Multi-Bit SDM Encoder for Lower-Power Noise-Shaped Output
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Solution Overview
Problem
Pulse density modulation (PDM) systems face significant energy loss when driving capacitive loads due to high-frequency signal toggling between maximum and minimum levels, leading to inefficient energy utilization and a compromised signal-to-quantization-noise ratio (SQNR).
Innovation Solution
The introduction of a signal density modulation (SDM) encoder, which employs a multi-bit quantizer and a sigma circuit to generate an output signal with more than two levels, replacing the traditional comparator, thereby reducing power consumption and enhancing SQNR through noise shaping capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If PDM system uses high-frequency signal toggling between maximum and minimum levels to drive capacitive load, then signal-to-quantization-noise ratio (SQNR) is maintained, but energy loss increases tremendously
Solution Approach 1:
The patent changes the output signal parameters by introducing intermediate levels between the maximum and minimum levels. The output stage generates signals with multiple amplitude levels rather than binary toggling, which reduces the voltage swing magnitude and consequently decreases energy consumption while maintaining adequate SQNR through controlled signal variations
Solution Approach 2:
The patent implements dynamic signal level adjustment where the output signal adapts its amplitude based on the input signal characteristics. By dynamically selecting appropriate output levels rather than fixed maximum-minimum toggling, the system optimizes energy consumption while preserving signal fidelity and SQNR performance
2Productivity
If PDM system uses 1-bit quantizer with high-frequency toggling, then encoding simplicity is maintained, but energy utilization efficiency deteriorates
Solution Approach 1:
The patent modifies the quantization output parameters by introducing multiple amplitude levels. This parameter change improves energy utilization efficiency by reducing unnecessary high-frequency toggling between extreme levels, while the encoding complexity remains manageable through structured level selection based on input signal characteristics
3Measurement precision
If PDM system toggles signal between maximum and minimum levels at extremely high frequency, then signal representation accuracy is maintained, but power consumption increases
Solution Approach 1:
The patent changes the signal amplitude parameters by introducing intermediate levels between maximum and minimum. This reduces the voltage swing magnitude and power consumption while maintaining signal representation accuracy through controlled variations in signal levels that preserve the essential information content
Solution Approach 2:
The patent employs periodic signal patterns with controlled duty cycles rather than continuous high-frequency toggling. By using periodic action with optimized timing and level duration, the system maintains accurate signal representation while reducing average power consumption through strategic use of intermediate levels
Data Source
AI summary
A signal density modulation (SDM) encoder includes a first subtractor, a sigma circuit and a multi-bit quantizer. The first subtractor is used for receiving an input signal. The sigma circuit is coupled to the first subtractor. The multi-bit quantizer, coupled to the first subtractor and the sigma circuit, is configured to generate an output signal. The sigma circuit or the multi-bit quantizer produces a first feedback signal to the first subtractor. The first subtractor performs a subtraction operation according to the first feedback signal and the input signal, and generates a delta signal. The sigma circuit performs an operation on the delta signal, such that the SDM encoder has a noise transfer function having a high pass filtering effect. The noise transfer function is a ratio of a quantization error brought by the multi-bit quantizer with respect to the input signal. The output signal has more than two levels.