Voltage-to-frequency converters are electronic devices that convert voltage inputs to linearly proportional frequency outputs. They consist of an analog input amplifier, a precision oscillator system, a resistor-capacitor (RC) network, and a power supply. Low-drift input amplifiers enable voltage-to-frequency converters to process small signals while offering high levels of input resistance. Input amplifiers provide high impedances to positive voltages and low impedances to negative voltages. Scaling resistors adjust and trim a range of voltages while timing capacitors determine the full-scale frequency. Typically, voltage-to-frequency linearity requires the use of capacitors with low dielectric absorption (DA). Charge-balanced voltage-to-frequency converters provide increased accuracy and linearity, but have greater supply voltage and current requirements.
Voltage-to-frequency converters can receive AC or DC voltage inputs and output frequencies or pulse signals by using techniques such as amplitude modulation (AM), frequency modulation (FM), and pulse width modulation. Some voltage-to-frequency converters send outputs to timers, counters, relays, switches, and potentiometers. Others can output voltage ranges such as 0 – 10 V or current loops such as 4 – 20 mA. Integral filters allow some frequencies to pass while attenuating others. Programmable filters allow users to set and change parameters such as the low pass frequency, the nominal frequency below which input signals are passed and above which input signals are blocked.
Device specifications for voltage-to-frequency 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 voltage-to-frequency converters include maximum output voltage, accuracy, bandwidth, and signal isolation. Accuracy, which is represented as a percentage of a full measurement range, depends on factors such as signal conditioning linearity, hysteresis, and temperature. Bandwidth, the difference between the high and low limits of the frequency response, is typically defined by a variation from a nominal value by a stated value such as 3 dB. Signal isolation can be achieved through optical isolation, magnetic induction, or the use of capacitors.
Form Factors Available
Voltage-to-frequency 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 voltage-to-frequency converters often feature full casings or cabinets and integral interfaces.
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