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. This is the output change that would occur for a change in the least significant bit. It is often necessary to convert analog signal to an accurate digital number, and vice versa. The r 2r network consists of resistors with only two values r and 2xr. An enhancement of the binaryweighted resistor dac is the r2r ladder network. 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. Analogue to digital and digital to analogue converters. Rather than using a second string of resistors, a binary r2r dac can be used to generate. Building one can be very simple, and the sound quality out of an r2r ladder is actually pretty good. Connects to the inverting terminal of external precision ivop amp for voltage.
We might call it entry level, but there is absolutely no entry level about. An r2r dac which has separate positive and negative references is shown in the figure below. Dac a reference input in 2quadrantmode, r2 terminal in 4quadrantmode. Analogue to digital and digital to analogue converters adcs and dacs are some of the most important components in measurement and control technology. Since publishing the above blog, tektronix is currently offering a free upgrade to 36 ghz spectrum analyzers and a free bundle of software. Digital to analog conversion circuits and experiment on 4bit r2r. For a 10bit r 2r there are 210 or 1024 possible binary combinations at the inputs. Making sound with digital logic usually calls for a digital to analog converter. Sam digitaltoanalog dac driver microchip technology. An enhancement of the binaryweighted resistor dac is the r 2r ladder network. The majority of modern audio converters utilize a switched capacitor. The transducers electrical analog output serves as the analog input to the adc. Fixed resistors r2r ladder networks application note.
The scheme achieves highspeed and lowpower operation thanks to the reference free technique. Dac a reference input in 2quadrant mode, r2 terminal in 4quadrant mode. Their job is to transfer information between the real world and the digital world as faithfully as possible. In 4quadrantmode, vrefa is driven by the external reference amplifier. Digital to analog converters dac 15 march 2006 doug hinckley lee huynh dooroo kim what is a dac. The architecture of a switchedcapacitor digitaltoanalog converter dac. Construction of digitaltoanalogue converters using different techniques, namely the scaled resistors into summing junction, and the r 2r ladder. An r2r ladderbased architecture for high linearity dacs.
Digital to analog conversion the r2r dac tektronix. Ee247 lecture 14 university of california, berkeley. Digital to analog conversion circuits and experiment on 4bit r2r dac. Adc and dac circuits download book free computer books. This type of dac utilizes thevenins theorem in arriving at the desired output voltages. A digital to analog converter dac converts a digital signal to an analog voltage or current output. Data converters dac design 2009 page 11 r2r ladder dac how does it work. R2r dac dc simulation in this post, the exact transfer function of an r2r dac will be developed for arbitrary ladder resistors and voltage references. Pdf an r2r ladderbased architecture for high linearity dacs. The dac will typically have the converter itself and a collection of support circuitry built into the chip.
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