SAW Bandpass Filter Design for 1.6-GHz PCM Timing Tank Applications

A 1.6-GHz surface acoustic wave (SAW) timing tank for a self-timed regenerative repeater for an ultrahigh-speed PCM optical fiber transmission system is described. A SAW narrow bandpass filter with 0.74-mu m linewidth interdigital transducers with double electrode geometry and 20-nm aluminum metallization on AT-quartz substrate is realized by conventional optical photolithography. Typical performance obtained is as follows: center frequency f₀ is 1.5993 GHz; insertion loss is 22 dB; stopband attenuation is above 23 dB with respect to the passbaand; stability is |2Q_L˙Delta f /f₀| < 0.1, where Q_L is loaded Q value and Delta f is mistuning due to temperature effects. It is demonstrated that SAW quartz transversal filters can be made into new practical filters which have both high Q value and high stability fn the GHz range and are satisfactory from the standpoints of precise design, fabrication technique, and performance.