An Integrated Solution for Suppressing WLAN Signals in UWB Receivers

1
An Integrated Solution for Suppressing WLAN
Signals in UWB Receivers

• LI BO

2
Motivation

• UWB system becomes more interested in Wireless
  Personal Area Networks (WPAN) due to its high
  bandwidth after federal release the unlicensed
  spectrum in 3.1-10.6 GHZ
• Wireless Local Area Network (WLAN) is operated
  in 4.9-5.825 GHZ

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Intermodulation products in UWB Band
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Suppressing WLAN signal

• Third-order intermodulation
• Second order intermodilation
• It is a natural idea to suppress WLAN and other
  noise to improve performance

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Possible solutions

• Off-chip pre-filter
• Increase cost due to additional external
  component
• signal lost
• lower speed
• Integrate a filter to avoid WLAN interferers
• Increase speed
• Low cost

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Wide-band filter VS tunable narrowband filter

• Wide-band
• High order filter
• Need many inductor ( a lot of space)
• Impairs gain of receiver
• Tunable narrowband filter
• Can be easily implemented through low order
  filter
• Must have tuning due to small band

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Tunable narrowband filter receiver scenario
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Low Noise Amplifier (LNA)

• LNA will determine noise figure of receivers
• Challenges in design LNA
• Input resistor need to be 50 ohms
• Very low noise figure
• Gain with high linearity which often measured in
  IP3
• Maximize output power

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Low noise amplifier (LNA)

• L1,C1,L2
• C2 use for matching
• Inductively degenerated common-source amplifier

• Lg is added to give flexibility to design\
• Cascode circuit to imporve frequency response

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Notch filter simple example

• At resonant frequency, Zf is equal to zero so
  steal all signals

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Notch Filter design

• Two resonant frequency
• Q4 works as a negative resistor
• It is tunable through varactor

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Mixer

• A multiply circuit
• R3,L4 are use to isolate RF signal
• L4 is 5 nH, an area of 70x70 um2

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LO input and output buffer
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Chips

• Due to Sidewall capacity of pad

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Measured noise figure (NF)

• Parasitic resistance of notch filter
• Poor model and layout of the varactor

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Measured results
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Performance
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Conclusion

• Implement tunable filter idea to suppress WLAN
  inference in 4.9-5.825 GHZ using SiGe 0.35um
  technology
• The LNA, Mixer and filter power consumptions are
  25.2,6 and 18 mW.
• The NF is not coherent with design which maybe
  due to poor model and layout of varactor