Pn sequence generator USING MAT LAB
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22062010, 09:46 PM
Pn sequence generator USING MAT LAB.ppt (Size: 1.25 MB / Downloads: 363) PN SEQUENCE GENERATOR USING MAT LAB Presented BY D.SAI KRISHNA WHAT IS PN SEQUENCE GENERATOR Pseudo random Noise sequence generator is a circuit which generates pseudo random noise sequences. A pseudo noise sequence is a binary sequence with a noise like wave form that usually generated by means of a Linear feedback shift registers. Block Diagram Of Linear Feedback Shift Register WHAT IS LINEAR FEEDBACK SHIFT REGISTER A Feedback shift register consists of an ordinary shift register made up of m FlipFlops . The flipflops in the shift register are regulated by a single timing clock. At each pulse of the clock, the state of each flipflop is shifted to the next one i.e. the contents of the register is shifted right by one position at each clock cycle. The feedback from the left most register are XOR ed together, to give a random sequence. But this binary sequence is not totally random, because it does repeat after many cycles, thatâ„¢s why it is so called as pseudo random noise sequence generator. Shift Register Length: This is often referred to as the degree, and in general, the longer the shift register, the longer the duration of the pn sequence before it repeats. The combination of taps and their location is often referred to as a polynomial, and expressed as: P(x)=1+x^2+x^3 Where the leading Ëœ1â„¢ represents x^0, which is the output of the last register, x^2 is the output of register stage 3 and x^3 the output of XOR. A maximal sequence for a shift register of length L is referred as msequence, and is defined as: L=2^m1. APPLICATIONS : These pn sequence generators are widely used in Cmos testing process as to generate test patterns. And also used to generate spreading codes in CDMA,FDMA and PCM. CMOS TESTING PROCESS In VLSI designing process we will spend 25% for manufacturing, and 75% for testing. By detecting a malfunctioning chip at an earlier level, the manufacturing cost may be kept low. Properties: In each period of a maximal â€œ length sequence, the number of 1â„¢s is always one more than the number of 0â„¢s.This property is called as the Balance property. Example: 101000111101001 Among the runs of 1â„¢s and of 0â„¢s in each period of a maximallength sequence, one half the runs of each kind are of length one, one fourth are of a length two, one eighth are of length three, and so on as long as these fractions represent meaningful numbers of runs. This property is called the Run property. The autocorrelation function of a maximallength sequence is periodic and binary value. This property is called as correlation property. PN sequences have single autocorrelation peak, this feature permits the transmission to be asynchronous. ADVANTAGES AND DISADVANTAGES : Advantages: The sequences generated by an LFSR can be nearly random with long periods, which aids in making the spread signal appear noise like. Easy of implementation. Output of lfsr is periodic. For any given size of LFSR, a maximum of different unique msequences can be generated . Disadvantages: Cross correlation properties are good for more than two users. Thatâ„¢s why we go for gold sequences. Thank You Use Search at http://topicideas.net/search.php wisely To Get Information About Project Topic and Seminar ideas with report/source code along pdf and ppt presenaion



