Analog Memory Circuit With Bootstrap Readout and Low Output Impedance
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Solution Overview
Problem
Semiconductor devices face challenges in holding and accurately reading analog data due to leakage current issues with thinner gate insulating films, necessitating a solution for improved data retention and reduced power consumption while maintaining large memory capacity and reliability.
Innovation Solution
A semiconductor device is designed with two holding circuits, two bootstrap circuits, and a source follower circuit using four transistors and two capacitors, where memory nodes are used to store data and reference potentials, and the source follower circuit reduces output impedance to enhance data reading accuracy and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the gate insulating film is made thinner to enable element miniaturization, then the transistor size is reduced and integration density increases, but leakage current through the gate insulating film increases
Solution Approach 1:
A bootstrap circuit is introduced as an intermediary mechanism to compensate for leakage current effects. The bootstrap circuit periodically refreshes the potential at the memory node by transferring charge from the bootstrap capacitor, thereby counteracting the potential degradation caused by gate insulating film leakage and enabling accurate analog data retention
Solution Approach 2:
The invention dynamically changes the potential parameter at the memory node through the bootstrap circuit operation. By periodically boosting the memory node potential back to its reference level, the system compensates for leakage-induced potential drift, maintaining data integrity despite thin gate insulating film leakage
2Device complexity
If conventional reading methods are used with high output impedance, then the circuit structure is simpler, but the accuracy of analog data reading is insufficient
Solution Approach 1:
Instead of directly reading the memory node potential with high impedance that would load and distort the signal, the invention inverts the approach by using a source follower circuit with inherently low output impedance. This allows the reading operation to drive the output strongly without loading the delicate memory node, thereby achieving high reading accuracy
Solution Approach 2:
The source follower circuit provides impedance transformation that effectively isolates the memory node from the output load. The gate of the source follower transistor is driven by the memory node potential, and the source output follows this potential with low output impedance, creating a feedback-like isolation that preserves signal integrity
3Reliability
If more transistors and capacitors are used to improve data holding and reading accuracy, then the reliability and performance increase, but the occupied area increases
Solution Approach 1:
Each transistor in the invention serves multiple functions: transistors act as switches for data writing, as part of the bootstrap circuit for potential refresh, and as part of the source follower for low-impedance output. The capacitors serve dual roles as memory nodes for data storage and as bootstrap capacitors for potential refresh. This multi-functionality reduces the total component count and occupied area while maintaining reliability
Solution Approach 2:
The invention merges the data holding function and the potential refresh function into a unified circuit structure. The same capacitor serves as both the memory node and the bootstrap capacitor at different operational phases, and the same transistor serves as both the write switch and the bootstrap switch, thereby reducing overall circuit complexity and area
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The semiconductor device effectively holds and reads analog data with reduced power consumption, increased memory capacity, and improved reliability, addressing leakage current issues and miniaturization challenges.
Implementation Method 1
two bootstrap circuits, and one source follower circuit are formed with use of four transistors and two capacitors
Data Source
AI summary
A semiconductor device capable of holding analog data is provided. Two holding circuits, two bootstrap circuits, and one source follower circuit are formed with use of four transistors and two capacitors. A memory node is provided in each of the two holding circuits; a data potential is written to one of the memory nodes and a reference potential is written to the other of the memory nodes. At the time of data reading, the potential of the one memory node is increased in one of the bootstrap circuits, and the potential of the other memory node is increased in the other of the bootstrap circuits. A potential difference between the two memory nodes is output by the source follower circuit. With use of the source follower circuit, the output impedance can be reduced.