SAR-Controlled Current Converter for Wide-Range Precision Sensing
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Solution Overview
Problem
Current current-to-digital converters face challenges in achieving a wide dynamic range of at least 100 dB with low power consumption while maintaining sub-pA current sensitivity, as existing solutions either consume high power or compromise on precision due to flicker noise and power-hungry components.
Innovation Solution
A current-to-digital converter utilizing a delta-sigma analogue-to-digital converter with a successive-approximation-register control logic and a 1-bit current digital-to-analogue converter for feedback, which modulates the input current using a modulation switch controlled by an optimal modulation clock, achieving high precision and linearity with reduced power consumption by using a small on-chip current reference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a low-noise trans-impedance amplifier (TIA) followed by an adapted analogue-to-digital converter (ADC) is used, then measurement precision is improved, but power consumption increases dramatically
Solution Approach 1:
The patent replaces the traditional TIA-ADC architecture with a current-mode VCO-based CDC (current-to-digital converter) architecture. This substitution eliminates the need for power-hungry TIAs and ADCs by directly converting current to digital signals using a voltage-controlled oscillator, achieving both low power consumption and high measurement precision through noise-shaping techniques
Solution Approach 2:
The patent changes the operating parameters by using a VCO-based quantizer with noise-shaping instead of traditional ADC conversion. The system operates in current-mode throughout the signal path and uses digital differentiator to realize 2nd order noise-shaping, fundamentally changing how current measurements are performed to reduce power consumption while maintaining precision
2Manufacturing precision
If dynamic-element-matching (DEM) is employed to suppress mismatches in the current-steering DAC, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The patent implements a feedback mechanism where the output of the VCO-based quantizer is fed back through a digital differentiator to achieve 2nd order noise-shaping. This feedback loop continuously corrects quantization errors and suppresses the impact of DAC mismatches, improving linearity without requiring complex DEM control circuits
3Measurement precision
If a revised asynchronous delta-sigma modulator is used to achieve wide dynamic range, then measurement precision is improved, but device complexity and power consumption increase due to DEM controls and backend calibration
Solution Approach 1:
The patent substitutes the complex asynchronous delta-sigma modulator with a simpler synchronous VCO-based CDC architecture. The system achieves wide dynamic range (73 dB) through the VCO's natural frequency modulation characteristics combined with noise-shaping, eliminating the need for complex asynchronous controls and backend calibration circuits
4Measurement precision
If on-chip current references larger than the input current are used, then measurement precision is improved, but power consumption increases when large input currents are sensed
Solution Approach 1:
The patent employs a dynamic current reference system where the reference current can be programmably adjusted to match the magnitude of the input current being measured. This dynamic adaptation allows the system to maintain high current sensitivity for small signals while consuming minimal power when measuring larger currents, as the reference current scales with the input signal level
Data Source
AI summary
This disclosure relates to a current-to-digital converter suitable for wide-ranging current sensing applications. In particular, the current-to-digital converter comprises a delta-sigma analogue-to-digital converter which utilizes a successive-approximation-register to control a modulation of the sensed current so that the digital conversion of the modulated sensed current by the delta-sigma analogue-to-digital converter may be done with high precision.