Digital-to-analog converter

      

                                                Digital to Analog Converters (DAC)

  DAC as following,

                                - Purpose of DAC

                                -Types    of DAC

                               - Performance Characteristics of DAC

                               -Applications of DAC

Purpose of DAC:-

    In DAC,To convert digital values to analog voltages

and Performs inverse operation of the Analog-to-Digital Converter (ADC)

Types of DAC:

   {1} The Binary Weighted Resistor

   {2}R-2R Ladder

   {3}Multiplier DAC, its The reference voltage is constant and is set by
 the manufacturer and in    Non-Multiplier DAC,  its The reference voltage
 can be changed during operation.

The weighted resistor(Binary ):-

   -  It is Weighted Resistors based on bit

   - It is Reduces current by a factor of 2 for each bit

R-2R Ladder:-

   In this  Same input switch setup as Binary Weighted Resistor DAC

     All bits pass through resistance of 2R

     In this , The less significant the bit, the more resistors the signal muss pass through before reaching the op-amp

      In this,The current is divided by a factor of 2 at each node

       

Characteristics of DAC:

¨     Comprised of switches, op-amps, and resistors

¨     Provides resistance inversely proportion to significance of bit

      on  Performance Specifications,we can say as followings:

-Resolution    

-Settling Time

-Reference Voltages

-Linearity

-Errors 
 -Speed

 (1) Resolution:
 in any DAC ,resolution is the quantity of difference in outcome voltage for every modify of the LSB in the digital input

How closely  can we estimated the preferred outcome signal(Higher Res. = finer detail=smaller Voltage  divisions)

We can say that a common DAC has a 8 - 12 bit Resolution

(2)  Reference Voltage:
 A specified voltage  used to figure out how each digital input will be allocated to each voltage division.

  Types:      Multiplier: external, variable, user specified

    and the non multiplier: internal, fixed, and it is defined by manufacturer

  

(3)  Settling Time:
  The time required for the input signal voltage to negotiate to  the predicted outcome voltage(within +/- VLSB).   Any modify in the input state will not be demonstrated in the outcome condition immediately. There 's time period lag, between the two actions or activities..

(4)  Linearity :
is the difference between the needed analog output and the actual output over the full range of estimated values.

  If at all possible, a DAC should produce a linear relationship between a digital input and the analog output, this is not always the case.

(5)  Speed:
 Rate of conversion of a single digital input to its analog equivalent

     Conversion Rate

    Depends on clock speed of input signal

     Depends on settling time of converter

     (6) Errors

    Non-linearity ( Differential   ,Integral)Error

                            Gain Error

                          Offset Error

                          Non-monotonicity Error

Differential Non-Linearity: the Difference in a voltage step size from the previous DAC output (Ideally All DLN’s = 1 VLSB) Integral Non-Linearity: Deviation of the actual DAC output from the ideal (Ideally all INL’s = 0)

Gain Error: the Difference in slope of the perfect curve and the actual DAC output.

Offset Error:  A continuous voltage difference or change between the perfect or ideal DAC outcome or output and the real or actual..

¨     The voltage axis intercept or indentify of the DAC output curve is different than the ideal or perfect.

Non-Monotonic: A decrease or reduce in output voltage with an increase or improve in the digital input

Common Applications:-

        In Generic use:-

it’s Used when a continuous analog signal is required and Signal from DAC can
 be smoothed by a Low pass filter

                In Circuit Components:-  
        such as Voltage controlled Amplifier digital input, External Reference Voltage as
        control and in Digitally operated attenuator:External Reference Voltage as input,
        digital control.

    Programmable Filters: - 

  as Digitally controlled cutoff frequency

    In Digital Audio:-

   Digital Telephone/Answering Machines ,CD Players,                            

       In Function Generators/Oscilloscopes:-  -
   Digital Oscilloscopes,Digital Input,Analog Ouput

  In Motor Controllers :- -Motor Control ,Cruise Control, Valve Control etc.