Surface acoustic wave filter device

A surface acoustic wave filter device comprising:

• a piezoelectric substrate;
• and
• first, second and third surface acoustic wave filter elements disposed on said piezoelectric substrate;
• wherein the first surface acoustic wave filter element includes a first IDT arranged along a surface acoustic wave propagation direction and also includes second and third IDTs disposed on respective opposite sides, in the surface acoustic wave propagation direction, of the first IDT;
• said second and third surface acoustic wave filter elements each include a plurality of IDTs disposed along the surface acoustic wave propagation direction;
• said second and third surface acoustic wave filter elements are arranged such that they are substantially equal in transmission amplitude characteristic within a band but different in transmission phase characteristic by about 180°;
• and
• the second IDT of the first surface acoustic wave filter element is connected to the second surface acoustic wave filter element, and the third IDT of the first surface acoustic wave filter element is connected to an IDT of the third surface acoustic wave filter element.

A surface acoustic wave filter device comprising:

• a piezoelectric substrate;
• and
• first, second and third surface acoustic wave filter elements disposed on said piezoelectric substrate;
• wherein the first surface acoustic wave filter element includes a first IDT, a second IDT, and a third IDT, said second and third IDTs being disposed on respective opposite sides, in a surface acoustic wave propagation direction, of said first IDT;
• the second surface acoustic wave filter element is connected to the second IDT of the first surface acoustic wave filter element;
• the third surface acoustic wave filter element is connected to the third IDT of the first surface acoustic wave filter element;
• and
• a phase difference of about 180° is provided within a passband between the inputs or the outputs of the second IDT and the third IDT of the first surface acoustic wave filter element.

A surface acoustic wave filter device comprising:

• a piezoelectric substrate;
• and
• first and second surface acoustic wave filter elements disposed on said piezoelectric substrate;
• wherein
• said first surface acoustic wave filter element includes a plurality of IDTs disposed along the surface acoustic wave propagation direction;
• said second surface acoustic wave filter element includes a plurality of IDTs disposed along the surface acoustic wave propagation direction;
• said second surface acoustic wave filter element is arranged such that the transmission amplitude characteristic of said second surface acoustic wave filter element is substantially equal to that of said first surface acoustic wave filter element and such that the transmission phase characteristic of said second surface acoustic wave filter element is different by about 180° from that of said first surface acoustic wave filter element;
• one end of each of the first and second surface acoustic wave filter elements is electrically connected in parallel, and the other end of each of the first and second surface acoustic wave filter elements is electrically connected in series, so that the parallel-connected terminals define unbalanced terminals and the series-connected terminals define balanced terminals.

A surface acoustic wave filter device comprising:

• a piezoelectric substrate;
• and
• first and second surface acoustic wave filter elements disposed on said piezoelectric substrate;
• wherein said first and second surface acoustic wave filter elements each include a first IDT, a second IDT, and a third IDT, said second and third IDTs being disposed on respective opposite sides, in a surface acoustic wave propagation direction, of the first IDT;
• a second space defined between the first IDT and the second or third IDT in the second surface acoustic wave filter element is different by about 0.48λ to about 0.525λ from a space defined between the first IDT and the second IDT or the third IDT in the first surface acoustic wave filter element, where λ is the wavelength of the surface acoustic wave, said first space is equal to about (n/2+1.22)×λ to about (n/2+1.33)×λ (n is an integer of 0 to 4), said second space is equal to about (n/2+1.72)×λ to about (n/2+1.83)×λ (n is an integer of 0 to 4), and the first IDT of the first surface acoustic wave filter element defines an unbalanced terminal, and the second and third IDTs of the second surface acoustic wave filter element are electrically connected in series so as to define balanced terminals.

A surface acoustic wave filter device comprising:

• a piezoelectric substrate;
• and
• first and second surface acoustic wave filter elements defined on said piezoelectric substrate;
• wherein
• said first and second surface acoustic wave filter elements each includes a first IDT, a second IDT, and a third IDT, said second and third IDTs being disposed on respective opposite sides, in a surface acoustic wave propagation direction, of the first IDT;
• a second space defined between the first IDT and the second IDT or the third IDT in the second surface acoustic wave filter element is different by about 0.48λ to about 0.525λ from a first space defined between the first IDT and the second IDT or the third IDT in the first surface acoustic wave filter element, where λ is the wavelength of the surface acoustic wave, said first space is equal to about (n/2+1.22)×λ to about (n/2+1.33)×λ (n is an integer of 0 to 2), said second space is equal to about (n/2+1.72)×λ to about (n/2+1.83)×λ (n is an integer of 0 to 2), and the first IDT of the first surface acoustic wave filter element defines an unbalanced terminal, and the second and third IDTs of the second surface acoustic wave filter element are electrically connected in series so as to define balanced terminals.

A surface acoustic wave filter device comprising:

• a piezoelectric substrate;
• and
• first and second surface acoustic wave filter elements disposed on said piezoelectric substrate;
• said first and second surface acoustic wave filter elements each include a first IDT, a second IDT, and a third IDT, said second and third IDTs being disposed on respective opposite sides, in a surface acoustic wave propagation direction, of the first IDT;
• a second space defined between the first IDT and the second IDT or the third IDT in the second surface acoustic wave filter element is different by about 0.48λ to about 0.525λ from a first space defined between the first IDT and the second IDT or the third IDT in the first surface acoustic wave filter element, where λ is the wavelength of the surface acoustic wave;
• said first space is equal to about 1.72λ to about 1.83λ;
• said second space is equal to about 2.22λ to about 2.33λ;
• and
• an IDT of the first surface acoustic wave filter element defines an unbalanced terminal, and the second and third IDTs of the second surface acoustic wave filter element are electrically connected in series so as to define balanced terminals.

A surface acoustic wave filter device comprising:

• a piezoelectric substrate made of a LiTaO3 single crystal with an orientation rotated about the X axis from the Y axis to the Z axis within the range from about 36° to about 44°;
• and
• first and second surface acoustic wave filter elements disposed on said piezoelectric substrate;
• the first and second surface acoustic wave filter elements each includes a first IDT disposed along a surface acoustic wave propagation direction and also includes second and third IDTs disposed on respective opposite sides, in the surface acoustic wave propagation direction, of the first IDT;
• a second space defined between the first IDT and the second IDT or the third IDT located on either side in the second surface acoustic wave filter element is different by about 0.48λ to about 0.525λ from a first space defined between the first IDT and the second IDT or the third IDT in the first surface acoustic wave filter element, where λ is the wavelength of the surface acoustic wave;
• and
• at least one electrode finger is disposed in each area between an electrode finger, which is one of the first IDT's electrode fingers connected to a signal line and which is disposed at an outermost location, and an electrode finger which is one of the second or third IDT's electrode fingers connected to a signal line and which is disposed at a location closest to the first IDT, so that the electrode covering ratio in each said area becomes equal to or greater than about 50%.