ADSL Noise Margin Values and Effects of Other Characteristic Parameters on Functionality

May 12, 2020 Cadence PCB Solutions

What You Can Expect

  • Learn about ADSL and designing with ADSL in mind

  • Defining key operating parameters for ADSL designs

  • Prepare electronics for verification and production through modeling and simulation

ADSL port on a transceiver for internet

The definition of noise is in the ear of the beholder or the device perceiving it. Unfortunately, in the field of wireless communications, noise is like Kryptonite, since it will undoubtedly weaken any transmission if presented in a significant enough quantity.

Therefore, with noise having such a profound effect on wireless functionality, it is only logical that there are acceptable parameters and guidelines in place. These noise margins afford universal industry standards in wireless functionality, and this includes Asymmetric Digital Subscriber Line (ADSL) as well.

The Asymmetric Digital Subscriber Line

ADSL is a type of internet access or connection that leverages your existing telephone lines. Furthermore, as one might imagine, this can be a very cost-effective method of providing internet access to areas otherwise without other options and can be considered for the electrification process. The principal methodology is currently in use in other devices, such as Powerline Ethernet Adapters, that we see on the market today.

Both ADSL and Ethernet utilize single-purpose physical lines to provide internet access; however, there are additional technologies where these types of networks are common. These types of lines are in use in video surveillance systems that utilize PoE (Power over Ethernet) cameras. As a person who has installation experience with systems of this type, I can attest to the cost-effectiveness of the technology. And before ADSL, there was dial-up utilizing our phone lines for internet access. 

The Characteristics and Functionality of ADSL

Although Fiber in many areas supplants the use of this technology as a whole, it still has its place in specific markets. The parameters that govern ADSL functionality include:

  • Standard: The ADSL connection standard in use to establish the connection to the DSL-switch.

  • Speed: We refer to this as the channel rate of the connection to the DSL-switch. Also, this consists of two speeds, Download (to the customer) and Upload (from the customer).

  • Noise Margin: We also refer to this as the Signal-to-Noise Ratio (SNR), and we express these values in decibels (dB). Furthermore, a higher value equates to better signal quality.

  • Signal Power Level: It is a reference to the output power. In other words, it is the output power of a signal at the instant of modem synchronization with the DSL-switch. In general, the standard output power is approximately 10 dBm (sending data).

  • Signal Attenuation: This refers to the signal attenuation in the line at the instant you achieve modem synchronization with the DSL-switch. Overall, this value should be less than 45 dB. Furthermore, attenuation directly correlates to the length of cable between the DSL switch and the ADSL modem. As a rule, a higher value means a lower signal quality and slower data speeds. When we refer to signal attenuation, we consider a value of 5 dB to 30 dB to be optimal, and above 45 dB to be unacceptable for ADSL use.

After understanding these basic characteristics of ADSL, you can then move into how to design around characteristic vulnerabilities. 

Characteristic Parameters that Negatively Affect ADSL Functionality

As you can see, several parameters govern the functionality of ADSL, and specific parameters are more detrimental to functionality than others, for example, noise margins. Although our signals do not originate from the planet Krypton, the weakening effects of exceeding the recommended noise margins are no less accurate. 

As I am sure you are aware, these margins represent the measurement of the line quality and define a minimum limit at which the signal level is above the noise level.

The minimum noise margin limit for data transmission is 6 dB, and a value lower than this will not support a stable ADSL connection. Moreover, a value of less than 6 dB will facilitate frequent interruptions in your communications. However, if the noise resistance is greater than 10 dB, the line is within acceptable parameters for data transmission. For ADSL, the higher the value, the better the line quality.

photo optics cable coming out of spark design

Maintaining optimum noise levels for your electronics ensures usability. 

Other Effects of Noise Margin Parameters

If we are connecting an ADSL-modem to a DSL-switch, there are several parameters we must take into consideration. These parameters include the connection speed, the length of the line, and the noise margin. Furthermore, the relationship between these parameters are as follows:

A set or fixed noise margin will facilitate a decrease in connection speed as the length of the connecting line increases. However, the opposite is valid if the length of the connecting line decreases, i.e., an increase in connection speeds.  

With a fixed or set line length, our noise margin decreases as connection speed increases. This also means that under these conditions, as connection speed decreases, our noise margin increases.

If the connection speed is set or fixed, a shorter line length increases the noise margin.

ADSL internet cables

Managing ADSL connections can improve signal quality through an entire region.

Several characteristic parameters affect ADSL connection functionality. In the case of noise margins, it appears to be even more critical to the overall functionality of ADSL connectivity. As I stated earlier, noise levels significantly affect the stability and quality of data transmission.  

Have your design and production teams ensure ADSL integrity with Cadence’s suite of design and analysis tools. For a comfortable layout solution in your design strategies, look no further than Allegro PCB Designer and its ease of implementation for proper noise margin design strategies into your current and future PCB designs. 

If you’re looking to learn more about how Cadence has the solution for you, talk to our team of experts and us

About the Author

Cadence PCB solutions is a complete front to back design tool to enable fast and efficient product creation. Cadence enables users accurately shorten design cycles to hand off to manufacturing through modern, IPC-2581 industry standard.

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