ISOIEC JTC 1SC 31WG 4SG 3 Optional Manchester Forward Link

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ISO/IEC JTC 1/SC 31/WG 4/SG 3 Optional
Manchester Forward Link

• Ed Farrell
• 31 October, 2006

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BATTERY ASSISTED TAGS ARE DIFFERENT

• PIE IS OPTIMIZED FOR PASSIVE POWER TRANSFER
• HIGH DUTY FACTOR DELIVERS MORE DC POWER TO TAG
• LONGER-RANGE BATTERY ASSISTED SIGNAL LEVELS ARE
  MUCH LOWER
• PERHAPS 20-30 dB WEAKER
• SQUARE-LAW DETECTOR WILL PRODUCE LESS THAN 1 AS
  MUCH VOLTAGE
• THEREFORE, AMPLIFICATION IS REQUIRED

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TAG PSEUDO-SCHEMATIC DC COUPLED CANDIDATE
ARCHITECTURE

• WHERE DO YOU SET THE SLICER THRESHOLD?

AMPLIFIER
DATA SLICER
DETECTOR
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DETECTOR OUTPUT for 90 AMPLITUDE MODULATION
SLICER THRESHOLD OPTIMISED FOR WEAK SIGNAL

• THE SIGNAL IS ALWAYS ABOVE THE SLICER THRESHOLD!
• ACTIVE AGC IS COMPLEX, POWER-CONSUMING, AND SLOW
• THEREFORE DC COUPLING IS UNSUITABLE

SLICER FAILS WITH STRONG SIGNAL !
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TAG PSEUDO-SCHEMATIC AC COUPLED CANDIDATE
ARCHITECTURE

• ADVANTAGE THE SLICER THRESHOLD IS ALWAYS
  CENTERED
• HOWEVER

DETECTOR
DATA SLICER
AMPLIFIER
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DIFFICULTIES WITH AC COUPLING

• AC-COUPLING IS SUBJECT TO BIAS SHIFTS DUE TO
  INPUT SIGNAL DUTY FACTOR (i.e., DC CONTENT)

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BIAS DISTORTION DUE TO SIGNAL DC CONTENTin
VARIOUS PIE WAVEFORMS
STRING of ZEROs BIAS 0 DISTORTION WITH AC
COUPLING IS NIL
STRING of ONEs BIAS 50 DISTORTION WITH AC
COUPLING IS MODERATE
RgtT PREAMBLE BIAS 85 DISTORTION WITH AC
COUPLING IS SEVERE

• PIE IS , GOOD FOR PASSIVE MODE POWER TRANSFER BUT
• BAD FOR AC COUPLING ASSOCIATED WITH HIGH
  SENSITIVITY

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DIFFICULTIES WITH AC COUPLING

• AC-COUPLING IS SUBJECT TO BIAS SHIFTS DUE TO
  INPUT SIGNAL DUTY FACTOR (i.e., DC CONTENT)
• BIAS SHIFTS WILL CAUSE TIMING DISTORTION AT THE
  SLICER
• PIE BIAS IS 0 FOR A STRING OF 0s, 50 FOR A
  STRING OF 1s.
• PIE RgtT PREAMBLE BIAS CAN BE AS MUCH AS 23/27,
  OR 85
• (BIAS DEFINED AS 100 X HIGH TIME / WHOLE TIME)
• AMPLIFIER/SLICER OFFSET ADDS TO BIAS SHIFT
• MAY DRIVE SIGNAL ENTIRELY OUT OF SLICER RANGE
  SLICER COMPLETELY FAILS
• THIS IS THE PRIMARY LIMIT ON TAGS SENSITIVITY
• THIS IS ALSO THE PRIMARY LIMIT ON RANGE
• FOR BATTERY ASSISTED PASSIVE
• SIGNALS WITH DC BIAS SQUANDER THE OFFSET BUDGET
• SIGNAL SHOULD BE DEVOID OF DC CONTENT
• LIKE MANCHESTER, UNLIKE PIE

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ALSO

• PIE REQUIRES 25-50 MORE BANDWIDTH THAN
  MANCHESTER
• MORE BASEBAND BANDWIDTH IMPLIES MORE DC AMPLIFIER
  CURRENT
• PIE SPECTRUM CONTAINS DISCRETE LINES MANCHESTER
  DOES NOT
• INCREASED READER-READER INTERFERENCE
• MANCHESTER EXHIBITS SNR ADVANTAGE
• MOSTLY APPARENT IN INTERFERENCE SITUATIONS