Two-Step Sense Amplifier Circuit for DRAM Leakage Reduction
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Solution Overview
Problem
The reduction in driving voltage level of bit line sense amplifiers (BLSA) in DRAMs leads to leakage currents through column select transistors due to the voltage difference with local input/output line sense amplifiers (LSA), affecting the speed and power consumption of the DRAM.
Innovation Solution
Implementing a 2-step sensing operation in the LSA circuit with a pre-sensing driver having weaker driving strength than the main-sensing driver, and using transistors with varying sizes to manage the enable signals, reducing leakage currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the driving voltage level of BLSA is lowered to support high-speed operation, then the operating speed of DRAM is improved, but leakage current occurs from LSA to BLSA through column select transistors due to voltage difference
Solution Approach 1:
The sensing operation is divided into two distinct phases: a pre-sensing phase with weaker driving strength and a main-sensing phase with stronger driving strength. This segmentation allows the system to first establish voltage levels with minimal leakage, then perform the main sensing function, thereby resolving the contradiction between speed and leakage current.
Solution Approach 2:
The pre-sensing operation is performed before the main-sensing operation to prepare the voltage levels on the local I/O lines. By conducting this preliminary action with weaker driving strength, the system establishes the necessary voltage conditions while minimizing leakage current through the column select transistors, thus enabling subsequent high-speed operation without excessive leakage.
2Reliability
If the driving voltage level of LSA is increased to improve sensing capability, then the sensing performance is improved, but leakage current through column select transistors increases due to larger voltage difference with BLSA
Solution Approach 1:
The driving strength of the LSA is made dynamic rather than static. The pre-sensing driver operates with weaker driving strength during the initial phase, then the main-sensing driver engages with stronger driving strength for the main sensing operation. This dynamic adjustment allows the system to maintain high sensing performance when needed while minimizing leakage current during voltage level establishment.
Solution Approach 2:
The sensing operation is structured as a periodic sequence of two distinct operations: pre-sensing and main-sensing. Each period consists of first applying weaker driving strength to establish voltage levels, then applying stronger driving strength for the actual sensing. This periodic alternation between different driving strengths resolves the contradiction by ensuring that high voltage difference (and thus high sensing capability) is only present when actually needed for sensing, not during the voltage establishment phase.
3Productivity
If stronger driving strength is used in LSA sensing operation, then sensing speed and performance are improved, but power consumption increases
Solution Approach 1:
Instead of applying full driving strength continuously, the system applies partial driving strength (weaker mode) during the pre-sensing operation and only uses excessive driving strength (stronger mode) when absolutely necessary for the main sensing operation. This partial application of force reduces overall power consumption while still achieving the required sensing performance and speed when needed.
Data Source
AI summary
An LSA circuit includes a first sensing transistor and a second sensing transistor connected in series between a local I/O line and a complementary local I/O line, a pre-sensing driver configured to drive an LSA sensing voltage to a connection node between the first sensing transistor and the second sensing transistor during a pre-sensing operation of the LSA circuit, and a main-sensing driver configured to drive the LSA sensing voltage to the connection node during a main-sensing operation of the LSA circuit. A driving strength of the pre-sensing driver is set to be weaker than a driving strength of the main-sensing driver, and the pre-sensing driver is driven before the main-sensing driver.