Characteristics of D/A converters

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Ten possible states of decade counters may be displayed with 4 binary states (BCD code). So, all the numbers from 0-999 can be presented with a total of 12 binary states using 3-decade with four binary members. A simplified scheme of this converter is shown in the following figure.

 BCD D/A converter  
Figure 7.1.7 Value of the resistor in the A/D converter.  

The resistance value of each decade in relation 8:4:2:1, and instead of mechanical switches are used to switching diodes. If the voltage Ud is equal to the voltage Ub diode do not conducts and resistor and her group do not participate in the conversion and vice versa. Negative logic is used to manage, or to invert the binary (replace the ' 0 ' with a ' 1 ' and vice versa - a method of I complement) and then brought to the diode terminals. All units on diodes would mean that no one does not occur, which makes the amount of current in a circuit is zero and that the conversion value 000000000000BCD.

Secured power is, then 1 per thousand. An instrument that measures the current in the illustration is just one of the ways of displaying analog values, in this case electricity, but would also be using the same power amplifier could use some engine management or control electrode.

On the overall accuracy affects production tolerance resistor. Thus, for example, the value of the resistor changed to 1% in the value of the units covered by hundreds. Therefore prefer to use the R-2R of resistor network with a constant current source in some branches of proof, what today's technology is not difficult to create.

 R-2R D/A converter  
Figure 7.1.8 Schema of R-2R converter with a current source.  

All nodes on the network, or the network connection with a resistance below each switch, having regard to the mass resistance in the amount equal to 2/3 R. In addition to the constant current source and turned on all the switches in all the nodes of the network resistance voltage drop is the same.

Of course not mechanical switches but some of the electronic version. At one point switch can be open or closed. The example in Figure uses negative logic, i.e. logic ' 1 ' means an open switch. So before the BCD used to manage switches to perform its conversion into I Complement (substitute ' 0 ' to ' 1 ' and vice versa).

Voltage drop of each nodal points of the network effect on the output voltage, the less the pivot further away from the exit. This effect can be seen as a multi-voltage divider where each additional member from the exit end of the damping voltage to the input of a member at a ratio of 2:1. Output voltage circuit in the image is computed according to the formula:

 Output equation

If all the switches are off then Uizl=0. Let multiply constant K=(4/3)•I•R, in order to simplify analysis, and Uizl=K•F, where F is the estimated amount in parentheses dependent of I Complement in accordance with the binary combination of BCD code. Therefore, management switches is based on the negative logic. The following table shows an example of three-node network.

'0' to '1'
F / Factor
of multiply
000 111 7/8
001 110 6/8
010 101 5/8
011 100 4/8
100 011 3/8
101 010 2/8
110 001 1/8
111 000 0/8

The jump in the values of the output transducers for the example above is 1/8 of the maximum output voltage. If you would use a converter with 4 nodes to maximize the accuracy of the jump of 1/16 maximum output voltage. Output voltage to the sample decreases with increasing values of BCD number. It is very easy to change on the output of the amplifier to change the reference level.

Resistor network in the D/A converter requires that the deviation from the declared value of the resistance value R is not greater than 1%. For the conversion accuracy is important and the exact relationship between individual resistors in each member of the network. The differences between these relationships must be less than 0.2%. So, it requires a very high precision manufacturing.

In almost every computer today can be for very little cash outflows incorporate musical card that allows recording and playback of music, that is designed for the frequency range of the analog signal of approximately 10 Hz to 20'000 Hz. In a general analysis and it can be used for analysis of analog signals when its changes within the specified frequency range.

Example IV

Musical card also uses some of the components listed in the previous events. Its basic components, according to the example of 'Creative Labs Sound Blaster' family unit includes:

DSP is used to add music effects already existing records and sampling analog input signal and its storage in the form of binary records. The quality and features of software and embedded electronic components is the main factors to be able to take advantage of the DSP.

Common parameters of musical cards are given in the following table.

Characteristics ISA or PCI slot, DMA access to the computer's memory
frequency (Hz)
6000, 8000, 11025, 16000,
22050, 2000, 44100, 48000,
Professional devices :
64000, 88200, 96000, 192000
Resolution (bits) 8, 16,
32 (distributed between the channels as needed)
Full duplex - for recording and playback
Electronic properties Frequency range (Hz) / Input : 10 - 20000
Frequency range (Hz) / Output : 10 - 21000
Noise ratio - S/N (dB) : 60 - 70 dB
Harmonic distortion : less than 0.03%
Crosstalk of channels : 70% - 90%
Signals intelligence Analog/digital mixer with input and output ports
Level control in steps of 2 dB
Mono, Stereo, 3D stereo controls
MIDI support 1 MB ROM with 128 of instruments + 6 sets of percussion
2-28 MB of additional RAM for user's needs
Music features Echo, Chorus,
QSound - stereo expanded to 180°
SRS (Sound Retrieval System) - spatial stereo
Program support
CD, Wave, MIDI player
Support for processing of digital music
Control panel for adjusting parameters of musical card

All these actions allow built-in A/D and D/A converters, often combined in a single integrated circuit usually called A/D/A converter. If the described card added more multimedia features, like support for home theater, its functionality is even more significant. Modern motherboards have embedded multimedia integrated circuits thanks to advances in technology, but by the characteristics they can not compare with the capabilities provided by one strictly dedicated musical cards. Of course, all the accessories cost.

In the computer world D/A converter is present as each graphics card. From memory graphics card, in which the graphics processor enrolled image content, it should be more than 50 times a second to read the contents and display it properly on screen. The device that performs this conversion often carries abbreviation RAMDAC. The amount of graphics memory and speed D/A conversion (often greater than 200 MHz) are the main indicators of quality PC graphics card.

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In this age of electronics applications, are increasingly resorting to solutions that will guarantee the future of the ease and accessibility of electronic devices for all users. Thus, the digital electronics in a very short period of envious application. A/D and D/A converters are already so widespread that it is already difficult to pass. Their use in the future will certainly be increased, particularly in systems for automating manufacturing processes.

Incidentally, the vehicles of 'Formula 1' have over 300 sensors and actuators, sensors convert mechanical changes in the size and electrical actuators for the reverse process, with a wireless connection to a computer that controls all the happenings of the vehicle and run around a hundred thousand measurements per second. The driver drives, and his 'race engineer' monitors all events of which he corrected something and something suggests the driver to make this the best possible way, of the properties of the vehicle. So, conducted telemetry - measurement and remote management, and also transmits the images from cameras installed on the vehicle regarding the broadcast. Communication speed between the vehicle and the computer is over 10 Mbps. And everything is linked together with the supervisory team race. 'Stopwatch' has definitely gone down in history.

Particular importance in the management or control of production processes have MICROCONTROLLERS, computers are often less processing power than the usual PC, which unlike the PC, do not communicate with people but mostly with machines.


  Citing of this page:
Radic, Drago. " IT - Informatics Alphabet " Split-Croatia.
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