The difference between SRAM and DRAM on chip

On-chip SRAM and on-chip DRAM are two kinds of storage media integrated in CPU,GPU and AI chip,which are essentially different in storage principle,performance,cost and applicable scenarios.On-chip storage is close to the computing core,which can greatly shorten the path of data reading and writing,and is the key carrier of the internal cache of the chip.
 

According to the storage principle,SRAM on chip adopts the classic 6T six-transistor structure,and relies on cross-coupled inverters to form a bistable latch circuit.As long as the power is continuously supplied,the data can be stably stored without additional refresh operation.On-chip DRAM is a 1T1C transistor+capacitor architecture,which relies on the capacitor to store charge and record data.The capacitor will naturally leak electricity,and the data will decay with time,so it must be refreshed periodically every 64ms,otherwise the data will be lost.
 

In terms of performance,the on-chip SRAM does not need to be refreshed,with lower access delay,faster reading and writing speed and better power control.However,due to the limitation of circuit structure,the integration of SRAM is low,and the storage capacity that can be realized under the same silicon chip area is much smaller than that of DRAM,so the unit capacity cost is higher.On-chip DRAM relies on capacitor storage,with simple structure,high integration,larger capacity in the same area,and obvious cost advantage.The disadvantage is that it needs to refresh the circuit,which brings extra power consumption and access delay.
 

In practical application,with its high speed and stability,on-chip SRAM is mostly used for in-chip cache,connecting the computing core with external large-capacity memory,and alleviating the bottleneck of data reading and writing.On-chip DRAM is used as a large-capacity cache inside the chip,which carries more intermediate data in AI chip and other scenes,balancing storage capacity and chip area.In short,on-chip SRAM focuses on low latency and high performance,while on-chip DRAM focuses on large capacity and low cost.