A Study on RF Front End Architecture for Improved Performance

Abstract

In the recent mobile terminal, low power consumption, low cost and small size package through high level integration of RF front end is the key challenge. In this thesis, we proposed the new method to solve the above issues. There is a limitation on implementing the simple RF front end by only packaging technology because of characteristics of surface acoustic wave (SAW) duplexer. Since the SAW duplexer consists of two highly sharp selective band pass lters (BPFs) for good isolation, it is very difficult to integrate duplexer within RF transceiver using semi-conductor process with low quality capacitor and inductor. Since 5G should ensure interoperability with past generations of wireless communications standard such as GSM, 3G and LTE, the RF front end module of future mobile terminals will be very complex if only the current technologies are employed. Therefore, in this thesis we propose new methods to realize the RF front end with simple structure. This thesis focuses on an advanced tunable wide band duplexer to reconfigure the RF front end with simple structure in the FDD, the TDD and, GSM dual band transmit module (TX-module). This duplexer can be used in 5G mobile implemented for high integration of multi-chips within the small single package. To integrate the multi-chips without oscillation, this module has been designed on a new substrate and implemented using various semi-conductor processes. First, a tunable wide band duplexer based on an electrical balance of hybrid transformer having two notches is proposed for FDD application. The duplexer consists of 4 spiral inductors, 2 capacitors, 2 balancing resistors for configuring the Tx and Rx by electrical balancing, and 50 ohm impedance matching to antenna is implemented with 1 inductor, 1 capacitor. To achieve low insertion loss, the duplexer has been eliminated the 2nd winding of the hybrid transformer. If the duplexer is used instead of a SAW duplexer, isolation of over 55 dB at the Tx band and over 45 dB at the Rx band across 145MHz bandwidth is achieved by two notches between the Tx and Rx. The duplexer operates as a tunable duplexer by tuning the 4 elements. When the proposed duplexer is combined with proper analogue and digital cancellation techniques, the duplexer will support in-band duplexing without having any self-interference in 5G mobile system. Second, GSM dual band transmit module for the TDD application has been presented. To simplify the RF front end of GSM application, The TX module is integrated with various devices into single package of 5.24 by 6.63 by 1.0 mm using FR4 4-layer laminated PCB. Two PAMs, RF switch and two low pass filters (LPF) have been implemented using IC processes and FR4 substrate, respectively. In the PAMs, the power cell of GSM900 PA has been optimized to obtain high efficiency, and a new substrate design to prevent oscillation has been implemented for high integration of the multi-chips. The RF switch is implemented to obtain good insertion loss and linearity. The TX module can support GSM900 TX band requiring maximum output power of 33 +/ 2dBm, DCS1800 TX band requiring maximum output power 30 +/- 2dBm and two receiver bands. All the works are related to effective reconfiguration of the RF front end for future wireless communication service.