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EE141 EECS141 1 Lecture #18

EE141 EECS141 2 Lecture #18

  Project Phase 2 now on the web-site.   Hw 6 due today.   New homework to be posted in a week.   Cory Hall closed on Monday (Power Outage)

  Instructional computers in 353 Cory should come back on line on Tu.

 Enjoy Spring Break!

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EE141 EECS141 3 Lecture #18

 Last lecture  Domino Logic   Introduction to registers

 Today’s lecture  Registers   Timing

 Reading (Ch 7)

EE141 EECS141 4 Lecture #16

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EE141 EECS141 5 Lecture #16

Output = f ( In ) Output = f ( In, Previous In )

EE141 EECS141 6 Lecture #16

D Clk

Q D Clk

Q

  Register: edge-triggered stores data when clock rises

Clk Clk D D Q Q

  Latch: level-sensitive clock is low - hold mode clock is high - transparent

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EE141 EECS141 7 Lecture #16

Register Latch

Clk

D Q

t C → Q

Clk

D Q

t C → Q

t D → Q

EE141 EECS141 8 Lecture #16

t CLK

t D

t c → q

t hold t su

t Q DATA

STABLE

DATA STABLE

Register

CLK

D Q

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EE141 EECS141 9 Lecture #16

D

CLK

CLK

Q

Dynamic Static

EE141 EECS141 10 Lecture #16

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EE141 EECS141 11 Lecture #16

Gain should be larger than 1 in the transition region

EE141 EECS141 12 Lecture #16

D

CLK

CLK

D

Converting into a MUX Forcing the state (can implement as NMOS-only)

Use the clock as a decoupling signal, that distinguishes between the transparent and opaque states

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EE141 EECS141 13 Lecture #16

D

CLK

CLK

D

EE141 EECS141 14 Lecture #16 EE141

Negative latch (transparent when CLK= 0)

Positive latch (transparent when CLK= 1)

CLK

1

0 D

Q 0

CLK

1 D

Q

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EE141 EECS141 15 Lecture #16

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NMOS only Non-overlapping clocks

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EE141 EECS141 17 Lecture #16

  N latch is transparent when Φ = 0

  P latch is transparent when Φ = 1

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Two opposite latches trigger on edge Also called master-slave latch pair

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EE141 EECS141 19 Lecture #16

Multiplexer-based latch pair

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D

Q

CLK

2 0.5

0.5

1.5

2.5

tclk-q(LH)

0.5 1 1.5 2 2.5 0 time, nsec

Volts

tclk-q(HL)

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EE141 EECS141 21 Lecture #16

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EE141 EECS141 23 Lecture #16

Circuit before clock arrival (Setup-1 case)

EE141 EECS141 24 Lecture #16

Circuit before clock arrival (Setup-1 case)

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EE141 EECS141 25 Lecture #16

Circuit before clock arrival (Setup-1 case)

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Circuit before clock arrival (Setup-1 case)

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Circuit before clock arrival (Setup-1 case)

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Hold-1 case

0

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Hold-1 case

0

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Hold-1 case

0

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EE141 EECS141 31 Lecture #16

Hold-1 case

0

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Hold-1 case

0

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EE141 EECS141 33 Lecture #16

Keepers can be added to “staticize (?!)”

EE141 EECS141 34 Lecture #16

Negative latch (transparent when CLK= 0)

Positive latch (transparent when CLK= 1)

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EE141 EECS141 35 Lecture #16

AND latch Example: logic inside the latch

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EE141 EECS141 37 Lecture #16

Master-Slave Latches

D Clk

Q D Clk

Q

Clk

Data D Clk

Q Clk Data

Pulse-Triggered Latch

L1 L2 L

Ways to design an edge-triggered sequential cell:

EE141 EECS141 38 Lecture #16

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EE141 EECS141 39 Lecture #16

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EE141 EECS141 41 Lecture #16

D Clk

Q

D

Q

Clk tclk-q thold

PWm tsetup

td-q

Delays can be different for rising and falling data transitions

T

EE141 EECS141 42 Lecture #16

D Clk

Q

D

Q

Clk

tclk-q

thold

T

tsetup

Delays can be different for rising and falling data transitions

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EE141 EECS141 43 Lecture #16

Cycle time (max): TClk > tclk-q + tlogic + tsetup

Race margin (min): thold < tclk-q,min + tlogic,min

tclk-q tclk-q,min

tlogic tlogic,min

tsetup, thold

EE141 EECS141 44 Lecture #16

  Clock skew   Spatial variation in temporally equivalent clock

edges; deterministic + random, tSK

  Clock jitter   Temporal variations in consecutive edges of the

clock signal; modulation + random noise   Cycle-to-cycle (short-term) tJS   Long term tJL

  Variation of the pulse width   Important for level sensitive clocking

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EE141 EECS141 45 Lecture #16

Sources of clock uncertainty

EE141 EECS141 46 Lecture #16

  Both skew and jitter affect the effective cycle time   Only skew affects the race margin (usually)

Clk

Clk

tSK

tJS

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EE141 EECS141 47 Lecture #16

# of registers

Clk delay Insertion delay Max Clk skew

Earliest occurrence of Clk edge Nominal – δ/2

Latest occurrence of Clk edge

Nominal + δ /2

δ