Unipolar

PresentationOn

Unipolar

BY: Roshan Chaudhary (13ITU031)

Unipolar

• All signal levels are on one side of the time axis -either above or below

• NRZ - Non Return to Zero scheme is an example of this code. The signal level does not return to zero during a symbol transmission.

• Scheme is prone to baseline wandering and DC components. It has no synchronization or any error detection. It is simple but costly in power consumption.

4.2

4.3

Figure 4.5 Unipolar NRZ scheme

Unipolar SignallingUnipolar Non-Return to Zero (NRZ):

In unipolar NRZ the duration of the MARK pulse (Ƭ ) isequal to the duration (To) of the symbol slot.

1 0 1 0 1 1 1 1 1 0

V

0


In unipolar NRZ the duration of the MARK pulse (Ƭ ) is equal to the duration (To) of the symbol slot.(put figure here).

Advantages:

– Simplicity in implementation.

– Doesn’t require a lot of bandwidth for transmission.

Disadvantages:

– Presence of DC level (indicated by spectral line at 0 Hz).

– Contains low frequency components. Causes “Signal Droop” (explained later).

– Does not have any error correction capability.

– Does not posses any clocking component for ease of synchronisation.

– Is not Transparent. Long string of zeros causes loss of synchronisation.


Figure. PSD of Unipolar NRZ

Unipolar SignallingReturn to Zero (RZ):

In unipolar RZ the duration of the MARK pulse (Ƭ ) is less than theduration (To) of the symbol slot. Typically RZ pulses fill only the firsthalf of the time slot, returning to zero for the second half.

1 0 1 0 1 1 1 0 0 0

V

0

To

Ƭ

Unipolar SignallingReturn to Zero (RZ):

In unipolar RZ the duration of the MARK pulse (Ƭ ) is less than the duration (To) of the symbol slot. Typically RZpulses fill only the first half of the time slot, returning to zero for the second half.

1 0 1 0 1 1 1 0 0 0

V

0

To

Ƭ

Unipolar SignallingUnipolar Return to Zero (RZ):

Advantages:

– Simplicity in implementation.

– Presence of a spectral line at symbol rate which can be used as symboltiming clock signal.

Disadvantages:

– Presence of DC level (indicated by spectral line at 0 Hz).

– Continuous part is non-zero at 0 Hz. Causes “Signal Droop”.

– Does not have any error correction capability.

– Occupies twice as much bandwidth as Unipolar NRZ.

– Is not Transparent

Unipolar SignallingUnipolar Return to Zero (RZ):

Figure. PSD of Unipolar RZ

Unipolar Signalling

In conclusion it can be said that neither variety ofunipolar signals is suitable for transmission over ACcoupled lines.

UNIPOLAR LOGIC FAMILIES

• MOS devices are unipolar devices and only MOSFETs are employed in MOS logic circuits.

• These families are:• PMOS (p-channel MOSFETs)• NMOS (n-channel MOSFETs)• CMOS (Both p- and n- channel MOSFETs

are fabricated on same silicon chip)

MOS

• Unipolar transistor depends on only one type of carrier.

• Carrier may be electrons or holes.

• Used in Lsi & vlsi

• Metal electrode is placed on top of oxide insulator ie the semiconductor material.

• Mosfet is used where power consumption is low.

PMOS,NMOS,CMOS

• P channel mos is referred as pmos.

• P oldest and slowest obsolete.

• Nmos n channel and used in circuits with one type of MOS transistor.

• Nmos used in microprocessor and memories.

• CMOS combination n and p channel.

• Cmos is also explained as “Complementary –Symmetry”.

• Cmos uses Symmetrical pairs of electronic devices p type and n type.

Characteristics of Cmos

• High input resistance.

• Compatible output of one device can be connected to another CMOS.

• High noise immunity

• Low static power

• High density on chip

• Simple

• Protection circuitry

• Absorb electric charges with no damage.

Usage Cmos• Microcontrollers, microprocessor, RAM

• Image sensors, data converter and integrated transceivers and other types of communication.

• Current IBM mainframes .

• Digital wristwatches, calculators and portable computers.

ADVANTAGE

Dissipate less power .

Operates on high speed.

Low cost

More economical operation

COMPARISONS TTL,ECL,CMOS

TTL

ECL

Cmos

Power consumption increase with clock speed

Power consumption is high

Power consumption does not increase

Less sensitive elecrostatic discharge

More sensitive electrostatic discharge

Nand gate Nor gate Not gate

Provides more heat cos power dissipation is more

Engineering

Unipolar