Digital-to-Analog Converters

Digital-to-analog converters transform a digital word representing an analog value such as a voltage into an output corresponding to that analog signal. The fineness of the signal is represented by resolution in bits. Important device specifications to consider when searching for digital-to-analog converters include output channels, resolution, maximum or reference voltage, bandwidth, accuracy, and output impedance.  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, twice the number of differential channels would be available as single-ended inputs.  Resolution refers to the degree of fineness of the digital word representing the analog value. A ten-bit number contains 2¹⁰, or 1024, increments. A 0-10V signal could therefore be resolved into approximately 0.01V increments. A 12-bit representation would be in 2¹² (4096) increments, or divisions of 0.0024V for the same signal. Each additional bit doubles the resolution, and one bit is required for the polarity (sign) of a number.  The maximum or reference voltage is the limit of output voltage.  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.  The output impedance is the impedance that the amplifier appears to present to its output terminals, and thus to its load's impedance.

Common outputs for digital-to-analog converters include voltage output, such as 0-10V, ±5V, etc, current output such as 0-20mA, 4-20 mA current loop, etc, frequency output such as AM, FM, or PWM monitoring or control, timer or counter output, counting or timing of measured events, relay switch type output; contacts are open or closed depending on the state of one or more of the inputs, and resistance or potentiometer output such as a potentiometer.  Form factor choices for digital-to-analog converters include IC or board mount, circuit board, panel or chassis mount, modular bay or slot system, rack mount, DIN rail, and stand-alone.

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