Large-amplitude Dithering Mitigates Glitches in Digital-to-analogue Converters

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This paper develops and experimentally evaluates a dither-based method for improved generation of arbitrary signals in digital-to-analogue converters that exhibits glitches --- essentially converting the glitches from high-frequency to low-frequency disturbances. One major benefit of this behaviour appears in closed-loop control applications, as the glitch disturbance can be moved from outside control law bandwidth to inside control law bandwidth, enabling suppression by feedback. A behavioural model of glitches is presented and the effect of applying a dither signal is analysed in detail. Analytical and experimental results demonstrate that a dither signal with sufficiently large amplitude can mitigate the effect of glitches, when used in conjunction with a low-pass filter. Severe glitches appear in various digital-to-analogue converter topologies, including converter topologies that are used in high-precision motion control applications, such as adaptive optics and scanning force microscopy. Glitches introduce impulse-like disturbances which have a broadband frequency distribution. Low-pass filtering alone does not provide sufficient attenuation, and in applications with feedback control only frequency content within the control law bandwidth is attenuated. Hence, a high-frequency disturbance such as a glitch will not be suppressed. The use of dithering to suppress glitches is therefore beneficial in applications where errors in signal conversion are a primary concern, such as high-precision motion control or accurate reference signal generation.