Switched-Capacitor Photodiode Input Stage for Low-Power Sigma-Delta ADCs
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Solution Overview
Problem
Conventional input stage circuits for interfacing current output from a photodiode to a sigma-delta analog-to-digital converter (ADC) circuit consume significant power, which is a concern for battery-powered or energy-harvested devices.
Innovation Solution
A low power consumption input stage circuit is designed, incorporating an integrator circuit, single bit quantization circuit, and feedback digital-to-analog converter circuit, utilizing capacitors and switches actuated by non-overlapping clock signals to convert photodiode current to a voltage, reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional input stage circuits (current integrator or source-follower) are used to convert photodiode current to voltage, then signal conversion is achieved, but power consumption is significant
Solution Approach 1:
The patent merges the input stage circuit with the sigma-delta modulator by directly coupling the photodiode current input to the integrator input node, eliminating the need for separate current-to-voltage conversion circuits. This integration reduces the number of active components and their associated power consumption while maintaining signal conversion functionality through the existing integrator circuit.
Solution Approach 2:
The patent extracts and eliminates the conventional current integrator or source-follower circuit from the signal path, relying instead on the sigma-delta modulator's internal integrator to perform the current-to-voltage conversion. This extraction removes the power-consuming intermediate conversion stage while preserving the essential signal transformation function.
2Device complexity
If conventional input stage circuits are used, then photodiode current can be converted to voltage, but the circuit complexity increases with additional components
Solution Approach 1:
The patent combines the input stage functionality with the sigma-delta modulator structure, using shared components such as the integrator capacitor and operational amplifier. This merging eliminates redundant components that would increase circuit complexity and power consumption, achieving a compact integrated design where the input stage and modulator functions are unified.
3Duration of action of moving object
If battery-powered or energy-harvested devices use conventional input stages, then signal conversion is possible, but operating duration is limited due to high power consumption
Solution Approach 1:
The patent employs the sigma-delta modulator's inherent periodic sampling and quantization process to efficiently convert the photodiode current signal. This periodic operation allows the system to achieve accurate signal conversion with lower average power consumption compared to continuous operation of conventional input stages, thereby extending operating duration for battery-powered devices.
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 solution effectively converts photodiode current to voltage with reduced power consumption, optimizing performance for battery-powered or energy-harvested devices by minimizing power usage while maintaining accurate signal conversion.
Implementation Method 1
consider the use of a photodiode as the signal source generating a photocurrent
Implementation Method 2
The output voltage from the circuit 40 is proportional to the integrated value of the photodiode current (or the total injected charge)
Data Source
AI summary
An input stage circuit for a sigma-delta analog-to-digital converter circuit receives a digital-to-analog converter generated feedback signal and an analog current input signal to generate a difference signal applied to an integrator circuit. A single bit quantization circuit quantizes an output of the integrator circuit to generate a bit signal that is applied to an input of the digital-to-analog converter. The input stage circuit includes a switched input capacitor controlled by first and second, non-overlapping, clock signals.