Voltage Controlled Surface Wave Resonator Oscillators

Abstract

O s c i l l a t o r s have been constructed using surface wave resonators as t h e frequency c o n t r o l element a t 194 MHz which a r e v o l t a g e tunable over a 30 kHz range. The s h o r t term s t a b i l i t y w i t h a 10 msec averaging time i s 1.5 x The two-port surface wave resonator has advantages o v e r one-port resonators ( e i t h e r surface wave o r p l a t e mode) f o r use i n o s c i l l a t o r s . The loaded Q and excess loop g a i n a r e c o n t r o l l e d t o e x e r c i s e the compromise between a v a i l a b l e t u n i n g range and s h o r t term s t a b i l i t y . l n t r o d u c t i o n The Surface Acoustic Wave (SAW) resonator i s a new element w i t h resonant behavioSm4 (Figure I ) . many resonators, i t i s u s e f u l as an o s c i l l a t o r f r equency c o n t r o l element. The r e s u l t i n g o s c i l l a t o r s a r e u s e f u l f o r many appl i c a t i o n s because o f t h e i r s h o r t term s t a b i l i t y i n t h e 200-IO00 MHz frequency range p r e v i o u s l y served by LC o s c i 1 l a t o r s , lower frequency o s c i l l a t o r s w i t h frequency m u l t i p l i e r s , and, t o a l e s s e r extent, SAW delay l i n e o s c i l l a t o r s . The long term s t a b i l i t y o f t h e SAW resonator has y e t t o be demonstrated. o f these o s c i l l a t o r s extends t h e i r u t i l i t y by allowing, f o r example, long term c o n t r o l from another source, doppler t r a c k i n g o f moving targets, or p e r i o d i c remote adjustment o f frequency. The SAW resonator has advantages o v e r e i t h e r SAW delay l i n e s or p l a t e mode resonators f o r use i n UHF o s c i l l a t o r s . L i k e The a d d i t i o n o f e l e c t r o n i c f i n e t u n i n g Fig. I Surface Acoustic Wave Resonator a t 200 M H r C i r c u i t Conf i q u r a t l o n s A wide v a r i e t y o f c i r c u i t c o n f i g u r a t i o n s e x i s t f o r t h e r e a l i z a t i o n o f o s c i l l a t o r s . The two shown i n F i g u r e 2 were used w i t h p a r t i c u l a r success by t h e author. connection o f amp1 i f i e r , resonator, and phase s h i f t e r . O s c i l l a t i o n s w i l l be maintained a t t h e frequency which a l l o w s 2nn phase s h i f t around t h e e n t i r e loop. Thus v a r i a t i o n s i n t h e i n s e r t i o n phase s h i f t o f t h e phase s h i f t network w i l l tune t h e o s c i l l a t o r o v e r t h e l i m i t s of t h e t r a n s i t i o n phase region shown i n F i g u r e I . To tune t h e frequency o v e r an a p p r e c i a b l e p o r t i o n o f the phase t r a n s i t i o n region, i t i s necessary t o e i t h e r prov i d e more g a i n than i s necessary t o m a i n t a i n o s c i l l a t i o n Tho b a s i c C o n f i g u r a t i o n c o n s i s t s of tandem a t t h e c e n t e r frequency (where the i n s e r t i o n loss o f the resonator i s lowest) o r p r o v i d e a phase s h i f t n e twork whose amp1 i tude response i s t h e complement o f t h e amp1 i tude response o f the resonator....