Chopped Sensor Readout Circuit for Low-Power High-Resolution ADC
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Solution Overview
Problem
There is a need for a semiconductor device that can read and output high-resolution signals from small-sized sensors operating in low frequency bands while consuming less power, as existing devices struggle with these requirements.
Innovation Solution
The semiconductor device includes a signal input circuit for selecting sensor signals, an amplifier circuit with capacitive feedback for amplification, and an analog-to-digital converter (ADC) with a delta-sigma modulator and filters to convert and process the signals, employing chopping operations to reduce noise and adjust phase, thereby enhancing signal quality and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional reading circuits are used for DC sensors, then the device structure is simple, but the signal resolution is poor and power consumption is high
Solution Approach 1:
The reading circuit is divided into multiple specialized functional blocks: a first chopping circuit for DC offset cancellation, a correlated double sampling circuit for noise reduction, a second chopping circuit for additional offset correction, and a delta-sigma ADC for high-resolution conversion. This segmentation allows each block to address specific signal quality issues independently, achieving high resolution without requiring a completely complex redesign.
Solution Approach 2:
Chopping circuits are introduced as intermediary components between the sensor and the ADC. These chopping circuits modulate the sensor output signal to a higher frequency range where noise is reduced, then demodulate it back to baseband. This intermediary processing step effectively separates the weak sensor signal from noise and DC offset, enabling high-resolution measurement without directly complicating the main signal path.
2Object-affected harmful factors
If conventional amplification methods are used, then the circuit is simple, but noise suppression is insufficient and linearity is poor
Solution Approach 1:
The chopping circuits employ periodic switching at a specific chopping frequency to modulate the sensor signal. By periodically switching the signal polarity and using correlated double sampling synchronized to this periodic action, the circuit effectively separates the periodic sensor signal from non-periodic noise and DC offset, achieving superior noise suppression through timing-based discrimination.
Solution Approach 2:
The correlated double sampling circuit uses feedback mechanisms to subtract previously sampled noise and offset components from the current signal. By feeding back reference samples taken during known noise-only periods and subtracting them from signal-containing periods, the circuit dynamically cancels noise and offset, improving signal quality through adaptive feedback processing.
3Measurement precision
If high-resolution ADCs are used, then signal precision is improved, but power consumption increases
Solution Approach 1:
The chopping circuits introduce a controlled oscillation (vibration) at the chopping frequency to modulate the sensor signal up to a higher frequency range. This frequency translation allows the use of simpler, lower-power ADCs that can operate at the chopped frequency rather than requiring high-resolution, high-power ADCs that would be needed to directly digitize the low-frequency sensor output with equivalent precision.
Solution Approach 2:
The system changes the frequency parameter of the signal through chopping, transforming the low-frequency sensor output into a higher-frequency modulated signal. This parameter transformation enables the use of more power-efficient ADC architectures that are optimized for higher frequencies, reducing overall power consumption while maintaining or improving effective resolution through the subsequent demodulation and filtering stages.
Data Source
AI summary
A semiconductor device includes a signal input circuit configured to select one of the plurality of differential sensor signals according to a channel selection signal; an amplifier circuit configured to amplify an output of the signal input circuit; and an analog-to-digital converter (ADC) configured to convert an output of the amplifier circuit into a digital value, wherein each of the plurality of sensor signals is a differential signals and the signal input circuit changes polarity of an output signal thereof according to a first chopping signal, and wherein the ADC includes a delta-sigma modulator configured to generate a bit stream from an output of the amplifier circuit; an output chopping circuit configured to adjust phase of the bit stream according to the first chopping signal; and a filter configured to filter an output of the output chopping circuit and to output the digital value.