EEC LowSwing Shifter

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EEC Low-Swing Shifter

• Tom Deane

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Circuit Diagram
Low-Swing Signal
Low Swing Driver
Decoder
Shifter Muxes
Amplifier
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Basic Idea
Pull-up NMOS should turn off pass-transistor
across shifter
Pull-down NMOS must fight PMOS across shifter
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Tradeoffs
Higher VBIAS Adv More current for NMOS
pull-down ? helps with the current fight ? faster
falling transition Disadv Cannot turn transistor
off unless we use higher Vswing ? more power for
two reasons.
Lower Vswing Adv Less dynamic power Disadv
Difficult to turn off n-pass transistor. Could
lower VBIAS but then pull-down NMOS cannot fight
the PMOS ? too little current.
Do we need to turn off amp n-pass? If we dont,
we draw static current in both logic states
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Waves
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Rough Energy and Delay Comparisons for Critical
Path
Restoring PMOS weaker Driving NMOS weaker
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Sources of Noise
Coupling with full-swing wires
Power Supply Noise

• More noise
• Process variations (Vth, transistor mismatch)
• Soft errors

Reference Voltage Variations
Coupling with adjacent low-swing wires
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Sources of Noise

• But most of these sources also exist in
  conventional CMOS.
• Differences
• No restoring stage anywhere in between
• path goes up and down the shifter a few times
  before being restored.
• Swing is about 6-10x less ? noise is 6-10x as
  significant

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Coupling Capacitances
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Effects of Coupling Capacitance Aligned
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Effects of Coupling cap - 90 Phase shift
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Coupling cap - 90 Phase shift
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Power Supply noise Coupling Cap
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Power Supply Noise
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Power supply noise (2)
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Ccouple Supply Vbias Vswing
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Ccouple Supply Vbias Vswing
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Ccouple Supply Vbias Vswing
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Waves
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Energy/Delay for Noise Models
LS(1) Coupling wires switching in opposite
directions simultaneously LS(2) Coupling wires
switching in opposite directions with 90 degress
phase-shift LS(3) LS(2) 17Vdd Drop LS(4)
LS(3) Vbias and Vswing Drop