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 r 2r network consists of resistors with only two values r and 2xr. 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. The nonlinear transfer function allocates more quantization levels out of the total range. By alan wolke 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 r 2r resistor ladder network as shown in figure 1below figure 1. Digital to analog conversion dac r2r ladder dac current dependent on bits position the current is divided by a factor of 2 at each node 08. The future of all kinds of applications that require a submilliwatt.
In a 4bit da converter, from 0000 to 1111, there are 15 discrete levels and hence it is convenient to divide the output analog signal into 15 discrete levels. Difference between dac typesweighted resistor,r 2r ladder. Two configurations are discussed below, a string resistor ladder and an r2r ladder. Therefore, for circuit stability, compensation capacitor c1 1pf to 5pf typ can be. Oct 18, 2014 digital to analog converter dac r 2r ladder dac general concept. The operation of r 2r ladder dac is easily explained considering the weights of the different bits one at a time. The operation of r2r ladder dac is easily explained considering the weights of the different bits one at a time. One of the most common dac buildingblock structures is the r2r resistor ladder. The experimental and measurement results show that the maximum frequency of the singlechip fourchannel 12bit r2r ladder highvoltage radiationtolerant dac is 100 khz, and the designed dac. 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.
Note that summing circuits are sometimes also referred to as summer circuits. Size size of a dac coressponds to number of binary inputs to it. If you were going to design a 16bit dac for audio purposes for a mp3 player output, how would the resistor tolerances affect the errors in the output for an r2r ladder dac. Details of the dac design is present below in section 2. The r 2r ladder is connected to an external reference input vref that. The r 2r ladder dac makes use of only two resistor values, but it requires 2n resistors to implement the nbit conversion. Da conversion using pwm and r2r ladders to generate sine. Ee247 lecture 14 university of california, berkeley. An 8bit value from the microcontroller port will be converted into an equivalent analog voltage by means of the r2r resistor network. 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. 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. In the voltage mode r2r ladder dac shown in figure 3. The most popular networks are the binary weighted ladder and the r2r ladder.
This is the alternative mode of dac and is called so because, the 2r resistance in the shunt path. Data converters dac design 2009 page 11 r 2r ladder dac how does it work. The dac1421 r 2r dac circuit is fully isolated from the noisy computer usb interface and the spdif inputs are also all transformer isolated. R2r ladder digital to analog converter, dac youtube. The most popular networks are the binary weighted ladder and the r 2r ladder. Also, nonoversampling nos dac is considered in that article.
A disadvantage of the former dac design was its requirement of several different precise input resistor values. 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. Chapter 2 introduction to digital to analog converter university of. One of the most common dac buildingblock structures is the r 2r resistor ladder. Digital to analog converter dac architecture and its. An option in contrast to the binary weightedinput dac is the supposed r2r dac, which. 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. Pdf 4bit digital to analog converter using r2r ladder and binary. Low power 10bit sar adc in 65nm cmos technology diva. An 8bit value from the microcontroller port will be converted into an equivalent analog voltage by means of the r 2r resistor network. Difference between dac typesweighted resistor,r2r ladder.
This page covers difference between various dac types including block diagram, equation etc. The r2r network consists of resistors with only two values r and 2xr. Hopefully, experiences with this unit will increase demand for other r2r dacs and, more broadly, well designed hiend dacs in general. The r2r ladder dac which is a binaryweighted dac that uses a repeating cascaded structure of resistor values r and 2r. Pdf the use of a 4bit digitaltoanalog converter using two methods. In current mode or inverted ladder type dacs, the stray capacitance do not affect the. The r 2r ladder dac is an 8bit digital to analog converter. The main technical problem of dac type comparison is the various inner working of the devices.
Electronicsdigital to analog converters wikibooks, open. Kelvin divider string dac the simplest structure of all is the kelvin divider or string dac as shown in figure 6. To design a 4bit digital to analog converter using binary weighted resistors 3. The r 2r dac circuit is an alternative to the binaryweightedinput r2nr dac which uses fewer unique resistor values. R2r dac board 8bit digital to analog converter r2r network. Counter type ad converter here one input of comparator is connected to the analog signal i. Next we will look at the various dac architectures. Unfortunately, the wikipedia page on r2r ladder dacs is incorrect when it says that the r2r ladder functions as a current divider in this application. 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 calculation includes non ideal resistors and the load at the r2r network output. This improves the precision due to the relative ease of producing equal valuedmatched resistors.
R2r ladder dacs in production 2015 steve hoffman music. An nbit version of this dac simply consists of 2n equal resistors in series. Pcm digitalanalog converter may be based on either resistor matrix r2r or sigmadelta modulator sdm. There is, of course, far more to any dac than conversion itself. This paper presents a dac architecture based on the conventional r2r ladder topology that is able to derive. R 2r ladder r 2r ladder r 2r ladder r 2r ladder r 2r ladder r 2r ladder advantages only two resistor values r and 2r does not require high precision resistors disadvantage lower conversion speed than binary weighted dac specifications of dacs resolution speed linearity settling time reference voltages errors resolution smallest analog. Read this article about the comparison of the digitalanalog converter types, its advantages and disadvantages by. In the picture, the impact of dacs internal modules to sound quality was shown for various converter types. Therefore, dac type comparison can include a comparison of audio file converter quality or recording tool difference at least. The resolution of the ladder is the smallest possible output change r2r ladder networksapplication note fixed resistors for any input change to the ladder and is given by 12n where n is the number of bits. The r 2r ladder dac which is a binaryweighted dac that uses a repeating cascaded structure of resistor values r and 2r.
A nbit dac have n bit binary inputs, and any given time analog output voltage of a da view the full answer previous question next question. Understanding the r2r ladder digital to analog conversion stephen mendes. It explains how the r2r ladder works based on the combination of input voltages which affects the output voltage range. The spurious free dynamic range sfdr is the level of highest spurious tone relative to the. Analog to digital adc and digital to analog dac converters.
The r2r ladder dac makes use of only two resistor valuesbut it requires 2 n resistors to implement an nbit converter. R 2r digital to analog converter pdf r 2r ladder dac. Both devices will convert digital voltage information to analog, but the. Feb 20, 2015 it explains how the r 2r ladder works based on the combination of input voltages which affects the output voltage range. For additional information see the following link for the r2r ladder digital. R 2r ladder digital to analog converter dac the above figure shows the 4bit r 2r ladder dac. While an r2r ladder can be used as a current divider, it actually functions as a voltage divider here. Simulation of a dac using r2r ladder using multisim. R 2r ladder dac vs sigmadelta pcm dac vs dsd dac read now.
As far as i understand it, the primary advantage of r2r is the absence of prepost ringing. R2r ladder networks application note fixed resistors. Pdf digital to analog conversion performance is mainly. R 2r resistor ladder dac the binary weighted resistor dac structure requires a. R 2r resistor ladder dac the binary weighted resistor dac. These r2r ladder designs take a different approach to conversion to analog from the typical oversampling delta sigma dacs. Building one can be very simple, and the sound quality out of an r2r ladder is actually pretty good. R2r ladder networksapplication note fixed resistors resistor ladder networks provide a simple, inexpensive way to perform digital to analog conversion dac. We only need 1r and 2r pair for each bit of resolution. The r2r ladder dac is an 8bit digital to analog converter. For a digital value val, of a r2r dac with n bits and 0 vvref logic levels. The successive approximation or cyclic dac, which successively constructs the output during each cycle. In order to achieve highlevel accuracy, we have chosen the resistor values as r and 2r. R2r dac input latch parallel bus cs rw dac7821 sbas365b october 2005 revised july 2007 12bit,parallel input, multiplying digitalto analogconverter 2.
Dac a reference input in 2quadrant mode, r2 terminal in 4quadrant mode. The r2r dac is a more complex method of realizing a r2r than, for instance, a string dac. Comments 0 copies 1 there are currently no comments. The dac1421 r2r dac circuit is fully isolated from the noisy computer usb interface and the spdif inputs are also all transformer isolated. An analogtodigital converter adc performs the reverse function there are several dac architectures. Hopefully, experiences with this unit will increase demand for other r 2r dacs and, more broadly, well designed hiend dacs in general. An analogtodigital converter adc performs the reverse function. R 2r digital to analog converter pdf r2r ladder popularity because the r2r thinfilm resistor dac in the successive. The r2r dac circuit is an alternative to the binaryweightedinput r2nr dac which uses fewer unique resistor values. Dac r2r network calculation this applet calculates the output voltage of a r2r network for a digital to analog converter. An enhancement of the binaryweighted resistor dac is the r 2r ladder network. This is the alternative mode of dac and is called so because, the 2r.
To design a 4bit digital to analog converter using r2r ladder 2. R2r ladder digital to analog converter dac the above figure shows the 4bit r2r ladder dac. As far as i understand it, the primary advantage of r 2r is the absence of prepost ringing. If each input is supplied either 0 volts or reference voltage, the output voltage will 1. The r2r resistor ladder network directly converts a parallel digital symbolword into an analog voltage. It covers weighted resistor dac, r2r inverting ladder dac, r2r noninverting ladder dac etc. If you recall, the classic inverting summing circuit is an operational amplifier using negative feedback for controlled gain, with. Dac digital to analogue converter as i described earlier the primary use of the binary weighted resistor ladder is for digital to analogue conversion as a dac. The r 2r ladder dac design was the starting point for the totaldac project. The r 2r resistor ladder network directly converts. Students use the electronic circuit simulation packages available 1,2 in the computer lab to analyze the binary weighted and r2r ladder type circuits. An intuitive way to consider the r2r dac is as a binary weighted. 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.
When we refer to dacs here we are referring to the basic converter rather than the complete system. The r2r dac digitaltoanalog converter digitalanalog. An r2r ladder is a simple and inexpensive way to perform digitaltoanalog. As the case with the binaryweighted dac design, we can modify the value of the feedback resistor to obtain any span desired thus the r 2r ladder logic is implemented using op amp 741, simulated output waveform is implemented using the solid thinkingactivate tool. Digital to analog conversion dac r 2r ladder dac current dependent on bits position the current is divided by a factor of 2 at each node 08. Pdf an r2r ladderbased architecture for high linearity. 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. While the resolution for r2r ladder type dac with voltage output is resolution example. R2r ladder many da converters are constructed with an internal resistor network driven by digital output drivers. An enhancement of the binaryweighted resistor dac is the r2r ladder network. The audio dac is a lowfrequency, highresolution type while the video dac is a highfrequency low to. The r2nr dac circuit, otherwise known as the binaryweightedinput dac, is a variation on the inverting summing opamp circuit. To design a 4bit digital to analog converter using r 2r ladder 2.
Weighted resistor type digitaltoanalog converter in the weighted resistor type da converter, each digital voltage is converted into an equivalent analog voltage or current. A resistor ladder is an electrical circuit made from repeating units of resistors. Jul 29, 2015 these r 2r ladder designs take a different approach to conversion to analog from the typical oversampling delta sigma dacs. R2r ladder resistor dac results v performance summary inputbinary output voltagev 0000 0. Different types of internal dacs, including resistive string, r2r, capacitive, and.
Suggest the values of resistors and reference voltage if resolution required is 0. There are two ways in which the r2r ladder network may be used as a dacknown. It covers weighted resistor dac, r 2r inverting ladder dac, r 2r noninverting ladder dac etc. R2r ladder r2r ladder r2r ladder r2r ladder r2r ladder r2r ladder advantages only two resistor values r and 2r does not require high precision resistors disadvantage lower conversion speed than binary weighted dac specifications of dacs resolution speed linearity settling time reference voltages errors resolution smallest analog.
The experimental and measurement results show that the maximum frequency of the singlechip fourchannel 12bit r 2r ladder highvoltage radiationtolerant dac is 100 khz, and the designed dac. In electronics, a digitaltoanalog converter dac, da, d2a, or dtoa is a system that converts a digital signal into an analog signal. This type of dac utilizes thevenins theorem in arriving at the desired output voltages. Data converters dac design 2009 page 11 r2r ladder dac how does it work. In addition, a lab assignment illustrates the construction of a r2r ladder type dac, and the use of this circuit to generate waveforms. Understanding the r2r ladder digital to analog conversion. Digital to analog conversion the r2r dac tektronix. An r2r ladder is a simple and inexpensive way to perform digitaltoanalog conversion, using repetitive arrangements of precise resistor networks in a ladderlike configuration. Vincent brient spent 2 years and 5 pcb revisions to improve upon it and finally opted for 0. The r2r ladder dac design was the starting point for the totaldac project. An r2r ladderbased architecture for high linearity dacs. Dacdigital to analog converter linkedin slideshare. Nov 05, 2015 making sound with digital logic usually calls for a digital to analog converter.
Fig 2 shows the schematic layout of 4bit r2r ladder base d dac. Da conversion using pwm and r2r ladders to generate. R 2r ladder many da converters are constructed with an internal resistor network driven by digital output drivers. The r2r resistor ladder network directly converts a parallel digital symbolword. Fixed resistors r2r ladder networks application note. Optimal design of r2r ladder based dac with better. 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.
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