Decoupling and filtering of RF Signals and noise

The new V Series capacitors deliver increased broadband rejection in a significantly reduced footprint for bypass capacitor filtering networks.  Released under the DLI brand from Knowles Precision Devices, this cost-effective capacitor line is built on a compact 30 mil by 30 mil footprint.  This superior RF signal blocking design tool will solve the needs of design engineers looking to decouple RF signals from DC bias lines in active circuit designs, such as MMICs, or filter out noise from switching power supplies.

Iy's more than just values
For designers looking to have broadband RF isolation, capacitors are the go-to components to complete the task. In practice, actual capacitors are modelled as a combination of capacitors, inductors, and resistors. At resonance the parasitic inductor and capacitor cancel out and an impedance low is realized. Above resonance the response of the inductor begins to dominate and cause the positive impedance slope. A common design rule is to consider 3 or 4 capacitors in shunt to ground, each with different values to provide broadband RF isolation. The end result is 3 or 4 capacitor curves superimposed, providing a broader frequency range of low resistive paths to ground for unwanted noise signals.

Application Recommendations (MMIC)
As an example the manufacturer of an MMIC is recommending ten (10) capacitors per MMIC to provide adequate grounding for DC supply lines. When taking such an approach one needs to consider the RF performance of the system as a whole. Rather than looking at the capacitor in isolation we should ask if the RF performance of the capacitors in practice is optimal for a design.

Measured Bypass Networks to verify performance
Using Measured Bypass Network results, DLI took the investigation one step further to consider what the performance of these devices could achieve in minimizing recurring harmonics from a hypothetical tone. To block frequencies below 100 MHz, they compared a traditional capacitor bypass network pulled from an industry datasheet (consisting of 3 capacitors ranging from pF to nFs), V-Series Capacitors, and a DLI UX series capacitor in combination with the V series part. They then ran a few different tones through the devices to simulate noise sources and compared the results. Once again, it is interesting to note that RF performance was not necessarily correlated to the choice of capacitor’s capacitance value, and verifying RF performance is the only way to guarantee performance.

Main Advantages

• High Capacitance Density
• Up to 10nF in 30 mil square size
• Up to 200WVDC for High Powered system needs
• Can be epoxy or AuSn mounted

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