Abstract – In recent years there has been a tremendous increase in density of digital circuits’ layouts using printed transmission lines at high frequency for high speed circuits . Signal degradation caused due to various discontinuities and external couplings, in the form of common mode noise in such transmission lines cause loss of signal integrity. EBG(electronic band gab) structures can be used to suppress the common mode noise and improve differential mode signal propagation.
Printed transmission lines are widely used, they provide circuits that are compact and light in weight. The microstrip line is a transmission line geometry with a single conductor trace on one side of a dielectric substrate and a single ground plane on the opposite side. There are numerous such transmission lines present on PCB leaving little space between the two lines, thus increasing the coupling between the two lines carrying different data signals. This acts as external additive noise, which once added cannot be removed and degrading signal quality. A very high coupling coefficient caused by a coupled microstrip lines is therefore to form serious crosstalk coupled to the other victim lines. Degradations also occur in printed microstrips due to reflections from discontinuities present in the form of bends, change in step widths, T junctions, etc. When single transmission line is used for propagation of signal, it forms single ended signaling and an equal current returns through the ground plane
II. Use of Differential Lines
The coupling effect causes crosstalk between nearby lines adding noise to the signal
, which is not removable. To reduce or suppress such noise use of differential lines is made. When two lines are used for signal propagation, one trace carries the positive signal and the other carries a negative signal that is both equal to
, and the opposite polarity from, the first and ideally ground carries zero current
; this is called differential signaling. when external noise couples to such a system it gets removed at the receiver. Since a pair of lines are required for differential signaling, microstrip coupled lines are used for high speed data transmission at microwave frequencies excited differentially.
Fig.1 : Differential Signaling 
The differential amplifier at the receiver subtracts the inverted version from the normal signal to yields a signal twice of original signal:
(V + n) – (-V + n) = 2V (1)
Where ‘n’ is the additive noise.
The noise coupled to the differential line is assumed to be equal and thus same amount of noise travels through the pair and thus called common mode signal.
For the lines to be perfectly differential:
For the voltages to be equal and opposite, as needed for balance, the following features must exist:
1. The amplitude in both circuits must be identical
2. The load impedance must be identical
3. There can be no skew between rising and falling edges
4. The rise and fall time must be identical
5. The physical trace routes must be not only equaled in length overall, but also balanced along their entire length
6. Coupling to any other conductors must be equal 
Advantage of differential signaling is
, it uses lower voltage levels than single ended signals because the threshold in differential receiver is better controlled than in single ended due to high noise immunity. The lower voltage swing leads to faster circuits and reduction in power consumption, thereby increasing the bandwidth.
Fig 2 : Differential signal at receiver with and without skew