DAC details

1. DAC FUNDAMENTALS AND
CURRENT SWITCHED&
RESISTIVE DAC
Presented by
VAIBHAVI P

2. INDEX
• Introduction-Analog , Discrete and Digital Signal
• Types of Converters
-A to D Converter
-D to A Converter
• Introduction-DAC
• Specifications
-Resolution
-Speed
-Linearity
-Settling Time
-Reference Voltages
-Errors
• Errors
• Types of D to A Converter
• Applications of DAC

3. INTRODUCTION-ANALOG,DISCRETE
AND DIGITAL SIGNAL
• Analog signal is a continuous signal in which one time-varying
quantity (such as voltage, pressure, etc.) represents another time-based
variable. In other words, one variable is an analog of the other.
• Discrete Signal-The signal which is defined for the discrete intervals
of time
• Digital Signal-The signal is discretised in both time and magnitude.
The magnitude axis is divided into fixed levels and the signal can take
value equal to these levels only

4. Types of Converters
1. Analog to Digital Converters
2. Digital to Analog Converters
WHY DO WE NEED CONVERTERS…??
• All Real Life Signals Are Analog Signal , Machine Can Understand Only Digital Signal
• A computer is a binary machine operating in an analog world, so to be able to produce an
output that is understandable by other devices a DAC is used.
• For example, a computer stores audio in the form of binary values of the sound wave. In
order to play these back as sound on a speaker we need analog signals, because as we
know the speaker’s diaphragm vibrates based on the intensity of the analog signal to
produce sound/music. So here, we will use a DAC to convert the digital audio file to
analog signal in order to play it on a speaker.

5. DATA CONVERTERS IN SIGNAL PROCESSING

7. Analog to Digital
Converter

8. Digital to Analog Converter
• Signal from DAC can be
smoothed by a Low pass filter

9. INTRODUCTION
• A Digital to Analog converter (DAC) is a
device that converts digital numbers
(binary) into an analog voltage or current
output.
• A Digital to Analog Converter commonly
referred as DAC, D/A or D2A is a device
that converts binary values (0s and 1s) to a
set of continuous analog voltages

10. Classification of DAC

11. Characterization and definition of Data Converters

12. Basic
architecture
of DAC
Converter

13. Static
Characterization
of D/A
Converters

14. Choosing a
DAC
• There are six main specifications that should
be considered when choosing a DAC for a
particular project
 Reference Voltage
Resolution
Linearity
Speed
Settling Time
Error

15. Resolution
• Reference voltage : To a large extent the
output properties of a DAC are determined
by the reference voltage
• Resolution is the smallest analog change
resulting from a 1 LSB digital change
(quantified in terms of N bits) Or Resolution
is the amount of variance in output
voltage for every change of the LSB in
the digital input . The voltage value is a
function of the number of input bits and
the reference voltage value
• Increasing the number of bits results in a
finite resolution

16. • Percentage resolution = 1 / (2n
− 1), expressed as a percentage
Step size = Vref / (2n
− 1)

17. Resolution-Example

18. Linearity
The linearity is the relationship
between the output voltage and the
digital signal input

19. Speed
Specified as the conversion rate or sampling rate
It is the rate at which the input register is
updated
High speed DACs are defined as operating at
greater than 1MHZ
Some state of 12-16 bit DAC can reach speeds of
1GHZ
The conversion of the digital input signal is
limited by the clock speed of the microprocessor
and the settling time of the DAC

20. Settling Time
• Ideally a DAC would
instantaneously change its
output value when the digital
input would change
• In a real DAC it takes time for the
DAC to reach the actual expected
output value

21. • Quantization Noise is the inherent uncertainty in digitizing an analog
value with a finite resolution converter.
• Full scale (FS) is the the maximum DAC analog output value. It is one LSB less
than VREF

23. ERROR
There are multiple
sources of error in
computing the analog
output
• Gain Error
• Offset Error
• Full scale Error
• Linearity
• Non-Monotonic Output Error
• Settling Time and Overshoot
• Resolution

24. Gain error
• Deviation in the slope of the
ideal curve and with respect
to the actual DAC output
• High Gain error: Step
amplitude is higher than the
desired output
• Low Gain error: Step
amplitude is lower than the
desired output

25. Offset Error
• Occurs when there is an
offset in the output voltage in
reference to the ideal
output.
• This error may be detected
when all input bits are low

26. Full scale error
• Occurs when there is an
offset in voltage form the
ideal output and a deviation
in slope from the ideal gain

27. Non-Linearity
• Differential nonlinearity (DNL) is the maximum deviation of any
analog output changes caused by an input LSB change from its ideal
change of or Voltage step size differences vary as digital input
increases. Ideally each step should be equivalent.

28. Non-Linearity
• Integral nonlinearity (INL) is
the maximum difference
between the actual finite
resolution characteristic and
the infinite resolution
characteristic. Or Occurs
when the output voltage is
non linear. Basically an
inability to adhere to the
ideal slope

29. Integral and
Differential Linearity
for a D/A Converter
• D/A Converter with ±1.5
LSB integral nonlinearity
and ±0.5 LSB differential
nonlinearity

30. Non-Monotonic
Output Error
• A monotonic D/A (A/D)
converter is one in which an
increasing digital input code
(analog input) produces a
continuously increasing
analog output value (digital
output code).
• Non-Monotonic Occurs when
the an increase in digital
input results in a lower
output voltage

32. Settling Time
and Overshoot
• Settling Time: The time
required for the voltage to
settle within +/- the voltage
associated with the
V(LSB).Any change in the
input time will not be
reflected immediately due to
the lag time.
• Overshoot : Occurs when the
output voltage overshoots
the desired analog output
voltage

33. Resolution
• Inherent errors associated with the resolution
• More Bits = Less error and greater resolution
• Less Bits = More error and less resolution

34. 3-BIT D/A
CONVERTER
ILLUSTRATION

35. TYPES OF D/A
CONVERTERS
R-2R ladder type DAC
Weighted resistor type
DAC
Switched current source
type DAC
Switched capacitor type
DAC

36. Weighted Resistor Type
DAC
• A weighted resistor DAC produces an analog
output, which is almost equal to the digital (binary)
input by using binary weighted resistors in the
inverting adder circuit. In short, a binary weighted
resistor DAC is called as weighted resistor DAC.
• The non-inverting input terminal of an op-amp is
connected to ground. That means zero volts is
applied at the non-inverting input terminal of op-
amp.
• According to the virtual short concept, the
voltage at the inverting input terminal of op-amp is
same as that of the voltage present at its non-
inverting input terminal. So, the voltage at the
inverting input terminal’s node will be zero volts.

41. Weighted Resistor Type DAC
• The nodal equation at the inverting input terminal’s node is:
• Substituting, R=2Rf R=2Rf 𝑓 in above equation
.

42. Weighted Resistor Type DAC
• The generalized output voltage equation of an N-bit binary weighted
resistor DAC as shown below:

43. • The disadvantages of a binary weighted resistor DAC are as follows
−
• The difference between the resistance values corresponding to LSB &
MSB will increase as the number of bits present in the digital input
increases.
• It is difficult to design more accurate resistors as the number of bits
present in the digital input increases.

44. R-2R LADDER
TYPE DAC
• The R-2R Ladder DAC
overcomes the disadvantages
of a binary weighted resistor
DAC. As the name suggests,
R-2R Ladder DAC produces
an analog output, which is
almost equal to the digital
(binary) input by using a R-
2R ladder network in the
inverting adder circuit.

50. R-2R
LADDER
TYPE DAC
• The advantages of a R-2R Ladder DAC are as
follows −
• R-2R Ladder DAC contains only two values of
resistor: R and 2R. So, it is easy to select and
design more accurate resistors.
• If more number of bits are present in the digital
input, then we have to include required number of
R-2R sections additionally.
• Due to the above advantages, R-2R Ladder DAC is
preferable over binary weighted resistor DAC.

51. Switch
Current
Source
Type DAC
• The R-2R Ladder Type Network DAC and the
Weighted Resistor DAC can be Regarded as a
Switch Voltage Source Type DAC.
• Because when the Input Position goes HIGH,
the High Voltage is Effectively Switched into
Circuit.
• Most of IC’s DAC use a form of Current
Switching Rather than Voltage Switching
Because Current can be Switched out Faster
than Voltage.

52. Switched Current Source Type DAC

54. APPLICATIONS OF DAC
1. Digital Signal Processing
• It is much easier to work with signals once they have been converted to binary.
• A good example of this is audio editing. The audio is converted to binary after which
operations can be performed on it. In order to play back this audio, a DAC is used to
convert it into a sound signal that can be played back on a speaker.
2. Digital Power Supplies
• Most microcontrollers are too slow to be a part of a power supply control loop. In order to
change the voltage or current of a power supply, the reference can be changed. This can
be done by connecting a DAC to the output of a microcontroller and using that to change
the reference voltage to a preselected value.

55. DIGITAL AUDIO
CD PLAYERS MP3 PLAYERS DIGITAL TELEPHONE/ANSWERING
MACHINES

56. FUNCTION GENERATORS
• Digital Oscilloscopes
– Digital Input
– Analog Ouput
• Signal Generators
– Sine wave generation
– Square wave generation
– Triangle wave generation
– Random noise generation

57. USAGE OF DAC
• DACs are available as separate ICs or even as embedded into a
microcontroller. But the most commonly used ones are the ones that
are available as a separate IC. The most commonly used ones
are DAC7715, DAC0832, DAC0808 etc..
• The MCP 4725 is a neat little DAC module that is commonly used in
conjunction with the Arduino, and that means documentation and
libraries are easily available.

58. References
• https://en.wikipedia.org/wiki/Digital-to-
analog_converter#:~:text=In%20electronics%2C%20a%20digital%2Dt
o,ADC)%20performs%20the%20reverse%20function.
• Allen Holmberg Book
• https://www.tutorialspoint.com/linear_integrated_circuits_applicatio
ns/linear_integrated_circuits_applications_digital_to_analog_convert
ers.htm
• https://www.sciencedirect.com/topics/engineering/digital-to-analog-
converter

59. THANK YOU