®
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 higly vesatile three node capacitive circuit containing two tightly matched, low inductance capacitors in a compact, four-
terminal SMT chip.
X2Y® Circuit 1: Filtering
Circuit 1 connects the X2Y filter capacitor across two signal lines. Common-mode noise is filtered to ground (or
Signal 1
A
®
G1
G2
®
reference) by the two Y-capacitors, A & B. Because X2Y is a balanced circuit that is tightly matched in both
Ground
Signal 2
phase and magnitude with respect to ground, common-to-differential mode noise conversion is minimized and
any differential-mode noise is cancelled within the device. The low inductance of the capacitors extends their high
frequency attenuation considerably over discrete MLCs.
B
Power
X2Y® Circuit 2: Power Bypass / Decoupling
A
Circuit 2 connects the A & B capacitors in parallel doubling the total capacitance while reducing the inductance.
X2Y capacitors exhibit up to 1/10th the device inductance and 1/5th the mounted inductance of similar sized MLC
capcitors enabling high-performance bypass networks with far fewer components and vias. Low ESL delivers
improved High Frequency performance into the GHz range.
G1
G2
B
Ground
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 70ꢀ vs.
conventional filter components that included 1ꢀ film Y-capacitors.
Parameter
X2Y®
10nF
Discrete
10nF, 2 @ 220 pF
Comments
DC offset shift
< 0.1 µV
91 dB
< 0.1 µV
92 dB
Referred to input
Common mode rejection
Source: Analog Devices, “A Designer’s Guide to Instrumentation Amplifiers (2nd Edition)” by Charles Kitchin and Lew Counts
4
www.johansondielectrics.com
JOHANSON [ JOHANSON TECHNOLOGY INC. ]
