Cordless phone system architectures based on SAW filters

Abstract

Today the development in design and application of cordless phone systems is concentrated on both technological evolution and new functional benefits. The evolution of Surface Acoustic Wave (SAW1 technology plays a major role in the system architecture and performance. The improved performance and continued miniaturisation of SAW components have already given rise to a simplification and cost reduction of the transceiver circuit allowing for further miniaturisation of mobile units.Cordless phone systems in the 900 MHz range like the analog CT1 in Europe and the digital CT900 in USA require high image frequency suppression in the RF and IF stages. For the reduction of total RF-circuit cost low-loss SAW filters offer the appropriate close-in selectivity for image frequency and oscillator frequency suppression. Time domain division systems like the Digital EuropeanCordless Telephone (DECTI are primarily based on a double conversion receiver with an IF frequency in the 110 MHz range. For these systems novel RF filters with sufficient image frequency suppression and an insertion loss as l o w as 2 dB are available. Housed in a miniaturised SMD package they offer a great opportunity for size reduction of the entire transceiver circuit.