RF Surface Acoustic Wave Filters Research Articles

A 70-mW ISDB-T Tuner for VHF and UHF Bands

This brief presents a highly integrated low-Intermediate Frequency receiver for use in UHF/VHF channel 7 and Channel 8 Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) systems (90-220 MHz). It features an ultralow power consumption of 68 mW (55 mW in attenuator mode) with a noise figure of 3 dB. The device fully complies with the ISDB-T standard and is implemented in 0.13-μm CMOS technology with fully integrated low-noise amplifier/matching networks, a voltage-controlled oscillator, a phase-locked loop/loop filter, a crystal oscillator, baseband filters, and Variable Gain Amplifier. The tuner only requires a prefiltering RF surface acoustic wave filter to notch out cellular frequencies and a biasing inductor to implement a fully compliant ISDB-T tuner. The full characterization of the tuner and the comparison with previous implementation are presented. The chip area is 2.1 mm × 2.1 mm.

Suppression of reflection coefficients of surface acoustic wave filters using quadrature hybrids

This paper proposes a simple technique to suppress the reflection coefficients S11 and S22 of surface acoustic wave (SAW) filters. Two identical SAW filters are sandwiched in between two quadrature hybrids, where their two ports are used as input and output, and others are terminated by matched loads. First, it is shown by simulation that both [S11] and [S22] are suppressed to be less than -20 dB without deteriorating the transmission characteristics. Next, two hybrids using microstrip lines were fabricated, and two RF SAW filters for GSM850 were sandwiched in between them. The result showed that the maximum [S11] within the passband was improved from -12.5 dB to -21.7 dB, i.e., 9.2 dB suppression of [S11] was achieved by sacrificing only the insertion loss of less than 0.6 dB. We also attempted to replace the microstrip lines with lumped elements. In this case, the maximum [S11] within the passband was improved more than 7.5 dB with the increased insertion loss of less than 1.5 dB. Finally, simple discussion is given on the inclusion of the transformer function in the quadrature hybrid.