Misplaced Pages

#791208

70-504: Although the technology for creating digital recordings from analog sources has existed for some time, it was not necessarily viewed as a "hole" until the widespread deployment of DRM in the late 1990s. However, if the correct equipment is not used to perform the conversion, the resulting copy may have distinguishable low fidelity (or other deformations) compared to the analog (or digital) original. Regardless of any digital or software copy control mechanisms, if sound can be captured by

140-486: A capacitor to store the analog voltage at the input, and using an electronic switch or gate to disconnect the capacitor from the input. Many ADC integrated circuits include the sample and hold subsystem internally. An ADC works by sampling the value of the input at discrete intervals in time. Provided that the input is sampled above the Nyquist rate , defined as twice the highest frequency of interest, then all frequencies in

210-463: A continuously variable signal, in contrast to digital electronics where signals usually take only two levels . The term analogue describes the proportional relationship between a signal and a voltage or current that represents the signal. The word analogue is derived from the Greek word ανάλογος analogos meaning proportional . An analogue signal uses some attribute of the medium to convey

280-437: A digital encoder logic circuit that generates a binary number on the output lines for each voltage range. ADCs of this type have a large die size and high power dissipation. They are often used for video , wideband communications , or other fast signals in optical and magnetic storage . The circuit consists of a resistive divider network, a set of op-amp comparators and a priority encoder. A small amount of hysteresis

350-412: A microphone , it can be either recorded by analog means (e.g. magnetic tape ), or stored digitally. And if images (static images or video/film), including text , can be seen by a camera, they can also be recorded. In the case of text the image can be converted back to text using optical character recognition (OCR). In the case of streaming music services, software exists that can digitally capture

420-447: A patent royalty to the watermark's inventor). The motion picture industry has also pursued several private-sector approaches to eliminating the analog hole; these might be implemented without additional legislation. In theory, it is possible to bypass all these measures by constructing a player that creates a copy of every frame and sound it plays. Although this is not within the capability of most people, many bootleggers simply record

490-438: A saw-tooth signal that ramps up or down then quickly returns to zero. When the ramp starts, a timer starts counting. When the ramp voltage matches the input, a comparator fires, and the timer's value is recorded. Timed ramp converters can be implemented economically, however, the ramp time may be sensitive to temperature because the circuit generating the ramp is often a simple analog integrator . A more accurate converter uses

560-464: A transducer which converts one type of energy into another (e.g. a microphone ). The signals take any value from a given range, and each unique signal value represents different information. Any change in the signal is meaningful, and each level of the signal represents a different level of the phenomenon that it represents. For example, suppose the signal is being used to represent temperature, with one volt representing one degree Celsius . In such

630-470: A 500 Hz sine wave. To avoid aliasing, the input to an ADC must be low-pass filtered to remove frequencies above half the sampling rate. This filter is called an anti-aliasing filter , and is essential for a practical ADC system that is applied to analog signals with higher frequency content. In applications where protection against aliasing is essential, oversampling may be used to greatly reduce or even eliminate it. Although aliasing in most systems

700-491: A clocked counter driving a DAC. A special advantage of the ramp-compare system is that converting a second signal just requires another comparator and another register to store the timer value. To reduce sensitivity to input changes during conversion, a sample and hold can charge a capacitor with the instantaneous input voltage and the converter can time the time required to discharge with a constant current . An integrating ADC (also dual-slope or multi-slope ADC) applies

770-525: A constant current source . The time required to discharge the capacitor is proportional to the amplitude of the input voltage. While the capacitor is discharging, pulses from a high-frequency oscillator clock are counted by a register. The number of clock pulses recorded in the register is also proportional to the input voltage. If the analog value to measure is represented by a resistance or capacitance, then by including that element in an RC circuit (with other resistances or capacitances fixed) and measuring

SECTION 10

#1732855418792

840-432: A faithful reproduction of the original signal is only possible if the sampling rate is higher than twice the highest frequency of the signal. Since a practical ADC cannot make an instantaneous conversion, the input value must necessarily be held constant during the time that the converter performs a conversion (called the conversion time ). An input circuit called a sample and hold performs this task—in most cases by using

910-446: A flow of digital values. It is therefore required to define the rate at which new digital values are sampled from the analog signal. The rate of new values is called the sampling rate or sampling frequency of the converter. A continuously varying bandlimited signal can be sampled and then the original signal can be reproduced from the discrete-time values by a reconstruction filter . The Nyquist–Shannon sampling theorem implies that

980-422: A known voltage charging and discharging curve that can be used to solve for an unknown analog value. The Wilkinson ADC was designed by Denys Wilkinson in 1950. The Wilkinson ADC is based on the comparison of an input voltage with that produced by a charging capacitor. The capacitor is allowed to charge until a comparator determines it matches the input voltage. Then, the capacitor is discharged linearly by using

1050-436: A longer time to measure than smaller one. And the accuracy is limited by the accuracy of the microcontroller clock and the amount of time available to measure the value, which potentially might even change during measurement or be affected by external parasitics . A direct-conversion or flash ADC has a bank of comparators sampling the input signal in parallel, each firing for a specific voltage range. The comparator bank feeds

1120-409: A pulse of a particular amplitude is always converted to the same digital value. The problem lies in that the ranges of analog values for the digitized values are not all of the same widths, and the differential linearity decreases proportionally with the divergence from the average width. The sliding scale principle uses an averaging effect to overcome this phenomenon. A random, but known analog voltage

1190-451: A sampler. It cannot improve the linearity, and thus accuracy does not necessarily improve. Quantization distortion in an audio signal of very low level with respect to the bit depth of the ADC is correlated with the signal and sounds distorted and unpleasant. With dithering, the distortion is transformed into noise. The undistorted signal may be recovered accurately by averaging over time. Dithering

1260-515: A sampling rate greater than twice the bandwidth of the signal, then per the Nyquist–Shannon sampling theorem , near-perfect reconstruction is possible. The presence of quantization error limits the SNDR of even an ideal ADC. However, if the SNDR of the ADC exceeds that of the input signal, then the effects of quantization error may be neglected, resulting in an essentially perfect digital representation of

1330-404: A signal is, mainly the noise present in the original signal and the noise added by processing (see signal-to-noise ratio ). Fundamental physical limits such as the shot noise in components limits the resolution of analogue signals. In digital electronics additional precision is obtained by using additional digits to represent the signal. The practical limit in the number of digits is determined by

1400-463: A system, 10 volts would represent 10 degrees, and 10.1 volts would represent 10.1 degrees. Another method of conveying an analogue signal is to use modulation . In this, some base carrier signal has one of its properties altered: amplitude modulation (AM) involves altering the amplitude of a sinusoidal voltage waveform by the source information, frequency modulation (FM) changes the frequency. Other techniques, such as phase modulation or changing

1470-430: Is a system that converts an analog signal , such as a sound picked up by a microphone or light entering a digital camera , into a digital signal . An ADC may also provide an isolated measurement such as an electronic device that converts an analog input voltage or current to a digital number representing the magnitude of the voltage or current. Typically the digital output is a two's complement binary number that

SECTION 20

#1732855418792

1540-451: Is a very small amount of random noise (e.g. white noise ), which is added to the input before conversion. Its effect is to randomize the state of the LSB based on the signal. Rather than the signal simply getting cut off altogether at low levels, it extends the effective range of signals that the ADC can convert, at the expense of a slight increase in noise. Dither can only increase the resolution of

1610-535: Is added to the sampled input voltage. It is then converted to digital form, and the equivalent digital amount is subtracted, thus restoring it to its original value. The advantage is that the conversion has taken place at a random point. The statistical distribution of the final levels is decided by a weighted average over a region of the range of the ADC. This in turn desensitizes it to the width of any specific level. These are several common ways of implementing an electronic ADC. Resistor-capacitor (RC) circuits have

1680-471: Is also used in integrating systems such as electricity meters . Since the values are added together, the dithering produces results that are more exact than the LSB of the analog-to-digital converter. Dither is often applied when quantizing photographic images to a fewer number of bits per pixel—the image becomes noisier but to the eye looks far more realistic than the quantized image, which otherwise becomes banded . This analogous process may help to visualize

1750-428: Is built into the comparator to resolve any problems at voltage boundaries. At each node of the resistive divider, a comparison voltage is available. The purpose of the circuit is to compare the analog input voltage with each of the node voltages. The circuit has the advantage of high speed as the conversion takes place simultaneously rather than sequentially. Typical conversion time is 100 ns or less. Conversion time

1820-427: Is limited only by the speed of the comparator and of the priority encoder. This type of ADC has the disadvantage that the number of comparators required almost doubles for each added bit. Also, the larger the value of n, the more complex is the priority encoder. A successive-approximation ADC uses a comparator and a binary search to successively narrow a range that contains the input voltage. At each successive step,

1890-467: Is proportional to the input, but there are other possibilities. There are several ADC architectures . Due to the complexity and the need for precisely matched components , all but the most specialized ADCs are implemented as integrated circuits (ICs). These typically take the form of metal–oxide–semiconductor (MOS) mixed-signal integrated circuit chips that integrate both analog and digital circuits . A digital-to-analog converter (DAC) performs

1960-608: Is random disturbances or variations, some caused by the random thermal vibrations of atomic particles. Since all variations of an analogue signal are significant, any disturbance is equivalent to a change in the original signal and so appears as noise. As the signal is copied and re-copied, or transmitted over long distances, these random variations become more significant and lead to signal degradation . Other sources of noise may include crosstalk from other signals or poorly designed components. These disturbances are reduced by shielding and by using low-noise amplifiers (LNA). Since

2030-459: Is the ADC's resolution in bits and E FSR is the full-scale voltage range (also called 'span'). E FSR is given by where V RefHi and V RefLow are the upper and lower extremes, respectively, of the voltages that can be coded. Normally, the number of voltage intervals is given by where M is the ADC's resolution in bits. That is, one voltage interval is assigned in between two consecutive code levels. Example: In many cases,

2100-414: Is the number of ADC bits. Clock jitter is caused by phase noise . The resolution of ADCs with a digitization bandwidth between 1 MHz and 1 GHz is limited by jitter. For lower bandwidth conversions such as when sampling audio signals at 44.1 kHz, clock jitter has a less significant impact on performance. An analog signal is continuous in time and it is necessary to convert this to

2170-407: Is uniformly distributed between − 1 ⁄ 2 LSB and + 1 ⁄ 2 LSB, and the signal has a uniform distribution covering all quantization levels, the signal-to-quantization-noise ratio (SQNR) is given by where Q is the number of quantization bits. For example, for a 16-bit ADC, the quantization error is 96.3 dB below the maximum level. Quantization error is distributed from DC to

Analog hole - Misplaced Pages Continue

2240-404: Is unwanted, it can be exploited to provide simultaneous down-mixing of a band-limited high-frequency signal (see undersampling and frequency mixer ). The alias is effectively the lower heterodyne of the signal frequency and sampling frequency. For economy, signals are often sampled at the minimum rate required with the result that the quantization error introduced is white noise spread over

2310-418: Is used to change a digital signal to an analogue signal. A DAC takes a series of binary numbers and converts it to an analogue signal. It is common to find a DAC in the gain-control system of an op-amp which in turn may be used to control digital amplifiers and filters. Analogue circuits are typically harder to design, requiring more skill than comparable digital systems to conceptualize. An analogue circuit

2380-436: Is usually designed by hand because the application is built into the hardware. Digital hardware, on the other hand, has a great deal of commonality across applications and can be mass-produced in a standardised form. Hardware design consists largely of repeated identical blocks and the design process can be highly automated. This is one of the main reasons that digital systems have become more common than analogue devices. However,

2450-498: The Content Protection Status Report , Consumer Broadband and Digital Television Promotion Act , and Analog Reconversion Discussion Group . Inventors of digital watermark technologies were particularly interested in this possibility because of the prospect that recording devices could be required to screen inputs for the presence of a particular watermark (and hence, presumably, their manufacturers would need to pay

2520-475: The Nyquist frequency . Consequently, if part of the ADC's bandwidth is not used, as is the case with oversampling , some of the quantization error will occur out-of-band , effectively improving the SQNR for the bandwidth in use. In an oversampled system, noise shaping can be used to further increase SQNR by forcing more quantization error out of band. In ADCs, performance can usually be improved using dither . This

2590-470: The bandlimited analog input signal. The resolution of the converter indicates the number of different, i.e. discrete, values it can produce over the allowed range of analog input values. Thus a particular resolution determines the magnitude of the quantization error and therefore determines the maximum possible signal-to-noise ratio for an ideal ADC without the use of oversampling . The input samples are usually stored electronically in binary form within

2660-463: The effective number of bits (ENOB) below that predicted by quantization error alone. The error is zero for DC, small at low frequencies, but significant with signals of high amplitude and high frequency. The effect of jitter on performance can be compared to quantization error: Δ t < 1 2 q π f 0 {\displaystyle \Delta t<{\frac {1}{2^{q}\pi f_{0}}}} , where q

2730-408: The signal-to-noise ratio performance of the ADC and thus reduce its effective resolution. When digitizing a sine wave x ( t ) = A sin ⁡ ( 2 π f 0 t ) {\displaystyle x(t)=A\sin {(2\pi f_{0}t)}} , the use of a non-ideal sampling clock will result in some uncertainty in when samples are recorded. Provided that

2800-421: The ADC, so the resolution is usually expressed as the audio bit depth . In consequence, the number of discrete values available is usually a power of two. For example, an ADC with a resolution of 8 bits can encode an analog input to one in 256 different levels (2  = 256). The values can represent the ranges from 0 to 255 (i.e. as unsigned integers) or from −128 to 127 (i.e. as signed integer), depending on

2870-519: The actual sampling time uncertainty due to clock jitter is Δ t {\displaystyle \Delta t} , the error caused by this phenomenon can be estimated as E a p ≤ | x ′ ( t ) Δ t | ≤ 2 A π f 0 Δ t {\displaystyle E_{ap}\leq |x'(t)\Delta t|\leq 2A\pi f_{0}\Delta t} . This will result in additional recorded noise that will reduce

Analog hole - Misplaced Pages Continue

2940-461: The analog output of a personal computer's sound card , and then save in a portable music format with no perceptible loss in quality. In 2002 and 2003, the U.S. motion picture industry publicly discussed the possibility of legislation to "close the analog hole"—most likely through regulation of digital recording devices, limiting their ability to record analog video signals that appear to be commercial audiovisual works. These proposals are discussed in

3010-505: The application of digital hardware is a function of the software / firmware and creating this is still largely a labour-intensive process. Since the early 2000s, there were some platforms that were developed which enabled analogue design to be defined using software - which allows faster prototyping. Furthermore, if a digital electronic device is to interact with the real world, it will always need an analogue interface. For example, every digital radio receiver has an analogue preamplifier as

3080-409: The application. Resolution can also be defined electrically, and expressed in volts . The change in voltage required to guarantee a change in the output code level is called the least significant bit (LSB) voltage. The resolution Q of the ADC is equal to the LSB voltage. The voltage resolution of an ADC is equal to its overall voltage measurement range divided by the number of intervals: where M

3150-419: The conversion periodically, sampling the input, and limiting the allowable bandwidth of the input signal. The performance of an ADC is primarily characterized by its bandwidth and signal-to-noise and distortion ratio (SNDR). The bandwidth of an ADC is characterized primarily by its sampling rate . The SNDR of an ADC is influenced by many factors, including the resolution , linearity and accuracy (how well

3220-415: The converter compares the input voltage to the output of an internal digital-to-analog converter (DAC) which initially represents the midpoint of the allowed input voltage range. At each step in this process, the approximation is stored in a successive approximation register (SAR) and the output of the digital-to-analog converter is updated for a comparison over a narrower range. A ramp-compare ADC produces

3290-417: The effect of dither on an analog audio signal that is converted to digital. An ADC has several sources of errors. Quantization error and (assuming the ADC is intended to be linear) non- linearity are intrinsic to any analog-to-digital conversion. These errors are measured in a unit called the least significant bit (LSB). In the above example of an eight-bit ADC, an error of one LSB is 1 ⁄ 256 of

3360-601: The first stage in the receive chain. Design of analogue circuits has been greatly eased by the advent of software circuit simulators such as SPICE . IBM developed their own in-house simulator, ASTAP , in the 1970s which used an unusual (compared to other simulators) sparse matrix method of circuit analysis. Analogue circuits can be entirely passive , consisting of resistors , capacitors and inductors . Active circuits also contain active elements such as transistors . Traditional circuits are built from lumped elements – that is, discrete components. However, an alternative

3430-499: The full signal range, or about 0.4%. All ADCs suffer from nonlinearity errors caused by their physical imperfections, causing their output to deviate from a linear function (or some other function, in the case of a deliberately nonlinear ADC) of their input. These errors can sometimes be mitigated by calibration , or prevented by testing. Important parameters for linearity are integral nonlinearity and differential nonlinearity . These nonlinearities introduce distortion that can reduce

3500-468: The information is quantized , as long as the signal stays inside a range of values, it represents the same information. In digital circuits the signal is regenerated at each logic gate , lessening or removing noise. In analogue circuits, signal loss can be regenerated with amplifiers . However, noise is cumulative throughout the system and the amplifier itself will add to the noise according to its noise figure . A number of factors affect how precise

3570-418: The information is encoded differently in analogue and digital electronics , the way they process a signal is consequently different. All operations that can be performed on an analogue signal such as amplification , filtering , limiting, and others, can also be duplicated in the digital domain. Every digital circuit is also an analogue circuit, in that the behaviour of any digital circuit can be explained using

SECTION 50

#1732855418792

3640-494: The logarithm of the resolution, i.e. the number of bits. Flash ADCs are certainly the fastest type of the three; The conversion is basically performed in a single parallel step. There is a potential tradeoff between speed and precision. Flash ADCs have drifts and uncertainties associated with the comparator levels results in poor linearity. To a lesser extent, poor linearity can also be an issue for successive-approximation ADCs. Here, nonlinearity arises from accumulating errors from

3710-516: The measured run-down time period. The run-down time measurement is usually made in units of the converter's clock, so longer integration times allow for higher resolutions. Likewise, the speed of the converter can be improved by sacrificing resolution. Converters of this type (or variations on the concept) are used in most digital voltmeters for their linearity and flexibility. Analogue electronics Analogue electronics ( American English : analog electronics ) are electronic systems with

3780-431: The other hand, are not affected at all by the presence of noise until a certain threshold is reached, at which point they fail catastrophically. For digital telecommunications , it is possible to increase the noise threshold with the use of error detection and correction coding schemes and algorithms. Nevertheless, there is still a point at which catastrophic failure of the link occurs. In digital electronics, because

3850-437: The performance of the analogue-to-digital converter (ADC), since digital operations can usually be performed without loss of precision. The ADC takes an analogue signal and changes it into a series of binary numbers . The ADC may be used in simple digital display devices, e. g., thermometers or light meters but it may also be used in digital sound recording and in data acquisition. However, a digital-to-analogue converter (DAC)

3920-410: The performance of the ADC can be greatly increased at little or no cost. Furthermore, as any aliased signals are also typically out of band, aliasing can often be eliminated using very low cost filters. The speed of an ADC varies by type. The Wilkinson ADC is limited by the clock rate which is processable by current digital circuits. For a successive-approximation ADC , the conversion time scales with

3990-534: The phase of the carrier signal, are also used. In an analogue sound recording, the variation in pressure of a sound striking a microphone creates a corresponding variation in the current passing through it or voltage across it. An increase in the volume of the sound causes the fluctuation of the current or voltage to increase proportionally while keeping the same waveform or shape. Mechanical , pneumatic , hydraulic , and other systems may also use analogue signals. Analogue systems invariably include noise that

4060-411: The quantization levels match the true analog signal), aliasing and jitter . The SNDR of an ADC is often summarized in terms of its effective number of bits (ENOB), the number of bits of each measure it returns that are on average not noise . An ideal ADC has an ENOB equal to its resolution. ADCs are chosen to match the bandwidth and required SNDR of the signal to be digitized. If an ADC operates at

4130-410: The reverse function; it converts a digital signal into an analog signal. An ADC converts a continuous-time and continuous-amplitude analog signal to a discrete-time and discrete-amplitude digital signal . The conversion involves quantization of the input, so it necessarily introduces a small amount of quantization error . Furthermore, instead of continuously performing the conversion, an ADC does

4200-485: The rules of analogue circuits. The use of microelectronics has made digital devices cheap and widely available. The effect of noise on an analogue circuit is a function of the level of noise. The greater the noise level, the more the analogue signal is disturbed, slowly becoming less usable. Because of this, analogue signals are said to "fail gracefully". Analogue signals can still contain intelligible information with very high levels of noise. Digital circuits, on

4270-499: The signal can be reconstructed. If frequencies above half the Nyquist rate are sampled, they are incorrectly detected as lower frequencies, a process referred to as aliasing. Aliasing occurs because instantaneously sampling a function at two or fewer times per cycle results in missed cycles, and therefore the appearance of an incorrectly lower frequency. For example, a 2 kHz sine wave being sampled at 1.5 kHz would be reconstructed as

SECTION 60

#1732855418792

4340-485: The signal's information. For example, an aneroid barometer uses the angular position of a needle on top of a contracting and expanding box as the signal to convey the information of changes in atmospheric pressure . Electrical signals may represent information by changing their voltage , current , frequency , or total charge . Information is converted from some other physical form (such as sound , light , temperature , pressure , position) to an electrical signal by

4410-406: The subtraction processes. Wilkinson ADCs have the best linearity of the three. The sliding scale or randomizing method can be employed to greatly improve the linearity of any type of ADC, but especially flash and successive approximation types. For any ADC the mapping from input voltage to digital output value is not exactly a floor or ceiling function as it should be. Under normal conditions,

4480-415: The time it takes to charge (and/or discharge) its capacitor from 1 ⁄ 3   V supply to 2 ⁄ 3   V supply . By sending this pulse into a microcontroller with an accurate clock, the duration of the pulse can be measured and converted using the capacitor charging equation to produce the value of the unknown resistance or capacitance. Larger resistances and capacitances will take

4550-550: The time to charge the capacitance from a known starting voltage to another known ending voltage through the resistance from a known voltage supply, the value of the unknown resistance or capacitance can be determined using the capacitor charging equation: V capacitor ( t ) = V supply ( 1 − e − t R C ) {\displaystyle V_{\text{capacitor}}(t)=V_{\text{supply}}\left(1-e^{-{\frac {t}{RC}}}\right)} and solving for

4620-411: The unknown input voltage to the input of an integrator and allows the voltage to ramp for a fixed time period (the run-up period). Then a known reference voltage of opposite polarity is applied to the integrator and is allowed to ramp until the integrator output returns to zero (the run-down period). The input voltage is computed as a function of the reference voltage, the constant run-up time period, and

4690-464: The unknown resistance or capacitance using those starting and ending datapoints. This is similar but contrasts to the Wilkinson ADC which measures an unknown voltage with a known resistance and capacitance, by instead measuring an unknown resistance or capacitance with a known voltage. For example, the positive (and/or negative) pulse width from a 555 Timer IC in monostable or astable mode represents

4760-418: The useful resolution of a converter is limited by the signal-to-noise ratio (SNR) and other errors in the overall system expressed as an ENOB. Quantization error is introduced by the quantization inherent in an ideal ADC. It is a rounding error between the analog input voltage to the ADC and the output digitized value. The error is nonlinear and signal-dependent. In an ideal ADC, where the quantization error

4830-557: The video being displayed with a video camera or use recording and playing devices that are not designed to use the protection measures. In fact, the Motion Picture Association of America has recommended use of a camcorder as an alternative to circumventing the Content Scrambling System on DVDs. Analog-to-digital converter In electronics , an analog-to-digital converter ( ADC , A/D , or A-to-D )

4900-433: The whole passband of the converter. If a signal is sampled at a rate much higher than the Nyquist rate and then digitally filtered to limit it to the signal bandwidth produces the following advantages: Oversampling is typically used in audio frequency ADCs where the required sampling rate (typically 44.1 or 48 kHz) is very low compared to the clock speed of typical transistor circuits (>1 MHz). In this case,

#791208