Current-Steering ADC Feedback Loop for Lower Power Imaging
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Solution Overview
Problem
The increasing number of digital-analog conversion sections in feedback loops of analog-digital converters leads to higher power consumption, which is undesirable for stability and efficiency, especially in applications like solid-state imaging elements.
Innovation Solution
Incorporating a current steering digital-analog conversion section with a loop filter having at least two cascaded integrators and a quantization circuit section, where the second input signal current cancels out the output current of one side of the digital-analog conversion section, reducing power consumption and input level dependence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple digital-analog conversion sections are provided in the feedback loop to stabilize the feedback loop, then feedback loop stability is improved, but power consumption of the digital-analog conversion sections increases
Solution Approach 1:
The patent combines multiple digital-analog conversion sections into a single integrated current steering digital-analog conversion section that processes multiple input signal currents simultaneously. This merging approach maintains the feedback loop stability function while reducing the total number of separate conversion sections, thereby lowering power consumption.
Solution Approach 2:
The current steering digital-analog conversion section is designed to handle multiple input signal currents (first input signal current and second input signal current) through a single unified structure. This multi-functional design allows one conversion section to perform the work of multiple separate sections, reducing overall power consumption while maintaining stability.
2Use of energy by moving object
If the second input signal current path and second feedback current path are both connected to the input end of the second stage integrator, then current cancellation occurs reducing power consumption, but circuit complexity increases
Solution Approach 1:
The patent implements current cancellation by connecting both the second input signal current path and second feedback current path to the input end of the second stage integrator. The second input signal current (opposite in sign to the first input signal current) acts as a counterweight that cancels out the output current from the digital-analog conversion section, reducing net current and power consumption.
Solution Approach 2:
The circuit employs asymmetric current paths where the first input signal current and second input signal current have opposite signs. This asymmetry in current direction and magnitude enables the cancellation effect at the second stage integrator input, achieving power reduction through deliberate current imbalance that resolves into balance at the output.
Data Source
AI summary
Included are a loop filter, a quantization circuit section, and a current steering digital-analog conversion section. The quantization circuit section converts a loop filter output into a digital value. The current steering digital-analog conversion section is provided in a feedback loop that feeds back the output of the quantization circuit section to the loop filter. Then, each of the analog-digital converters includes a first input signal current path, a second input signal current path, a first feedback current path, and a second feedback current path. The first input signal current path feeds a first input signal current to an input end of a first stage integrator of the loop filter. The second input signal current path feeds a second input signal current, a current opposite in sign to the first input signal current, to an input end of a second stage integrator of the loop filter. The first feedback current path connects one feedback output end of the current steering digital-analog conversion section to the input end of the first stage integrator of the loop filter. The second feedback current path connects other feedback output end of the current steering digital-analog conversion section to the input end of the second stage integrator of the loop filter.