Semiconductor Memory Reference Cell Trimming Circuit
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Solution Overview
Problem
Conventional methods for trimming reference cells in semiconductor memory devices require complex hardware and software, are difficult to precisely measure, and result in lengthy trimming test times, increasing labor costs.
Innovation Solution
A method and apparatus that utilize first and second voltage-to-current circuits, resistors, and comparators to generate and compare currents based on bias and control voltages, allowing for precise trimming of reference cells, with a parallel trimming apparatus enabling simultaneous trimming of multiple devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional trimming methods are used with external testers providing constant current, then reference cell trimming can be performed, but the hardware and software become complex and trimming time increases
Solution Approach 1:
The semiconductor memory device performs reference cell trimming autonomously using internal voltage-to-current conversion circuits and comparators, eliminating the need for complex external tester hardware and software. The device self-trims by comparing reference cell current with converted currents and adjusting programming/erasing accordingly
Solution Approach 2:
The trimming function is extracted from the external tester and integrated into the semiconductor memory device itself. The voltage-to-current conversion circuits and comparison logic are moved inside the device, removing the burden of complex external testing equipment
2Reliability
If conventional trimming methods are used, then reference cell trimming can be performed, but measurement precision becomes difficult to achieve
Solution Approach 1:
A voltage-to-current conversion circuit serves as an intermediary to convert a controllable voltage into a precise reference current for comparison. This intermediary circuit enables accurate current measurement by using voltage control and conversion rather than direct current measurement
Solution Approach 2:
The external current measurement and control system is replaced with an internal voltage-to-current conversion system. Instead of using external testers to measure and control currents, the device uses internal circuits to convert voltages into precise currents for comparison
3Reliability
If conventional sequential trimming methods are used, then reference cell trimming can be performed, but trimming test time increases labor costs
Solution Approach 1:
The trimming process is segmented into multiple parallel operations using multiple voltage-to-current conversion circuits and comparators. Each circuit handles a specific current comparison task simultaneously, enabling parallel processing of multiple reference cells or multiple current comparisons within a single device
Solution Approach 2:
Multiple trimming operations are merged into a single integrated system within the semiconductor memory device. The voltage-to-current conversion circuits, comparators, and control logic are combined to perform multiple current comparisons and trimming operations simultaneously, reducing overall trimming time
Data Source
AI summary
A method of trimming a reference cell in a semiconductor memory device comprises the steps of: generating a reference current based on a bias voltage applied to the reference cell; generating a first current and a second current based on the value of a control voltage and the resistance of a precision resistor disposed outside the semiconductor memory device; comparing the reference current with the first current; comparing the reference current with the second current; programming the reference cell if the value of the reference current is greater than that of the first current; and erasing the reference cell if the value of the reference current is less than that of the second current. The value of the second current is less than that of the first current.