Memory Clock Synchronization in CS Gear Down Mode
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Solution Overview
Problem
In semiconductor memory devices, it is challenging to increase the set-up/hold margin of command/address signals in 2N mode due to the limited holding period of the chip select (CS) signal, which is typically one clock period, making it difficult to stabilize memory operations. To address this, a CS gear down mode is introduced, where the CS signal holding period is extended to two clock periods, but this requires an internal clock signal with a lower frequency than the external clock signal.
Innovation Solution
A semiconductor device is designed with a chip-select (CS) gear down mode that uses an internal clock signal with a lower frequency than the external clock signal, incorporating a chip select signal flip-flop and a clock control circuit to generate propagation clock signals with opposite phases, allowing for selective output based on the enable levels of the chip select enable signals, thereby increasing the set-up/hold margin of command/address signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the holding period of the chip select signal is extended to two clock periods in 2N mode, then the set-up/hold margin of command/address signals is improved, but the device complexity increases due to the need for additional clock control circuits and flip-flops
Solution Approach 1:
The chip select signal holding period is divided into two separate clock periods (2tCK), with each period controlled by a dedicated flip-flop (first and second chip select signal flip-flops). This segmentation allows the signal to be held for exactly two clock cycles, providing the necessary set-up/hold margin while maintaining precise temporal control through discrete staging elements.
Solution Approach 2:
Clock control circuits are introduced as intermediary elements that generate propagation clock signals (first and second propagation clock signals) with opposite phases. These intermediary clock signals coordinate the operation of multiple flip-flops and ensure proper timing synchronization across the extended holding period, resolving the timing coordination challenges without requiring complex direct control logic.
2Reliability
If an internal clock signal with lower frequency is used to extend the CS signal holding period, then the set-up/hold margin is increased, but the productivity decreases due to the reduced clock frequency
Solution Approach 1:
The system employs periodic action by using two propagation clock signals with opposite phases, where each clock signal operates at a reduced frequency but together they provide continuous timing coverage. The first propagation clock signal operates during one phase while the second operates during the opposite phase, creating a coordinated periodic rhythm that extends the holding period to 2tCK while maintaining systematic operation.
Solution Approach 2:
The clock control circuit dynamically selects and activates appropriate propagation clock signals based on the operational phase. During the extended holding period, the system transitions between using the first propagation clock signal and the second propagation clock signal, allowing flexible adaptation to the two-cycle timing requirement without permanently reducing the overall system clock frequency, thus balancing reliability improvement with productivity maintenance.
Data Source
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AI summary
A semiconductor device includes a chip select signal flip-flop configured to: latch a chip select signal (CS) in-sync with a first propagation clock signal (PCLK_E), and output a first chip select enable signal (CS_E), and latch the chip select signal (CS) in-sync with a second propagation clock signal (PCLK_O) having a phase opposite to a phase of the first propagation clock signal (PCLK_E), and output a second chip select enable signal (CS_O); and a clock control circuit (122) configured to generate the first propagation clock signal (PCLK_E) and the second propagation clock signal (PCLK_O) based on a clock signal (CLK), and selectively output one of the first propagation clock signal (PCLK_E) and the second propagation clock signal(PCLK_O) based on an enable level of the first chip select enable signal (CS_E) and an enable level of the second chip select enable signal (CS_O).