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An introduction to the D/A conversion design and process.

What are d/a and a/d converters

Digital to Analog (D/A) and Analog to Digital (A/D) converters are pervasive and essential in the technology of today. Televisions, smart phones, radars, and even sensors in your car all require quality conversion in order to work effectively. The improvements and characteristics of these converters have significantly supported the digital revolution in past decades. D/A and A/D converters are intrinsically inversely related. Digital to analog converters are systems that take discrete digital data and convert it into continuous analog signals, whereas analog to digital converters achieve the opposite effect. Specifically, we will be investigating and implementing a D/A converter that takes stored digital data and reproduces the original audio signal. An important concept to note is that digital signals can undergo manipulation and storage without damaging or losing the original data because of their discrete nature. For our project, we chose an R/2R implementation of a D/A converter using a BeagleBone Black. We will further explore these new concepts later in this educational document, but here is our poster which gives a surface-level explanation on most of the topics.

Our poster for presenting our project

Characteristics of d/a converter

There are multiples D/A architecture designs that one can choose to implement. Depending on which architecture one selects, the characteristics of the digital to analog conversion are affected. Some characteristics to keep in mind when designing a digital to analog converter are speed, accuracy, cost, resolution, power consumption, and size. The speed characterizes the frequency of the sample production of the audio signal. Accuracy determines how true the produced signal is compared to the original. Cost is determined by the price of the components used in making the converter and can also impacted by the power consumption if measured over time. The resolution is the number of voltage output levels which is based on how many bits the converter uses. We chose to have 8 bits in our converter so we had 2^8bits = 256 voltage levels. There also exists a reciprocity between speed and resolution because the more bits it uses, the more difficult it is to reproduce them at a high frequency. The power consumption of the circuit depends on how high these other characteristics are and whether one chose to implement a passive (low consumption) or active (high consumption) system. Active systems include components that control flow and inject power in a circuit, such as transistors, while passive systems have components that cannot amplify the signal, such as resistors. Finally, the size of a D/A converter relies on the scale and number of components used.

The d/a process

First, we will discuss the conversion process in terms of systems and signals, and then provide a real world example so that one can see these concepts realized.

Displays D/A conversion process

Take note that the graphs on the left represent signals in the frequency domain while graphs on the right are signals in the time domain. Typically, when reproducing an analog signal from digital values, one starts with stored discrete data that looks like (1) in the frequency domain when produced into a quantized signal. Looking at the time domain in (1), you can see the quantized nature of the signal. Note that in the example, the original digital signal has nonzero amplitude from -20kHz to 20kHz. This range is because our D/A converter has the purpose of reproducing audio and the human ear can only hear up to the 20kHz range. Anything above this range we cannot hear. However, as you can see there are copies of this original digital signal at higher frequencies. We do not want these high frequency copies because they consume power when outputted, even though we cannot hear them. When experimentally outputting this unfiltered digital signal, we also found that they also introduced noise and damaged our speaker. So, in order to remove these harmful high frequency copies and isolate the original digital signal that occurs at lower frequencies, we want to apply a low pass filter as seen in (2). In the time domain, we display the impulse response of a simple resistor-capacitor low pass filter to help show this cutoff of higher frequencies. Now, in (3), one can see that the high frequency copies of the original quantized signal have been filtered out. The converter then output this result which is actually an exact reproduction of the original analog signal!

Now, armed with the general D/A conversion process in mind, consider an mp3 player producing a song through a speaker. The song audio is originally a digital stream of bits that is stored in the player’s memory. This digital data can be stored into groups, called packets, or just outputted raw into the D/A converter. It takes these bit streams and turns them into a digital signal with distinct quantization levels and high frequency copies. Then, this digitized signal goes through a low pass filter which effectively smoothes out this quantized signal into a continuous analog signal and removes the high frequency copies above 20kHz. This signal is a reproduction of the original analog signal that was recorded by means of a A/D converter! In order to amplify this signal so that we can hear it, the analog signal powers an audio amplifier that in turn powers a speaker which produces the sounds that we hear.

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, R/2r implementation of a d/a converter. OpenStax CNX. Dec 17, 2014 Download for free at http://legacy.cnx.org/content/col11732/1.1
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