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5962-9152101M3A 参数 Datasheet PDF下载

5962-9152101M3A图片预览
型号: 5962-9152101M3A
PDF下载: 下载PDF文件 查看货源
内容描述: [4-channel Simultaneous Sampling, 12-Bit Data Acquisition System]
分类和应用: 信息通信管理转换器
文件页数/大小: 16 页 / 413 K
品牌: ADI [ ADI ]
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AD7874  
Total H ar m onic D istor tion (TH D )  
P eak H ar m onic or Spur ious Noise  
T otal Harmonic Distortion (T HD) is the ratio of the rms sum  
of harmonics to the rms value of the fundamental. For the  
AD7874, T HD is defined as  
Harmonic or Spurious Noise is defined as the ratio of the rms  
value of the next largest component in the ADC output spec-  
trum (up to fs/2 and excluding dc) to the rms value of the fun-  
damental. Normally, the value of this specification will be  
determined by the largest harmonic in the spectrum, but for  
parts where the harmonics are buried in the noise floor the peak  
will be a noise peak.  
2
2
2
2
2
V2 +V3 +V4 +V5 +V6  
THD = 20 log  
V1  
where V1 is the rms amplitude of the fundamental and V2, V3,  
V4, V5 and V6 are the rms amplitudes of the second through the  
sixth harmonic. T he T HD is also derived from the FFT plot of  
the ADC output spectrum.  
AC Linear ity P lot  
When a sine wave of specified frequency is applied to the VIN in-  
put of the AD7874 and several million samples are taken, a his-  
togram showing the frequency of occurrence of each of the 4096  
ADC codes can be generated. From this histogram data it is  
possible to generate an ac integral linearity plot as shown in Fig-  
ure 11. T his shows very good integral linearity performance  
from the AD7874 at an input frequency of 10 kHz. T he absence  
of large spikes in the plot shows good differential linearity. Sim-  
plified versions of the formulae used are outlined below.  
Inter m odulation D istor tion  
With inputs consisting of sine waves at two frequencies, fa and  
fb, any active device with nonlinearities will create distortion  
products at sum and difference frequencies of mfa ± nfb where  
m, n = 0, 1, 2, 3 . . ., etc. Intermodulation terms are those for  
which neither m or n are equal to zero. For example, the second  
order terms include (fa + fb) and (fa – fb) while the third order  
terms include (2fa + fb), (2fa – fb), (fa + 2fb) and (fa – 2fb).  
(V(i) V(o)) 4096  
INL(i) =  
i  
V( fs) V(o)  
Using the CCIF standard where two input frequencies near the  
top end of the input bandwidth are used, the second and third  
order terms are of different significance. T he second order terms  
are usually distanced in frequency from the original sine waves  
while the third order terms are usually at a frequency close to  
the input frequencies. As a result, the second and third order  
terms are specified separately. T he calculation of the intermodu-  
lation distortion is as per the T HD specification where it is the  
ratio of the rms sum of the individual distortion products to the  
rms amplitude of the fundamental expressed in dBs. In this case,  
the input consists of two, equal amplitude, low distortion sine  
waves. Figure 10 shows a typical IMD plot for the AD7874.  
where INL(i) is the integral linearity at code i. V(fs) and V(o) are  
the estimated full-scale and offset transitions, and V(i) is the es-  
timated transition for the ith code.  
V(i), the estimated code transition point is derived as follows:  
π cum(i)  
[
]
V(i) = A Cos  
N
where A is the peak signal amplitude, N is the number of histo-  
gram samples  
i
and cum(i) =  
V(n)occurrences  
n=o  
Figure 11. AD7874 AC INL Plot  
Figure 10. AD7874 IMD Plot  
REV. C  
–9–