Frequency converters and translators scale and/or filter frequency inputs to produce outputs signals with frequencies that are a function of the inputs. Differential analog inputs, bandwidth, accuracy, and signal isolation are the most important device specifications to consider when searching for frequency converters and translators. Differential channels use the difference between two signals as an input; common mode is filtered out. In some systems, differential inputs are combinations of two single-ended inputs; in this case, half the number of differential channels would be available as single-ended inputs. Bandwidth is the difference between the high and low limits of the frequency response, typically defined by a variation from a nominal value by a stated value such as 3 dB. Accuracy depends on the signal conditioning linearity, hysteresis, temperature considerations, etc. It is represented here as percent full scale of measurement range. Signal isolation is the separation of any direct electrical contact of a signal. This can be done in various ways including optical isolation, capacitors, and magnetic induction.
Signal inputs can be AC voltage input or AC current input. Choices for form factor for frequency converters and translators can be IC or board mount, circuit board, panel or chassis mount, modular bay or slot system, DIN rail, rack mount, and stand-alone. Filter specifications to consider when searching for frequency converters and translators include integral filters, filter architecture, filter function, low pass cutoff frequency, high pass cutoff frequency, and programming. A filter will allow certain signal frequencies to pass while attenuating others. Filters can operate on signal phase also. Filter architecture can be analog or RC, or digital FIR or IIR. An analog filter is designed with resistors and capacitors. It is used for analog signals only and is often used in low-noise requirement applications. A digital filter is designed with solid-state components and is used for digital signals and quantized signals from a sample-and-hold amplifier. This category includes Finite Impulse Response (FIR) and Infinite Impulse Response (IIR) filters. Digital filtering can approach ideal bandpass characteristics. The filter function can be low pass, high pass, band pass, band stop, and all pass. The low pass cutoff frequency is the nominal frequency below, which input signal is passed and above which the signal is blocked. The high pass cutoff frequency the nominal frequency above which the input signal is passed and below which the signal is blocked. In a programmable filter the filter user may interactively program parameters such as cutoff frequencies.
Amplifier specifications for frequency converters and translators are also important to consider. Amplifiers multiply a signal to the matching scale of the input device. Amplifier gains, or multiplication factors, may be greater than one or fractional for signal reduction. Amplifier gain may be adjusted according to the application needs. Adjustment may be from a local interface (such as a front panel) or from a computer interface. Gain is the factor by which the input signal is multiplied. Gains are frequently greater than unity, but may be fractional when a reduction (attenuation) of signal amplitude is desired. The maximum output of the amplifier is the limit of output voltage. User interface choices for frequency converters and translators include none, front panel and display, touch screen, handheld or remote programmer, and computer programmable.
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