DATA GENERATORS Using Linear feedback shift register LFSR

DATA GENERATORS

Using Linear feedback shift register (LFSR) • Linear feedback shift register (LFSR). LFSRs are one of the simplest ways to generate pseudorandom sequences. In an LFSR, any bit is determined by a linear combination of the previous n bits, for a suitable choice of n. In particular, we may have an LFSR in which • Bn = A 0 B 0 ⊕ A 1 B 1 ⊕ A 2 B 2 ⊕. . . ⊕ An− 1 Bn− 1

LFSR • Since any bit is a function of the previous n bits, we can show that every LFSR has a period of 2 n− 1. • Consider any window of n bits. • As we slide 2 n− 1 times forward, we cover 2 n− 1 n-bit strings. If any two of the strings repeat, then we already have the period at most 2 n − 1. • Furthermore, since the all 0 s cannot be generated (unless the initial value is all 0 s in which all values remain all 0 s), within 2 n steps at least one window is identical to another n-bit window encountered earlier in the process; this the period of the sequence is 2 n − 1.

CIRCUIT DIAGRAM OF PSEUDORANDOM BIT SEQUENCE GENERATOR (PRBS)

OUTPUT BIT SEQUENCE FROM Q 1, Q 2 AND Q 3

CLOCK FROM IC 555

OUTPUT WAVEFORM OF CLOCK AND PRBS

Variable DATA Generator

CIRCUIT DESCRIPTION • The circuit can be divided into two main sections namely clock generator and the PRBS generator. • The clock signal is generated using IC 555 and the D flip flop is used to maintain 50%duty cycle. • The data sequence is generated using a set of 8 SPST switches, 8: 1 MUX and divide by 8 counter and its output is given to the 3 select lines of 4051 to select the inputs randomly. • If the switch is closed, then it is considered as data’ 1’ and if the switch is open, then the data considered as’ 0’. • If we keep the input switches as 10100100, then the output will be shown in the following,

Output Waveforms