Analogue to digital and digital to analogue converters. The digital inputs could be ttl voltages which close the switches on a logical 1 and leave it grounded for a logical 0. The number of digits per binary word is assumed to be two i. There is, of course, far more to any dac than conversion itself. An r2r ladder is a simple and inexpensive way to perform digitaltoanalog conversion, using repetitive arrangements of precise resistor networks in a ladderlike configuration. What is the advantage of r2r ladder dacs over those that use binary weighted resistors. To overcome huge range of resistor used in weighted resistor da converter, r2r ladder da converter is introduced. An enhancement of the binaryweighted resistor dac is the r2r ladder network. Fixed resistors r2r ladder networks application note. This terminal out is commonly used to drive an operational amplifier. Basics of r2r ladder dac digital analog conversion, tutorial r2r dac thevenin superposition. A disadvantage of the former dac design was its requirement of several different precise input resistor values. The al12a has a r2r ladder block for 8bit and an opamp block for driving output.
Instrumentation and industrial designs by delabs and generic application designs. Ad7533 cmos low cost, 10bit multiplying dac data sheet. Digital to analog with r2r ladder network this is a r2r digital to analog converter, it converts a byte 8 bit to a analog value. It works by the principle of superposition where switching on binary inputs adds more voltage at the output. Pdf 4bit digital to analog converter using r2r ladder and binary. Ee247 lecture 15 university of california, berkeley. It uses resistors of only two different values, and. This type of dac utilizes thevenins theorem in arriving at the desired output voltages. While googling around, i came across a priceless snippet on wikipedia which read. Digital to analog converter dac architecture and its. The following circuit diagram shows the basic 2 bit r 2r ladder dac circuit using opamp.
The r2r ladder dac makes use of only two resistor valuesbut it requires 2 n resistors to implement an nbit. The most popular networks are the binary weighted ladder and the r 2r ladder. The resistors are wired in a ladder fashion, with resistors of the same value being used for the rails, and resistors with 2x that v alue being used f or the digital por t outputs. The r2r network consists of resistors with only two values r and 2xr. R2r ladder converter it is not easy to construct a resistorbased dac with a high resolution, due to the resistance spread, and the needs for n 2 serial resistors.
Optimal design of r2r ladder based dac with better. Output of the r2r ladder block is driven by opamp sec asic 5 11 analog al12a, typ this digital to analog converter consists of a r2r maximum conversion rate. Analogue to digital and digital to analogue converters adcs and dacs are some of the most important components in measurement and control technology. The r 2r network consists of resistors with only two values r and 2xr. Their job is to transfer information between the real world and the digital world as faithfully as possible. Well, it is just a cleverly arranged set of resistors that gives you the unique action of. R2r ladder digital to analog converter dac the above figure shows the 4bit r2r ladder dac. But the vital problem in weighted register da converter is use of huge range of different resistance. R2r ladder da converter electronics engineering study.
In this configuration the r2r ladder behaves as a binary weighted voltage divider, instead of a current divider, and the high impedance input of the amplifier input keeps the divider isolated from the load. Nevertheless, this simple circuit illustrates the operation of the r2r ladder function. The effective impedance to ground is 3r, so the current injected into the r2r ladder is i 0 v ref 3r. Most applications require the addition of only an output operational amplifier and a voltage or current reference. Construction of digitaltoanalogue converters using different techniques, namely the scaled resistors into summing junction, and the r2r ladder. Study of r2r 4bit and 8bit dac circuit using multisim. Digital to analog converter georgia institute of technology. It covers weighted resistor dac, r2r inverting ladder dac, r2r noninverting ladder dac etc. An enhancement of the binaryweighted resistor dac is the r 2r ladder network. The main disadvantage is a shortcoming of some sort in the treble.
Rt the terminating resistor is always connected to ground. This board is useful for students to study and understand the operation of r2r ladder circuit as 4 bit digital to. R2r resistor ladder digital to analog converter objective. Assuming that the daq digital output high level is exactly 5v, what is the full scale value largest output of the dac in this exercise. The most popular networks are the binary weighted ladder and the r2r ladder.
Da conversion using pwm and r2r ladders to generate. Digitaltoanalog conversion this worksheet and all related files are. The objective of this exercise is to explore the concepts of digital to analog conversion making use of the cmos inverter as reference switches for a resistor ladder divider used in dac. The high speed dac design uses a high speed ingaasgaas hemt device in its summer block. One of the most common dac buildingblock structures is the r2r resistor ladder network shown in figure 4. Joint pdf of a random variable affected by two uniformly. The application of multisim for realizing r2r dac bridges the gap be. Resistor string dacs continued serial charge redistribution dacs charge scaling dacs r2r type dacs. This is illustrated for 4 bits, but can be extended to any number with just the resistance values r and 2r. Well, it is just a cleverly arranged set of resistors that gives you the unique action of turning binary signals into an analogue output voltage. The biggest problem is the large difference in resistor values between the lsb. Two configurations are discussed below, a string resistor ladder and an r2r ladder.
R2r 12 bit ladder dac extra gnd gnd di 02 d3 d4 output 6. The summing amplifier with the r2r ladder of resistances shown produces the output. The r2r ladder dac makes use of only two resistor valuesbut it requires 2 n resistors to implement an nbit converter. This page covers difference between various dac types including block diagram, equation etc. Ee247 lecture 14 administrative issues midterm exam postponed to thurs. R 2r digital to analog converter pdf r2r ladder popularity because the r2r thinfilm resistor dac in the successive. In current mode or inverted ladder type dacs, the stray capacitance do not affect the. Digital to analog conversion circuits and experiment on 4bit r2r. R2r ladder many da converters are constructed with an internal resistor network driven by digital output drivers. An inverted r 2r ladder structure is used, that is, the binarily weighted. The 3 msbs are thermometer coded, while the lower 6 bits are a straight r2r ladder. Abstract 4bit high speed r2r ladder digital to analog converter dac design is presented in this paper. In my previous post i discussed about weighted resistor da converter.
Although the resistors must be precisely matched, the actual value of the resistors is not critical. Mt016 buffer amplifiers have offset, of course, and this can cause nonmonotonicity in a buffered. R2r ladder dac explained with solved example duration. If your page number is set as 1, then the two output pdf files will contains the first page and the later three pages respectively. Explain how this digitaltoanalog converter dac circuit is. A typical thermometer plus r2r architecture 1 would include the 64x branch in the r2r ladder, hence placing 2 resistors in the 64x branch and adding a resistor between the 32x and 64x branches. A certain sixbit dac uses binaryweighted resistors. Scientech db16 digital to analog converter r 2r ladder is a compact, ready to use experiment board for digital to analog converter using r2r ladder. R2r topologies for dacs the currentmode r2r dac the r2r dac can be classi. This is the alternative mode of dac and is called so because, the 2r.
Differentiator using opamp, rahul and divyansh duration. Both devices will convert digital voltage information to analog, but the. To begin with, an r2r ladder circuit is a seriesparallel circuitwhich includes both series and parallel connections of that contains only two resistor components values. The dac circuits we have looked at, has some practical limitations. One of the most common dac buildingblock structures is the r2r resistor ladder. This paper justifies the use of hemt devices for high speed converter applications. As far as i understand it, the primary advantage of r2r is the absence of prepost ringing. Digital to analog conversion circuits and experiment on 4bit r2r dac. An r 2r ladder is a simple and inexpensive way to perform digital to analog conversion, using repetitive arrangements of precision resistor networks in a ladder like configuration. Ph315 portland state university digital to analog converter dac 1.
Lab 10 analog to digital and digital to analog conversion. Let the binary value b3 b2 b1 b0, if b31, b2b1b00, then the circuit is shown in the figure below it is a simplified form of the above dac circuit. A type of resistor network known as an r2r ladder is often used in. It uses high quality miniature latching relays and precision discrete resistors to achieve a level of performance unattainable with conventional potentiometers or mechanical switchbased rotary stepped attenuators. These r2r ladder designs take a different approach to conversion to analog from the typical oversampling delta sigma dacs. Currentmode operation has a larger switching glitch than voltage mode since the switches.
A resistor ladder is an electrical circuit made from repeating units of resistors. In order to achieve highlevel accuracy, we have chosen the resistor values as r and 2r. Making a pure r2r resistor ladder dac with adjustable. Binary weighted resistors and r2r ladder is designed and presented. What will happen to both resolution and fullscale output when v ref is increased by 20. Ee247 lecture 14 university of california, berkeley.
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