Temperature Compensation of Crystals with Parabolic Temperature Coefficients

Abstract

I n t h i s p a p e r a n o s c i l l a t o r t e m p e r a t u r e Compensation technique i s outlined which can be used to compensate any resonator having a parab o l i c a l l y r e l a t e d f r e q u e n c y v e r s u s t e m p e r a t u r e c h a r a c t e r i s t i c . T h i s a p p r o a c h c o u l d b e u s e d with many of t h e low f r e q u e n c y c r y s t a l c u t s i n a d d i t i o n t o t h e BT-cut, but i s o f p a r t i c u l a r i n t e r e s t f o r u s e w i t h ST q u a r t z t y p e SAW devices. The t y p i c a l r e s o n a t o r o f t h i s t y p e h a s a t u r n i n g p o i n t i n t h e v i c i n i t y o f room temperature with a f r e q u e n c y v e r s u s t e m p e r a t u r e c h a r a c t e ri s t i c w h i c h d e c r e a s e s w i t h i n c r e a s i n g o r d ec r e a s i n g t e m p e r a t u r e . To compensate t h i s r es o n a t o r , a p a r a b o l i c c a p a c i t y f u n c t i o n i s generated which has a maximum a t t h e t u r n i n g point temperature. The c o m p e n s a t i o n c i r c u i t c o n s i s t s of two series connected varactors, with a h i g h t u n i n g r a t i o , which a r e d r i v e n by a l i n e a r v o l t a g e v e r s u s t e m p e r a t u r e f u n c t i o n . A n a l y s i s of t h i s c i r c u i t shows t h a t by a p p r o p r i a t e s e l e c t i o n o f v a r a c t o r t y p e s , a n e x a c t p a r a b o l i c c a p a c i t y f u n c t i o n c a n b e g e n e r a t e d a c r o s s a wide temperature range. Adjustment of the compensation n e t w o r k i n v o l v e s s e t t i n g t h e s l o p e and l e v e l o f t h e l i n e a r f u n c t i o n o n l y . C i r c u i t s and e x p e r im e n t a l r e s u l t s a r e shown f o r a 150 MHz SAW o s c i l l a t o r and f o r a t y p i c a l BT-cut c r y s t a l o s c i l l a t o r . I n t r o d u c t i o n A c o n s i d e r a b l e amount of work has been done in developing temperature compensation techniques f o r c r y s t a l o s c i l l a t o r s . T h i s c a n b e a t t e s t e d t o by t h e many papers which have been presented i n p a s t y e a r s a t t h i s symposium. Various approaches have been proposed including the use of t h e r m i s t o r -c a p a c i t o r n e t w o r k s i n t h e c r y s t a l o s c i l l a t i n g c i r c u i t o r p l a c i n g a v a r a c t o r i n t h e c r y s t a l l o o p a n d a p p l y i n g a c o n t r o l v o l t a g e generated by a v a r i e t y o f t e m p e r a t u r e s e n s i t i v e schemes. Most of t h i s work has involved compens a t i o n of t h e AT c u t c r y s t a l w h i c h h a s a t h i r d order type frequency versus temperature charact e r i s t i c . The p o p u l a r i t y of t h e AT c u t c r y s t a l f o r TCXO's i s understandable considering i t s s u p e r i o r a g i n g c h a r a c t e r i s t i c and t h e f a c t t h a t i t s f r e q u e n c y v e r s u s t e m p e r a t u r e i s t h e most s t a b l e o f t h e commonly u s e d c r y s t a l c u t s . Some work has been done in the past on ...

Receiver Design of Radio-Controlled Clocks Based on the New WWVB Broadcast Format

“…(a) Tracking scenario; (b) acquisition scenario. parabolic coefficient K 1 is 4 × 10 −8 [18]. Since tracking is assumed to perform daily, we assume the time error of the local crystal is normally distributed with variance σ 2 t = 4 s 2 within the maximum timing offset max(Δt) = 6 s. In tracking, to prevent the timing drift from exceeding the receiver's timing search interval t s , t s should equal the maximum timing offset, i.e., t s = max(Δt) = 6 s. For acquisition, the timing search interval t s = 30 s. The time information represented by the transmitted signal is randomly chosen among all the possible dates in this century for acquisition, and among all the possible dates in this century at the default tracking time for tracking [3].…”

1 GHz STW based oscillator with continuous temperature compensation

“…EMPERATURE COMPENSATION (TC) techniques using analogue and digital methods have been widely used in crystal and surfa.ce acoustic wave oscillators to improve their temperature stability [4], [5]. In 1991 a novel combined TC method was proposed that was successfully applied to a 1 GHz oscillator stabilized with a surface skimming bulk wave/surface transverse wave (SSBW/STW) combined mode resonator filter (CMRF) [l], [6], [7].…”