Why adc is used

Everything we see, feel or measure is analog in nature such as light, temperature, speed, pressure etc. But most of the electronic devices around us starting from a simple digital watch to a super computer are all digital devices.

So, it is obvious that we need something that could convert these analog parameters to digital value for a microcontroller or micro-processor to understand it.

An analog to digital converter is a circuit that converts a continuous voltage value analog to a binary value digital that can be understood by a digital device which could then be used for digital computation.

Modern day electronics is purely digital — gone are the good old days of analog computers. Unfortunately for digital systems, the world we live in is still analog and full of colour, not just black and white.

For example a temperature sensor like the LM35 outputs a voltage dependent on the temperature, in the case of that specific device 10mV per degree rise in temperature. If we directly connect this to a digital input, it will register either as a high or a low depending on the input thresholds, which is completely useless.

Instead we use an ADC to convert the analog voltage input to a series of bits that can be directly connected to the data bus of the microprocessor and used for computation. A good way to look at the working of an ADC is to imagine it as a mathematical scaler. Scaling is basically mapping values from one range to another, so an ADC maps a voltage value to a binary number.

What we need is something that can convert a voltage to a series of logic levels, for example in a register. Something in between the logic and the analog input voltage needs to act like an interface. Of course, no ADC is absolute, so the voltage mapped to the maximum binary value is called the reference voltage. For example in a 10 bit converter with 5V as the reference voltage, all bits one, the highest possible 10 bit binary number correspond to 5V and the lowest number corresponds to 0V.

So each binary step up represents around 4. What if the voltage changes are below the 4. This puts the ADC in a dead zone, the conversion result therefore always has a small error. This can be prevented by using an ADC with a higher resolution. ADCs up to 24 bits are available, though conversion frequencies are low, in the order of a few hertz. The number of analog to digital conversions the converter can make every second is called the sample speed.

This is to be read as megasamples per second, meaning a million samples per second. Note that SI prefixes apply here.

For example, if you want to record sounds from a microphone, the audio must be converted from the microphone's analog signal into a digital signal that the computer can understand. This is why all sound cards that have an analog audio input also require an ADC that converts the incoming audio signal to a digital format. The accuracy of the audio conversion depends on the sampling rate used in the conversion process.

Higher sampling rates provide a better estimation of the analog signal, and therefore produce a higher-quality sound. While ADCs convert analog inputs into a digital format that computers can recognize, sometimes a computer must output an analog signal. For this type of conversion, a digital-to-analog converter DAC is used. If you would like to reference this page or cite this definition, you can use the green citation links above.

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In modern life, electronic equipment is frequently used in different fields such as communication, transportation, entertainment, etc.

Since most real world signals are analog, these two converting interfaces are necessary to allow digital electronic equipments to process the analog signals.

Take the audio signal processing in Figure 1 as an example, ADC converts the analog signal collected by audio input equipment, such as a microphone, into a digital signal that can be processed by computer.

The computer may add sound effect such as echo and adjust the tempo and pitch of the music. DAC converts the processed digital signal back into the analog signal that is used by audio output equipment such as a speaker. The resistors are scaled to represent weights for the different input bits.

In the real world, most of the signals sensed and processed by humans are analog signals. Analog-to-Digital conversion is the primary means by which analog signal are converted into digital data that can be processed by computers for various purposes, Figure 3.

There are many types of ADC for different applications.