In a multi-band wireless communication network, wireless stations communicate by sending signals to each other in multiple, preassigned communication frequency bands. Each station in the network must be able to receive and process signals in each of these frequency bands. For example, in a GSM/DCS dual-mode system, each station must process radio frequency (RF) signals in both the Global System for Mobile (GSM) and the Digital Communication Service (DCS) bands. In general, much of the circuitry in a multi-mode wireless station is replicated once for each communication band in which the station must communicate.
FIG. 1 is a simplified schematic diagram of a typical GSM/DCS dual-mode wireless phone 10. The phone 10 includes a transmitter 12 and a receiver 14 that send and receive signals, respectively, through a wireless network via an antenna 16 and an antenna interface circuit 18. The receiver 14 includes two front-end filtering circuits coupled to the antenna interface circuit 18: a GSM circuit, which processes only those signals transmitted in the GSM band; and a DCS circuit, which processes only those signals transmitted in the DCS band. The GSM and DCS front-end receiver circuits are virtually identical in structure, with the GSM circuit including a GSM-band surface acoustic wave (SAW) filter 20, a low-noise amplifier 22, and a GSM-band image-reject filter 24 arranged in series; and with the DCS circuit including a DCS-band SAW filter 26, a low-noise amplifier 28, and DCS-band image reject filter 30 arranged in series. The image reject filters 24, 30 remove unwanted shadow, or "image," signals received at frequencies other than the GSM and DCS carrier frequencies. A switch 32 applies the output signal from one of the front-end receiver circuits, via a power amplifier 34, to a double side band (DSB) mixer 36. The double side band mixer 36 mixes the signal from the front-end receiver circuits with an amplified signal from a voltage controlled oscillator (VCO) 38 and delivers the resulting intermediate frequency (IF) signals to subsequent circuitry for processing and demodulation.
FIG. 2 shows a typical structure for both the GSM-band and the DCS-band low-noise amplifiers 22, 28 (FIG. 1). Each amplifier includes a transistor-based linear amplifier 40 coupled to two matching circuits: an input matching circuit 42 that receives a GSM-band or DCS-band signal from one of the SAW filters 20, 26 (FIG. 1) and provides the signal as input to the linear amplifier 40; and an output matching circuit 44 that receives the amplified signal from the linear amplifier 40 and delivers it to one of the image reject filters 24, 30 (FIG. 1). Because a conventional multi-mode wireless phone includes a low-noise amplifier for each communication band, the conventional phone includes multiple copies of each of the components shown in FIG. 2.