Pattern Detection Circuit for 8-Bit Silence in Audio Bit Streams
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Solution Overview
Problem
Audio reproduction devices using sigma-delta modulation face issues with detecting repetitive 8-bit silence patterns, leading to spectral tones that can overload amplifiers or speakers, causing audible artifacts or damage.
Innovation Solution
A pattern detection circuit that sums and inverses sequences of alternate bits in a bit stream, comparing these sums to determine if they are equal, allowing for the detection of repetitive patterns with equal numbers of logic values without detecting other patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple pattern detection method is used, then the circuit complexity is reduced, but the detection precision deteriorates leading to false detection of non-silence patterns
Solution Approach 1:
The bit stream is divided into alternate sequences (first sequence and second sequence) that are processed separately. The summing circuitry processes the first sequence during first alternate time periods and the second sequence during second alternate time periods, allowing independent analysis of different bit patterns to improve detection accuracy while maintaining manageable circuit complexity
Solution Approach 2:
The invention forms an inverse of the sum of the second sequence and compares it with the sum of the first sequence. This inversion approach allows the circuit to detect patterns where equal numbers of ones and zeros occur in specific alternating positions, enabling precise identification of silence patterns while rejecting false positives from other repetitive patterns
2Measurement precision
If the pattern detection is made more selective to avoid false detection, then the detection precision is improved, but the device complexity increases
Solution Approach 1:
The summing circuitry operates in periodic alternating time periods, processing the first sequence during first alternate time periods and the second sequence during second alternate time periods. This periodic operation allows the circuit to systematically compare different bit positions over time, achieving high detection precision through time-multiplexed processing rather than requiring complex parallel circuitry
Solution Approach 2:
The invention changes the temporal parameter of processing by alternating between different sequences at different time periods. This parameter change allows a single summing circuit to effectively perform multiple comparison functions sequentially, achieving high detection precision without proportionally increasing circuit complexity
Data Source
AI summary
A pattern detection circuit detects a pattern in a received bit stream, for example a repetitive 8-bit silence pattern in a stream of digital audio data. Summing circuitry forms during first alternate time periods a sum of a first sequence comprising a predetermined number of alternate bits in the bit stream; and forms during second alternate time periods an inverse of a sum of a second sequence comprising the predetermined number of alternate bits in the bit stream. It is then determined whether successive sums formed by the summing circuitry are equal.