EMI® Filter & Decoupling Capacitors
- Amplifier FIlter & Decoupling
- High Speed Data Filtering
- EMC I/O Filtering
- FPGA / ASIC / μ-P Decoupling
- DDR Memory Decoupling
- One device for EMI suppression or decoupling
- Replace up to 7 components with one X2Y
- Differential and common mode attenuation
- Matched capacitance line to ground, both lines
- Low inductance due to cancellation effect
EMI® filter capacitors employ a unique, patented low inductance design featuring two balanced capacitors that are immune to temperature, voltage and aging performance differences.These components offer superior decoupling and EMI filtering performance, virtually eliminate parasitics, and can replace multiple capacitors and inductors saving board space and reducing assembly costs.
- Same component sizes (0603, 0805, 1206, etc.)
- Same pick and place equipment
- Same voltage ratings
- Same dielectric, electrode and termination materials
- Same industry test standards for component reliability
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 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.
- No input filter, 2 discrete MLC 100nF power bypass caps.
- 2 discrete MLC 1nF input filter, 2 discrete MLC 100nF power bypass caps.
- 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.
When used in circuit 1 configuration the X2Y® filter capacitor is connected across two signal lines. Differential mode noise is filtered to ground by the two Y capacitors, A & B. Common mode noise is cancelled within the device.
Experts agree that balance is the key to a "quiet" circuit. X2Y® is a balanced circuit device with two equal halves, tightly matched in both phase and magnitude with respect to ground. Several advantages are gained by two balanced capacitors sharing a single ceramic component body.
- Exceptional common mode rejection
- Effects of aging & temperature are equal on both caps
- Effect of voltage variation eliminated
- Matched line-to-ground capacitance
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.
|Parameter||X2Y® 10nF||Discrete 10nF, 2@220 pF||Comments|
|DC offset shift||< 0.1 µV||< 0.1 µV||Referred to input|
|Common mode rejection||91 dB||92 dB|
Source: Analog Devices, “A Designer’s Guide to Instrumentation Amplifiers (2nd Edition)” by Charles Kitchin and Lew Counts
- Superior High Frequency Emissions Reduction
- Smaller Sizes, Lighter Weight
- No Current Limitation
- Vibration Resistant
- No Saturation Concerns
One X2Y® component has successfully replaced 7 discrete filter components while achieving superior EMI filtering.
A common design practice is to parallel decade capacitance values to extend the high frequency performance of the filter network. This causes an unintended and often over-looked effect of anti-resonant peaks in the filter networks combined impedance. X2Y’s very low mounted inductance allows designers to use a single, higher value part and completely avoid the anti-resonance problem. The impedance graph on right shows the combined mounted impedance of a 1nF, 10nF & 100nF 0402 MLC in parrallel in RED. The MLC networks anti-resonance peaks are nearly 10 times the desired impedance. A 100nF and 47nF X2Y are plotted in BLUE and GREEN. (The total capacitance of X2Y (Circuit 2) is twice the value, or 200nF and 98nF in this example.) The sigle X2Y is clearly superior to the three paralleled MLCs.
One X2Y® component can effectively filter high speed signal lines replacing replacing multiple inductive and ferrite components.
DC-DC converters, power I/O, connectors (RJ45, D-sub), audio/voice/data, CAN, high-speed differential.
Effectively replaces common mode chokes, inductors, ferrites and feedthru capacitors.
Use of solder mask beneath component is NOT recommended because of flux/contaminant entrapment.
X2Y capacitors deliver excellent performance in EMI/RFI filtering and Power Bypass applications. Physical and electrical placement on the PCB is critical in achieving good results. A low inductance, dual ground connection is mandatory.
For EMI Filter applications, low inductance PCB routing examples are shown in figures 1 and 2. Figures 3-5 show unbalanced and high inductance connections and should be avoided. For more information see X2Y EMI Filter Evaluation and PCB Design Guidelines.
EMI Filter Applications: stray inductance must be minimized between signals and the A and B capacitor pads.G1 and G2 connections should be low inductance connections as well. Use star or daisy chain routes, rather than "T" to capacitor pads as show in Figure 1. Read: NEW - X2Y EMI Filter Evaluation & Design Guide for comprehensive information.
For PDN / Bypass applications the figures on the right compare the X2Y recommended layout against a poor layout. Because of its long extents from device terminals to vias, and the wide via separation, the poor layout exhibits approximately 200% L1 inductance, and 150% L2 inductance compared to recommended X2Y layouts. For more information see X2Y Power Bypass Mounting.
Ceramic capacitors (X2Y® and standard MLC types) can be easily damaged when hand soldered. Thermal cracking of the ceramic body is often invisible even under a microscope. Factors that increase thermal cracking risk:
- 4 terminals to solder can increase hand-soldering time and temperature exposure
- Pb-free solders have higher reflow temperatures
- Low inductance connections to ground are inherently good heat-sinks
A damaged component may exhibit a short circuit immediately and not recover, or may operate with intermittent Insulation Resistance (IR) levels. If you are not achieving expected results and have followed the other guidelines carefully, check to see you are adhering to the soldering guidelines below:
- Always pre-heat the PCB and component to within 50°C of solder reflow temperature at 2°C/sec. maximum.
- Use contact-less hand solder tools such as a hot air pencil, IR lamp, etc.
- Avoid over-heating of the ceramic component, temperature limit: 260°C for 20-30 seconds max.
- Use a soldering iron as last resort; 20W max. tip, NO CONTACT with ceramic, limit solder time to 5 seconds max.
A reliable, cost effective prototype PCB reflow soldering process is possible using a household toaster oven. There are several good procedures available on-line by googling "Toaster Oven Soldering"
When used in circuit 2 configuration, A & B capacitors are placed in parallel effectively doubling the effective capacitance while maintaining an ultra-low inductance. The low inductance advantages of the X2Y® Capacitor Circuit enables high-performance bypass networks at reduced system cost.
- Lower via count, improves routing
- Reduces component count
- Lowers placement cost
- Low ESL (device only and mounted)
- Broadband Performance
- Effective on PCB or package
Actual measured performance of two high performance SerDes FPGA designs demonstrate how a 13 component X2Y bypass network significantly out performs a 38 component MLC network.
The X2Y® has short, multiple and opposing current paths resulting in lower device inductance
1:5 MLCC REPLACEMENT EXAMPLE X2Y's proven technology enables end-users to use one X2Y capacitor to replace five conventional MLCCs in a typical high performance IC bypass design. Vias are nearly cut in half, board space is reduced and savings are in dollars per PCB.
34% NOISE IMPROVEMENT 1:3 MLCC REPLACEMENT
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