CCD Driver Circuit Drive Capability via Voltage Level Shifting
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Solution Overview
Problem
Current driver circuits for CCD image sensors face challenges in increasing drive capability while maintaining a smaller size, as larger MOSFETs are required to achieve higher pulse amplitude, leading to increased chip size.
Innovation Solution
A driver circuit integrated on a semiconductor substrate with a control-stage and output-stage circuit configuration, utilizing multiple voltage levels and level shift circuits to enhance gate-to-source voltage and drive capability without increasing transistor size, by configuring transistors to operate with different voltage thresholds and using booster circuits to generate required voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the MOSFET channel width is increased to raise drive capability, then the drive capability and pulse amplitude are improved, but the chip size increases
Solution Approach 1:
The invention changes the voltage parameters by introducing multiple voltage levels (first high voltage, first low voltage, second high voltage, second low voltage) with different voltage differences. The control-stage circuit operates with a first voltage difference (VDD1-VSS1) that is greater than the second voltage difference (VDD-VSS) used in the output-stage circuit. This parameter change allows the output transistors to operate with enhanced gate-to-source voltage while maintaining a smaller channel width, thus improving drive capability without increasing chip size.
2Power
If the transistor size is increased to maintain MOSFET Vgs at (VDD−VLOW), then the drive capability is improved, but the chip size increases
Solution Approach 1:
The invention changes the operating voltage parameters by using a control-stage circuit with a larger voltage difference (VDD1-VSS1 > VDD-VSS). This allows the output transistors to achieve the required gate-to-source voltage for high drive capability while operating at a smaller size, as the enhanced voltage swing in the control stage compensates for the reduced transistor dimensions in the output stage.
Data Source
AI summary
A driver circuit is improved in drive capability corresponding to a resolution increase for a CCD sensor while suppressing chip size of a driver circuit. A preceding-stage circuit, operating on VDD2 (>VDD) and VLOW2 (<VLOW), is provided in a stage preceding an output-stage circuit operating on VDD and VLOW. The output-stage has a transistor QPd that turns on when supplied with a gate voltage VLOW2 from the preceding-stage circuit, thus outputting, onto an output terminal Vout, a voltage VDD and a current according to a voltage Vgs (=VDD−VLOW2). In addition, a transistor QNd turns on when supplied with a gate voltage VDD2 from the preceding-stage circuit, thus outputting, onto an output terminal Vout, a voltage VLOW and a current according to a voltage Vgs (=VDD2−VLOW). Because these Vgs are greater than VDD−VLOW, the output-stage circuit can be improved in drive capability and transistor size be correspondingly suppressed.