Differential surface acoustic wave filter having balanced outputs
AssigneeResearch In Motion Limited
InventorPeter J. Edmonson
Life of this patent
Estimating the term…
Abstract
A differential SAW filter having a cascaded structure includes including an input SAW stage and an output SAW stage. The two SAW stages are configured so that the distance of travel of the surface acoustic waves from a single unbalanced input of the input stage to the dual balanced outputs of the output stage is electrically equidistant, thus resulting in a balanced differential output. The input stage includes a single unbalanced input coupled to a pair of outer IDTs, which both launch a surface acoustic wave to a single input stage inner IDT. The input stage inner IDT connects to the input IDT of the output SAW stage, which launches a surface acoustic wave to a pair of identical, but inverted output IDTs that form the differential, balanced output signals.
Claims27
A differential surface acoustic wave (SAW) filter, comprising:
- (a) an input filter stage for receiving an unbalanced electric signal and for filtering the unbalanced electrical signal into a conditioned electrical signal;
- and
- (b) an output filter stage for receiving the conditioned electrical signal via an output stage inner interdigital transducer (IDT), the output stage inner IDT converting the conditioned electrical signal into an acoustic wave and producing balanced first and second differential output signals via, respectively, first and second outer output IDTs, the first and second outer output IDTs being identical but inverted relative to each other.
A wireless communications device, comprising:
- (a) an antenna;
- (b) communications circuitry;
- and,
- (c) at least one multistage differential surface acoustic wave (SAW) filter coupled between the antenna and the communications circuitry, characterized by:
- an input filter stage for receiving an unbalanced electric signal and for filtering the unbalanced electric signal into a conditioned electric signal;
- and
- an output filter stage for receiving the conditioned electric signal via an output stage inner interdigital transducer (IDT), the output stage inner IDT converting the conditioned electric signal into an acoustic wave and producing balanced first and second differential output signals via, respectively, first and second outer output IDTs, the first and second outer output IDTs being identical but inverted relative to each other.
A differential surface acoustic filter, comprising:
- (a) a first stage comprising a balanced filter for receiving two balanced electric signals via, respectively, a first and second outer input interdigital transducer (IDT), the first and second outer input IDTs being identical but inverted relative to each other, and for filtering the two balanced electric signals into a single unbalanced electric signal;
- and
- (b) a second stage for receiving the single unbalanced electric signal and for converting the single unbalanced electric signal into acoustic waves and producing a further unbalanced electric output signal.
A wireless communications device, comprising:
- (a) an antenna;
- (b) communications circuitry;
- and
- (c) at least one reversed multistage differential SAW filter coupled between the antenna and the communications circuitry characterized by:
- a first stage comprising a balanced filter for receiving two balanced electric signals via, respectively, a first and second IDT, the first and second IDTs being identical but inverted relative to each other and for converting the balanced electric signals into acoustic waves and producing a single non-distorted unbalanced electric signal;
- and
- a second stage for receiving the single unbalanced electric signal and for filtering the single unbalanced electric signal into a further unbalanced electric output signal.
Dependencies are inferred from the claim text.