|
|
Q: Jitter Spectrum on DCA-J versus Jitter Spectrum with EZJIT+
! q _6 z( L/ v% n) ~' ~1 K7 P
+ R7 f9 U" X* ?, NA: When measuring Jitter Spectrum using the 83496B with the 86100CU-400 PLL and Jitter Spectrum software the measurement is made by first demodulating the jitter signal from the incoming clock or data signal. A sampler inside the clock recovery circuit then samples the jitter signal typically at 52MSa/s and an fft transforms to the frequency domain. " m9 _0 e1 g( X2 j, z1 i* c3 B
' F" o$ o% }7 n# E( V: W5 y
EZJit Plus uses a very different technique. The incoming clock or data signal is sampled at full speed (typically 40GSa/s). Software clock recovery then allows the jitter to be extracted in the form of a Time Interval Error signal. An fft can then be performed on the TIE to get the Jitter Spectrum.
3 P5 D6 f$ v0 N- |! R) M6 C2 Q. M+ }8 j( z1 e( A
There are many differences in the acquisition hardware and measurement techniques that will affect the measured outcome.
8 A& z9 m. [ O5 w7 P9 |. e4 j9 Q8 r9 j; S7 Z' U, w x
A couple of important points: " q6 V% U4 T u5 s+ i1 @5 T
# p/ o8 l- a+ j& n& |: E
1. EZJit Plus is used on a wideband oscilloscope that captures the entire frequency content of the signal. This high bandwidth also means that there is more noise that transfers through to the jitter spectrum than with the DCA-J method. Thus the DCA-J method typically has a lower noise floor than the EZJit Plus method. 7 Q9 V. J/ E% _4 |- ?. Y
+ V$ q" @( Y5 t5 T9 ^
% j4 t& r) {3 E& H6 \
2. Since EZJit Plus captures the entire signal, the Jitter Spectrum can be viewed up to Data Rate/2 whereas with the DCA-J the Jitter Spectrum is limited to 26MHz offset.
6 @8 [6 M) [, A. ]- d5 W, V
( ^# o/ y: b# v& E- e \虽然DCA-J做出来的抖动频谱只能到26MHz，但是对于大部分应用还是足够啦，因为PLL的带宽通常都不会超过10MHz，而且+ V+ ]2 }, c1 B, t5 [3 w3 ~5 K' W
|
|
楼主: stupid
[复制链接]
/1 
发表于 2010-7-1 18:44
楼主
