Delta-Sigma Modulator Feedback for Out-of-Band Noise Suppression
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Solution Overview
Problem
Delta-sigma modulators and converters face challenges with low clock jitter tolerance due to noise folding back into the frequency band of interest, leading to degraded noise characteristics and increased circuit size from the need for multiple DACs in existing configurations.
Innovation Solution
A delta-sigma modulator configuration that feeds back the output signal of a quantizer and a differentiated error signal to the integrator, reducing out-of-band quantization noise through low-pass filtering without increasing the number of DACs, thereby maintaining noise suppression and circuit efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If multiple DACs are disposed in the feedback path to calculate moving sum, then out-of-band quantization noise is suppressed, but circuit size increases
Solution Approach 1:
The patent extracts the moving sum calculation function from the feedback path by removing multiple DACs. Instead, it calculates the moving sum of the quantizer output in the digital domain before feedback, thereby eliminating the need for multiple analog DACs in the feedback path while still achieving suppression of out-of-band quantization noise.
Solution Approach 2:
The patent replaces the analog moving sum calculation mechanism (using multiple DACs in the feedback path) with a digital domain calculation mechanism. The digital signal processor or logic circuit computes the moving sum of the quantizer output bits, substituting the mechanical/analog approach with a digital one that consumes less area.
2Area of stationary object
If digital moving sum calculation is performed, then circuit size is reduced, but bit number of digital signal increases
Solution Approach 1:
The patent applies partial action by calculating the moving sum of only the necessary number of recent quantizer output bits (e.g., 2-tap moving sum using current and previous bit) rather than processing the entire signal history. This limits the bit width increase to a manageable level while still achieving noise suppression at the Nyquist frequency.
3Object-affected harmful factors
If AFIR filter DAC is used, then out-of-band quantization noise is suppressed, but number of DACs increases
Solution Approach 1:
The patent removes the AFIR filter DAC structure from the system by extracting its noise suppression function and implementing it differently. Instead of using an AFIR filter followed by multiple DACs, the patent directly calculates the moving sum of the quantizer output in the digital domain and feeds it back, achieving the same noise suppression effect with a single DAC.
4Manufacturing precision
If DEM circuit is added for mismatch correction, then analog circuit performance is improved, but additional logic circuit is required
Solution Approach 1:
The patent replaces the analog DEM circuit with a digital domain solution. By performing the moving sum calculation digitally and using digital logic for feedback, the system eliminates the need for complex analog DEM circuits while achieving similar or better performance through digital signal processing.
Data Source
AI summary
A delta-sigma modulator is configured to feedback an output signal of a quantizer to an input of an integrator, and also feedback to the input of the integrator a differentiated error signal representing derivative of quantization error caused by the quantizer.