標題: about FSK data question.... [打印本頁] 作者: super 時間: 2007-11-8 06:41 PM 標題: about FSK data question.... Dear all : 1 [( w# ]% X [+ x$ J E( p6 t* W In fsk close loop direct Frequency modulation , 2 z* ~( ^. a( M; U& @( f* p 1. data rate is higher than loop BW or lower than loop BW ?& ~5 U7 [0 R# L6 v* x
2. And what's the relation between data rate and Loop BW ? 1 t0 i* R# [+ ]$ d $ X2 D# \$ G8 M4 H! Q: a: A: ~ b! } Because modulation from VCO , it's a high pass function for VCO vs PLL. + M& p5 n' Q/ T8 L: _' x, v& U, i ^1 F If modulation frequency > BW , it will be supress by VCO vs PLL transfer function.& l* j- f% c8 B2 j+ M. Q
It will be trace and fix it. So modulation function is fail. 1 i7 {7 _0 T0 ^7 @9 [ Is this concept is right ? 9 X) K) G+ o8 c$ P $ F; R- I) I) g; S9 Z Thanks .作者: simenkid 時間: 2007-11-10 02:34 AM
1.data rate可以高於loop bandwidth, 也不可以.端看用什麼architecture % C% F6 s5 A* o3 R5 H" `& C+ n2.假使單純在multi-modulus或是由reference端做調制, data-rate高於loop bandwidth則勢必產生失真- p- n9 i/ s6 Z k
8 g# t$ e0 B' u3 r' I2 w+ i
直接由PLL Synthesizer調制提升FSK, FM, GMSK等固定波包調制之data rate3 }% R; f; W! W7 j- G
可選擇如pre-emphasis或two-point modulation(同時兼顧inband與outband,理論上無頻寬限制)的方式