Delta-Sigma Quantizer Code Suppression for Lower PWM Noise
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Solution Overview
Problem
Digital delta-sigma modulators experience noise performance degradation due to non-linearities in transducers driven by PWM output signals, caused by factors like clock jitter, driver mismatch, load current, and transducer impedance variations.
Innovation Solution
A digital delta-sigma modulator with a loop filter and a multi-bit quantizer that operates in two modes: normal mode and code suppression mode, where the quantizer generates values from a set or subset of quantization levels, respectively, to mitigate noise by increasing linearity and load-current settling time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a multi-bit quantizer operates in normal mode using the full set of quantization levels, then the dynamic range and resolution are improved, but noise performance deteriorates due to inter-symbol interference and transducer non-linearities
Solution Approach 1:
The quantizer dynamically switches between two operating modes: normal mode using the full set of quantization levels for high resolution, and code suppression mode using a restricted subset of codes to reduce noise. This dynamic adaptation allows the system to optimize between resolution and noise performance based on operating conditions
Solution Approach 2:
The system changes the parameter of available quantization codes by restricting the code set during code suppression mode. This parameter change reduces the interaction between quantizer output and transducer non-linearities, thereby reducing noise while maintaining acceptable resolution
2Reliability
If the quantizer uses all available quantization levels, then the signal fidelity is improved, but inter-symbol interference increases causing noise performance degradation
Solution Approach 1:
The invention extracts and removes certain quantization codes from the available code set during code suppression mode. By taking out specific codes that contribute most to inter-symbol interference, the system reduces noise while maintaining signal fidelity through the remaining codes
3Object-affected harmful factors
If code suppression mode is used to reduce noise, then noise performance is improved, but the effective quantization levels are reduced
Solution Approach 1:
The system dynamically selects between normal mode and code suppression mode based on operating conditions. This dynamic operation allows the system to achieve low noise performance when using the restricted code set while maintaining high resolution when the full code set is utilized
Data Source
AI summary
A digital delta-sigma modulator may include a loop filter having a loop filter input configured to receive an input signal and generate an intermediate signal responsive to the input signal and a multi-bit quantizer configured to quantize the intermediate signal into a quantized output signal which is fed back as an input to the loop filter. The multi-bit quantizer may further be configured to operate in at least two modes comprising: (a) a normal mode in which, for each sample of the intermediate signal, the multi-bit quantizer generates a corresponding sample having a value selected from a set of a plurality of quantization levels; and (b) a code suppression mode in which, for each sample of the intermediate signal, the multi-bit quantizer generates a corresponding sample having a value selected from a subset of the set of a plurality of quantization levels.