The resistance r is normally selected any value between 2. The voltagemode binaryweighted resistor dac shown in figure 1 is usually the simplest. Equivalent offset voltage at the input of the gain stage a. Also please note that while discussing dac, whenever we are talking about resolution, it is not actually the resolution of dac rather. Summing amplifier is an opamp voltage adder electronicstutorials. Hopefully, experiences with this unit will increase demand for other r 2r dacs and, more broadly, well designed hiend dacs in general. The dac is an inverted r2r ladder network that con verts a digital input 12 data bits. In this video, we discuss r2r ladder dac, inverted type r 2r ladder dac this type of dac and very important topic for gate exam. An improved switch compensation technique for inverted r. In general, the inversion layer current of an mos transistor consists of a drift. Although r2r ladders are commonly used as digitaltoanalog converter dac cores, complete equivalent circuits are still missing from the literature for most of the configurations used in practice.
The dac implementation in this project is based on a 10bit r 2r ladder input stage followed by a 3stage opamp configured as a noninverting voltage follower. The problem with dynamic response for higher frequencies causing probably from time constant at the output node of a ladder it seems to be around 2us and the current capability of microcontroler. Dac output drives the inverting input of an op amp, with the output voltage. R2r ladder dac current switched watch more videos at lecture by. Although simple in design and function, applying an r 2r resistor network to a real application requires attention to how the device is specified.
The dac is designed to operate at 25mhz while driving a capacitive load of up to 30pf and a resistive load as low as 5k. 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 summing amplifier with the r2r ladder of resistances shown produces the output. We learned the output analog voltage expressions for r2r ladder type dac and various advantages and disadvantages of it. The ladder is formed by resistance r in the series path and resistance 2r in. 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. In current mode or inverted ladder type dacs, the stray capacitance do not affect the. Digital to analog converters, binary weighted resistor, r2r. In this session, were going to be putting together a simple dac so that later on we can use our logic circuits to put out analog control voltages. This terminal out is commonly used to drive an operational amplifier.
The r2r ladder dac makes use of only two resistor valuesbut it requires 2 n resistors to implement an nbit converter. Details of the dac design is present below in section 2. The r2r ladder dac is an 8bit digital to analog converter. The r 2r ladder dac is an 8bit digital to analog converter. It uses resistors of only two different values, and their ratio is 2. An intuitive way to consider the r2r dac is as a binary weighted. Jun 18, 2015 now see the practical circuit arrangement of 4bit r 2r ladder da converter using op amp. It covers weighted resistor dac, r 2r inverting ladder dac, r 2r noninverting ladder dac etc. The r2r dac digitaltoanalog converter digitalanalog. Dac converts digital information into analog information either voltage or current.
The r2r network consists of resistors with only two values r and 2xr. Max5352max5353 lowpower, 12bit voltageoutput dacs with. As an example, suppose we wish to have a dac with an output range of 0 v to 2. R2r ladder dac the upper circuit in the figure to the right illustrates a section of a periodic network. Jul 31, 2017 welcome to the course on digital electronics. An 8bit value from the microcontroller port will be converted into an equivalent analog voltage by means of the r 2r resistor network. Standard r2r ladder networks availability is as follows.
In this video, we discuss r 2r ladder dac, inverted type r 2r ladder dac this type of dac and very important topic for gate exam. Gowthami swarna, tutorials point india private limited. As the name implies, current mode dacs operates based on the ladder currents. Although r 2r ladders are commonly used as digitaltoanalog converter dac cores, complete equivalent circuits are still missing from the literature for most of the configurations used in practice. String resistor network is good for, say, up to 10 bit dac requiring 1024 identical resistors. Therefore, inverting input is at virtual ground v3 v2 v1 v0 find equivalent resistance r2r dac example cont.
Digital to analog conversion the r2r dac tektronix. The most popular networks are the binary weighted ladder and the r2r ladder. The r2r ladder dac makes use of only two resistor values, but it requires 2n. As we know dac is the short form of d to a converter. To compare the output of both circuits to determine which of the two methods is more accurate and efficient to use as a digitaltoanalog converter 3. The r 2rnetwork consists of resistors with only two values r and 2xr. In the currentmode r2r ladder dac shown in figure 6. Soekris dam1021 sign magnitude r2r dac h i f i d u i n o but the original, allencompassing, source of info, including direct input from soren, the dacs designer, are the various threads on just search there. A digitaltoanalog converter prufrock poem pdf dac takes a set of binary levels and creates a single analog value. R2r ladder networksapplication note fixed resistors resistor ladder networks provide a simple, inexpensive way to perform digital to analog conversion dac. Da conversion using pwm and r2r ladders to generate. R2r ladder digital to analog converter dac the above figure shows the 4bit r2r ladder dac. This is the alternative mode of dac and is called so because, the 2r. R2r dac board 8bit digital to analog converter r2r network.
The currentinput comparator which results from combining the in. This change makes the r2r ladder a current divider rather than a voltage divider. In order to achieve highlevel accuracy, we have chosen the resistor values as r and 2r. Now see the practical circuit arrangement of 4bit r2r ladder da converter using op amp. Cmos can make acceptable amplifiers and processes combining bipolar and cmos.
The dac is an inverted r2r ladder network that con verts a digital input 10 data bits. Fixed resistors r2r ladder networks application note. Dac7821 r rfb vdd vref i 1out i 2out gnd db0 db11 12bit r2r dac input latch parallel bus cs rw dac7821 sbas365b october 2005 revised july 2007 12bit,parallel input, multiplying digitalto analogconverter 2. The digital inputs could be ttl voltages which close the switches on a logical 1 and leave it grounded for a logical 0. Output errors due to resistor tolerances are often overlooked in the design of the digital to analog conversion dac circuit and in the selection of the r 2r ladder itself. One of the most common dac buildingblock structures is the r 2r resistor ladder network shown in figure 4. The r2rnetwork consists of resistors with only two values r and 2xr. This is the alternative mode of dac and is called so because, the 2r resistance in the shunt path. Analog devices sharc dsp this r2r dac is not nos the yggy must be the most wellknown resistor ladder dac among audiophiles in the states. A digital to analog converter with an r 2r ladder network as shown in figure 2 eliminates these complications at the expense of an additional resistor for each bit. The summing amplifier with the r 2r ladder of resistances shown produces the output.
An improved switch compensation technique for inverted r2r. Digitaltoanalog conversion objectives understand how a weightedresister dac can be used to convert numbers with binary or nonbinary bit weightings understand the meaning of the terms used to specify dac accuracy ud t dh runderstand how an r2r l dd b d t2r ladder can be used to convert both unsigned and signed binary numbers. The operation of the above ladder type dac is explained with the binary word b1b0 01 the above circuit can be drawn as. 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. Lecture 9 digitaltoanalogue conversion compatibility. The dac implementation in this project is based on a 10bit r2r ladder input stage followed by a 3stage opamp configured as a noninverting voltage follower. Because of this a transimpedance output stage is required to convert from current output to voltage output. If you want a 16bit dac, you would need 65536 resistors. But in case of r2r ladder da converter, resistors of only two value r and 2r are used. Both devices will convert digital voltage information to analog, but the. Weighted resistors da converter circuit and binary ladder or r2r ladder da converter circuit.
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 r 2r ladder dac makes use of only two resistor values, but it requires 2n resistors to implement the nbit conversion. Jan 26, 2018 r 2r ladder dac current switched watch more videos at lecture by. R2r ladder da converter electronics engineering study center. The r2r dac circuit is an alternative to the binaryweightedinput r2nr dac which uses fewer unique resistor values r2r dac vs. A new switch compensation technique for inverted r2r ladder.
Standard r2r ladder networks have a resistance tolerance of 2. Data converters dac design 2009 page 11 r2r ladder dac how does it work. An r2r ladder is a simple and inexpensive way to perform digitaltoanalog conversion, using repetitive arrangements of precise resistor networks in a ladderlike configuration. A resistor ladder is an electrical circuit made from repeating units of resistors. The r2r resistor ladder network directly converts a parallel digital. This will produce a bipolar output voltage which will swing from 3.
To design a 4bit digital to analog converter using r2r ladder 2. An r2r dac using three digital input levels rather than two is pro posed as well as a. We only need 1r and 2r pair for each bit of resolution. Weighted resistors da converter here an opamp is used as summing amplifier. This type of dac utilizes thevenins theorem in arriving at the desired output voltages.
If you dont want to do it with an r2r ladder, then consider a thermometer dac, which is an ageold principle. The 16channels 12bit r2r dac contains a three principal blocks. The r2r dac is a more complex method of realizing a r2r than, for instance, a string dac. Jul 29, 2015 analog devices sharc dsp this r 2r dac is not nos the yggy must be the most wellknown resistor ladder dac among audiophiles in the states. The r 2r dac circuit is an alternative to the binaryweightedinput r 2nr dac which uses fewer unique resistor values r 2r dac vs. The digital input to the dac is a 4bit binary number represented by bits b0, b1, b2 and. Optimal design of r2r ladder based dac with better. To design a 4bit digital to analog converter using r 2r ladder 2. Dac r2r network calculation this applet calculates the output voltage of a r2r network for a digital to analog converter.
An nbit dac requires 2n resistors, and they are quite easily trimmed. This voltage are used in more applications, because of their increasingly efficient, reliable, and economical operation with the development of the microprocessor, data processing has become an integral part of various systems data processing involves transfer of data to and from the microcomputer via inputoutput devices. The r2r ladder the r2r ladder dates to the 1960s, as exemplified by the circuit shown in figure 1 1. Fig 2 shows the schematic layout of 4bit r2r ladder base d dac. Request pdf an improved switch compensation technique for inverted r2r ladder dacs many recent applications are based on dsps interfaced to. Switches, resistors, opamps are used to implement dac. Making a pure r2r resistor ladder dac with adjustable offset. A disadvantage of the former dac design was its requirement of several different precise input resistor values. Problem with r2r ladder dac r2r ladder is also a binary weighted network. An 8bit value from the microcontroller port will be converted into an equivalent analog voltage by means of the r2r resistor network. R2r ladder many da converters are constructed with an internal resistor network driven by digital output drivers. R 2r ladder dac the upper circuit in the figure to the right illustrates a section of a periodic network. Rt the terminating resistor is always connected to ground.
The inverting input terminal of the op amp work as a summing amplifier for the ladder inputs. The calculation includes non ideal resistors and the load at the r2r network output. This is illustrated for 4 bits, but can be extended to any number with just the resistance values r and 2r. Lecture 9 digitaltoanalogue conversion compatibility mode. Naturally we choose an r2r dac, and thus require a 2. Here, resistors 78 81 are equal to r, and 7177 are equal to 2r, with units 6064 acting as switches. Two configurations are discussed below, a string resistor ladder and an r2r ladder.
In ladder circuit the output voltage is also weighted sum of the corresponding digital input. 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. Therefore, inverting input is at virtual ground v3 v2 v1 v0 find equivalent resistance r 2r dac example cont. If the inputs resistors, r1, r2, r3 etc, are all equal a unity gain inverting. R 2r resistor ladder digital to analog converter objective. An enhancement of the binaryweighted resistor dac is the r 2r ladder network. If the resistors are selected correctly you can shift in a sequence of ones thermometer goes up to generate a cosinusoidal half wave current, followed by shifting in a sequence of zeros shifting the ones out, thermometer goes down for the second. A new switch compensation technique for inverted r2r.
R 2r ladder dac current switched watch more videos at lecture by. The circuit can be viewed as a voltagemode digitaltoanalog converter dac or a programmable attenuator operating on the signal. The chief benefit of the r 2r dac is that the number of resistors required to realize the design is much fewer than the string dac. Difference between dac typesweighted resistor,r2r ladder. Ee247 lecture 14 university of california, berkeley. Monolithic r2r resistor networks are available from various resistor component manufacturers, making it easy to incorporate them into your designs. The operation of r 2r ladder dac is easily explained considering the weights of the different bits one at a time. Dac core consist of 16 identical r2r dac, each of which include differential r2r ladder and output operational amplifier ab class. The basic idea is to produce current io, 2io, 4io etc. In this lecture, we discussed about the noninverting and inverting r2r ladder type dac. The max5354max5355 combine a lowpower, voltage output, 10bit. An intuitive way to consider the r 2r dac is as a binary weighted. There are four resistors r, 2r, 4r and 8r at the input terminals of the opamp with r as feedback resistor.
Finally a third section is added to provide a threebit binary current division. Each bit in the circuit controls a switch between ground and the inverting input op amp. The r2r resistor ladder based digitaltoanalog converter dac is a simple, effective, accurate and inexpensive way to create analog voltages from digital values. An enhancement of the binaryweighted resistor dac is the r2r ladder network. The mdac, or multiplying dac, as seen in figure 2, uses a very similar topology the same r2r ladder in fact except that the position of the reference input node and the output node are swapped.
The operation of r2r ladder dac is easily explained considering the weights of the different bits one at a time. A digital to analog converter with an r2r ladder network as shown in figure 2 eliminates these complications at the expense of an additional resistor for each bit. R2r ladder dacs in production 2015 discussion in audio hardware started by jh901, jul 29, 2015. The output of this dac is obtained from the leftmost ladder node. R 2r ladder many da converters are constructed with an internal resistor network driven by digital output drivers. Apr 04, 2016 the r 2r dac is a more complex method of realizing a r 2r than, for instance, a string dac. This is the alternative mode of dac and is called so because, the 2r resistance in the shunt path is switched between two voltages named as vl and vh. Hopefully, experiences with this unit will increase demand for other r2r dacs and, more broadly, well designed hiend dacs in general. The second network cascades a second section onto the first, replacing the 2r termination resistor. Digital to analog converter dac architecture and its.
If each input is supplied either 0 volts or reference voltage, the output voltage will be an analog equivalent of the binary value of the three bits. The max5352max5353 combine a lowpower, voltage output, 12bit. In the voltage mode r2r ladder dac shown in figure 5, the rungs or arms. The chief benefit of the r2r dac is that the number of resistors required to realize the design is much fewer than the string dac. R2r ladder da converter electronics engineering study. It covers weighted resistor dac, r2r inverting ladder dac, r2r noninverting ladder dac etc. To design a 4bit digital to analog converter using binary weighted resistors 3. It is not necessary that each rung of the r2r ladder use the same resistor values. Da conversion using pwm and r2r ladders to generate sine. R 2r ladder digital to analog converter dac the above figure shows the 4bit r 2r ladder dac. An improved switch compensation technique for inverted r2r ladder dacs article in circuits and systems i. Where n is the number of r2r elements in the dacs r2r ladder.