Row Driver Amplifier Topology for Low-Current Image Sensor Readout
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Solution Overview
Problem
Designing satisfactory row control circuitry for image sensors is challenging due to issues with inter-circulation currents in conventional class AB amplifiers, which increase power consumption and affect readout performance.
Innovation Solution
The implementation of p-type and n-type row driver amplifiers with cross-coupled transistors and cascode configurations to minimize DC offset inter-circulation currents, providing stable and efficient power supply signals to row driver circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional class AB amplifiers are used in row driver circuitry, then high slew currents are achieved, but DC offset inter-circulation currents increase power consumption
Solution Approach 1:
The amplifier circuit is segmented into separate p-type and n-type amplifiers, each handling different aspects of the signal. This segmentation allows independent optimization of each amplifier type to minimize inter-circulation currents while maintaining high slew currents for signal settling.
Solution Approach 2:
Common center-tapped inductors are introduced as intermediary elements to couple the p-type and n-type amplifiers. These inductors serve as mediators that enable signal transmission while blocking DC offset inter-circulation currents, thus reducing power consumption without sacrificing slew current performance.
2Device complexity
If conventional amplifier configurations are used, then circuit simplicity is maintained, but tolerance to DC mismatches is reduced
Solution Approach 1:
The invention changes the electrical parameters of the amplifier circuit by introducing common center-tapped inductors and configuring p-type and n-type amplifiers with specific impedance matching. This parameter change enhances the circuit's tolerance to DC mismatches while maintaining a relatively simple overall configuration.
Solution Approach 2:
The circuit employs asymmetric configuration where p-type and n-type amplifiers are differently optimized for their respective signal components. The common center-tapped inductor structure introduces asymmetry in the coupling path, which helps cancel out DC offset inter-circulation currents and improves tolerance to mismatches.
Data Source
AI summary
An image sensor may include an array of image sensor pixels. The array of image sensor pixels may be controlled by row driver circuitry. The row driver circuitry may include row drivers that receive power supply signals from transconductance amplifier circuitry. The transconductance amplifier circuitry may include multiple amplifiers with output ports shorted to one another. Each amplifier may include input transistors, cross-coupled transistors with a low threshold voltage, and additional transistors coupled in series with the cross-coupled transistors and having a moderate or high threshold voltage.