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Test AD7880(ADC) by the Teradyne FLEX Tester

时间:2010-01-26 10:36来源:www.ictest8.com 作者:Larry Lovell 点击:

  本文讲述了如何使用Teradyne的FLEX测试机,开发一款混合信号芯片AD7880---12位ADC测试的详细过程,从ADC静态及动态参数的意义,到测试程序的编写都非常细致入微,相信对FLEX测试机的学习,ADC参数的理解方面都有非常高的参考价值!好资料不需要很多,一份足矣!详细如下:

      ADC – 101 Testing on the FLEX
      
                           Presented by: Larry Lovell
                            Teradyne, Inc.
                            Richardson, TX

Outline for Today
 Static Definitions
 ADC Static Code Example
 Dynamic Definitions
 ADC Dynamic Code Example

Static Testing of ADC Device
 Following this discussion we should:
 Be able to describe what is to be measured
by Static Testing.
 Offset Error
 LSB of device
 Gain Error
 INL
 DNL
 Gain an understanding of these terms and
how to measure them using one of the
many methods available.

Definitions: Static Testing of
ADC’s

  Zero Scale
  FSR = Full Scale Range
  LSB = Least Significant Bit
  Offset Error
  Gain Error
  DNL = Differential Non Linearity
  INL = Integral Non Linearity

 

Least Significant Bit
  LSB = Least Significant Bit = FSR/(2n-2)
  LSB for an 8 bit part is 256 - 2 = FSR/254
  LSB for an 4 bit part is 16 – 2 = FSR/14
  LSB for a 12 bit part is 4096 – 2 = FSR/4094
  Example:
 FSR = 5 volts
 For an 8 bit ADC, the LSB would be 19.68 mV
 For a 12 bit ADC, the LSB would be 1.22 mV

………………

Dynamic Testing
 Following this discussion we should:
 Be able to describe what is gained by using an FFT when testing an ADC device.
 Describe and define the difference between SNR, THD and SINAD.
 Be able to describe the key elements of a coherent signal and why it is important to maintain coherency
 Describe basic concepts of Sampling both from the concept of Sourcing and Capturing of Analog Signals

Dynamic Single Tone
Testing
  When testing an ADC in Dynamic mode, the following need to be created:
 A sinusoidal input signal low in distortion and harmonic content.
 Reference voltage that is highly stable
 Good grounding techniques

VERY IMPORTANT EQUATIONS
Source and Capture
Coherency Formula for Testing
fs /N=ft /M
  fres = fs/sample_size
  fbin = fi/fres
UTP = M/ft= N/fs
fres = 1/UTP = fs/N = ft /M
fs = Sample Rate
ft = fi =Frequency of Interest or Test Frequency
N = Number of Samples
M = fbin or Number of cycles in Time Domain = fbin
UTP = Unit Test Period
FF = Fourier Frequency = fres
The Nyquist frequency is defined as fs/2

Dynamic Single Tone
Testing
  When testing an ADC in Static mode, it is important that we start the ramp signal below the all 0’s and first transition point and that we stop the ramp signal above the all 1’s transition point.
  When testing an ADC in Dynamic mode, we need to avoid the all 0’s and all 1’s codes. This will cause clipping or distortion in our signal.
 Most devices specify the amplitude to use when testing in Dynamic mode.

Dynamic Single Tone
Testing
  SNR (Signal to Noise Ratio): The power ratio of carrier signal against the sum of all non-harmonic noise power within a captured waveform.
  THD (Total Harmonic Distortion): The power sum of all harmonics to the power of the carrier.
  SINAD (Signal to Noise And Distortion): The power ratio of carrier signal against the sum of all remaining power including noise and harmonics within a captured waveform.
  SFDR (Spurious Free Dynamic Range): The power ratio of carrier signal against the power of the second highest frequency component (not including DC).
Note: Because of magnitude considerations, all ratios above are
usually expressed in dB.

………………

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Test AD7880(ADC) by the Teradyne FLEX Tester

作者:derek sun 整理
2010/01/26

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