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Amplifier Decoupling: EMI vs MLCC

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EMI Amplifier Decoupling

  • Test #1 uses an AD8221 instrumentation amplifier
  • Pin pattern is amenable to EMI circuit 1” use
  • +V / -V power pins are on the same side of the device
x2y-ad8221.jpg ad8221-schematic.gif
  • Test #2 uses an INA121 instrumentation amplifier
  • Pin pattern is amenable to EMI”circuit 2” use
  • +V / -V power pins are on the opposite sides of the device
x2y-ina121.jpg ina121-schematic.gif

Compare Bypass Conventional MLCC vs. EMI

Test #1

  • Compares external noise rejection of power bypass networks
    – Single EMI 330nF rated part, versus four total MLCCs
  • Noise voltage measured directly across IC pins
dut-configurations.png

PCB Configuration

Test #1

  • Two layer 1.5mm PCB
  • Single EMI 330nF rated part, versus four total MLCCs
  • Noise voltage probed directly across IC pins at IC body
pcb-configuration.jpg

PCB Configuration

Test #1

  • Equalized layout parasitics
  • Ground attachment matched between set-ups
  • Capacitor set-backs matched between set-ups
ground-and-capacitor-set-back-matched.jpg

Noise Injection

  • 200ps edges
    – Comparable to memory
  • 100MHz pulse rate
    – Isolate any cavity / capacitor ringing
  • 400mV on 15V power
    – Alternate tests:
    +15V / -15V
  • – 2.7% pp
noise-injection-+15v.png noise-injection--15v.png

VCC_15V+

vcc-15v+.png
  • EMI 3.7mV pp, conventional 5.6mV pp
  • Conventional noise 151% greater than EMI

VCC_15V-

vcc-15v-.png
  • EMI 5.3mV pp, conventional 8.9mV pp
  • Conventional noise 168% greater than EMI

Compare Bypass Conventional MLCC vs. EMI

Test #2

  • Amplifier power pin pattern amenable to EMI “circuit 2” use
    – the +/- power pins are on the same side of the device
  • Compares single EMI 100nF rated (200nF total) per pin vs. a single MLCC 220nF per pin
dut-configurations2.png

PCB Configuration

Test #2

  • Ground attachment is matched between set-ups
  • Capacitor set-backs are matched between set-ups
  • Compares single EMI 100nF rated (200nF total) per pin vs. a single MLCC 220nF per pin
ground-and-capacitor-set-back-matched2.jpg

VCC_15V-

vcc-15v-3.6mv.png
  • EMI 3.6mV pp, conventional 10.1mV pp
  • Conventional noise 280% greater than EMI

VCC_15V+

vcc-15v-4.9mv.png
  • EMI 4.9mV pp, conventional 17.3mV pp
  • Conventional noise 353% greater than EMI

Summary

Test #1

  • Conventional filter using two capacitor values per power pin, four capacitors total results in >= 150% voltage noise compared to just one EMI used for both power pins.

Test #2

  • Conventional filter using one capacitor value per power pin, two capacitors total results in >= 280% voltage noise compared to one EMI used for each power pin.
  • Benefits: smaller space, fewer parts, better economy and performance when using EMI components.