Balanced drive distributed acoustic reflection transducer structure

Abstract

High volume communication transceivers such as mobile phones for GSM and CDMA systems utilize RF integrated circuits which need to operate with a low power supply voltage (typically 3.5 V). This voltage can be effectively doubled by using differential inputs and outputs, resulting in the requirement for IF filters with balanced drive input and output. The balanced drive is required to achieve a high level of I/O isolation consistent with the high circuit impedances of RF circuits. Balanced drive filters have in the past been designed using a pair of series connected transducers to obtain the required impedance balance. The disadvantage of this approach is that the resulting filter impedances are four times as large as for a one channel single ended filter. This paper presents a balanced drive distributed acoustic reflection transducer structure which retains the impedances of a single channel unbalanced filter. A description of the structure will be presented. Typical results of IF filters at 85.38 MHz for CDMA applications using both the series connected structure and this new structure will be presented.