Balanced front-end SAW modules with improved selectivity at low frequency offsets for handheld transceivers

This paper presents the new balanced front-end SAW modules with the improved selectivity at the low frequency offsets and fractional bandwidth of 1.5-4% for the 440-470 MHz handheld transceivers. The modules contain 2 SAW filters connected across a low noise bipolar transistor amplifier. The balanced longitudinally-coupled resonator SAW filters on 42deg YX LiTaO₃, 64deg YX, 41deg YX LiNbO₃ were used in these modules to suppress the high frequency (HF) shoulder in the frequency response. The first filter is realized in a 4-pole three-transducer scheme. The second filter with a wider fractional bandwidth is realized in the 4-pole two- or three-transducer scheme. A combination of these two types of the filters with the different fractional bandwidths provides an efficient suppression of the HF shoulder in the frequency response of the modules. The optimization of a SAW filter-amplifier-SAW filter system is provided with a computer simulation using an equivalent circuit model. The 440-470 MHz samples of the balanced front-end modules have shown an amplitude ripple of 1 dB within a 3-dB bandwidth of 6.6-20.2 MHz, 10 dB gain, improved suppression up to 60 dB at the low offsets of plusmn13divide plusmn30 MHz from the center frequency. The modules provided a noise factor of 2 dB with a current consumption of 5-7 mA and supply voltage of 3 V in the 13.3times6.5times1.8 mm SMD packages.