Digital to Analog And Analog to Digital Conversion

Digital to Analog Conversion

(This image about is  Digital to Analog Conversion  by creatingmm.com)

One common requirement in electronics to convert signals back and forth between analog and digital form. Most such conversions are Ultimately based on a digital to analog converter circuit. therefore, it is worth exploring just how we can convert a digital number that represents a voltage value into an actual analog voltage.

The circuit to the above is a basic digital-to-analog (D to A ) converter. It assume a 4-bit binary number in binary-coded decimal (BCD)  format, using +5 volts as a logic 1 and 0 volts as a logic 0. it will convert the applied BCD  number to a matching (inverted) output voltage. The digits 1,2,4, and 8 refer to the relative weights assigned to each input thus, 1 is the least significant bit (LSB) of the input binary number, and 8 is the most significant bit (MSB).

If the input voltages are accurately 0 and +5 volts, then the "1" input will cause on outputvoltage of -5* (4k/20k) = -5 * (1/5) = -1 volt whenever it is a logic 1. similarly, the "2," "4"  and "8" inputs will control output voltage of -2,-4, and -8 volts, respectively. As a result, the output voltage will take on one of 10 specific voltage, in accordance with the input BCD CODE.

Unfortunately, there are several practical problems with this circuit. First, most digital logic gates do not accurately produce 0 and +5 volts as their outputs. therefore, the resulting analog voltages will be close, but not really accurate. in addition, the different input resistors will load the digital circuit outputs differently, which will almost certainly result in different voltages being applied to the summer inputs.

The circuit above performs D to B conversion a little differently. Typically the inputs are driven by CMOS  gates, which have low but equal resistance for both logic 0 and logic 1. Also, if we use the same logic levels, CMOS  gates really do provide +5 and 0 volts for their logic levels. The maximum output voltage from this circuit will be one step of the least significant bit below 10 volts. thus, an 8-bit ladder can produce output voltages up to  9.961 volts  (255/256*10 volts). This is fine for many applications. If you have an application that requires a 0-9 volt output from a BCD  input, you can easily scale the output upwards using an amplifier with a gain of 1.6 (8/5).

If you want an inverting D to A  converter, the circuit shown above will work well. You may need to scale the output voltage, depending on your requirements. Also, it is possible to have a biporal D to A converter.  If you apply the most significant bit to an analog inverter and use that output for the MSB  position of the R-2R  ladder, the binary number applied to the ladder will be handled as  a two' s-complement number, going both positive and negative.

Analog to Digital Conversion 

(This image is about analog to digital conversion by creatingmm.com)

To convert a digital code to an analog voltage, we only had to find a way to effectively assign an appropriate voltage to each bit, and then combine them. But is there some equally easy way of finding the digital code that corresponds to a given analog voltage?

Consider the very simple requirement to determine whether an analog voltage was closest to 0,1, or 3 volts. The result would be stored as a two-bit binary number. The first step in making this determination might be a set of three comparators, connected as shown to the right. Ads the analog voltage increases, the comparators will, one by one from the bottom up, change state from false to true. Of course, additional digital circuitry will be required to encode these signals into the corresponding digital number. But this circuit forms the sensing array that will determine directly which code will be closest to the actual analog voltage.

This approach will work, and can be expanded to any number of steps for finer resolution of the analog voltage. However, as you have probably already perceived, there is problem with this approach, in that the number of comparators required increases exponentially with the number of binary bits used to store the code. Thus, using this approach to convert a 0  to 9-volt range to be a BCD number will require nine comparators. A 4-bit binary number, (counting from 0 to 15, requires 15 comparators. And a typical 8-bit circuit will require 255 comparators! clearly this approach becomes rapidly too expensive for ordinary use, although it is practical if very high speed is required.

A slow but mutch less expensive approach involves the use of D to A Converter a single comparator. The output voltage of the D to A  converter is compared with the unknown analog voltage, then changed and compared again. we won't go into much detail about digital  circuit here, but suppose a digital counter were to have its outputs applied to thre D to A  converter inputs. The counter would start at zero, and would begin counting upwards. At some point, the count would causes the output of the D to A  converter to exceed the unknown analog voltage, Thus causing the comparator output to change. The count that causes this to happen is taken as the digital code that most accurately represents the unknown analog voltage.

Advantages and limitations of Digital Techniques 

(This image is about  analog to conversion by creatingmm.com)

Advantages

1. Easy to design. Exact values of voltage or current are not important, only the range (HIGH or LOW ) in which they fall.
2. Information storage is easy.
3. Accuracy and precision are greater.
4. Operating can be programmed. analog systems can also be programmed, but the variety and complexity of the available operations severally limited.
5. Digital circuits are less affected by noise. as long as the noise is not large enough to prevent us from distinguishing a HIGH from a LOW.
6. More digital circuitry can be fabricated on IC  chips.

Limitations

There is really only one major drawback when using digital techniques: The real world is mainly analog   Most physical quantities are analog in nature, and it is these quantities that are often the inputs and outputs that are being monitored, operated on, and controlled by a system. To take advantage of digital techniques when dealing with analog inputs and outputs, three steps must be followed:

1. Convert the real-world analog inputs to digital form (ADC) 
2. Process (operate on ) the digital information.
3. Convert the digital outputs back to real-world analog form (DCA)

The following diagram shows a temperature control system that requires analog/digital conversions in order to allow the use of digital processing techniques.

Some Advane Tips

If you like this article so please share this post , and if you know to interest about RAM, ROM, and PC so visit my site : https://www.digitaltech.net.in