遥遥领先MTRONPTI基本晶体滤波器样式

遥遥领先MTRONPTI基本晶体滤波器样式

Basic Crystal Filter Styles

Narrow Band Filters

Both discrete resonators and monolithic dual resonators have electrode pairs on opposite faces of a quartz wafer. These electrodes, in addition to exciting the natural mechanical resonances of the wafer, unavoidably produce a static capacitance (C0 ). A narrow band filter is one where the network can be designed so the (C0 ) is part of the network, supplemented in most cases by additional external capacitance. As the bandwidth increases the allowable amount of supplemental capacitance decreases and eventually becomes negative. For a filter to be narrow band, the allowable supplemental capacitance must be greater than or equal to zero. Maximum inductorless bandwidth is the bandwidth at which the supplemental capacitance is equal to zero and is the maximum bandwidth at which a narrow band design can be realized. The capacitance ratio C0/C1 of the resonator equivalent circuit determines this maximum bandwidth. For filters using fundamental mode AT-cut resonators, under ideal conditions this maximum bandwidth is approximately 0.32% of the center frequency. At bandwidths exceeding this limit, the network design must be changed to incorporate inductors that appear in shunt with the crystal resonators.

Intermediate Band Filters

Intermediate band filters use inductors to remove excess capacitance presented by the resonator (C0) and unavoidable supplemental stray capacitance. There are two types of intermediate band filters. The first type is sometimes called a narrow band filter with spreading coils (inductors). The inductors are treated as negative capacitances that absorb some of the (C0 ) and stray shunt capacitance, leaving the reduced amount necessary for a narrow band design. In this type of filter the parasitic coil losses may cause severe rounding of the upper passband (or in some cases, rounding of the lower passband). The second type of intermediate band filter is designed with no capacitance in parallel with the motional elements of the crystal resonator. The passband of this is largely unaffected by parasitic coil loss until the bandwidths become close to wide band. Filters of this type use redundant crystals. An 8-resonator design may only give 7 poles of performance. This disadvantage is offset by the flexibility of the design technique that allows the realization of elliptical function and single-sided responses. Most intermediate band designs use discrete resonators but they may incorporate monolithic dual resonators. Bandwidths are between 0.3% and 1.0% for fundamental resonators. Spurious responses will sometimes be present in the filter bandpass, will often be present in the transition region, and will usually be strongly excited in the filter stopband.

Wide Band Filters

These filters use inductors to contribute poles to the filter response at the same time as accommodating the resonator (C0). For this reason, the filter response is very sensitive to inductance and Q values and requires precise temperature compensation of inductors if performance is to be maintained. Bandwidths are between 1% and 10% of center frequency. Discrete resonators are generally used. When AT-cut crystals are used, spurious responses will often be present in the filter passband and transition region. The inductors, since they add poles, may suppress spurious response in the filter stopband.

遥遥领先MTRONPTI基本晶体滤波器样式

窄带滤波器
MTRONPTI麦特伦皮滤波器，分立谐振器和单片双谐振器都在石英晶振晶片的相对面上具有电极对。这些电极除了激发晶片的自然机械共振之外，还不可避免地产生静态电容（C0）。窄带滤波器是可以设计网络的滤波器，因此（C0）是网络的一部分，在大多数情况下由额外的外部电容补充。随着带宽的增加，可允许的补充电容量减少并最终变为负。对于窄带滤波器，允许的补充电容必须大于或等于零。最大无电感带宽是补充电容等于零的带宽，也是可以实现窄带设计的最大带宽。石英晶体谐振器等效电路的电容比C0/C1决定了这个最大带宽。对于使用基模AT截止谐振器的滤波器，在理想条件下，该最大带宽约为中心频率的0.32%。在带宽超过这一限制的情况下，必须改变网络设计，以包含与晶体谐振器并联的电感器。

中间带滤波器
中频滤波器使用电感器来去除谐振器（C0）产生的多余电容和不可避免的补充杂散电容。有两种类型的中频滤波器。第一种类型有时被称为具有扩展线圈（电感器）的窄带滤波器。声表面滤波器，电感器被视为吸收部分（C0）和杂散分流电容的负电容，从而减少窄带设计所需的数量。在这种类型的滤波器中，寄生线圈损耗可能会导致上通带的严重舍入（或在某些情况下，下通带的舍入）。第二种类型的中频滤波器设计为没有与晶体谐振器的运动元件并联的电容。其通带在很大程度上不受寄生线圈损耗的影响，直到带宽接近宽带。这种类型的过滤器使用多余的贴片晶振晶体。8谐振器的设计可能只提供7极的性能。这种缺点被允许实现椭圆函数和单面响应的设计技术的灵活性所抵消。大多数中频带设计使用分立谐振器，但它们可能包含单片双谐振器。基本谐振器的带宽在0.3%和1.0%之间。杂散响应有时会出现在滤波器带通中，通常会出现在过渡区，并且通常会在滤波器阻带中被强烈激发。

宽带滤波器
这些滤波器在容纳谐振器（C0）的同时使用电感器为滤波器响应贡献极点。因此，滤波器响应对电感和Q值非常敏感，并且如果要保持性能，则需要对电感器进行精确的温度补偿。带宽在中心频率的1%和10%之间。通常使用离散谐振器。当使用AT切割晶体时，在滤波器通带和过渡区中通常会出现杂散响应。电感器由于增加了极点，可以抑制滤波器阻带中的杂散响应。