The High Precision Linear Current Isolator is a linear current source that is optimized for the stimulation of extracellular and electrically excitable tissues. The output is capable of both source and sink the current, giving a full four-quadrant performance. Its high input impedance and high common mode voltage prevents a ground loop. With high bandwidth and high voltage slew rate, it can be used for high frequency stimulations or sharp waveforms. The LCI High Precision has a best in class DC accuracy. Optional charge balanced stimulation compensates the DC offset of function generators. The LCI High Precision includes a unique selectable feature that can remove DC offset of output, stimulates without causing harm to tissue or corroding electrodes. The LCI High Precision 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. Caputron High Precision Linear Current Isolator Overview High DC and AC precision High Bandwidth Can compensate input offset for accurate charge balanced stimulation Capable of removing output DC offset voltage EMI shielded to reduce noise Rechargeable batteries with increased lifespan and capacity Simple user interface High Precision Linear Current Isolator Features Isolator Input Input signal range is ±10 V with overvoltage protection. If the input exceeded 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 ground loop. A BNC connector carries the signal inside the device. Isolator Output The output compliance voltage of the 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. Selectable Gain High Precision and Low current modes with a conversion ratio of 1 mA/V and 100 µA/V respectively Surge free switching between gains 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. The following figure shows the absolute error of output in -1 mA to 1 mA range, with both conversion ratios. DC Offset Removal Since the main application of the device is the stimulation of tissues, the output is applied to electrodes inside a solution. Connecting the current source to electrodes in saline cause DC voltage offset at electrodes, nevertheless, 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 value” of the output signal is measured with an integrator with 0.1 s time constant. Stimulating with metal electrodes inside saline, cause voltage offset at electrodes. The following figures illustrate the effect of using “0 VDC” and compare it with a normal output of a current source. DC Transfer Characteristics DC transfer characteristics describe the conversion of input voltage to the output current and the precision of the conversion in steady-state. AC Transfer Characteristics AC characteristics describe the process of output following the input. Bode plot is a good tool to show the accuracy of input-output conversion. The following plots show the output gain and the output phase with a 1 Vpp sinusoid as the input signal. Charge Balance Stimulation In order to have a charge-balanced stimulation, the device should sink the exact same amount of charge that is delivered to the target. 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, cause current leakage at the output, which will be accumulated after multiple cycles and cause electrode corrosion. This feature subtracts DC value from input signal. DC value of signal is driven by an integrator with a time constant of 0.1 s. CAUTION: Only if charge-balanced stimulation is required, toggle the charge-balanced switch from “Normal” state to “Chrg blncd”. Battery and Charging Battery capacity of 10 Ah with fresh batteries 4 level battery indicator 15 V DC 2 A wall adapter Charging status LED (Red: Charging, Green: Charged) Caputron Linear Current Isolator High Current uses high capacity Li-ion batteries. The lifetime of these batteries is around 1200 periods of charging and discharging, and they need the least amount of maintenance. Batteries can power the device on for more than 4 hours of continuous stimulation with 1mA output current. Beyond the rated lifespan of the battery, the capacity of them fall and the device needs to be charged more frequently. It is recommended to not use batteries beyond their rated lifespan. Batteries can be easily replaced by opening the device and inserting new batteries with the same specifications. Isolator Device Comparison Table and Specifications This device comparison table provides an overview of the specifications and features between the Caputron High Precision Linear Current Isolator, Caputron High Precision Linear Current Isolator, Caputron High Voltage Linear Current Isolator, Stanford Research Systems Model CS580 Voltage Controlled Current Source, A-M Systems Model 2200 Analog Stimulus Isolator and World Precision Instruments A395RC Linear Stimulus Isolator. Below is a table containing detailed data of different parameters that can be useful for the assessment of each product. All products were new, calibrated and tested under the same exact conditions. Device comparison highlights (1) Scaled performance of highlighted parameters Device ranges were set to 1 mA/v in all tests (LCI HC output is scaled down by 2.5) Percentage of Full Scale Range error CS580 is powered by main power (unlimited power) Measurements are normalized to the best performance Download Caputron Isolator Overview and Spectifications
