Electronics for Physicists Lecture 15 Memories

Electronics for physicists Data Memory Memory is as important as processing power or data transmission bandwidth! What memory characteristics should you care for ? Volatile (storage while powered) or non-volatile („permanent“ storage) Memory size and density Write and read times In some applications watch max. number of program and erase cycles (P/E cycles), long-term duration, radiation hardness and always costs! December 2018 Electronics for physicists

Electronics for physicists Memory types ROM (Read-only memory) RAM (Random access memory) Flash memory Magnetic memory (tape, standard hard drive) Optical memory (CD, DVD) Here we do not care about bit preservation over 10,000 years, but ~10 years maximum. Sometimes care only about storage over 1 ms… What is memory good for ? Note R ≠ R December 2018 Electronics for physicists

Memory classification  December 2018 Electronics for physicists

Electronics for physicists Storage cells … PROM DRAM SRAM Many different technologies Optimized for size, power, price, speed, etc. December 2018 Electronics for physicists

Read-only memory (ROM) wordline (address) bit line (data) Decoder Pull-down resistance sets default data to “0” Decoder asserts “1” to corresponding address line Xi Presence or absence of diodes defines content of ROM Example: A1 A0 D3 D2 D1 D0 1 December 2018 Electronics for physicists

Electronics for physicists DRAM A Dynamic RAM (DRAM) cell consists of a capactor, transistor switch, data lines and address lines data line address line Information is stored as charge on a capacitor. Charge must be refreshed every few ms due to leakage of capacitor. DRAMs are compact and inexpensive. Same principle is used in analog pipelines of many detector readout ICs December 2018 Electronics for physicists

Electronics for physicists DDR3 RAM DDR SDRAM = Double Data Rate Synchronous DRAM Photo of a DDR SDRAM from Infineon for PC memory Typical size: 8 GB Bandwidth: at least 6.4 GB/s Costs: ~ 60 € for 8 GB December 2018 Electronics for physicists

Electronics for physicists SRAM A SRAM (static RAM) cell consists of cross-coupled inverters (flip-flops) ≈ SRAMs are fast and do not need refreshing. Lower power consumption than DRAMs. SRAMs are less compact than DRAMs and are more expensive. SRAM principle is used in digital pipelines of some detector readout ICs. December 2018 Electronics for physicists

Electronics for physicists Memory architecture Elements: individual storage cells (00, 01, … , 33) address decoder read amplifiers bitline drivers December 2018 Electronics for physicists

SRAM read and write conditions large W/L: low resistance Read 𝑄 = “0”: set BL and to UDD. Close switches M5 and M6. Need Write: overwrite stored =“1” with “0”. Need December 2018 Electronics for physicists

Electronics for physicists SRAM read operation Example: read content Q = “1”, 𝑄 = “0” “1” “0” UDD Read: set BL and 𝐵𝐿 to “1” (UDD) Set WL to “1” to close switches M5 and M6  BL stays high, Q stays high  𝐵𝐿 discharges, but 𝑄 voltage increases somewhat while reading Note: M1 must be stronger than M5 (M1 > M5 ) to avoid bit flip. (“stronger” means lower impedance, larger currents) Note: For Q = “0”, get condition M3 > M6 UDD December 2018 Electronics for physicists

Electronics for physicists SRAM write operation Example: overwrite Q = “1”, 𝑄 = “0” to store Q = “0”, 𝑄 = “1” instead “1” “0” Set BL = “0”, 𝐵𝐿 = “1” Set WL = “1” to close switches M5 and M0  Q is discharged, 𝑄 charges up Note: M6 must be stronger than M4 (M6 > M4) to flip Q Note: 𝑄 is flipped by Q rather than 𝐵𝐿 December 2018 Electronics for physicists

Electronics for physicists SRAM write operation Example: overwrite Q = “1”, 𝑄 = “0” to store Q = “0”, 𝑄 = “1” instead “1” “0” weak medium strong Set BL = “0”, 𝐵𝐿 = “1” Set WL = “1” to close switches M5 and M0  Q is discharged, 𝑄 charges up Note: M6 must be stronger than M4 (M6 > M4) to flip Q Note: 𝑄 is flipped by Q rather than 𝐵𝐿 Note: For Q = “0”, get condition M5 > M2 December 2018 Electronics for physicists

Realistic SRAM block diagram Block diagram of a CY7C1061AV33 SRAM December 2018 Electronics for physicists

Electronics for physicists Hard drives are not used in detector instrumentation … but are very popular since they are reliable, cheap and have large storage capacity 4 TB costs ≈ 150 € 5400 or 7200 rotations per minute up to 150 MB/s data rates December 2018 Electronics for physicists

nor is optical storage or flash memory used … Build-up of a floating gate transistor Floating gate transistor technology is not compatible with conventional readout IC technology Solid state disks (SSD) are expensive, robust and fast (≈ 500 MB/s) Storage capacity: ≤1 TB Flash memory supports only a limited number of write/erase cycles (1K to 1M) December 2018 Electronics for physicists

Electronics for physicists Associative memory Standard memory Input: address Output: addressed data word Associative memory Input: data word Output: address of corresponding storage location Application example What is phone number (content) of Angela Merkel (address)? Is the number 030/18 272 2720 (address) stored in the phone book (content)? December 2018 Electronics for physicists

Block diagram of associative memory ML Searchline (SL) rather than bitline (BL) Matchline (ML) rather than wordline (WL) Matchline is preset to “1”. Cells which do not fit search content pull matchline to “0”. Associative memory finishes search in just one clock cycle! December 2018 Electronics for physicists

Content-adressable memory cell (CAM) Sample implementation of a CAM cell We are searching for the content „1“ (SL = „1“ , SL = „0“) If Q = 1 , Q = 0  M1 on , M3 off  M2 on If Q = 0 , Q = 1  M1 off, M3 on  M2 off December 2018 Electronics for physicists

Electronics for physicists Incomplete overview December 2018 Electronics for physicists