Power Matters™

Delay Lines

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Surface Acoustic Wave (SAW) techniques are extremely general: any linear bandpass filter or delay line may be synthesized, with arbitrary amplitude and phase, limited only by line width and substrate size. The devices are small, rugged, very stable, and capable of high volume low cost production. Delay lines are simply bandpass filters with ~.13in/us additional path length between the transducers to achieve the desired insertion delay. The path can be folded to conserve substrate length.


Adjustment of electrode length and position allows the SAW designer to synthesize any finite impulse response. For delay lines specified in the frequency domain, FIR digital filter design techniques are used to find the initial optimum, i.e. shortest, time response. Delay lines may also be specified directly in the time domain. Delay lines may be specified by defining templates or mathematical functions in the frequency or time domains.


  Typical Limit
Center Frequency fo MHz 20 – 1500 10 – 2500
PassBandWidth B*100/fo for quartz .5 – 5 .1 – 10
for lithium tantalite  5 – 10 1 – 40
for lithium niobate 10 – 30 5 – 150
Amplitude ripple in B dB pp >1 .2
Phase ripple in B degrees pp >10 2
Min insertion loss IL dB >25 10
Return loss in B dB none 14
Delay T us <10 100
Time spurious dB -40 -60

When appropriate, key system level performance parameters may be specified. They can be verified by computer simulation based on measured frequency data. Simulation software has been prepared for: time response for any input signal, pulse widths and sidelobes, and signal to noise ratio loss.