In electronics, the DAC circuit is a kind of system. It is she who converts the digital signal to analog.
There are several DAC circuits. Suitability for a specific application is determined by quality indicators, including resolution, maximum sampling rate, and others.
Digital-to-analog conversion can degrade signal transmission, so you need to find a tool that has minor errors in terms of application.
Applications
DACs, as a rule, are used in music players with the aim of converting numerical streams of information into analog audio signals. They are also used in televisions and mobile phones to convert video data into video signals, respectively, which are connected to screen drivers to reflect monochromatic or multi-colored images.
It is these two applications that use DACs at opposite ends of the trade-off between density and pixel count. Audio is a low-frequency type with a high resolution, and video is a high-frequency version with a low and medium image.
Due to the complexity and necessity of precisely selected components, all but the most specialized DACs are implemented as integrated circuits (ICs). Discrete communications are typically extremely fast, energy-efficient, low-resolution types that are used in military radar systems. Very high speed test equipment, especially sampling oscilloscopes, can also use discrete DACs.
Overview
The partially-constant output signal of a conventional DAC without a filter is built into almost any device, and the initial image or final bandwidth of the structure smooths the response of the step into a continuous curve.
Answering the question: “What is a DAC?”, It is worth noting that this component converts an abstract number of finite accuracy (usually a binary digit with a fixed decimal point) into a physical quantity (for example, voltage or pressure). In particular, digital-to-analog conversion is often used to change time series data into a continuously changing physical signal.
An ideal DAC converts abstract numbers into a conceptual sequence of pulses, which are then processed using a reconstruction filter, using some form of interpolation to fill in the data between pulses. A common practical digital-to-analog converter changes numbers into a piecewise constant function made up of a sequence of rectangular models that are created with zero-order retention. In addition, answering the question: “What is a DAC?” it is worth noting other methods (for example, based on delta-sigma modulation). They create an output with a modulated pulse density, which can be similarly filtered to produce a smoothly varying signal.
According to the Nyquist-Shannon sampling theorem, the DAC can reconstruct the initial vibration from the sample data, provided that its insertion zone meets certain requirements (for example, a main-frequency pulse with a lower density transmission line). Digital sampling represents a quantization error, which appears as low-level noise in the reconstructed signal.
Simplified functional diagram of an 8-bit tool
Immediately it is worth noting that the most popular model is the Digital-to-Analog Converter Real Cable NANO-DAC. The DAC is part of an advanced technology that has made a significant contribution to the digital revolution. To illustrate, it is worth considering the typical long-distance telephone calls.
The voice of the caller is converted into an analog electrical signal using a microphone, and then this pulse is already changed into a digital stream along with the DAC. After that, the latter is divided into network packets, where it can be sent along with other digital data. And it may be optional audio.
Then the packets are received at the destination, but each of them can go on a completely different route and not even reach the destination in the right order and at the right time. Digital voice data is then retrieved from the packets and collected in a shared data stream. The DAC converts this back to an analog electrical signal that drives an audio amplifier (for example, the Digital-to-Analog Converter Real Cable NANO-DAC). And he, in turn, activates the loudspeaker, which finally produces the necessary sound.
Audio
Most modern acoustic signals are stored digitally (e.g. MP3 and CD). In order for them to be heard through the speakers, they must be converted into a similar impulse. Thus, you can find the digital-to-analog converter for the TV, CD player, digital music systems and sound cards for the PC.
Specialized autonomous DACs can also be found in high-quality Hi-Fi systems. Usually they take the digital output of a compatible CD player or dedicated transport and convert the signal to a line level analog output, which can then be fed to an amplifier to control the speakers.
Similar digital-to-analog converters can be found in digital speakers such as USB speakers, and in sound cards.
In applications that use voice over IP, the source must first be digitized for transmission, so it is converted through an ADC and then converted to analog using the DAC on the receiving side. For example, this method is used for some digital-to-analog converters (TV).
Picture
Sampling tends to work on a completely different scale, in general, due to the extremely non-linear response of both cathode ray tubes (for which the vast majority of digital video work was intended) and the human eye, using the gamma curve to ensure the appearance of uniformly distributed brightness steps across the entire dynamic range of the display. Hence the need to use RAMDAC in computer video applications with a fairly deep color resolution in order to impractically create a hard-coded value in the DAC for each output level of each channel (for example, Atari ST or Sega Genesis will need 24 such values; for a 24-bit video card, 768 will be required).
Given this inherent distortion, it is often true for a television or video projector that a linear contrast ratio (the difference between the darkest and brightest output levels) is 1,000: 1 or more. This is equivalent to 10 bits of sound fidelity, even if it can only receive signals with 8-bit accuracy and use an LCD panel that displays barely six or seven bits per channel. On this basis, reviews of DACs are published.
Video signals from a digital source, such as a computer, must be converted to analog form if they need to be displayed on a monitor. Since 2007, similar inputs have been used more often than digital ones, but this has changed as flat panel displays with DVI or HDMI connections have become more common. However, the DAC for video is built into any digital video player with the same outputs. A digital-to-analog sound converter is usually integrated with some memory (RAM), which contains reorganization tables for gamma correction, contrast and brightness to create a device called RAMDAC.
The device, which is remotely connected to the DAC, is a digitally controlled potentiometer used to pick up the signal.
Mechanical construction
For example, an IBM Selectric typewriter already uses a non-manual DAC to control the ball.
The digital-to-analog converter circuit looks like this.
A single-bit mechanical drive takes two positions: one when turned on, the other when turned off. The movement of several single-bit actuators can be combined and weighted using a device without hesitation to obtain more accurate steps.
It is the IBM Selectric typewriter that uses such a system.
The main types of digital-to-analog converters
- A pulse-width modulator, where a stable current or voltage is switched into a low-pass analog filter with a duration determined by a digital input code. This method is often used to control the speed of an electric motor and dimming LED lamps.
- Oversampling digital to analog audio converters or interpolating DACs, for example, using delta-sigma modulation, use the method of changing pulse density. Speeds of more than 100 thousand samples per second (for example, 180 kHz) and a resolution of 28 bits are achievable with a delta-sigma device.
- A binary-weighted element that contains separate electrical components for each bit of the DAC connected to the summation point. It is she who can fold the operational amplifier. The current strength of the source is proportional to the weight of the bit to which it corresponds. Thus, all nonzero code bits are summed with weight. This happens because they have the same voltage source. This is one of the fastest conversion methods, but it is not ideal. Since there is a problem: low fidelity due to the large data required for each individual voltage or current. Such precision components are expensive, so this type of model is usually limited to 8-bit resolution or even less. The switched resistor has the purpose of digital-to-analog converters in parallel network sources. Separate instances are included in the electricity based on a digital input. The principle of operation of a digital-to-analog converter of this type consists in a switched DAC current source, from which different keys are selected based on a numerical input. It includes a synchronous capacitor line. These single elements are connected or disconnected using a special mechanism (paws), which is located near all the plugs.
- Digital-to-analog converters of the ladder type, which is a binary-weighted element. He, in turn, uses the repeating structure of the cascade values of the resistor R and 2R. This increases accuracy due to the relative simplicity of manufacturing a mechanism with the same rating (or current sources).
- A sequential offensive or a cyclic DAC, which builds output data one after another during each stage. The individual bits of the digital input are processed by all the connectors until the entire object is taken into account.
- A thermometer is an encoded DAC that contains an equal resistor or current-source segment for each possible value of the DAC output. The 8-bit DAC of the thermometer will have 255 elements, and the 16-charged DAC of the thermometer will have 65,535 parts. This is perhaps the fastest and most accurate DAC architecture, but at the expense of high cost. Thanks to this type of DAC, conversion rates of more than one billion samples per second are achieved.
- Hybrid DACs that use a combination of the above methods in a single converter. Most DAC integrated circuits are of this type because of the difficulty of simultaneously obtaining low cost, high speed and correctness in one device.
- A segmented DAC that combines the principle of encoding a thermometer for high-order bits and binary weighing for low-order components. Thus, a compromise is achieved between accuracy (using the principle of encoding the thermometer) and the number of resistors or current sources (using binary weighing). A deep double acting device means 0% segmentation, and a full thermometric coding design has 100%.
Most of the DACS presented on this list rely on a constant reference voltage to create their output value. Alternatively, the multiplying DAC accepts an alternating input voltage to convert them. This imposes additional design restrictions on the bandwidth of the reorganization scheme. Now it’s clear why various types of digital-to-analog converters are needed.
Performance
DACs are very important for the fruitfulness of the system. The most significant characteristics of these devices is the resolution, which is created for the use of a digital-to-analog converter.
The number of possible output levels that the DACs are intended to be reproduced is usually indicated as the number of bits it uses, which is the basis of the two logarithms of the number of levels. For example, a 1-bit DAC is designed to reproduce two, while an 8-bit DAC is designed for 256 circuits. The addition is related to the effective number of bits, which is a measure of the actual resolution achieved by the DAC. Resolution determines the color depth in video applications and the bit frequency of sound in audio devices.
Maximum frequency
The measurement of the highest speed at which the DAC circuitry can operate while generating the correct output signal determines the relationship between it and the bandwidth of the sampled signal. As indicated above, the Nyquist-Shannon sampling theorem connects continuous and discrete signals and states that any signal can be reconstructed with any accuracy from its discrete reports.
Monotone
This concept means the ability of the analog output of the DAC to move only in the direction in which the digital input moves. This characteristic is very important for DACs used as a low frequency signal source.
Total Harmonic Distortion and Noise (THD + N)
Measurement of distortions and extraneous sounds introduced by the DAC into the signal is expressed as a percentage of the total power of the unwanted harmonic distortion and noise that accompany the desired signal. This is a very important feature for DAC applications with dynamic and low output.
Range
Measuring the difference between the largest and smallest signals that the DAC can reproduce, expressed in decibels, is usually related to resolution and noise level.
Other measurements, such as phase distortion and jitter, can also be very important for some applications. They have those (such as wireless data transfer, composite video) that can even rely on accurate phase-controlled reception of signals.
Linear PCM audio sampling usually works based on the resolution of each bit, equivalent to six decibels of amplitude (double the volume or accuracy).
Non-linear PCM encodings (A-law / μ-law, ADPCM, NICAM) try to improve their effective dynamic ranges in various ways - by the logarithmic step sizes between the output sound levels represented by each data bit.
Classification of D / A Converters
Classification by nonlinearity divides them into:
- Distinctive non-linearity, which shows how two adjacent code values deviate from the perfect LSB step 1.
- The accumulated nonlinearity shows how far the DAC transmission deviates from ideal.
That is, the ideal characteristic is usually a straight line. INL shows how much the actual voltage at a given code value differs from this line in the lower bits.
Gain
Ultimately, the noise is limited to the thermal hum generated by passive components such as resistors. For audio applications and at room temperature, such a sound is usually a little less than 1 μV (microvolt) of the white signal. This limits performance to less than 20 bits, even on 24-bit DACs.
Frequency Performance
Parasite Free Dynamic Range (SFDR) indicates in dB the ratio of the powers of the transformed main signal and the largest undesired outlier.
The ratio of noise and distortion (SNDR) indicates in dB the property of the powers of the converted main sound to its total.
Total Harmonized Distortion (THD) is the addition of the powers of all HDi.
If the maximum DNL error is less than 1 LSB, then the digital-to-analog converter is guaranteed to be uniform. DNL 1 LSB.
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