A Harmonic Low Pass Filter with a Lead-free LGA Termination
AVX Corp. is now offering the LP0603 harmonic low pass filter with lead-free land grid array (LGA) termination. The ITF LGA low pass filter is based on thin-film technology and provides a miniature part with excellent high frequency performance and rugged construction for reliable automatic assembly. The ITF low pass filters are offered in a variety of frequency bands compatible with various types of high frequency wireless systems. The filter’s design also results in an inherent low profile, self-alignment during reflow, excellent solderability and better heat dissipation.
Harmonic low pass filters are used to reduce and eliminate unwanted harmonics in telecommunications applications such as mobile communications, satellite TV receivers, GPS, vehicle location systems, wireless LANs and WiMAX. While discrete components such as capacitors and inductors can be used to meet the same ends, it would be necessary to use a minimum of four or five of those components to achieve the same results as one LP0603. For handheld and portable equipment, such as cell phones, this can take up significant space, which is at a premium. The LP0603 takes the place of multiple components and also offers electrical performance unmatched in any other low pass filter available in a similar package size. The LP0603 would be found on the outside of a cell phone’s power amplifier to eliminate unwanted harmonics generated by the amplifier. For example, in Wi-Fi applications, where a piece of equipment might be operating at 900 MHz, the amplifier will normally generate unwanted second and third harmonics. The LP0603 filters out the unwanted harmonics to prevent interference in the operation of the components and therefore the end product.
The AVX's LP0603 has a lower insertion loss than most other low pass filters on the market, while the attenuation levels are higher. At a frequency of 902 GHz, for example, the LP0603 shows an insertion loss of –0.35 dB and attenuation at the second harmonic of –25 dB. Table 1 shows the electrical characteristics of the available LP0603 harmonic low pass filters that are guaranteed over the –40° to +85°C operating temperature range. Figure 1 shows the typical frequency response for a LP0603A0902ANTR harmonic low pass filter.
In using its thin-film technology in constructing the filter, AVX uses pure metals and controls the thickness and physical dimensions of the layers in a way that is not possible with MLCC technology and that allows for a much higher level of uniformity and consistency from component to component. The land grid array offers several advantages: an inherent low profile packaging, self-alignment during reflow soldering, excellent solderability, low parasitics and better heat dissipation. The package dimensions are shown in Figure 2. The nickel/lead-free solder coating is compatible with automatic soldering technologies such as reflow, wave soldering, vapor phase and manual. The finish parts are 100 percent tested for electrical parameters and visual characteristics. Each production lot is evaluated on a sample basis for static humidity, at 85°C, 85 percent RH, for 160 hours, and for endurance at 125°C, IR for four hours.
Low Pass Filter Test Jigs
There are specific jigs designed for testing the LP0603 LGA low pass filters using a vector network analyzer. They consist of a dielectric substrate, having 50 W microstrips as conducting lines and a bottom ground plane located at a distance of 0.127 mm from the microstrips. The substrate used is Neltec's NH9338ST0127C1BC (or similar). The connectors are SMA females. Both a measurement jig and a calibration jig are provided. The calibration jig is designed for a full two-port calibration and consists of an open line, a shorted line and a through line. The load calibration can be done by a 50 ? SMA termination. Figure 3 shows the layout of the jigs.
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