Digital-to-Digital Conversion

Line Coding

The process of converting the digital data into digital signal is called as line coding which helps the receiver to get the original bits. The data that is in the form of text, numbers, audio, or video is represented internally as series of 1s and 0s. Line coding therefore transforms a set of bits into a digital signal. The sender side encrypts digital data into digital signals, while the receiving side decodes the digital signal to regenerate the digital data. The primary goal of utilizing line coding is to prevent the overlapping of pulses and distortions. The digital signal is discreet in nature. Example is sending data from computer to printer.

There are basically three different types of line coding technique:

• Unipolar
• Polar
• Bipolar

Definition

Digital-to-Digital conversion is the process of transforming one digital signal into another digital signal. This transformation is necessary to create more reliable and noise-resistant digital signals for data transmission, ensuring that digital data can be transmitted effectively over longer distances.

Detailed Explanation

Digital-to-Digital conversion is fundamental to modern digital communications. The process involves taking binary data (1s and 0s) and converting it into a digital signal format that’s more suitable for transmission over communication channels.

The main purposes of this conversion include:

• Creating signal patterns that are self-clocking
• Reducing transmission errors
• Maintaining signal integrity over longer distances
• Ensuring reliable timing recovery at the receiver

Common encoding schemes include:

1. NRZ (Non-Return to Zero): The simplest form where voltage levels directly represent binary values
2. Manchester Encoding: Combines clock and data by ensuring a transition in the middle of each bit
3. Differential Manchester: Similar to Manchester but uses transitions to represent data

The choice of encoding method depends on factors like:

• Required bandwidth
• Error detection capabilities
• Synchronization needs
• Hardware complexity

Unipolar

In Unipolar encoding, only one polarity is used i.e., bit 1 is used to represent positive voltage and bit 0 is used to represent zero voltage or idle line. It is also known as Unipolar-Non-return-to-zero. Signaling of this kind is also referred to as on-off signaling.

Problem in Unipolar

• DC Component: When we find out the average amplitude of a unipolar signal, then the value would always be non-zero because of which it creates DC component. And the signal having DC component is not able to travel through the medium which cannot handle DC component.
• Synchronization: When a signal is constant, the receiver cannot distinguish between the start and finish of each bit. For that the receiver has to rely on a timer to track the starting of each bit.

Unipolar encoding

Polar

The polar encoding is of four types. In polar encoding two levels of voltage amplitude is used. The DC component issue of unipolar encoding is minimized, and the average voltage level on the line is decreased.

• **Polar Non-Return to Zero (Polar [[NRZ]])

• [[Manchester]] Encoding

Bipolar Encoding

In Bipolar encoding, three types of different voltage level is used that is positive, negative and zero. The zero level is used to represent binary 0, positive and negative voltage represents alternatives 1’s to prevent DC component. Alternate Mark Inversion (AMI) and Pseudoternary are the types of bipolar encoding.

Bipolar Encoding

Table: Comparison of Different Digital-to-Digital Line Encoding Techniques

Notes

References