A/D Converter Definition Of Terms
ANALOG INPUT BANDWIDTH is a measure of the fre-quency at which the reconstructed output fundamental drops 3dB below its low frequency value for a full scale input.The test is performed with f IN equal to 100kHz plus integer mul-tiples of f CLK .The input frequency at which the output is −3dB relative to the low frequency input signal is the full power bandwidth.
APERTURE JITTER is the variation in aperture delay from sample to sample.Aperture jitter shows up as input noi.APERTURE DELAY See Sampling Delay.
BOTTOM OFFSET is the difference between the input volt-age that just caus the output code to transition to the first code and the negative reference voltage.Bottom Offt is defined as E OB =V ZT –V RB ,where V ZT is the first code tran-sition input voltage and V RB is the lower reference voltage.Note that this is different from the normal Zero Scale Error.CONVERSION LATENCY See PIPELINE DELAY.
CONVERSION TIME is the time required for a complete measurement by an analog-to-digital converter.Since the Conversion Time does not include acquisition time,multi-plexer t up time,or other elements of a complete conver-sion cycle,the conversion time may be less than the Throughput Time.
DC COMMON-MODE ERROR is a specification which ap-plies to ADCs with differential inputs.It is the change in the output code that occurs when the analog voltages on the two inputs are changed by an equal amount.It is usually ex-presd in LSBs.
DIFFERENTIAL GAIN ERROR is the percentage difference between the output amplitudes of a given amplitude small signal,high frequency sine wave input at two different dc in-put levels.
DIFFERENTIAL NON-LINEARITY (DNL)is the measure of the maximum deviation from the ideal step size of 1LSB.DNL is commonly measured at the rated clock frequency with a ramp input.
DIFFERENTIAL PHASE ERROR is the difference in the out-put pha of a reconstructed small signal sine wave at two different dc input levels.
DYNAMIC SPECIFICATIONS of an ADC are tho pertain-ing to an AC input signal.The include S/N ratio,SNR,SI-NAD,S/(N+D),ENOB,THD,IMD,FPBW,and SSBW.
EFFECTIVE NUMBER OF BITS (ENOB,or EFFECTIVE BITS)is another method of specifying Signal-to-Noi and Distortion Ratio,or SINAD.ENOB is defined as (SINAD -1.76)/6.02and says that the converter is equivalent to a per-fect ADC of this (ENOB)number of bits.
FULL POWER BANDWIDTH is the frequency at which the reconstructed output fundamental drops 3dB below its low frequency value for a full scale input.The test is performed with f IN equal to 100kHz plus integer multiples of f CLK .The input frequency at which the output is −3dB relative to the low frequency input signal is the full power bandwidth.
FULL SCALE (FS)INPUT RANGE of the ADC is the input range of voltages over which the ADC will digitize that input.For V REF +=3.5V and V REF −=1.5V,FS =(V REF +)–(V REF −)=2.0V.
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FULL SCALE ERROR is a measure of how far the last code transition is from the ideal 11⁄2LSB below V REF +and is de-fined as:
V max +1.5LSB –V REF +where V max is the voltage at which the transition to the max code occurs.
FULL SCALE STEP RESPONSE is defined as the time re-quired after V IN goes from V REF −to V REF +,or V REF +to V REF −,and ttles sufficiently for the converter to recover and make a conversion with its rated accuracy.
GAIN ERROR (FULL SCALE ERROR)is the difference be-tween the input voltage just causing a transition to positive full scale and V REF -1.5LSB.
GAIN TEMPERATURE COEFFICIENT (FULL SCALE TEM-PERATURE COEFFICIENT)is the change in gain error di-vided by change in temperature.Usually expresd in parts per million per degree Celsius (ppm/˚C).
INTEGRAL NON-LINEARITY (INL)is a measure of the de-viation of each individual code from a line drawn from zero scale or negative full scale (1⁄2LSB below the first code tran-sition)through positive full scale (1⁄2LSB above the last code transition).The deviation of any given code from this straight line is measured from the center of that code value.The end point test method is ud.INL is commonly measured at rated clock frequency with a ramp input.
INTERMODULATION DISTORTION (IMD)is the creation of additional spectral components as a result of two sinusoidal frequencies being applied to the ADC input at the same time.It is defined as the ratio of the power in the intermodulation products to the total power in the original frequencies.IMD is usually expresd in dB.
MISSING CODES are tho output codes that are skipped or will never appear at the ADC outputs.T
he codes cannot be reached by any input value.
MSB (MOST SIGNIFICANT BIT)is the bit that has the larg-est value or weight.Its value is on half of full scale.
黄河俗语OFFSET ERROR is the difference between the ideal LSB transition to the actual transition point.
OUTPUT DELAY is the time delay after the edge of the input clock before the data update is prent at the output pins.OUTPUT HOLD TIME is the length of time that the output data is valid after the edge of the input clock.
OVERRANGE RECOVERY TIME is the time required after V IN goes from AGND to V REF +or V IN goes from V A to V REF −for the converter to recover and make a conversion with its rated accuracy.
PIPELINE DELAY (LATENCY)is the number of clock cycles between initiation of conversion and when that data is pre-nted to the output driver stage.Data for any given sample is available the Pipeline Delay plus the Output Delay after
January 2000
A/D Converter Definition Of Terms
©2000National Semiconductor Corporation MS101150
that sample is taken.New data is available at every clock cycle,but the data lags the conversion by the Pipeline Delay plus the Output Delay.
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PSRR (POWER SUPPLY REJECTION RATIO)is the ratio of the change in dc power supply voltage to the resulting change in Full Scale Error,expresd in dB.
QUANTIZATION ERROR is the error inherent in all A/D con-versions.Since even an ’ideal’converter
has finite resolu-tion,any analog voltage that falls beween two adjacent out-put codes will result in an output code that is inaccurate by up to 1⁄2LSB.
RATIOMETRIC OPERATION us the same reference volt-age that is ud for the ADC to drive the signal source such that the ratio of the output of that signal source to the refer-ence is a constant.When the driving voltage for that source is also ud as the voltage reference for the ADC,the ADC output code is a function of the ratio of the signal source out-put to the reference voltage and,for a limited reference volt-age range,is independent of the value of that reference volt-age.
RESOLUTION is the smallest analog increment correspond-ing to a 1LSB converter code change.For converters,reso-lution is normally expresd in bits,where the number of digital codes is equal to 2n .As an example,a 12-bit con-verter maps the analog signal into 212=4096digital codes.SAMPLING (APERTURE)DELAY is the time after the edge of the clock to when the input signal is acquired or held for conversion.
SIGNAL TO NOISE RATIO (SNR)is the ratio,expresd in dB,of the rms value of the input signal at the output to the rms value of the sum of all other spectral components below one-half the sampling frequency,not including harmonics or dc.
SIGNAL TO NOISE PLUS DISTORTION (S/(N+D)or SINAD)is the ratio,expresd in dB,of the rms value of the input signal at the output to the rms value of all of the other spectral components below half the clock frequency,includ-ing harmonics but excluding dc.
SPURIOUS FREE DYNAMIC RANGE (SFDR)is the differ-ence,expresd in dB,between the rms values of the input signal at the output and the peak spurious signal.where a spurious signal is any signal prent in the output spectrum that is not prent at the input.
STATIC SPECIFICATIONS are the specifications of an ADC pertaining to a DC signal input.The include gain error,off-t error,and differential and integral linearity errors.THROUGHPUT RATE is the maximun continuous conver-sion rate of the ADC.
THROUGHPUT TIME is the inver of the Throughput Rate.TOP OFFSET is the difference between the positive refer-ence voltage and the input voltage that just caus the out-put code to transition to full scale and is defined as E OT =V FT –V REF +where V FT is the full scale transition input volt-age.Note that this is different from the normal Full Scale Er-ror.
李敏镐吻戏TOTAL HARMONIC DISTORTION (THD)is the ratio,ex-presd in dB or dBc,of the rms total of the first six harmonic components to the RMS value of the input signal at the out-put.
TOTAL UNADJUSTED ERROR (TUE)is the maximum de-viation of the voltage corresponding to the center of a digital code’s associated input voltage span from the ideal ca.Total unadjusted error includes offt error,Gain error,and differential and integral nonlinearity errors.
ZERO SCALE OFFSET ERROR is the difference between the ideal input voltage (1⁄2LSB)and the actual input voltage that just caus a transition from an output code of zero to an output code of one.
ZERO ERROR is the difference between the ideal input volt-age (1⁄2LSB)and the actual input voltage that just caus a transition from an output code of zero to an output code of one.
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