Solid-State Image Pickup Device Column Amplifier Leakage Control
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Solution Overview
Problem
Solid-state image pickup devices face challenges in minimizing power consumption and preventing subthreshold current flow, which leads to signal attenuation due to the scaling down of transistors, especially in power saving modes.
Innovation Solution
The device incorporates a switch capable of switching between normal and power saving modes, utilizing a voltage supply unit to control the potential at the output node of the column amplifier unit, and a CMOS switch with PMOS and NMOS transistors in parallel to inhibit off-state current by using a voltage VM different from the gate off-state voltage, thereby reducing leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If current to the column amplifier unit is shut off during OFF period to decrease power consumption, then power consumption is reduced, but subthreshold current flows through the transfer MOS transistor causing signal attenuation
Solution Approach 1:
The invention changes the potential parameter at the output node of the column amplifier unit during the OFF period. By controlling the potential to be different from both the gate potential (VDD or ground) and the source potential of the transfer MOS transistor, the patent creates a voltage difference that prevents subthreshold current flow while maintaining low power consumption. This parameter change resolves the contradiction by eliminating the condition that causes signal attenuation.
2Loss of energy
If the potential at the output node of the column amplifier unit is equal to the gate potential (VDD or ground) during OFF period, then power consumption is minimized, but subthreshold current flows through the transfer MOS transistor
Solution Approach 1:
The invention applies preliminary anti-action by preemptively controlling the potential at the output node to prevent subthreshold current flow before it can occur. By maintaining a potential difference between the output node and the source of the transfer MOS transistor during the OFF period, the patent counteracts the tendency for subthreshold current to flow, thereby eliminating the harmful effect while keeping power consumption low.
Data Source
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AI summary
A solid-state image pickup device includes common output lines (2) receiving signals from pixels, column amplifier units (14) amplifying the signals output to the corresponding common output lines, storage capacitors (10) storing the signals from the corresponding column amplifier units, a first transistor (9) controlling electrical conduction between the output node of the column amplifier unit and the input node of the storage capacitor, switching means (15) switching current operating the column amplifier unit between a first current and a second current smaller than the first current, and controlling means (8) inhibiting, while the second current is flowing through the column amplifier unit, a potential at the output node of the column amplifier unit from approaching an off-state voltage supplied to a gate of the first transistor in an OFF state thereof.