WhatIs.com DEFINITION analog-to-digital conversion (ADC) Analog-to-digital conversion (ADC) is an electronic process in which a continuously variable, or analog, signal is changed into a multilevel digital signal without altering its essential content. Paul Kirvan 13 Jul 2022 What is analog-to-digital conversion (ADC)? Analog-to-digital conversion (ADC) is an electronic process in which a continuously variable, or analog, signal is changed into a multilevel digital signal without altering its essential content. An analog-to-digital converter changes an analog signal that's continuous in terms of both time and amplitude to a digital signal that's discrete in terms of both time and amplitude. The analog input to a converter consists of a voltage that varies among a theoretically infinite number of values. Examples are sine waves, the waveforms representing human speech and the signals from a conventional television camera. The output of the analog-to-digital converter has defined levels or states. The number of states is almost always a power of two -- that is, 2, 4, 8, 16, etc. The simplest digital signals have only two states and are called binary. All whole numbers can be represented in binary form as strings of ones and zeros. Diagram of how a digital converter works Analog-to-digital conversion changes continuous analog signals to discrete digital ones. Why is digitization important? Digital signals propagate more efficiently than analog signals, largely because digital impulses are well defined and orderly. They're also easier for electronic circuits to distinguish from noise, which is chaotic. That is the chief advantage of digital communication modes. Computers "talk" and "think" in terms of binary digital data. While a microprocessor can analyze analog data, it must be converted into digital form for the computer to make sense of it. A typical telephone modem makes use of ADC to convert the incoming audio from a twisted-pair line into signals the computer can understand. In a digital signal processing system, an analog-to-digital converter is required if the input signal is analog. What is the Nyquist theorem and why is it important? The Nyquist or sampling theorem describes analog-to-digital conversion. It enables the reproduction of a pure sine wave measurement, which is also known as the sample rate. The way people experience the world is mostly analog; think sound and light waves. For these signals to be used in computing, they must be converted to digital ones. However, digital electronics works in discrete numbers. To convert an analog signal to a digital one, measurements must be sampled at a regular frequency. The sample rate must be at least twice its frequency. This approach is used in digital audio and video to reduce aliasing, or the production of a false frequency. A sample rate that is too low won't accurately depict the original signal; it will be distorted or have aliasing when reproduced. A rate that is very .

1. ADC in AVR controller

2. ADC in AVR controller
• Analog-to-digital converters are among the
most widely used devices for data acquisition.

3. ADC in AVR controller

4. Characteristics of the ADC
Resolution
• The ADC has n-bit resolution, where n can be 8, 10, 12, 16, or
even 24 bits.
• Higher-resolution ADCs provide a smaller step size, where
step size is the smallest change that can be discerned by an
ADC

5. Characteristics of the ADC
• Although the resolution of an ADC chip is
decided at the time of its design and cannot
be changed, we can control the step size with
the help of what is called Vref
• Vref is an input voltage used for the reference
voltage. The voltage connected to this pin,
along with the resolution of the ADC chip,
dictate the step size.
• For an 8-bitADC, the step size is Vref/256

6. Characteristics of the ADC

7. Characteristics of the ADC

8. Characteristics of the ADC
• In an 8-bit ADC we have an 8-bit digital data output
of DO-D7
• Output voltage is given by :
where Dout = digital data output (in decimal), Vin =
analog input voltage, and step size (resolution) is the
smallest change, which is Vref/256 for an 8-bit ADC.

9. Example

10. ATmega32 ADC features
• It is a 10-bit ADC
• It has 8 analog input channels, 7 differential input channels,
and 2 differential input channels with optional gain of 10x and
200x.
• The converted output binary data is held by two special
function registers called ADCL (ND Result Low) and ADCH (ND
Result High).
• Because the ADCH:ADCL registers give us 16 bits and the ADC
data out is only 10 bits wide, 6 bits of the 16 are unused. We
have the option of making either the upper 6 bits or the lower
6 bits unused.
• We have three options for Vref. It can be connected to AVCC
(Analog V cc), internal 2.56 V reference, or external AREF pin.

11. AVR programming in C
• In the AVR microcontroller five major registers are
associated with the ADC that we deal with in this
chapter. They are ADCH (high data), ADCL (low data),
ADCSRA (ADC Control and Status Register), ADMUX
(ADC multiplexer selection register), and SPIOR
(Special Function I/O Register).

12. ADMUX Register

13. ADMUX Register
If as the Vref = 2.56 V the step size of ADC will be 2.56 / 1024= 10/4 = 2.5 mV.

14. ADMUX Register

15. ADMUX Register
• If you set the ADLAR bit in ADMUX
• register, the result bits will be left-justified;
otherwise, the result bits will be right justified.

16. ADCSRA register
• The ADC SRA register is the status and control register of ADC. Bits of this
register control or monitor the operation of the ADC.

17. AVR ADC Clock Selection

18. Reading ADC Using Polling
Method in C