参数资料
| 型号： | HSC-ADC-AD922XFFAZ |
| 厂商： | Analog Devices Inc |
| 文件页数： | 43/44页 |
| 文件大小： | 0K |
| 描述： | ADAPTER FOR AD922X FAMILY |
| 标准包装： | 1 |
| 附件类型： | 适配器 |
| 适用于相关产品： | AD922X 系列 |
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HSC-ADC-EVALA-SC/HSC-ADC-EVALA-DC
APPENDIX: SAMPLING AND FFT FUNDAMENTALS
Wn = 0.5 ? 0.5 × cos ?
? ?
COHERENT SAMPLING
In a coherent system, the analog and clock sources must be
synchronized, and the analog and clock input frequencies must
be selected such that given 2 N ( N is an integer number) samples,
there is an integer number of whole sine wave cycles. The
number of cycles should ideally be a prime number. Selecting a
prime number ensures that the same converter codes are not
repeated over and over, therefore exercising as many converter
codes as possible. Although a crystal oscillator can be used as an
clock source in this technique, two synchronized signal
synthesizers are generally preferred because special hardware
may be required to ensure the crystal oscillator is synchronized
with the analog source. The following equation can be used to
mathematically calculate the correct analog and clock
frequencies for a coherent system:
M = Sample Size (2 N )
n = Indexed Sample Number
The weighting function for a Hanning window is:
? 2π × n ?
? M ?
where:
M = Sample Size(2 N )
n = Indexed Sample Number
FFT CALCULATIONS
Whether a system is coherent or a windowing function has
fin
fs
where:
=
M
Mc
been applied, the resulting data will be processed via a discrete
fourier analysis that translates the discrete time-domain
samples into the frequency domain. Because in practice
processing the data quickly is desired, a Fast Fourier Transform
(FFT) is used, which is simply an algorithm that reduces the
Wn = a 0 ? a 1 × cos ? ?
? 2 π × n ? ? 2 π × 2 n ? ? 2 π × 3 n ?
M ? ?
M ? ?
? + a 2 × cos ? ? ? a 3 × cos ? ?
? M ?
?
?
dB = 10 × log 10 ? ?
? Magnitude ?
fin = Analog Input Frequency
fs = Sampling Clock (encode) Frequency
M = Sample Size (2 N )
Mc = Number of Cycles of Sine Wave
If the requirements of the coherent system defined above are
not met, the discrete time samples will appear discontinuous at
the end of the captured samples and the results will be invalid.
WINDOWING FUNCTIONS
It is sometimes desirable to use a windowing function instead of
coherent sampling to reduce the restrictions on the analog and
encode sources. Two popular windowing functions are the
Blackman Harris 4-Term and the Hanning window. With
windowing, the time-domain samples are multiplied by the
appropriate weighting function that weights the time-domain
data such that the discontinuities at the end of the captured
samples have less significance. The weighting function for a
Blackman Harris 4-Term window is:
?
where:
a0 = 0.35875
a1 = 0.48829
a2 = 0.14128
a3 = 0.01168
required mathematical calculations. There are many FFT
algorithms available but the most popular is the radix 2
algorithm. Regardless of the algorithm, for each time-domain
sample a complex conjugate pair ( r ± jx ) will be generated from
the FFT. For example, if the time-domain sample size is 16,384,
the resulting FFT array will contain 16,384 complex samples. To
generate a frequency domain plot from this data, the magnitude
of each complex sample must be calculated. The magnitude can
be computed using the following equation:
Magnitude = Re 2 + Im 2
If the input data to the FFT is complex, the FFT will contain
16,384 magnitudes representing frequencies between plus and
minus fs / 2. Although complex ADCs are not available, it is very
common to use two ADCs to synchronously sample the I and Q
data streams from a quadrature demodulator. If the data input
to the FFT is real, representing the data from a single ADC, the
last 8192 samples represent a mirror image of the first 8192
samples. Because this is an exact mirror image, the last 8192
samples can be ignored.
With the data set processed, there are two ways to evaluate the
ADC performance, graphically and computationally. To plot the
data in a meaningful way, the magnitude data must be
converted to decibels (dB). This can be done with the formula:
?
? FullScale ?
where Magnitude is the individual array elements computed
above, and FullScale is the FullScale magnitude. It is important
to note that the computation for dB assumes the square root
Rev. 0 | Page 43 of 44
相关PDF资料 |
PDF描述 |
|---|---|
| HSC-ADC-EVALB-DCZ | KIT EVAL ADC FIFO DUAL-CH USB HS |
| HSC-ADC-EVALCZ | KIT EVAL ADC FIFO HI SPEED |
| HSHM-GUIDE-PIN-4 | CONN GUIDE PIN 8-32 UNC-2A |
| HSHM-GUIDE-SOCKET-1 | CONN HSHM GUIDE SOCKET 1 |
| HTC-10M | FUSEBLOCK 250V FOR 5X20 FUSE UL |
相关代理商/技术参数 |
参数描述 |
|---|---|
| HSC-ADC-AD9283FFAZ | 制造商:Analog Devices 功能描述:ADAPTER FOR AD9283, AD9057 - Bulk |
| HSC-ADC-EVALA-DC | 制造商:Analog Devices 功能描述:FIFO ADC DUAL CHANNEL USB EVAL KIT - Bulk |
| HSC-ADC-EVALA-SC | 制造商:Analog Devices 功能描述:FIFO ADC SINGLE CHANNEL USB EVAL KIT - Bulk |
| HSC-ADC-EVALB-DC | 制造商:AD 制造商全称:Analog Devices 功能描述:High Speed ADC USB FIFO Evaluation Kit |
| HSC-ADC-EVALB-DCZ | 功能描述:KIT EVAL ADC FIFO DUAL-CH USB HS RoHS:是 类别:编程器，开发系统 >> 配件 系列:- 标准包装:1 系列:- 附件类型:适配器板 适用于相关产品:RCB230，RCB231，RCB212 配用:26790D-ND - RCB BREAKOUT BOARD RS232 CABLE |
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