Sensor Interface Voltage Control Using a Digital Servo-Loop
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing sensor assemblies face challenges with noise, capacitive loading, and power consumption due to large filter capacitors and analog servo-loops, which affect the accuracy and efficiency of signal processing.
Innovation Solution
The implementation of a digital servo-loop (DSL) with a low-power ADC and a selectable forward signal-path ADC, which reduces capacitive loading, noise, and power consumption while improving low-frequency roll-off control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an analog servo-loop (ASL) with a large filter capacitor is used, then voltage regulation at the interface circuit input is achieved, but capacitive loading attenuates the input signal and noise increases
Solution Approach 1:
The patent replaces the analog servo-loop (ASL) with a digital servo-loop (DSL) that uses a sigma-delta modulator and digital filter instead of analog components. This substitution eliminates the large filter capacitor and associated capacitive loading, while maintaining voltage regulation functionality through digital control of a current source that compensates for leakage current at the high-impedance input node.
Solution Approach 2:
The invention changes the operating parameters by using a small capacitor in the DSL compared to the large capacitor in the ASL. The digital approach allows for precise control of the compensation current parameters, enabling effective voltage regulation with minimal capacitive loading. The sigma-delta modulation technique transforms the regulation problem into a digital domain where parameters can be optimized independently of capacitive effects.
2Reliability
If an analog servo-loop (ASL) is used, then voltage regulation is provided, but the ASL itself becomes a source of noise
Solution Approach 1:
The patent replaces the analog servo-loop with a digital servo-loop that performs voltage regulation in the digital domain. The sigma-delta modulator converts the analog voltage error signal into a digital bit stream, which is then processed by a digital filter and converted back to control a current source. This digital intermediary processing eliminates the noise generation inherent in analog feedback loops while preserving the regulation function.
3Object-affected harmful factors
If a digital servo-loop (DSL) with ADC is used, then capacitive loading and noise are reduced, but power consumption increases due to ADC current draw
Solution Approach 1:
The patent extracts the voltage regulation function from the main signal processing path by using a separate feedback loop that monitors the input node voltage and controls a compensation current source. The sigma-delta modulator in this feedback loop operates at low power by utilizing the existing high-impedance input node for sampling, avoiding the need for a full-power ADC that would otherwise be required for accurate voltage measurement.
Solution Approach 2:
The invention makes the sigma-delta modulator multi-functional by using it both for voltage regulation in the feedback loop and for the main signal conversion function. The same modulator circuit serves dual purposes, eliminating the need for separate high-power ADCs and reducing overall power consumption while maintaining the benefits of digital control.
Data Source
AI summary
A sensor assembly including a transducer and interface circuit with a DSL-controlled input voltage is disclosed. The interface circuit includes a logic circuit configured to generate and provide a pulse width and amplitude modulated (PWAM) signal to an n-bit iDAC coupled to an analog front end (AFE) amplifier or buffer. The PWAM signal is based on an output of a forward signal-path ADC or low-power ADC coupled to the AFE amplifier or buffer, wherein the n-bit iDAC regulates a voltage at the input of the AFE amplifier or buffer based on the PWAM signal.