Current-to-Voltage Converters

Current-to-voltage converters are electronic devices that convert current signal inputs to proportional voltage outputs. They include an operational amplifier for simple linear signal processing and a resistor for dissipating current. The resistance between the operational amplifier’s input and output determines the voltage range for specific current signals. Additional circuitry such as an instrumentation amplifier removes small amounts of reverse or dark current. In current-to-voltage converters that handle a range of currents, design considerations account for the DC offset caused by both the input device and the operational amplifier. To remove unwanted signals, current-to-voltage converters often include passive filters that use only capacitors or active filters that use gain and feedback. 

Device specifications for current-to-voltage converters include the number of analog channels and the number of differential channels. When single-ended outputs are available, suppliers often specify the maximum number of analog channel outputs as twice the number of differential outputs. Differential channels, which have two inputs, define the voltage as the signal to process between the two inputs. Other device specifications for current-to-voltage converters include maximum output voltage, accuracy, signal isolation, and multiplexing. Accuracy, which is represented as a percentage of a full measurement range, depends on factors such as signal conditioning linearity, hysteresis, and temperature. Signal isolation can be achieved through optical isolation, magnetic induction, or the use of capacitors. Current-to-voltage converters that include multiplexers can combine several AC or DC inputs serially into one output.

The operational amplifiers that current-to-voltage converters use vary in terms of gain range, programmable gain, and bandwidth. Gain, the factor by which input signals are multiplied, is frequently greater than unity; however, gain can be fractional when a reduction (attenuation) of signal amplitude is desired. Current-to-voltage converters that include operational amplifiers with programmable gain allow users to adjust gain from a local panel or computer interface. Some current-to-voltage converters feature a touch screen. Others provide handheld or programmable devices. Bandwidth, the difference between the high and low limits of the frequency response, is a measurement that is typically defined by a variation from a nominal value by a stated value such as 3 dB.

Current-to-voltage converters are available in a variety of form factors. Some devices mount on integrated circuits (ICs), standard DIN rails, or printed circuit boards (PCBs) that attach to enclosures or plug into computer backplanes. Others bolt into walls, cabinets, enclosures, or panels. Rack-mounted units fit inside a standard 19” telecommunications rack. Modular styles include stackable units that dock in bays, slots, or boxes. Benchtop or freestanding current-to-voltage converters often feature full casings or cabinets and integral interfaces.