High-Pass Dither Injection for CT ADC Quantizer Linearity
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Solution Overview
Problem
Continuous-time (CT) residue generation systems in analog-to-digital converters (ADCs) face challenges in minimizing quantization errors, which lead to signal-dependent distortion and corruption of the output spectrum due to insufficient quantization error cancellation.
Innovation Solution
The implementation of a high-pass shaped dither signal, generated using a dither generation circuit that includes a pseudorandom binary sequence generator and a high-pass filter, is injected into the quantizer to reduce correlation between quantization error and digitized output, thereby improving quantizer linearity and minimizing signal-dependent distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional dither signals are used in CT residue generation systems, then quantization error correlation is reduced, but signal-dependent distortion increases and error correction range is reduced
Solution Approach 1:
The patent applies spectral shaping to the dither signal by modifying its frequency domain characteristics through a high-pass filter. This transforms the dither signal from a conventional flat spectrum to a high-pass shaped spectrum, concentrating dither energy at higher frequencies while maintaining its noise-shaping function. This parameter change in the dither signal's spectral distribution resolves the contradiction by preserving quantizer linearity while reducing signal-dependent distortion and maintaining error correction range.
Solution Approach 2:
The patent applies different spectral characteristics to different frequency regions of the dither signal. By using high-pass filtering, the dither signal acquires localized high-energy characteristics at high frequencies and low-energy characteristics at low frequencies. This local quality differentiation allows the dither to effectively reduce quantization error correlation in the signal band while minimizing its impact on signal-dependent distortion and residue signal power.
2Measurement precision
If dither signals are injected to reduce quantization error, then quantizer linearity improves, but residue signal power increases
Solution Approach 1:
The patent changes the spectral parameter of the dither signal by applying high-pass filtering, which redistributes the dither energy across the frequency spectrum. This spectral transformation maintains the dither's ability to reduce quantization error correlation while concentrating its energy away from the signal band, thereby minimizing the increase in residue signal power that would otherwise occur with conventional dither signals.
Solution Approach 2:
The patent converts what would normally be harmful dither energy (which increases residue signal power) into a beneficial effect by spectrally shaping it. The high-pass filtering transforms the dither signal so that its energy is concentrated at frequencies where it provides quantization error reduction without significantly impacting the signal band, thus converting potential harm into benefit.
3Reliability
If high-pass shaped dither is used to minimize residue signal power impact, then error correction range is maintained, but system complexity increases
Solution Approach 1:
The patent implements high-pass spectral shaping of the dither signal using a relatively simple filtering approach. By applying a high-pass filter to the dither signal, the system achieves spectral shaping that maintains error correction range while avoiding the need for complex multi-bit dither sequences or sophisticated modulation schemes. This parameter change in the dither generation approach preserves reliability without proportionally increasing device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The use of high-pass shaped dither signals effectively reduces signal-dependent distortion and maintains the error correction range, enhancing the linearity and noise performance of the ADC system by spectrally shaping the dither signal to minimize its impact on the residue signal power.
Implementation Method 1
a high-pass filter L(s) to shape the dither signal r(t)
Data Source
AI summary
Mechanisms for reducing or eliminating a quantization error caused by a quantizer of a continuous-time (CT) residue generation system are disclosed. In particular, systems and methods described herein are based on using a dither generation and injection circuit that can perform a high-pass filtering of the additive dither signal (i.e., a high-pass shaped dither signal). Using high-pass shaped dither signals is expected to improve quantizer linearity without significantly reducing the available error correction range. The applied dither may be particularly effective at minimizing signal-dependent distortion in ADC output spectrum caused by the quantizer when the quantization error cancellation accuracy may be insufficient.