Hybrid wide-band VCOs using low-loss leaky SAW ring filters

Summary form only given. The transceivers for the mobile communication systems require wide-band voltage controlled oscillators (VCOs). A widely known Colpitts-type VCO with a SAW resonator provides the fractional variable frequency range of 0.38%. To extend the fractional variable frequency range to 3-5%, wide-band slanted interdigital transducers (IDTs) may be used in this VCO. We used VCO with SAW delay line and external phase shifter in the amplifier feedback loop for 146-174, 440-470 MHz mobile communication receivers. For delay line we used previously developed low-loss leaky SAW ring filter with insertion loss of 1 dB having linear phase response with the phase shift of ±180° at 3 dB fractional bandwidth of 5% on 49°YX LiNbO₃. Ring filters consisted of input/output IDTs placed in parallel acoustic tracks and 2 reflective multistrip couplers, which provided the SAW transmission between these tracks. The hybrid module with VCO contained the SAW filter, amplifier, phase shifter, buffer stages. The amplifier of VCO contained the single bipolar transistor with the cutoff frequency of 7.5 GHz. The optimization of the amplifier-phase shifter-SAW filter system was provided for achieving the maximal variable frequency range with specified maximal control voltage of 6 volts, current consumption of 5 mA and the carrier to noise ratio C/N no less than 70 dB (offset frequency from the carrier: 25 kHz, bandwidth: 3 kHz). 185, 480 MHz hybrid VCO using leaky SAW filters on 49°YX LiNbO₃ provided variable frequency range of 5 and 13 MHz (2.7%) when the control voltage varied from 0.5 to 6 volts and C/N was 77-82 dB