Oscilent designs, manufactures, and promotes a full line of IF and RF SAW Filter products and solutions for wireless applications including GPS, PCS, PCN, CDMA, Wireless LAN, GMS, CATV, Bluetooth, keyless entry, and other datacom, handset, and broadband commercial and military/aerospace applications. Our capabilities span both low and high volume programs with particular focus on signal processing applications. In addition to our extensive offering of standard SAW Filter products, Oscilent has diverse Engineering experience spanning hundreds of custom designed SAW Filters, Bandpass Filters, Low Loss Filters and SAW based subsystems. Our custom/design/testing capabilities are unparalleled in our industry.
SAW Filter General Information
Advantages of SAW Filter technology include compact packages, low shape factors, superior linear phase characteristics, rejection qualities, and the relatively stable performance over temperatures. Many other advantages are derived from the physical structure of SAW Filters which allow for extremely robust and reliable designs that remain stable in the field/application. Additionally, the inherent design and wafer processing techniques of Saw Filters provide for a repeatable device in both low and high volume production.
Surface Accoustic Wave (SAW) fundamentals provide for a piezoelectric material that converts an incoming electromagnetic signal into an acoustic signal, and vice versa. In its most basic form, a SAW filter consists of a polished piezoelectric substrate with a deposit of two transducers with interdigital arrays of thin electrodes. The electrodes making up the arrays alternate polarities so that when an RF signal voltage is applied across them, a surface wave is then generated. In designing a SAW Filter, the overall frequency response characteristics are determined by deriving two impulse responses for the two transducers whose transforms are added together in dB. The surface of a piezoelectric substrate is then etched with the two impulse responses.
Selecting an Oscilent SAW Filter
Generally, a SAW Filter manufacturer will offer their most popular devices as standards creating a reference for Engineers to design from. Typically, and especially true in the RF SAW Filter category, a standard device is available for most common applications. However, for applications requiring parameters that are not currently considered industry standards, Oscilent is uniquely equipped to offer design and development services at comparatively lower costs than our competitors. In this case, the following information is required to effectively design a SAW Filter:
The following link can be used to print and fax your SAW Filter requirements to our Engineering Staff:
a. Center Frequency (Fo)
b. Passband Width (Bp)
Simply stated, the Passband Width will pass a signal occupying a specific frequency band, and reject others falling outside the band. From a SAW Filter design perspective, the first parameter to consider is the Fractional Bandwidth (Bp/Fo) because of the influence on the substrate material to be used in the design. The substrate material influences many parameters, most importantly the Temperature Stability specifications.
c. Amplitude Ripple over Passband Width (AR)
The Amplitude Ripple is a measure (dB) of the variation, or differential value, of attenuation in the passband of a filter, typically a SAW Filter will be specified as having a Typical and Maximum allowable value.
d. Group Delay Variation over Passband Width (GDR)
From a mathematical perspective measured in time, the Group Delay of a SAW Filter is the first differential value of time for phase frequency of phase changing (variation) in pass band. Otherwise, we can reference the Group Delay as the slope of the Phase vs. Frequency Curve. In simple terms, the Group Delay represents the time it takes for the signal to pass through the SAW Filter.
e. Transition Bandwidth (Bt)
Otherwise referred to as Skirts, the area between the Stop Band and the Passband found on both sides of the Passband.
f. Rejection (REJ.)
All ranges of the SAW Filter not including the Passband. The Rejection can also be referred to as the Rejection Range, or Stop Band. We can refer to this as the range in which the Relative Attenuation is larger than the specified Rejection side. With proper material selection and design, Rejection of 50dB, or greater, is possible within a wide selection of fractional bandwidths and shape factors.
g. Insertion Loss (IL)
Advances in SAW Filter design techniques routinely allow for a design incorporating a specification of under 10dB Insertion Loss, however, the minimum attainable Insertion Loss is generally influenced by the Fractional Bandwidth and the influences of this ratio on the applicable substrate material. The Insertion Loss value will generally increase when approaching the fractional bandwidth limit of a substrate material. For instance, a Fractional Bandwidth value of 8% will generally produce lower Insertion Loss than a Fractional Bandwidth value of 30% using the same substrate material.
h. Package
Factors affecting the size of the package used in SAW Filter design include parameters associated with Center Frequency, Bandwidth, and Shape Factor, among other minor considerations. For instance, lower Frequencies require larger substrate, thereby increasing the size of the packages available to the designer. Consequently, an equally important challenge of package size reduction is always considered by Oscilent Design Engineers in an attempt to meet the desired parameters in the smallest package possible. In selecting a package, we recommend stating general preferences. Without this input, Oscilent will design using the most cost effective approach balancing parameter requirements with cost and manufacturability.
Ver blogger original: http://nubia-anc.blogspot.com/
Materia: CRF
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