CTDSM Noise Transfer Synthesis for Stable High-SQNR Modulators
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Solution Overview
Problem
Higher-order continuous-time delta-sigma modulators (CTDSMs) face limitations in stability and signal-to-noise ratio (SNR) due to the order of their loop filters, which restricts their performance in achieving high linearity and bandwidth requirements for applications like high-quality radio and car radar systems.
Innovation Solution
The synthesis of a noise transfer function with a first-order roll-off at high frequencies is achieved by configuring a CTDSM with a cascade of integrators and feed-forward loop filters, using coefficients determined through mathematical tools like Matlab, to enhance the signal-to-quantization-noise ratio (SQNR) and enable reduced sampling frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If higher-order loop filters are used to aggressively shape in-band quantization noise, then in-band SQNR is improved, but stability of the feedback loop deteriorates
Solution Approach 1:
The patent changes the parameter of the noise transfer function by introducing a first-order roll-off at high frequencies. This modifies the conventional higher-order noise transfer function to have reduced gain at frequencies above the signal bandwidth, thereby improving feedback loop stability while preserving in-band noise shaping performance. The modified transfer function maintains the aggressive in-band noise shaping benefits while preventing the stability issues that arise from high-frequency gain in traditional higher-order designs.
2Measurement precision
If higher-order loop filters are used to shape quantization noise, then in-band SQNR is improved, but the sampling frequency must be increased, increasing device complexity
Solution Approach 1:
The patent modifies the noise transfer function parameters to include a first-order roll-off characteristic that suppresses out-of-band noise. This parameter change allows the system to achieve the same or better in-band SQNR performance at lower sampling frequencies, thereby reducing the complexity requirements for high-speed operation while maintaining effective quantization noise shaping in the signal band.
Data Source
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AI summary
Embodiments of circuits and methods are described below that may provide a modulator that has an enhanced signal-to-quantization-noise ratio (SQNR) for a given sampling frequency and bandwidth or that may enable a reduced sampling frequency for a target SQNR and bandwidth. In one or more embodiments, a modulator circuit may include a first modulator including an input and a first output, and including one or more feed-forward components; an output circuit including an input coupled to the first output and including an output, the output circuit including one of a noise-shaping circuit, a noise-shaped quantizer circuit, or an integrator and feed-forward component; and coefficients of the one or more feed-forward components of the first modulator and a transfer function of the output circuit provide a higher-order modulator with a first-order roll-off at high out-of-band frequencies.