Analog to Digital Converter Specifications - Report Example

Analog to Digital Converter (ADC) Specifications Introduction Notwithstanding the fact that analog-to-digital converters (ADC) come with terms that are commonly known, yet, the relevant terminology is rather perplexing. The paper is an attempt to enable the users in developing a basic understanding of the various requirements and technical specifications pertinent to ADCs. This aspect of having a sound knowledge is highly essential for choosing the appropriate converter for any given application. (1) (Len Staller, February 2005) Basic Understanding of an ADC To begin with, it needs to be understood that the primary function of an ADC is to transform an analog signal input into a digital output. There is a variation in ADC measurements when they are related with the accepted standards. The same is attributable to both differences in various manufacturing procedures of integrated circuits, and also the causes of inexactness found in the analog-to-digital conversion process. (1) (Len Staller, February 2005). The various specifications related to ADC performance are in classified in two patterns: DC accuracy and dynamic performance. A substantial chunk of applications utilize ADCs for measuring comparatively static signals such as those of a DC, or for dynamic signals. Eventually, the most appropriate specifications are determined by the one who has designed the particular application in question. (1) (Len Staller, February 2005). Specifications Firstly, the specifications pertaining to DC accuracy would be examined. Many signals such as those originating from pressure transducers and temperature sensors are comparatively static. In all applications of that type, the actual measured voltage is compared with findings of a physical measurement. Here, it needs to be noted that, the aspect of paramount relevance is the total accuracy of voltage measurement. The specifications of ADC focusing on the above mentioned accuracy are as follows: offset error, full- scale error, differential nonlinearity (DNL) and integral nonlinearity. Before elaborating on them, it would help in understanding about the aspect of ideal transfer function. This particular function is comparing ADC voltage input with output of the code generated by ADC. When analog input voltage and digital output code are presented on a graph, with the former on X- axis and the latter Y- axis, the ideal transfer function is a straight line resulting from small lines drawn from one point to the other, with these points being the codes. The focus of the paper would now shift to elaborating further on the aforesaid four types of errors. (1) (Len Staller, February 2005). Offset Error: When the above-mentioned graph is considered, an offset error is the total shifting of transfer function either left or right of the axis representing input voltage. While considering this error, the relevant point to be noted is that some ADCs have about 1/2 LSB (code width) of error wantonly brought about in them. (1) (Len Staller, February 2005). Full-Scale Error: This error is synonymous with the variation between actual transition towards output code and the apt code transition for the highest output code. This particular error is noted when the offset error is recorded as being zero. (1) (Len Staller, February 2005). Differential Nonlinearity: As per ideal standards, in the graph mentioned, every LSB of transducer function of ADC needs to be of similar size. Differential nonlinearity is the variation observed in those code widths. (1) (Len Staller, February 2005). Integral Nonlinearity: When the transfer function deviates from the ideal transfer function (straight line), it is treated as an error of integral nonlinearity. This error is ascertained by measuring voltage pertinent to all code transitions and relating it with the one conforming to ideal standards. (1) (Len Staller, February 2005). Now, the specifications pertaining to the aspect of Dynamic performance need to be dwelled upon. The dynamic performance of an ADC is assessed by observations resulting from frequency- domain analysis, and is ascertained by carrying out a FFT (fast Fourier Transform) of ADC output codes. The specifications of this aspect (Dynamic performance) are:- Signal-to-noise ratio (SNR): This specification is an ascertainment of the discrepancy between the anticipated noise and the signal that is actually measured. (1) (Len Staller, February 2005). Harmonic distortion: This is an outcome of nonlinearity attributable to data converter. Harmonic distortion, which is not included while assessing SNR, minimizes in severity at enhanced frequencies, even to the extent of being lower than either the noise floor or the concerned bandwidth. The manufacturers specify about the precise calculation of this distortion. (1) (Len Staller, February 2005). Signal-to-noise and distortion (SiNAD): This particular specification is a blend of both SNR and harmonic distortion, and is hence more exhaustive. (1) (Len Staller, February 2005). Spurious-free dynamic range: This is the variation noted while comparing measured signal’s magnitude and its topmost spur peak. (1) (Len Staller, February 2005). More on ADC Errors Opting for an ADC of a specific resolution is no guarantee for ensuring the same level of accuracy of the system. In fact, utilizing an ADC that is the most apt one for the given system is the solution for being assured of enhanced accuracy. For this, it is of topmost relevance to precisely determine the specific requirements of the system in question. Each element of a system would be having a corresponding error, and ADC plays a pivotal role in making sure that the errors are lower than a specified mark. There are two widely used methods for determining overall errors of the system:- (2) (NP, July 2002). RSS (root-sum-square): Here, all the error values are added after separately squaring each of them. Then, the square root is calculated for this sum total. This method ensures high level of accuracy when error values are not correlated. (2) (NP, July 2002). Worst-case method: In this pattern, all error values are added, and this method makes sure that the error is below a specified point. (2) (NP, July 2002). Advanced Digital Audio Techniques Digital recording is in total contrast to the analog form of recording, with audio tapes being an example of the latter (analog). Digital audio files are enabled to be copied countless number of times, and that too without compromising on quality. Additionally, editing can be carried out for digital files in a relatively simplified manner. These two features are not supported by the conventional system of analog recording. (3) (Audacity, ND). ADC essays a highly relevant role in the process of digital recording, by swiftly capturing electric voltage of audio line and transforming it into a digital number, for usage by the computer. A typical ADC is capable of performing the above operation of capture, thousands of times for each second. (3) (Audacity, ND). A Glance at Few Audio Recording Techniques It would now be worthwhile to have a brief look at few of the numerous recording techniques, which are the order of the day in this era of technological revolution. FILTERS: Filters, which are named also as EQ, bring about either a rise or a drop in the level of audio frequencies related to a particular range. The most widely used filters are treble controls and simple bass present in some stereo systems. (4) (David Ciccarelli, 2010). BANDPASS FILTERS: These are utilized for controlling the audio level of two sides of a center frequency, with midrange filters being the way in which they are mostly used. (4) (David Ciccarelli, 2010). COMPRESSORS: The primary function of a compressor is to minimize the variation between highest and the lowest level of sensitive sounds moving in the recording chain. This difference is known as dynamic range of audio recording. (4) (David Ciccarelli, 2010). EXPANDERS: The function of an expander is totally the reverse of the one related to compressor. The expander further enhances the loudness of the loud signals, proportionate to the louder audio signals. Also, an expander is helpful by being a part of a procedure named “downward expansion” aimed at lessening the noise. (4) (David Ciccarelli, 2010). Conclusion The topic in question is an exhaustive one, and it is just not possible to encompass all the aspects related to it in a brief paper such as this one. Yet, the paper made a sincere attempt to cover most of the points that are highly vital for the subject. SOURCES 1) “Understanding analog to digital converter specifications”, webcache.googleusercontent.com/search?q=cache:http://www.eetimes.com/design/other/4025078/Understanding-analog-to-digital-converter-specifications, Internet, Len Staller, February 2005. 2) “The ABCs of ADCs: Understanding How ADC Errors Affect System Performance”, maxim-ic.com/app-notes/index.mvp/id/748, Internet, NP, July 2002. 3) “Digital Audio”, audacity.sourceforge.net/manual-1.2/tutorial_basics_1.html, Internet, Internet, Audacity, ND. 4) “Advanced Recording Techniques”, webcache.googleusercontent.com/search?q=cache:http://blogs.voices.com/voxdaily/2007/05/advanced_digital_audio_recording_techniques.html, Internet, David Ciccarelli, 2010. Read More