Digital- to- analog converter - Wikipedia, the free encyclopedia. In electronics, a digital- to- analog converter (DAC, D/A, D. An analog- to- digital converter (ADC) performs the reverse function. There are several DAC architectures; the suitability of a DAC for a particular application is determined by six main parameters: physical size, power consumption, resolution, maximum sampling frequency, accuracy and cost. Digital- to- analog conversion can degrade a signal, so a DAC should be specified that has insignificant errors in terms of the application. DACs are commonly used in music players to convert digital data streams into analog audio signals. They are also used in televisions and mobile phones to convert digital video data into analog video signals which connect to the screen drivers to display monochrome or color images. These two applications use DACs at opposite ends of the speed/resolution trade- off. The audio DAC is a low speed high resolution type while the video DAC is a high speed low to medium resolution type. Discrete DACs would typically be extremely high speed low resolution power hungry types, as used in military radar systems. Very high speed test equipment, especially sampling oscilloscopes, may also use discrete DACs. Overview. In particular, DACs are often used to convert finite- precision time series data to a continually varying physical signal. An ideal DAC converts the abstract numbers into a conceptual sequence of impulses that are then processed by a reconstruction filter using some form of interpolation to fill in data between the impulses. A conventional practical DAC converts the numbers into a piecewise constant function made up of a sequence of rectangular functions that is modeled with the zero- order hold. Other DAC methods such as those based on delta- sigma modulation) produce a pulse- density modulated output that can be similarly filtered to produce a smoothly varying signal. As per the Nyquist. Digital sampling introduces quantization error that manifests as low- level noise added to the reconstructed signal. In a practical DAC, a filter or the finite bandwidth of the device smooths out the step response into a continuous curve. Instead of impulses, a conventional practical DAC updates the analog voltage at uniform sampling intervals, which is then interpolated via a reconstruction filter to continuously varied levels. These numbers are written to the DAC, typically with a clock signal that causes each number to be latched in sequence, at which time the DAC output voltage changes rapidly from the previous value to the value represented by the currently latched number. The effect of this is that the output voltage is held in time at the current value until the next input number is latched, resulting in a piecewise constant or staircase- shaped output. This is equivalent to a zero- order hold operation and has an effect on the frequency response of the reconstructed signal. The fact that DACs output a sequence of piecewise constant values (known as zero- order hold in sample data textbooks) or rectangular pulses causes multiple harmonics above the Nyquist frequency. Usually, these are removed with a low pass filter acting as a reconstruction filter in applications that require it. Other DAC methods (e. Applications. To illustrate, consider a typical long- distance telephone call. The caller's voice is converted into an analog electrical signal by a microphone, then the analog signal is converted to a digital stream by an ADC. HOME > PRODUCTS > Electromechanical > Switches > RF > RF Coaxial Switch. An RF Coaxial Switch is an. Our optical portfolio supports. RF Frequency Divider, Multiplier. Analog Devices amplifiers deliver high performance by combining circuit design and. The circuit described here uses a. Home > Technologies > Displays > Build your own optical. A conventional frequency-to-voltage converter. RF Modulator TV Switch Audio Video RCA Ant Input to. Blusmart Digital Optical Coax to Analog RCA Audio Converter Adapter with 3.28ft Optical Toslink Cable and 3.5mm. This page contain electronic circuits about RF at category rf converter circuit : Converter CircuitsCircuits and. RF Converter Circuits . The digital stream is then divided into network packets where it may be sent along with other digital data, not necessarily audio. The packets are then received at the destination, but each packet may take a completely different route and may not even arrive at the destination in the correct time order. The digital voice data is then extracted from the packets and assembled into a digital data stream. A DAC converts this back into an analog electrical signal, which drives an audio amplifier, which in turn drives a loudspeaker, which finally produces sound. Most modern audio signals are stored in digital form (for example MP3s and CDs) and in order to be heard through speakers they must be converted into an analog signal. DACs are therefore found in CD players, digital music players, and PC sound cards. Specialist standalone DACs can also be found in high- end hi- fi systems. These normally take the digital output of a compatible CD player or dedicated transport (which is basically a CD player with no internal DAC) and convert the signal into an analog line- level output that can then be fed into an amplifier to drive speakers. Similar digital- to- analog converters can be found in digital speakers such as USB speakers, and in sound cards. In Vo. IP (Voice over IP) applications, the source must first be digitized for transmission, so it undergoes conversion via an analog- to- digital converter, and is then reconstructed into analog using a DAC on the receiving party's end. Home > Satcom Solutions > Platinum RF/Fiber Links. Variety of RF and optical connectors. Locking switch circuit; Read More. In electronics, a digital-to-analog converter (DAC, D/A, D–A, D2A. This puts additional design constraints on the bandwidth of the conversion circuit. Optically isolated input, single-supply true. The trick that makes this possible is an optically isolated rectifier input circuit. RF can be sent along the Fibre optic cable for distances up to 6 km. This circuit uses a bootstrap follower as a simple modulator. Buy Insten Audio Converter - Optical Digital Toslink Coaxial Coax to Analog RCA R/L Audio. RCA CRF907 Compact RF Modulator. 4.5 stars 93 ratings. Given this inherent distortion, it is not unusual for a television or video projector to truthfully claim a linear contrast ratio (difference between darkest and brightest output levels) of 1. LCD panel that only represents 6 or 7 bits per channel. Video signals from a digital source, such as a computer, must be converted to analog form if they are to be displayed on an analog monitor. As of 2. 00. 7, analog inputs were more commonly used than digital, but this changed as flat panel displays with DVI and/or HDMI connections became more widespread. The DAC is usually integrated with some memory (RAM), which contains conversion tables for gamma correction, contrast and brightness, to make a device called a RAMDAC. A device that is distantly related to the DAC is the digitally controlled potentiometer, used to control an analog signal digitally. Mechanical. A stable current or voltage is switched into a low- pass analog filter with a duration determined by the digital input code. This technique is often used for electric motor speed control, but has many other applications as well. Oversampling DACs or interpolating DACs such as the delta- sigma DAC, use a pulse density conversion technique. The oversampling technique allows for the use of a lower resolution DAC internally. A simple 1- bit DAC is often chosen because the oversampled result is inherently linear. The DAC is driven with a pulse- density modulated signal, created with the use of a low- pass filter, step nonlinearity (the actual 1- bit DAC), and negative feedback loop, in a technique called delta- sigma modulation. This results in an effective high- pass filter acting on the quantization (signal processing) noise, thus steering this noise out of the low frequencies of interest into the megahertz frequencies of little interest, which is called noise shaping. The quantization noise at these high frequencies is removed or greatly attenuated by use of an analog low- pass filter at the output (sometimes a simple RC low- pass circuit is sufficient). Most very high resolution DACs (greater than 1. Higher oversampling rates can relax the specifications of the output low- pass filter and enable further suppression of quantization noise. Speeds of greater than 1. Hz) and resolutions of 2. DACs. A short comparison with pulse- width modulation shows that a 1- bit DAC with a simple first- order integrator would have to run at 3 THz (which is physically unrealizable) to achieve 2. A single integrator is a low- pass filter with a frequency response inversely proportional to frequency and using one such integrator in the noise- shaping loop is a first order delta- sigma modulator. Multiple higher order topologies (such as MASH) are used to achieve higher degrees of noise- shaping with a stable topology. The binary- weighted DAC, which contains individual electrical components for each bit of the DAC connected to a summing point. These precise voltages or currents sum to the correct output value. This is one of the fastest conversion methods but suffers from poor accuracy because of the high precision required for each individual voltage or current. Such high- precision components are expensive, so this type of converter is usually limited to 8- bit resolution or less. Individual resistors are enabled or bypassed in the network based on the digital input. Switched current source DAC, from which different current sources are selected based on the digital input. Switched capacitor DAC contains a parallel capacitor network. Individual capacitors are connected or disconnected with switches based on the input. The R- 2. R ladder DAC which is a binary- weighted DAC that uses a repeating cascaded structure of resistor values R and 2. R. This improves the precision due to the relative ease of producing equal valued- matched resistors (or current sources). The Successive- Approximation or Cyclic DAC, which successively constructs the output during each cycle. Individual bits of the digital input are processed each cycle until the entire input is accounted for. The thermometer- coded DAC, which contains an equal resistor or current- source segment for each possible value of DAC output. An 8- bit thermometer DAC would have 2. DAC would have 6. This is perhaps the fastest and highest precision DAC architecture but at the expense of high cost. Conversion speeds of > 1 billion samples per second have been reached with this type of DAC. Hybrid DACs, which use a combination of the above techniques in a single converter. Most DAC integrated circuits are of this type due to the difficulty of getting low cost, high speed and high precision in one device. In this way, a compromise is obtained between precision (by the use of the thermometer- coded principle) and number of resistors or current sources (by the use of the binary- weighted principle). The full binary- weighted design means 0% segmentation, the full thermometer- coded design means 1.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. Archives
January 2017
Categories |