Masking Circuit for Solid-State Imaging Power Reduction
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Solution Overview
Problem
In solid-state imaging devices using a column-parallel AD conversion scheme, power consumption is increased due to unnecessary through currents when the input offset between pixel signals and reference signals is canceled, leading to wasteful energy usage.
Innovation Solution
Incorporating a masking circuit that suppresses the output of the inverting circuit during the input offset canceling period, specifically using a NAND circuit to mask the difference signal to a subsequent stage, thereby reducing through current and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If the inverting circuit continuously operates to process difference signals, then the signal processing function is maintained, but unnecessary through currents flow during input offset canceling period increasing power consumption
Solution Approach 1:
The masking circuit is configured to mask the output of the inverting circuit in advance during the input offset canceling period, before the through current problem occurs. This preliminary masking action prevents the unnecessary current flow while maintaining the signal processing capability when needed
Solution Approach 2:
The masking circuit extracts and removes the problematic through current component during the offset canceling period by masking the inverting circuit output. This separates the useful signal processing function from the harmful current consumption, allowing the system to maintain reliability while reducing power consumption
2Loss of energy
If the masking circuit masks the inverting circuit output during input offset canceling period, then through current is reduced, but the circuit complexity increases
Solution Approach 1:
The masking circuit is merged with the existing inverting circuit and comparator structure. By integrating the masking function into the signal processing path, the patent reduces the need for completely separate control circuits, thereby limiting the increase in device complexity while still achieving through current reduction
Solution Approach 2:
The masking circuit serves multiple functions: it masks the inverting circuit output during offset canceling to reduce through current, and simultaneously maintains signal processing continuity when needed. This multi-functionality reduces the need for additional dedicated circuits, limiting the overall device complexity increase
Data Source
AI summary
A solid-state imaging including a comparing circuit, an inverting circuit, and a masking circuit, and that performs column parallel AD conversion processing of analog pixel signals output from a plurality of pixels arranged in a two-dimensional matrix form. The comparing circuit outputs a difference signal obtained by comparing each of the pixel signals outputted from the pixels with a reference signal having a ramp waveform. The inverting circuit inverts a logic of the difference signal outputted from the comparing circuit. The masking circuit masks an output of an output signal of the inverting circuit to a circuit in a subsequent stage during an input offset canceling period in which the comparing circuit cancels an input offset between the pixel signal and the reference signal.