Single-Bit DAC Element Rotation to Shift Audible Noise Tones
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Solution Overview
Problem
Digital-to-analog converters experience noise tones due to repetitive selection of elements when processing consecutive input signals, leading to audible tones in the output, especially when input signals include DC components.
Innovation Solution
A digital-to-analog converter method and apparatus that selects elements in a predetermined order, starting from the last selected element in the preceding time period, and excluding a temporarily omitted element, to shift noise tones to higher frequencies, making them inaudible.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If elements are selected consecutively in a logical ring based on input signal value, then distortion is reduced and low frequency noise components are minimized, but noise tones appear at specific frequencies when the same input signal is received consecutively
Solution Approach 1:
The patent implements periodic action by systematically varying the starting element selection in each time period based on a counter value. Instead of always starting from the same element for a given input value, the selection wraps around the logical ring of elements periodically, ensuring that the same group of elements is not repeatedly selected for consecutive identical input signals. This periodic variation shifts noise tones to higher frequencies where they become inaudible.
Solution Approach 2:
The patent applies dynamics by making the element selection process adaptive and time-varying. The starting element for selection is dynamically determined by a counter that increments over time, causing the selection pattern to change even when the input signal remains constant. This dynamic behavior prevents the system from settling into a fixed repetitive pattern that would generate audible noise tones.
2Ease of operation
If the same group of elements is selected repeatedly for consecutive input signals, then the conversion process is simple and deterministic, but tones appear in the output at frequencies corresponding to the repetition rate
Solution Approach 1:
The patent introduces periodic action by implementing a counter that systematically varies the starting element selection across time periods. This creates a controlled periodic variation in element selection that prevents repetitive patterns while maintaining a systematic and predictable selection process. The periodic shifting of selection patterns moves noise energy to higher frequencies.
Solution Approach 2:
The patent changes the selection parameter (starting element position) over time using a counter variable. This parameter change ensures that even when the input signal value remains constant, the actual elements selected change periodically, preventing the generation of tones at the repetition frequency while maintaining ease of implementation through simple counter logic.
Data Source
AI summary
A digital-to-analog converter having an input for receiving a digital input signal during each time period. A plurality of elements are each adapted to produce an analog output in response to an input, and an encoder selects a number of the elements and applies inputs to the selected elements. An analog output signal is then formed by summing outputs of the plurality of elements. The encoder selects the number of elements based on a value of the digital input signal, and selects the elements in a predetermined order from the plurality of elements, starting from an element determined by the elements selected in an immediately preceding time period, and excluding a temporarily omitted one of the plurality of elements.