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5962-8951801RA 参数 Datasheet PDF下载

5962-8951801RA图片预览
型号: 5962-8951801RA
PDF下载: 下载PDF文件 查看货源
内容描述: [High Speed, µP-Compatible, CMOS, 8-Bit Sampling ADC]
分类和应用: 转换器
文件页数/大小: 16 页 / 290 K
品牌: ADI [ ADI ]
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AD7821  
TERMINOLOGY  
INTERMODULATION DISTORTION  
LEAST SIGNIFICANT BIT (LSB)  
With inputs consisting of sine waves at two frequencies, fa and  
fb, any active device with nonlinearities will create distortion  
products, of order (m+n), at sum and difference frequencies of  
mfa+nfb, where m, n = 0, 1, 2, 3…. Intermodulation terms are  
those for which m or n is not equal to zero. For example, the  
second order terms include (fa + fb) and (fa – fb), and the third  
order terms include (2fa + fb), (2fa – fb), (fa + 2fb) and  
(fa – 2fb). For the AD7821 intermodulation distortion is calcu-  
lated separately for both the second and third order terms.  
An ADC with 8-bit resolution can resolve one part in 28 (1/256  
of full scale). For the AD7821 operating in either the unipolar  
or bipolar input range with 5 V full scale, one LSB is 19.53 mV.  
TOTAL UNADJUSTED ERROR  
This is a comprehensive specification which includes relative  
accuracy, offset error, and full-scale error.  
SLEW RATE  
Slew rate is the maximum allowable rate of change of input  
signal such that the digital sample values are not in error.  
SIGNAL-TO-NOISE RATIO (SNR)  
Signal-to-noise ratio is measured signal-to-noise at the output of  
the ADC. The signal is the rms magnitude of the fundamental.  
Noise is the rms sum of all nonfundamental signals (excluding  
dc) up to half the sampling frequency. SNR is dependent on the  
number of quantization levels used in the digitization process.  
The theoretical SNR for a sine wave input is given by:  
TOTAL HARMONIC DISTORTION (THD)  
Total harmonic distortion is the ratio of the square root of the  
sum of the squares of the rms value of the harmonics to the rms  
value of the fundamental. For the AD7821, total harmonic dis-  
tortion is defined as  
SNR = 6.02N + 1.76 dB  
where N is the number of bits in the ADC. Thus, for an ideal  
8-bit ADC, SNR = 50 dB.  
(
)
V22 +V32 +V42 +V52 +V62  
(
)
20 log  
dB  
V
1
PEAK HARMONIC OR SPURIOUS NOISE  
where V1 is the rms amplitude of the fundamental and V2, V3, V4,  
V5, and V6 are the rms amplitudes of the individual harmonics.  
Peak harmonic or spurious noise is the rms value of the largest  
nonfundamental frequency (excluding dc) up to half the sam-  
pling frequency to the rms value of the fundamental.  
REV. B  
–5–