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Digital to Analog Converter. Nov. 1, 2005 Fabian Goericke, Keunhan Park, Geoffrey Williams. Outline. What is a DAC? Types of DAC Circuits Resistor-string DAC Binary weighted DAC R-2R Ladder DAC Specifications of DAC Errors Applications. What is a DAC?.

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Advanced to Analog Converter Nov. 1, 2005 Fabian Goericke, Keunhan Park, Geoffrey Williams

Outline What is a DAC? Sorts of DAC Circuits Resistor-string DAC Binary weighted DAC R-2R Ladder DAC Specifications of DAC Errors Applications

What is a DAC? A computerized to simple converter (DAC) is a gadget that proselytes advanced numbers (double) into a simple voltage or current yield. 1001 0101 0011 0111 1001 1010 1011 DAC

What is a DAC? Simple Output Signal Digital Input Signal

Types of DAC Circuits 1. Resistor String 2. Twofold Weighted Resistor 3. R-2R Ladder

Resistor String DAC Components of a String DAC Resistor String supply discrete voltage levels Selection Switches associate the right voltage level to operation amp as indicated by information bits Op-amp increases the discrete voltage levels to craved range, keeps the present low

Resistor String DAC Resistor String Example

Resistor String DAC Selection Switches 1 0 6V 1 7V 1 0 4V 0 0V

Resistor String DAC Advantages: basic quick for < 8 bits Disadvantages: high component mean higher resolutions, reason: number of resistors: number of switches: moderate for > 10 bits

R 2R 4R 2 n R Rf - V out + Binary Weighted Resistor DAC Basic Idea: Use a summing operation amp circuit Use transistors to switch amongst high and ground Use resistors scaled by two to gap voltage on every branch by a force of two

Binary Weighted Resistor DAC non-upsetting contribution on ground virtual ground at rearranging info KIRCHHOFF\'s present law and no info current into operation amp I1 + I2 = 0 I1 = V1/R + V2/(2R) + V3/(4R) + …

Binary Weighted Resistor DAC Most huge piece Least huge piece Rf = R/2 Vn = Vref, if bit is set Vn = 0, if bit is clear Terms have less impact

Binary Weighted Resistor DAC Advantages Simple Fast Disadvantages Needs huge scope of resistor qualities (2000:1 for 12-bit) with high accuracy in low resistor values Needs little switch resistances

R-2R Resistor Ladder DAC V ref Each piece controls a switch amongst ground and the reversing contribution of the operation amp. Least difficult kind of DAC Requires just two accuracy resistance valuce (R and 2R) The change is associated with ground if the comparing bit is zero. 0 4 bit converter

R-2R DAC Example Convert 0001 to simple V 0 V 1 V 0 V 1 = V 2 V 1 V 0 V 3 V ref

R-2R DAC Example Convert 0001 to simple R 2R V ref V 0

R-2R DAC Summary Conversion comes about for every piece Conversion condition for N - bit DAC for

R-2R DAC Summary Advantages Only two resistor values Does not require the sort of exactness as Binary weighted DACs Easy to fabricate Faster reaction time Disadvantages More befuddling investigation

Specification of DAC Resolution Speed Settling time Linearity Reference voltage

Specification - Resolution The measure of fluctuation in yield voltage for each change of the LSB in the advanced info. How nearly would we be able to inexact the sought yield signal(Higher Res. = better detail=smaller Voltage divisions) A typical DAC has a 8 - 16 bit Resolution N = Number of bits

Specification - Speed Rate of transformation of a solitary computerized contribution to its simple equal Conversion Rate relies on upon clock speed of information flag settling time of converter When the info changes quickly, the DAC transformation speed must be high.

Specification – Settling Time The time required for the information flag voltage to settle to the normal yield voltage (inside +/ - ½ of V LSB ). Preferably, a quick change in simple voltage would happen when another parallel word goes into DAC Fast converters decrease slew time, however more often than not bring about longer ring time. t slew t ring t delay

Specification – Linearity The distinction between the coveted simple yield and the real yield over the full scope of expected qualities.

Linearity(Ideal Case) NON-Linearity(Real World) Desired Output Desired/Approximate Output Approximate yield Analog Output Voltage Analog Output Voltage Digital Input Digital Input Miss-arrangement Perfect Agreement Specification – Linearity Ideally, a DAC ought to create a direct relationship between a computerized input and the simple yield, this is not generally the situation.

Specification – Reference Voltage A predetermined voltage used to decide how each advanced information will be allocated to every voltage division. Sorts: Non-multiplier DAC: V ref is settled (determined by the producer) Multiplier DAC: V ref is given by means of an outside source

Specification – Reference Voltage Full Scale Voltage Defined as the yield when computerized info is each of the 1\'s.

Errors There are a different wellsprings of blunder connected with DAC Common DAC Errors: Gain Error Offset Error Full Scale Error Non Linearity Non-Monotonic Resolution Errors Settling Time and Overshoot

High Gain Desired/Ideal Output Analog Output Voltage Low Gain Digital Input Gain Error Gain Error: Deviation in the incline of the perfect bend and as for the real DAC yield. High Gain Error: Step abundancy is higher than the sought yield Low Gain Error: Step plentifulness is lower than the coveted yield

Offset Error Offset Error: Occurs when there is a balanced in the yield voltage in reference to the perfect yield. Yield Voltage Desired/Ideal Output This blunder might be distinguished when all information bits are low (i.e. 0). Positive Offset Digital Input Negative Offset

Full Scale Error Full Scale Error: happens when there is a balanced in voltage shape the perfect yield and a deviation in incline from the perfect pick up.

Ideal Output Analog Output Voltage Diff. Non-Linearity = 2V LSB 2V LSB V LSB Digital Input Differential Non-Linearity Differential Non-Linearity: Voltage step measure changes fluctuate with as advanced info increments. In a perfect world every progression ought to be identical.

Integral Non-Linearity Integral Non-Linearity: Occurs when the yield voltage is non direct. Fundamentally a powerlessness to hold fast to the perfect slant. Perfect Output Analog Output Voltage Int. Non-Linearity = 1V LSB 1V LSB Digital Input

Non-Monotonic Output Error Non-Monotonic Output Error: Occurs when the an expansion in advanced info brings about a lower yield voltage. Wanted Output Non Monotonic Analog Output Voltage Digital Input

Poor Resolution(1 bit) V out Desired Analog flag 1 2 Volt. Levels 0 Digital Input Approximate yield Resolution Errors Does not precisely estimated the fancied yield due vast voltage divisions.

Better Resolution(3 bit) V out Desired Analog flag 111 110 8 Volt. Levels 101 100 011 010 001 000 Digital Input Approximate yield Resolution Errors Better guess of the of the coveted yield motion because of the littler voltage divisions.

Analog Output Voltage +V LSB Expected Voltage - V LSB Time Settling time Settling Time and Overshoot Settling Time : The time required for the voltage to settle inside +/ - the voltage connected with the V LSB . Any adjustment in the info time won\'t be reflected instantly because of the slack time. Overshoot: happens when the yield voltage overshoots the wanted simple yield voltage.

Common Applications Audio: Most present day sound signs are put away in advanced frame (for instance MP3s and CDs ) and so as to be heard through speakers they should be changed over into a simple flag Video: Video signals from a computerized source, for example, a PC, must be changed over to simple shape in the event that they are to be shown on a simple screen. http://en.wikipedia.org/wiki/Digital-to-analog_converter

References Alciatore, "Prologue to Mechatronics and Measurement Systems," McGraw-Hill, 2003 Horowitz and Hill, "The Art of Electronics," Cambridge University Press, 2 nd Ed. 1995 http://products.analog.com/items/info.asp?product=AD7224 http://courses.washington.edu/jbcallis/addresses/C464_Lec5_Sp-02.pdf http://www.eecg.toronto.edu/~kphang/ece1371/chap11_slides.pdf Previous understudies\' addresses on DAC

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