High-Isolation SAW Duplexer With On-Chip SAW Compensation Circuit Optimized for Isolated Multiple Frequency Bands

This article describes the simulation analysis and experimental verification of a new type of high-isolation surface-acoustic wave (SAW) duplexer by using an SAW on-chip compensation circuit designed to cancel the leakage signal of the main SAW duplexer at multiple frequency bands. First, an analysis of amplitude and phase change of the SAW duplexer consists of a ladder-type transmitter (Tx) filter, and the double-mode SAW (DMS) receiver (Rx) filter is applied to clarify the cancellation conditions. Then, the feasibility of the SAW compensation circuit using a three-interdigital transducer (IDT) DMS resonator specially designed to satisfy the cancellation conditions is studied in circuit simulation based on the coupling-of-mode (COM) theory. Finally, we analyzed this concept in detail for a long-term-evolution (LTE) Band-I SAW duplexer for Tx and Rx band isolation in both a circuit simulation and experiment. Results showed that around 10-dB improvement of isolation in both the Tx and Rx bands was obtained without sacrificing other properties (e.g., insertion loss and attenuation) and that it agrees well with the result obtained by simulation analysis. These results are expected to be useful for now, considering that future mobile systems demand higher Rx sensitivity in multiple frequency bands.