RFIC_Lecture_Note_No15_p256-p275 _Oscillators2, PLLs, Powà

RFIC_Lecture_Note_No15_p256-p275 _Oscillators2, PLLs, Powà

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ECE695F RFIC Prof. S. Mohammadi - - 256 Loading of a LC ckt p R tank x R x L x C 000 , 50 ~ 0 x x orig L R Q ω = x x C L 1 0 = + = = p x p orig x x p eff R R R Q L R R Q 0 x p L R R R = = x L orig eff R R Q Q * Biasing the device in xtal Osc. through F R Pierce Osc. F R 1 C 2 C F R 1 C 2 C eff L F R O r 1 C 2 C eff L ' L R ' ' L R O r due to x R due to F R O r of transistor
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ECE695F RFIC Prof. S. Mohammadi - - 257 Assume the only resistance is F R i Z eff L F R = + + + + + = C F C F C F C F L jX R jX R jX jX jX jX R jX R jX Z 2 1 1 2 ' ' () 2 1 1 2 2 1 1 2 1 2 2 2 ' ' 1 C C j C C C R X X jX X X R Z F C C F L + + + = = ω skipping a lot of math 400 50 ~ = K R F 200 2 2 1 1 ' ' + = C C C R R F L O L L L r R R R ' ' ' = internal xtal loss = ' L L orig eff R R Q Q Let s find ' ' L R Xtal Power ' 2 0 2 L R V Power Xtal = make sure that this power level is within xtal sating models loss in xtal AT - cut take 10mws
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ECE695F RFIC Prof. S. Mohammadi - - 258 Relaxation Oscillators Astable Ring Oscilaator DD V 1 Cg 2 Cg 3 Cg 1 2 3 size of capacitances and strength of driving determines the freq. of oscillation P P P P Nt t t t T = + + = 3 2 1 2 1 P Nt T 2 = P Nt f 2 1 = gate propagation delay 50% Æ 50% # of inverters has to be odd to get oscillation T t t t 1 2 3 DD V 50% 0 1 P t 2 P t 3 P t
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ECE695F RFIC Prof. S. Mohammadi - - 259 Calculating average propagation delay PLH t response time of a gate to a low Æ high output transition PHL t response time of a gate to a high Æ low output transition 2 PLH PHL P t t t + = () = 2 1 V V L P V i dV C t different as driving capabilities of NMOS and PMOS are different PHL t 0 1 = V 2 2 DD V V = initial V out final V out ( ) avg L P I V V C t 1 2 = average of currents at the each points of the voltage transition avg OL OH L P I V V C t 2 = DD V L C calculate PLH t * assumption V in changes abruptly NMOS is off immediately PMOS contribute to charging current
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ECE695F RFIC Prof. S. Mohammadi - - 260 note : PMOS is in saturation as long as p t out V V < () ( ) saturated I V I out = = 0 linear I V V I DD out = = 2 OL OH DD V V V = 2 2 2 0 lin sat DD out avg I I V V I V I I + = = + = = long channel device 2 2 Th GS OX sat V V L W C I = µ ( ) 2 2 2 DS DS Th GS OX lin V V V V L W C I =
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This note was uploaded on 02/19/2012 for the course ECE 695f taught by Professor Mohammadi during the Fall '09 term at Purdue University-West Lafayette.

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RFIC_Lecture_Note_No15_p256-p275 _Oscillators2, PLLs, Powà

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