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RENUKA N
 Sense Amplifier reads the low power signals of
memory cell, amplifies to recognizable logic levels.
 Modern sense amplifier circuits consists of 2 to 6
transistors, while early one were having as many as
13 transistors.
 Major role of sense amplifier is in functionality,
performance and reliability of memory circuits
 Amplification: In 1T DRAM, amplification is very much
needed for proper functionality
 Delay Reduction: The amplifier compensates for the
restricted fan-out driving capability of the memory cell by
accelerating the bit line transition, or by detecting &
amplifying small transitions on the bit line
 Power Reduction: Reducing the signal swing on the bit
lines can eliminate the power dissipation
 Signal Restoration: As read and refresh functions are
intrinsically linked, it is necessary to drive the bit lines to
full signal range after sensing
 A differential amplifier takes small signal
differential inputs, and amplifies them to a
large signal single ended output
 Most advantageous part is CMRR and PSRR
 Its widely used in SRAM memories, as these
are the only memory cells that offer a true
differential output
 The gain of Differential-to-single-ended
amplifiers is given by
Asense = -gm1(r02 ||r04 )
 Bit lines are precharged to VDD by pulling PC
low,EQ-PMOS transistor becomes
ON,ensuring initial voltages identical,called
as equalization
 The read operation is started by disabling
the precharge & equalization
devices,enabling word lines
 Once a sufficient signal is built up,the sense
amplifier is turned on by raising SE.
 Finally the output is produced at the o/p
terminals of the inverter
 CMOS Inverter exhibits a High Gain when
positioned in transient region
 Once sufficient voltage is built up sense
amplifier is enabled using SE
 Depending on input according output is
created
 Cross coupled is usually used in 1T DRAM,
as here rail to rail transition is enforced on bit
lines, refreshing can be easily done
 Usually EEPROMs,DRAMs are single ended ,we can also use a
precharges asymmetrically biased inverter as a sense amplifier
and are called as charge redistribution amplifier
 Two Capacitors Clarge and csmall are isolated by pass transistor M1
 Initial voltages VL & Vs precharged to (Vref –Vth) & VDD by
connecting S to supply voltage
 Once M2 is turned ON, charge capacitance discharges slowly,
once voltage drops below ( Vref –Vth),M1 pass transistor
turns ON, a charge redistribution is initiated, then nodes L
and S Equalise
 As Csmall is very, within small time a greater output is
established at the output node, hence it can be used as an
amplifier
 The resulting output can be fed to an inverter with a
switching Threshold > (Vref –Vth) to produce a rail to rail
swing
 Only disadvantage is very small Noise margin
 Larger memories >1Mbit affects by noise disturbances, to
overcome that single to differential conversion is used
 Depending upon the values on BL ,amplifier toggles.
 Creation of Reference voltage is not easy and needs careful
design
Reference Voltage Generation in 1T DRAM
 When EQ is raised, bit lines BLL & BLR are
precharged to VDD/2,enables L & L ,and a
particular Ref Voltage is generated
 Dividing the bit lines to two halves effectively
reduces the bit line capacitance, this doubles
Transfer Ratio and improves SNR
T

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Sense ampliers

  • 2.  Sense Amplifier reads the low power signals of memory cell, amplifies to recognizable logic levels.  Modern sense amplifier circuits consists of 2 to 6 transistors, while early one were having as many as 13 transistors.  Major role of sense amplifier is in functionality, performance and reliability of memory circuits
  • 3.  Amplification: In 1T DRAM, amplification is very much needed for proper functionality  Delay Reduction: The amplifier compensates for the restricted fan-out driving capability of the memory cell by accelerating the bit line transition, or by detecting & amplifying small transitions on the bit line  Power Reduction: Reducing the signal swing on the bit lines can eliminate the power dissipation  Signal Restoration: As read and refresh functions are intrinsically linked, it is necessary to drive the bit lines to full signal range after sensing
  • 4.
  • 5.  A differential amplifier takes small signal differential inputs, and amplifies them to a large signal single ended output  Most advantageous part is CMRR and PSRR  Its widely used in SRAM memories, as these are the only memory cells that offer a true differential output  The gain of Differential-to-single-ended amplifiers is given by Asense = -gm1(r02 ||r04 )
  • 6.
  • 7.  Bit lines are precharged to VDD by pulling PC low,EQ-PMOS transistor becomes ON,ensuring initial voltages identical,called as equalization  The read operation is started by disabling the precharge & equalization devices,enabling word lines  Once a sufficient signal is built up,the sense amplifier is turned on by raising SE.  Finally the output is produced at the o/p terminals of the inverter
  • 8.
  • 9.  CMOS Inverter exhibits a High Gain when positioned in transient region  Once sufficient voltage is built up sense amplifier is enabled using SE  Depending on input according output is created  Cross coupled is usually used in 1T DRAM, as here rail to rail transition is enforced on bit lines, refreshing can be easily done
  • 10.  Usually EEPROMs,DRAMs are single ended ,we can also use a precharges asymmetrically biased inverter as a sense amplifier and are called as charge redistribution amplifier  Two Capacitors Clarge and csmall are isolated by pass transistor M1
  • 11.  Initial voltages VL & Vs precharged to (Vref –Vth) & VDD by connecting S to supply voltage  Once M2 is turned ON, charge capacitance discharges slowly, once voltage drops below ( Vref –Vth),M1 pass transistor turns ON, a charge redistribution is initiated, then nodes L and S Equalise  As Csmall is very, within small time a greater output is established at the output node, hence it can be used as an amplifier  The resulting output can be fed to an inverter with a switching Threshold > (Vref –Vth) to produce a rail to rail swing  Only disadvantage is very small Noise margin
  • 12.  Larger memories >1Mbit affects by noise disturbances, to overcome that single to differential conversion is used  Depending upon the values on BL ,amplifier toggles.  Creation of Reference voltage is not easy and needs careful design
  • 14.  When EQ is raised, bit lines BLL & BLR are precharged to VDD/2,enables L & L ,and a particular Ref Voltage is generated  Dividing the bit lines to two halves effectively reduces the bit line capacitance, this doubles Transfer Ratio and improves SNR
  • 15.
  • 16. T