Appliances today must meet global compliance requirements for Electromagnetic Compatibility (EMC), and meeting regulatory compliance is complicated by the ever increasing use and density of electronic components. Within a larger appliance are various circuit components and modules that are generators of electromagnetic interference (EMI), and those that are highly susceptible to EMI noise. Each circuit portion must be individually filtered to suppress EMI, or the appliance product as a whole could fail EMC compliance. (See Fig. 1.)

A traditional EMI filter consists of passive components: capacitors, inductors, or resistors used singly, or combined together to form a filter network. A unique three-node capacitor technology called X2Y® can now be employed to routinely replace conventional EMI filter networks with a single component. The X2Y technology can mitigate various noise issues, including radiated emissions, power-plane noise in IC power delivery networks, and susceptibility to audible noise in electronic products. Several examples that compare X2Y against conventional EMI filters can illustrate how noise reduction can be achieved to help appliances meet global EMC requirements.

Technology difference

Enlarge this picture Fig. 1. Noise interference example in an appliance.

X2Y capacitors share many of the same characteristics as standard 2-terminal multi-layer ceramic capacitors (MLCCs). They are made using the same dielectric, electrode, termination materials, and manufacturing processes as MLCCs and are available in the same voltage, capacitance ratings and sizes as conventional MLCCs. Component pick-and-place and soldering equipment handle assembly of X2Y components seamlessly.

The main difference between an X2Y and a conventional ceramic capacitor is the internal electrode structure, which results in a three-node, four-terminal capacitor that is more effective for both EMI filtering and IC power bypass applications. (See Fig. 2.)

Enlarge this picture Fig. 2. A three-node X2Y capacitor compared to a two-node conventional capacitor. (Illustration/image courtesy Johanson Dielectrics.).

Insertion loss (IL) measured on a microstrip test fixture using a Vector Network Analyzer (VNA) is one measure of filter effectiveness. From the IL data, the contribution of the test fixture can be removed and the inductance values of various DUTs extracted [1]. As seen in Fig. 3, inductance comparisons of same size 0603 MLCCs and X2Y capacitors show that X2Y capacitors have approximately 1/10th the inductance, and as low as 1/25th the inductance of larger component sizes (1206, 1812, etc.), which are often used to filter motors and power converters. The lower inductance characteristic of X2Y is due to the added side terminations that form four small opposing current loops when X2Y is attached in-circuit, and a cancellation effect that reduces the net inductance to the circuit.

In addition, the device is inherently balanced by design, so when properly mounted in-circuit between the +/- power lines and grounded, an X2Y capacitor provides tightly matched line-to-ground shunt capacitance, which greatly reduces EMI [2]. The combination of low inductance and tight matching results in dramatically improved EMI filter performance and a significant cost savings achieved by reducing passive components and their associated assembly costs.

Radiated emissions examples

Enlarge this picture Fig. 3. Extracted inductance, X2Y capacitors compared to MLCCs.

Many appliance manufacturers use DC brush motors for motion control in their products. Brush commutated motors are spark generators that combine with transmission lines such as power cables, wires, traces, to radiate broadband electromagnetic interference into a larger electrical system. (See Fig. 4.) The EMI can cause malfunction when coupled to other nearby circuit components that are susceptible to interference. In one example, application engineers at X2Y Attenuators were contacted by a blender manufacturer that was plagued by integrated circuit (IC) latch-up. The manufacturer’s engineers had isolated the source of the problem as the blender’s DC motor, which gave them a choice of placing the noise filter at the IC that was susceptible to EMI, or at the EMI source, the DC motor. Attempts to filter the DC motor with conventional capacitors had failed to stop the IC malfunction. However, a single X2Y filter capacitor placed between the DC motor’s power leads as they exit the motor housing (I/O) completely eliminated the malfunction issue. An added benefit of suppressing EMI at the source is that it may solve susceptibility issues with other components that may have yet to surface under different DC motor operating conditions.

Enlarge this picture Fig. 4. Applying X2Y capacitors in DC motors.

A closer look at the noise source and cause of emissions reveals that switching DC motors and power supplies have power delivery cables that also serve as convenient and efficient antenna for the transmission of unwanted emissions. Through these cables, DC motors can generate conducted (CE) and radiated emissions (RE) to the extent that a product will fail EMC compliance. EMI noise propagates when there is a voltage difference between the power cables and the motor case/enclosure, and a difference between each cable of a pair. Effective noise reduction with any EMI filter requires placing the filter at the cable I/O to stop propagation of EMI and, ideally, the filter components should provide a balanced voltage potential between power cables and the enclosure. (See Fig. 5.)

Enlarge this picture Fig. 5. An EMI example, unfiltered motor, or enclosure.

Typical EMI suppression required for DC motors in automotive applications consists of four to seven capacitors and inductors in combination as shown in Fig. 6 [3, 4]. Many filter components are needed because self-imposed automotive radiated emission limits are well below commercial or military limits [5].

How does the X2Y capacitor outperform a network of conventional shunt capacitors and the series inductors? Conventional filtering uses separate capacitors and inductors, one applied on each +/- line, or between the lines. The wired connections between components and the mismatched component tolerances create an imbalance in the EMI filtering. (See Fig. 7.) The difference in EMI filtering on each power line translates to increased emissions. A single X2Y capacitor properly mounted at the cable I/O provides balanced filtering on both +/- lines while simultaneously minimizing the potential difference to the motor case. Since only one X2Y component is used, imbalances caused by wire connections are minimized in the application. (See Fig. 8.)

Enlarge this picture Fig. 6. Radiated emissions: EMI filter comparisons.

A single X2Y component has met automotive requirements for CE and RE, transient suppression, and various motor-stall requirements. In appliance applications, a single X2Y filter component can often provide the needed filtering to meet less stringent FCC EMC compliance at a lower cost than conventional EMI filter measures.

For AC powered appliances, the advent of more efficient, faster switching power supplies makes meeting agency compliance an increasingly difficult task. Schurter offers an AC powerline filter product with an X2Y capacitor inside that meets IEC and UL agency safety requirements and is designed specifically for high-frequency filtering of radiated emissions [6] to GHz frequencies. Low inductance improves high frequency filtering.

Location benefits

Enlarge this picture Fig. 7. A conventional EMI filter, motor, or enclosure.

Power switchers inside a product can propagate noise outside the product by way of power cables. Traditional AC filter solutions combine multiple passive components on a dedicated printed circuit board (PCB). Physically locating many components at the power lead exit is simply not possible. At high frequencies, wire lengths connecting the components in a filter network degrade high frequency filter performance. In many cases, a large ferrite is integrated into the AC power cord as a secondary measure to meet EMC compliance requirements that can go to 1GHz or higher frequencies.

Schurter’s 5150 filtered IEC connector solves the proximity issue by integrating a single X2Y AC capacitor inside the connector, which can eliminate multiple passive components used for high-frequency filtering and their associated PCB. The 5150 connector can be ideally located at the AC power cable I/O to deliver optimized high frequency EMI filtering. (See Fig. 9.)

Power plane noise

Enlarge this picture Fig. 8. X2Y EMI filter, motor or enclosure.

Today, even modest appliances use integrated circuits (ICs). Many appliances use programmable logic [7] (FPGAs) to manage a variety of functions that include motor control, power management, network interface, and LCD drivers, to name a few. Logic transition with fast signal edges can result in EMI issues as printed circuit boards with copper planes and traces become resonant structures.

To evaluate real world performance, X2Y and industry experts [8, 9] built an active FPGA board [10] to demonstrate passive component reduction and noise reduction on the I/O power plane. (See Fig. 10.)

The power island surrounding the FPGA supports the bypass capacitors used for the power delivery network (PDN) supporting the IC. To directly compare performance, capacitor mounting pads for 16 X2Y 0603 capacitors and up to 64 conventional 0402 capacitors were located around all four sides of the FPGA. The left and right FPGA I/O banks drive 50 Ohm transmission lines: 60 lines from each 6 banks terminate on the left and right side of PCB. An SMA connector shown at the top right of the FPGA power island was used to probe I/O voltage with the FPGA driving all 360 of the left and right bank outputs simultaneously. (See Fig. 11.)

Fig. 9. Schurter 5150 PowerLine Filter.

An oscilloscope was used to compare the various capacitor configurations and peak-to-peak noise voltage results on the I/O power plane at the SMA connector. The following networks were measured:

• No capacitors, which yielded maximum peak-peak noise and caused IC malfunction.
• 16 conventional capacitors, which reduced I/O plane peak-peak noise to 283 mV.
• 16 X2Y capacitors, which reduced I/O plane peak-peak noise to 100 mV.

To achieve the same peak-peak noise reduction so that component replacement ratios could be quantified, additional conventional capacitors were added and periodically measured until peak-peak noise equivalency was achieved. Peak-peak noise was finally reached when 58 conventional capacitors were used around the FPGA. The results of the test showed that 16-X2Y capacitors either reduced conventional capacitor count by 73 percent and eliminated drilled vias by nearly 60 percent, or reduced peak-peak noise by 3:1 noise reduction when compared to 16 conventional capacitors.

Noise susceptibility

Enlarge this picture Fig. 10. Active FPGA demonstration board.

In the not-to-distant past, home appliances with multiple functions that interacted with people seemed like a fantastic premise. But today’s appliances often incorporate multiple functions, such as refrigerators that contain entertainment devices such as a built-in stereo or LCD televisions with embedded speakers. In addition, wireless phones have proliferated and many people, especially the younger generation, have grown up carrying cell phones from morning to night, much like a wallet. (See Fig. 12.) But wireless telephones can also generate EMI that disrupts susceptible kitchen appliances. EMI problems can occur when a cell phone is in close proximity to appliances with embedded speaker systems.

Enlarge this picture Fig. 11. Data comparisons: X2Y capacitors vs. conventional MLCCs.

An example of one such EMI problem is GSM cell phone buzz. Coherent high-frequency noise from GSM cell phones can alias to low frequencies. The “buzz” is caused by the phone transmitter pulsing at a repetition rate of 217 Hz during a call, the 217-Hz signal is harmonic-rich; it can result in an audible buzz in television or stereo speakers when coupled into amplifier circuitry. Because cell phones operate in multiple high-frequency bands, a broadband, low-inductance filter solution is needed.

Fig. 12. Wireless phone, and a cell phone tower.

To demonstrate the effectiveness of X2Y capacitors in eliminating audible GSM buzz, a test was set up in X2Y’s metrology lab consisting of a GSM handset secured to a 900 MHz antenna on shielded coax attached to an amplifier circuit board placed inside a shielded enclosure. A power divider delivered the cell phone’s offending signal to the positive/negative amplifier inputs. Conventional and X2Y capacitors were applied at the amplifier’s input and power pins. A spectrum analyzer was connected at the amplifier output for comparative measurements. (See Fig. 13.)

Fig. 13. Test setup, amplifier input filtering for GSM noise.

These tests, along with current applications in the field, have proven that low inductance, three-node X2Y capacitors can be used for noise suppression in products that need to meet EMC compliance. By efficient design, X2Y capacitors can replace multiple passive components to improve circuit performance and lower assembly costs.

The test showed that X2Y provided a nearly flat response above the ambient, was typically 12 dB below the no-filter result, and provided 4 dB to 10 dB better rejection than the conventional MLCC filter. X2Y successfully eliminated GSM buzz [11]. (See Fig. 14.)

Fig. 14. Data plots, GSM noise suppression.

X2Y Attenuators is an intellectual property developer that has licensed the X2Y capacitor technology to a number of passive component manufacturers. For more information, visit: www.X2Y.com

References:
[1] Accurate capacitor inductance extraction from s21 measurements.
[2] Noise Reduction Techniques in Electronic Systems, 2nd Edition, by Henry Ott.
[3] GTEM cell simplifies EMC test.
[4] Broadband testing of low cost solutions for DC motors.
[5] EMI Design Techniques for Microcontrollers in Automotive Applications.
[6] Schurter 5150 Series IEC inlet.
[7] Altera in home appliances.
[8] Howard Johnson.
[9] Steve Weir, Teraspeed Consulting, LLC.
[10] X2Y live FPGA power bypass.
[11] Cell phone GSM interference.