P1K-2 Improvement of Balance Performance of SAW Filters by Common-Mode Signal Suppression

A new design concept for improvement of balance performance of SAW filters has been investigated. The balance performance is degraded by common-mode signals in the balance terminals. The concept employed is the suppression of the common-mode signals using a common-mode signal suppression circuit, connected to the balanced terminals. In the circuit, the impedance of balance terminals for the differential-mode signals becomes open to the ground level by the resonance circuit. And, the impedance of balance terminals for the common-mode signals becomes short to the ground level. And, the circuit has an impedance matching scheme. The improvement in balance performance was confirmed. This design concept could be applied to the circuit design for balanced-type SAW filter circuit designs