X2Y® FILTER & DECOUPLING CAPACITORS
THE X2Y® DESIGN - A BALANCED, LOW ESL, “CAPACITOR CIRCUIT”
The X2Y® capacitor design starts with standard 2 terminal MLC capacitor’s opposing electrode sets, A & B, and adds a third electrode set (G) which
surround each A & B electrode. The result is a highly vesatile three node capacitive circuit containing two tightly matched, low inductance capacitors
in a compact, four-terminal SMT chip.
The X2Y® component contains two shunt or “line-to-ground” Y capacitors. Ultra-low ESL (equivalent
series inductance) and tightly matched inductance of these capacitors provides unequaled high frequency
Common-Mode noise filtering with low noise mode conversion. X2Y® components reduce EMI emissions
far better than unbalanced discrete shunt capacitors or series inductive filters. Differential signal loss is
determined by the cut off frequency of the single line-to-ground (Y) capacitor value of an X2Y®.
POWER BYPASS / DECOUPLING
For Power Bypass applications, X2Ys® two “Y” capacitors are connected in parallel. This doubles the total
capacitance and reduces their mounted inductance by 80% or 1/5th the mounted inductance of similar sized
MLC capacitors enabling high-performance bypass networks with far fewer components and vias. Low ESL
delivers improved High Frequency performance into the GHz range.
GSM RFI ATTENUATION IN AUDIO & ANALOG
GSM handsets transmit in the 850 and 1850 MHz bands using a TDMA pulse
rate of 217Hz. These signals cause the GSM buzz heard in a wide range of audio
products from headphones to concert hall PA systems or “silent” signal errors
created in medical, industrial process control, and security applications. Testing
was conducted where an 840MHz GSM handset signal was delivered to the
inputs of three different amplifier test circuit configurations shown below whose
outputs were measured on a HF spectrum analyzer.
1) No input filter, 2 discrete MLC 100nF power bypass caps.
2) 2 discrete MLC 1nF input filter, 2 discrete MLC 100nF power bypass caps.
3) A single X2Y 1nF input filter, a single X2Y 100nF power bypass cap.
X2Y configuration provided a nearly flat response above the ambient and up to
10 dB imrpoved rejection than the conventional MLCC configuration.
AMPLIFIER INPUT FILTER EXAMPLE
In this example, a single Johanson X2Y® component was used to filter noise at the input of a
DC instrumentation amplifier. This reduced component count by 3-to-1 and costs by over 70%
vs. conventional filter components that included 1% film Y-capacitors.
DC offset shift
Common mode rejection
< 0.1 µV
10nF, 2 @ 220 pF
< 0.1 µV
Referred to input
Source: Analog Devices, “A Designer’s Guide to Instrumentation Amplifiers (2nd Edition)” by Charles Kitchin and Lew Counts
12 www.johanson dielectrics.com