1. Electronics for Physicists
Lecture 15
Memories

2. 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!
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Electronics for physicists

3. 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
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4. Memory classification
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5. Electronics for physicists
Storage cells …
PROM
DRAM
SRAM
Many different technologies
Optimized for size, power, price, speed, etc.
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Electronics for physicists

6. 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
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7. 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
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8. 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
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9. 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.
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10. Electronics for physicists
Memory architecture
Elements:
individual storage cells (00, 01, … , 33)
address decoder
read amplifiers
bitline drivers
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11. 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
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12. 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
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13. 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
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14. 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
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15. Realistic SRAM block diagram
Block diagram of a CY7C1061AV33 SRAM
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16. 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
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17. 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)
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18. 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/ (address) stored in the phone book (content)?
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19. Block diagram of associative memoryML
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!
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20. 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
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21. Electronics for physicists
Incomplete overview
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