Linear Current Isolator

Linear current source with high precision and high bandwidth. Isolate and scale any signal that you generate. Charge Balanced Stimulation.

Soterix Medical Linear Current Isolator Device

Soterix Medical introduces the best in class current source which can isolate and scale any signal you create. The Linear Current Isolator (LCI) can be used for a variety of physiological stimulation protocols. Its high input impedance and high common mode voltage prevents ground loop. With high bandwidth and high voltage slew rate, it can be used for high frequency stimulations or sharp waveforms. The LCI has un-matched DC accuracy and provides option for charge balanced stimulation to compensate the DC offset of function generators. The LCI includes an unique selectable feature that can remove DC offset of output. This ensures stimulation without causing harm to tissue or corroding electrodes. The LCI is easy to use and has a simple user interface and requires minimal maintenance due to an error detection system, internal calibration, and advanced power management.


A Complete Linear Current Isolator

Isolator Input

Input signal range is ±10 V with overvoltage protection. If the input exceeds this range, the indicator LED on the panel lights up. While the device is on, the input section is designed to show a very high impedance to output (10 GΩ || 220 pF) to prevent a ground loop. A BNC connector carries the signal inside the device.

Input Specifications
Range ±10 V
Impedance 47 kΩ
Connector BNC
Common-mode Voltage of Isolation The compliance voltage of the device
Features Low distortion Isolation
Over Load Indicator (Red LED)
Optional Charge Balanced Stimulation

Isolator Output

The output compliance voltage of device is ±34 V. The output impedance of the device is more than 60 MΩ. The circuit is floating and the impedance between input and output is more than 1 GΩ. The maximum drivable load at 1 V input, is 33 kΩ for 1 mA/V and 330 kΩ for 100 μA/V gains.

Output Specifications
Compliance Voltage ±34 V
Impedance > 60 MΩ
Bandwidth (-3dB) 440 kHz (Input: sine, 2 Vpp, Load:1 kΩ)
Connector Banana
Features Input/Output Mismatch Detector (Red LED)
Optional DC Offset Removal

Charge Balanced Stimulation

In order to deliver charge balanced stimulation, the device is required to sink the exact same amount of charge that is delivered to the tissue. Function generators or DACs which can be used to command the current source, have DC offset at the output. Even a small amount of offset at the device input, causes current leakage at output, which will be accumulated after multiple cycles and cause electrode corrosion. This feature subtracts DC value from input signal.

DC offset removal

Connecting current source to electrodes in saline causes DC voltage offset at electrodes. The tissue and electrodes are sensitive to even less than 1 V. DC offset removal monitors the output voltage and keeps the DC offset at 0 V during stimulation. The mechanism of removing DC offset, is to subtract the DC value from command.

DC offset removal graph

Selectable Gain

The device is equipped with two different feedback networks, one provides 1 mA at output per 1 V of input command, and the other converts 1 V of input command to 100 μA of current at the output. Changing current gain does not cause any surge at the output unlike other isolated current stimulators. Following figure shows the absolute error of output in -1 mA to 1 mA range, with both conversion ratios.

Absolute Error in both conversion raios

DC Transfer Characteristics

DC transfer characteristics describe conversion of input voltage to output current and the precision of the conversion in steady state.

DC Transfer Characteristics
DC Transfer Characteristics

AC Transfer Characteristics

AC characteristics describe the process of output following the input. The following plots show the output gain and the output phase with a 1 Vpp sinusoid as input signal.

AC Transfer Characteristics
Slew Rate 11 V/μs
Bandwidth (-3dB) 440 kHz
Input to Output Propagation Delay 600 ns
AC Transfer

Unique Features

Minimum 0.03% ( 1mA/V); Minimum 0.02% (100 uA/V)

Slew rate (11 V/us) ; Input to Output propagation delay (600 ns)

Shielded to reduce noise

Simple and obvious to use controls

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