to the target in the Faraday-cage). The Input GND point of the amplifier is used to provide a low impedance ground to the biological object only. The Input GND point to the biological object is the GND pin at the input of the headstage.
The BioAmp system must not be used in human experiments!
BioAmp amplifier version:
This product version is a 1-channel version from the UBA series, without Digital Offset Voltage Controller.
Descriptions
About BioAmp amplifiers
BioAmp is a programmable amplifier, but it has no sampling circuits in the signal path at all. In other words, it is controlled by a built-in microcontroller or a remote computer, but it has got only high-performance, low noise, low distortion analogue amplifier circuits. We keep this traditional construction style, because it provides supreme accuracy and unsurpassable linearity. This full-analog feature is indispensable when you use averaging techniques for processing its output signal. The internal Amplifier Setup Controller and the optional digital port (which offers remote control facility from a PC) are optically isolated from the amplifier stages. This way we could connect all the advantages of high accuracy analogue amplifier circuits and easy usage of digital control.
Although BioAmp is programmable equipment, it does not need a separate computer to work. According to this fact, it can be used as a stand-alone amplifier (while possessing an optional serial port to communicate with a PC). This stand-alone feature is very comfortable, because the computer is always given, but it should be used to collect and to process the experimental data. Every Amplifier Setup Controller on the front panel has got a 3-button keypad and menu-driven internal firmware, so it is very friendly to use.
The internal structure of BioAmp is modular, so the number of the amplifier channels and the number of the Amplifier Setup Controllers built in the equipment can be decided independently. Only the aspects of the application field should be considered when we decide, how many amplifier channels and how many Amplifier Setup Controllers will be placed in the equipment cage (for example it is comfortable to use only one Amplifier Setup Controller to program all the EEG channels together, but another Amplifier Setup Controller should be used if there is a single unit channel in the system, and a third Amplifier Setup Controller is necessary, if there are further channels for ECG). The front plate Amplifier Setup Controller drives an internal serial bus. On this bus the Amplifier Setup Controller is the master and the amplifier boards are the slaves. The slaves cannot be addressed on the bus. All slaves that are connected to the bus receive the commands from the master at the same time. An Amplifier Setup Controller can drive any number of amplifier boards. The slaves are wired on the bus on a fixed way. This is the reason, why usually more than one Controller is located on the front plate. Examples: a 16-channel equipment can be designed with three Amplifier Setup Controllers on the front: Arrangement (1): channels 1 to 8 are connected to the 1st Controller, channels 9 to 12 are connected to the 2nd Controller and channels 13 to 16 are connected to the 3rd Controller. Arrangement (2): channels 1 to 12 are connected to the 1st Controller, channels 13 to 15 are connected to the 2nd Controller and only channel 16 is connected to the 3rd Controller. Other convenient arrangements can be created, too.
Specifications and Technical Data
In the BioAmp system there are 8 positions of gain, 8 positions of high pass filter and 8 position of low pass filter in the menu to choose from. The actual values, what should be realized during the manufacturing process can be ordered with the default parameters, but they can be requested with special values, to meet any special requirements, as well. The default values for the filter and gain sections are listed below. Any combination of the parameters can be selected, even the invalid settings (for instance if the high pass filter is set to higher frequency, than the low pass filter). The invalid settings result no faults in the equipment, only the output voltage will be driven to zero.
| High Pass Filter | Low Pass Filter | Gain |
| DC (0 Hz) | 15 Hz | 500 |
| 0.16 Hz (1 s) | 30 Hz | 1,000 |
| 0.53 Hz (0.3 s) | 70 Hz | 2,000 |
| 1.6 Hz (0.1 s) | 150 Hz | 5,000 |
| 5.3 Hz (0.03 s) | 500 Hz | 10,000 |
| 10 Hz | 2 kHz | 20,000 |
| 30 Hz | 5 kHz | 50,000 |
| 100 Hz | 10 kHz | 100,000 |
There is a possibility to select the full amplifier chain of BioAmp as Inverting or Noninverting characteristics. This selection is also a menu point of the firmware running on the Amplifier Setup Controller.
Offset voltage arisen on the recording electrodes can be corrected on three different ways, depending on the actual amplifier model. All the below mentioned voltages are referring to the input of the preamplifier (in other words referring to the electrode).
Analog offset voltage correction in the Preamplifier:
- Offset voltage correction range: +/- 700 mV
- Control method: 10-turn helical potentiometers
- It can be built into the Monopolar (single-ended) preamplifiers only
Digital offset voltage correction in the Main Amplifier:
- Offset voltage correction range: +/- 200 mV
- Resolution: 100 µV
- Control method: Digital Offset Voltage Controller unit
The above two methods combined together:
- Coarse offset voltage correction in the preamplifier
- Fine digital offset voltage correction in the Main Amplifier
Fields of Applications
- Extracellular recording
- Microelectrode recording (Single-unit activity, Juxtacellular recording, Field Potential, Motor Units, etc.)
- Multi-channel DC recording in epilepsy research
- Evoked Potentials in the brain (EVP)
- Body-surface potentials (ECG, EMG, EEG, ERG, etc.)
- Heart micropotentials (HIS-bundle, Late Potential, etc.)
- Multi-channel applications (EEG Brain Mapping, Cortical Depth Mapping, etc.)
Noise
The noise level of BioAmp was measured under the following conditions. A monopolar (single-ended) headstage was used. The input signal of the headstage was generated by a battery-powered square wave generator. The output impedance of this generator was 470 Ohms. The measured noise voltages were referring to the input of the headstage (in other words, they were measured at the output, but they were calculated to the input, divided by the actual gain). The actual settings of the BioAmp Main Amplifier, except the low pass filter, have negligible effect for the total noise characteristics. The noise level depends mainly on the type of the preamplifier and the low pass filter setting. The results of the noise measurement are:
- If the bandwidth is 10 kHz (the low pass filter is opened to the widest range), the input noise RMS voltage is less than 12 µV (50 µV peak-to-peak).
- If the bandwidth is limited to 2 kHz with the low pass filter, the input noise RMS voltage is less than 4 µV (20 µV peak-to-peak).
- If the bandwidth is limited to 500 Hz with the low pass filter, the input noise RMS voltage is less than 2 µV (10 µV peak-to-peak).
The difference between amplifier models mostly depends on the quality of the design. Such features as hum noise, square wave transient response, phase response, frequency domain characteristics, ability of parasite oscillations, thermal stability, reliability, etc. are responsibility of the designer. But there is no real difference in the signal to noise ratios of biological amplifiers manufactured by different firms. The signal to noise ratio depends on the internal design of the amplifier integrated circuits. The race of the smaller electronic noise is a race of the semiconductor manufacturers. The designer can choose the best amplifier ICs of the leader semiconductor factories.
Ground Topology
There is a general design method in the high gain amplifiers, what is applied in BioAmp, as well. Usually in the biological amplifiers, as in our amplifiers, too (if optical isolators are not used) the Input GND and Output GND points are connected together internally. The resistance between them is less than 0.05 Ohms. However they are signed as different points, because in the interior of the amplifier the ground network forms a linear topology, not a single-point GND (as it is advised in the text-books). The suppression of the hum noise is better if the ground line follows the signal line linearly according to the increasing signal amplitudes from the input to the output. To establish a single-point shielding ground is a good solution at the output end of the signal ground line. Unfortunately the security ground wires are also connected to the metal enclosures of the equipments. The security ground wires are usually hum noise sources for the biological amplifiers (because they usually drive some mains-frequency fault currents from other equipments, from other rooms), but they must not be disconnected, they are compulsory to be used. If you use a mains isolation transformer with symmetrical secondary coil, you can eliminate the disadvantage of the security ground (if in your lab it is allowed to use, please check the local rules). The vibration isolation table, the manipulators, the Faraday-cage, metal parts in the Faraday-cage, the oscilloscope, the PC, the Output GND of the amplifier and the real, separated signal ground line (coming from the earth directly, if it is available) should be connected to this single-point shielding ground. But the ground point of the biological target (the slice chamber or the body of the animal) should be isolated from the shielding ground point (special care should be taken with the metal parts close to the target in the Faraday-cage). The Input GND point of the amplifier is used to provide a low impedance ground to the biological object only. The Input GND point to the biological object is the GND pin at the input of the headstage.
The BioAmp system must not be used in human experiments!
BioAmp amplifier version:
This product version is a 1-channel version from the UBA series, without Digital Offset Voltage Controller.
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