R2r ladder network is fully integrated electronic products. Da conversion using pwm and r2r ladders to generate sine and dtmf waveforms. The most popular networks are the binary weighted ladder and the r2r ladder. The r2r ladder dac overcomes the disadvantages of a binary weighted resistor dac. Digital to analog conversion the r2r dac, alan wolke, may 20. There is an interesting method, however, that uses a ladder network to significantly reduce the number of resistors. To help apprehend this, a diagram of an r2r ladder circuit is placed below. Digital to analog converter r2r binary ladder duration. Alan wolke has already explained about the proof of the impedance r2r ladder is equal to r using thevenin equivalent analysis at his blog. You can think of a resistor ladder as a multileveled voltage divider. Digital to analog conversion the r2r dac tektronix.
Using a ladder network is a common way of creating an 8 bit dac digital to analogue converter as each control bit contributes to a binary weighted output. I used to have a whole bunch of em, for various dds projects, but not anymore. International journal for research in applied science. In the voltage mode r2r ladder dac shown in figure 5, the rungs or arms of the ladder are. Similarly it can be found that using above process for bit 0100 the output will be v r 4, for bit 0010 output will be vr8 and for bit 0001 output will be vr16 by using superposition theorem we can find in any nbit ladder network the. By putting all of the resistances of the circuit above to the same value r, the opamp will have a voltage gain of unity and an output voltage equal. Show that 1 ss 11 22 vvv, 2 2 11 24 vvv, 3 3 ss 11 28 vvv and 4 4 ss 11 216 vvv solution reduce the circuit using equivalent resistances as follows. 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. Fig 2 shows the schematic layout of 4bit r2r ladder base d dac. R2r resistor ladder digital to analog converter objective. Figure 1 shows two varieties of segmented voltageoutput dac. A disadvantage of the former dac design was its requirement of several different precise input resistor values. Digital to analog converter using r2r ladder pdf r 2r digital to analog converter pdf.
The voltagemode binaryweighted resistor dac shown in figure 1 is usually the simplest textbook example of a dac. There are two ways in which the r2r ladder network may be used as a dacknown respectively as the. If you want a 16bit dac, you would need 65536 resistors. Basics of r2r ladder dac digital analog conversion, tutorial. The r2rnetwork consists of resistors with only two values r and 2xr. R2r ladder dac explained with solved example youtube.
This integrated format results in over a 50% reduction in board space compared to conventional discrete, thickfilm r2r ladder implementations. 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. Computer aided manufacturing tech 453350 2 ladder logic learning objectives. Fixed resistors r2r ladder networks application note. Optimal design of r2r ladder based dac with better. This terminal out is commonly used to drive an operational amplifier. A basic fourbit r2r voltagemode dac is shown in figure 3. Either way, r2r ladder networks have low emi emissions, and reduced high frequency har. The commercial digitaltoanalogconverters have those resistor networks on board, within their integrated circuits, associated with an operational amplifier. The following circuit diagram shows the basic 2 bit r2r ladder dac circuit using opamp.
Lecture 9 digitaltoanalogue conversion compatibility. The number of digits per binary word is assumed to be two i. This is the alternative mode of dac and is called so because, the 2r. The operation and characteristics of voltagemode r2r.
The r2r resistor ladder network directly converts a parallel digital symbolword into an analog voltage. The operation of r2r ladder dac is easily explained considering the weights of the different bits one at a time. R2r ladder network is fully integrated the ipec r2r precision ladder network combines 16 resistors in a standard ladder configuration in 25 or 50mil pitch surfacemount packages. Rt the terminating resistor is always connected to ground. In current mode or inverted ladder type dacs, the stray capacitance do not affect the. This page covers difference between various dac types including block diagram, equation etc. Basics of r2r ladder dac digital analog conversion. This configuration consists of network of resistors alternating in value of r and 2r.
From there, we can conclude that each bit in r2r ladder is a binary weighting function to the voltage output of the r2r ladder. As the name suggests, r2r ladder dac produces an analog output, which is almost equal to the digital binary input by using a r2r ladder network in the inverting adder circuit. Mathematically analyzing this ladder network is a bit more complex than for the previous circuit, where each input resistor provided an easilycalculated gain for that bit. These structures, called r2r dacs, are discussed in the next section. Da conversion using pwm and r2r ladders to generate. Draw and explain r2r ladder network dac for 3 bitinput. As the ladder logic program is scanned, it reads the input data table then writes to a portion of plc memory the output data, table as it executes.
At the right of this network is output voltage vout. The r2r ladder network is commonly used for digital to analogue conversion and analogue to digital conversion by successive approximations. String resistor network is good for, say, up to 10 bit dac requiring 1024 identical resistors. An enhancement of the binaryweighted resistor dac is the r2r ladder network. Using a ladder network is a common way of creating an 8 bit dac digital to analogue converter as each control bit contributes to a binary weighted output voltage. An alternative to the binaryweightedinput dac is the socalled r2r dac, which uses fewer.
The r2r network consists of resistors with only two values r and 2xr. Figure shown below is a diagram of the basic r2r ladder network with n bits. The output of an avr port doesnt drive much current, if its voltages should stay near either ground output low or. Data in clean binary digital form can be converted to an analog form by using a summing amplifier. Now at n4, if we calculate the output analog equivalent voltage then we will get. The resistor ladder ill be demonstrating in this tutorial is an 8bit dac, this means it can produce 256 28 different voltage levels between 0 and 5v. It covers weighted resistor dac, r2r inverting ladder dac, r2r noninverting ladder dac etc. Currentmode ladder networks and cmos switches permit positive, negative, and ac vref as previously shown in figure 6. Ph315 portland state university digital to analog converter dac 1. R2r ladder networks application note fixed resistors. An r2r ladder is a simple and inexpensive way to perform digitaltoanalog conversion, using repetitive arrangements of precise resistor networks in a ladder like. Difference between dac typesweighted resistor,r2r ladder.
A resistor ladder is an electrical circuit made from repeating units of resistors. Sometimes we need a summing circuit to just add together two or more voltage signals without any amplification. With the recent announcement of the worlds fastest digital to analog converter dac from tektronix component solutions, i thought it would be interesting to take a quick tutorial tour through one of the simplest dac architectures the r2r resistor ladder network. The resolution of the ladder is the smallest possible output change r2r ladder networks application note fixed resistors for any input change to the ladder and is given by 12n where n is the number of bits. For example, a simple 4bit da converter can be made with a fourinput summing amplifier. This application note discusses the important parameters that should be considered when implementing dac designs using an r2r resistor ladder. The r2r dac circuit is an alternative to the binaryweightedinput r2nr.
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. Standard r2r ladder networks have a resistance tolerance of. Thats the only thing i can see that might be an issue might need to ac couple the ladder. Bolton this and the following chapter comes from the book programmable logic controllers by w. This type of dac utilizes thevenins theorem in arriving at the desired output voltages. While this is a simple implementation of an mdac, several others. Digital to analog converter georgia institute of technology. The main components used are an operational amplifier and r2r ladder network. R2r ladder networks example consider the r2r ladder network. Results 1 to 6 of 6 c2c ladder network rather than r2r dac question. The r2r ladder dac makes use of only two resistor valuesbut it requires 2 n resistors to implement an nbit converter.
R2r ladder da converter electronics engineering study. One of the most common dac buildingblock structures is the r2r resistor ladder. B1 b0 the typical value of feedback resistor is rf 2r. Arduino forum using arduino project guidance arduino uno audio output with r2r dac. R 2r digital to analog converter pdf r2r ladder popularity because the r2r thinfilm resistor dac in the successive. This video gives the basics of r2r resistor networks and their use for digital to analog conversion dac. 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. This is the output change that would occur for a change in the least significant bit. Two configurations are discussed below, a string resistor ladder and an r2r ladder. Both devices will convert digital voltage information to analog, but the r2r ladder has become the most popular due to the network s inherent accuracy superiority and ease of manufacture. The first edition of the book was published in 1996, which explains why the author commences the preface by saying. Construction of digitaltoanalogue converters using different techniques, namely the scaled resistors into summing junction, and the r2r ladder.
1303 467 819 577 1128 436 1197 28 1535 357 1562 1421 848 1194 495 185 421 263 1421 1143 1472 533 254 645 613 837 855 266 122 417 1250 1387 1298