Extending the Flexibility of an RFIC Transceiver Through Modifications to the External Circuit

Abstract

The recent trend in the RF and microwave industry has been a move towards increasing the number of components realized on one radio frequency integrated circuit (RFIC) (or microwave integrated circuit (MIC)). This trend has resulted in complex RFICs which often require reactive as well as other circuit components to be supplied in the form of an external circuit. Because the manufacturer's suggested circuit is often developed with a specific application in mind, the same circuit may not satisfy the demands of another application. Provided the necessary functionality and connections are possible, the external circuit may be altered such that the requirements of the other application can be met, thus extending the flexibility of the RFIC.

The work presented here is focused on investigating modifications to RF Microdevices' suggested external circuit for the RF29X5 family of low cost, half duplex, FM/AM/ASK/FSK RFIC transceivers originally intended for operation in the 433, 868, or 902-928 MHz industrial, scientific, and measurement (ISM) bands. Examinations of the operating principles of the transceiver components were performed which facilitated the identification of suitable modifications. Among the modifications identified were implementation of a phase locked detector, various methods for extending the FSK data rate limitations of the transmitter, improving the phase noise of the VCO, and the implementation of a fractional-N synthesizer using the RF2905 internal phase-locked loop (PLL) components and external inexpensive logic circuits. In addition to these modifications to the external circuit, the investigation of the oscillators of the RF2905 resulted in a potentially improved implementation of the VCO by modifying the internal active circuitry as well.