adc testing 2
TRANSCRIPT
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ADC TEST
Mixed Signal VLSI
Xunyu Zhu
Dr. Chris Hutchens
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ADC TEST
Test methods1. Static test - SIN Histogram
i.e. Gain and Offset2. Dynamic test –
i.e. ENOB using 16K FFTSIN fit.
Outline
Does this make sense??
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ADC TEST
Static Tests• Number of digitized bits• Gain • Offset • Differential Nonlinearity (DNL)• Integral Nonlinearity (INL)• Monotonicity
Test Specification
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ADC TEST
• Dynamic Tests• Effective number of bits (ENOB)• Signal-to-noise ration (SNR)• Total Harmonic distortion (THD)• Total spurious distortion (TSD)• Spurious-free dynamic range (SFDR)
Test Specification
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ADC TEST
Objective:• Converter accuracy • Transfer function of the converter• Monotonicity of the converter• Quantify the gain, offset, DNL and INL of the converter
Disadvantage:• Nonlinearites which coupled to the input signal bandwidth cannot be revealed• For high bit converters, measurement is lengthy
Static Test
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ADC TESTTest Setup
Clock
AnalogDigital
DigitalDigital Control
Ramp???? test setup
• Each voltage step less or equal to 1/8 LSB• At lest 10 samples sampled at each voltage level
Logic Analyzer -Word length > NWord depth > > 20π*2N
Pattern generator -Period jitter (peak to peak)less than
122
1 N
Bf
fB is the input signal frequencyN is the ADC resolution
Source generator-Resolution N +3 bits
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ADC TESTStatic Test
ADC static test result
G is the GainVos is the offsetT1 is the ideal value corresponding to T[1]T[k] is the input valueQ is the ideal width of a code binε[k] is the residual error
Transfer function described as below
Using conventional linear least-squares estimation techniques, get G and Vos as below
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ADC TEST
Differential nonlinearity
Static Test
Too Many fonts
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ADC TESTStatic Test
Illustration of DNL and INL
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ADC TESTStatic Test
Integral nonlinearity
Q is the ideal code bin width, expressed in input units,VFS is the full-scale range of the ADC in input units.
The maximum INL is the maximum value of |INL[k]| for all k.
Where INL(k) is the integral nonlinearity at output code k, ε[k] is the difference between ideal output bin T’[k] and T[k] computed from G and Vos,
that is,
osVkTGTkQkTkTk ][)1(][]['][ 1
Too many different fonts
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ADC TEST
• Objective- Measure– Harmonic and spurious distortion information
– Input bandwidth
– Signal-to-noise ratio
– Effective number of bits (ENOB)
– Spurious-free dynamic range (SFDR)
Dynamic Test
Think about the consistency with slide 4
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ADC TEST
• Disadvantage– Cannot test for monotonicity of the ADC– Input signal must be sampled using an integer
number of cycles– Histogram test measure the noise of the ADC
• Test methods– Histogram test– FFT test
Dynamic Test
What is the recommended method for measuring the noise of an ADC?
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ADC TEST
Test setup for histogram and FFT test
Dynamic Test
Clock
AnalogDigital
Digital
Logic Analyzer -Word length > NWord depth > 2π*2N ???
Pattern generator -Period jitter (peak to peak)less than
122
1 N
Bf
fB is the input signal frequencyN is the ADC resolution
Source generator-Resolution N +3 bits
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ADC TEST
• Record length selection
There must be an exact integer number of cycles in a record, and the number of cycles in a record must be relatively prime to the number of samples in the record.
si fM
Jf
fi is the input signal frequencyfs is the sampling signal frequencyJ is the number of cycles per recordM is a record length
Histogram Test
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ADC TEST
The procedure to find the near-optimum input signal frequency
a) Find an integer, r, such that the desired frequency is approximately fs/r.
b) Let J equal the number of full cycles that can be recorded at the frequency in step a)
J=int(M/r)
c) Let fi equal
1i
rJ
Jff s
Histogram Test cont’
a) b) etc are NOT consistent with the rest of the ppt slides
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ADC TESTHistogram Test cont’
Illustration of histogram test results
Review SIN reconstruction after this slide
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ADC TEST
• Total harmonic distortion
The THD is also often expressed as a dB ratio with respect to rms amplitude of the fundamental component of the output,
FFT Test
bandwidthfullinfrequencyalfundermenttheof
mirrorofmagnitudeaveragedtheisffX
frequencyalfundermenttheofmagnitudeaveragedtheisfX
ffXfXA
A
THDTHD
isavm
iavm
isavmiavmrms
rmsdB
)(
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))(())((2
1
)(log20
22
10
Too Many Fonts
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ADC TESTFFT Test
• Total spurious distortion
Each of the spurious frequencies in fsp is the frequency of a persistent spectral output component that is neither the fundamental nor a harmonic
distortion component.
samplesofnumbertheisM
distortionspurioustheisf
fXM
TSD
sp
nnspavm )(
1][
Too Many Fonts
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ADC TESTFFT Test
• Spurious-free dynamic range (SFDR)
The ratio of the amplitude of the ADC output averaged spectral component at the input frequency, fi, to the amplitude of the largest harmonic or spurious spectral component observed over the full Nyquist band:
)})()({max
)((log20)(
,
10havgsavg
ff
iavg
fXorfX
fXdBSFDR
hs
WhereXavg is the averaged spectrum of the ADC output,fi is the input signal frequency,fs and fh are the frequencies of the set of harmonic and
spurious spectral components
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ADC TESTFFT Test
Spectrum of a sine wave and its harmonics
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ADC TESTFFT Test
Spectrum of a real ADC FFT test result
Fundamentalfrequency Harmonics
Spurious frequency
SFDR
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ADC TEST
• SINAD is the ration of the signal to the total noise• Time domain calculation
noiserms
signalrmsSINAD
givenisSINADratiodistortionandnoisetosignalThe
waveefitbesttheofsetdatatheisy
setdatasampletheisy
where
yyM
noiserms
n
n
M
nnn
)(
sin
)(1
'
2/1
1
2'
Signal-to-noise and distortion ratio (SINAD)
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ADC TEST
• Frequency domain calculation
2/11
0
2
22
)(1
))(())((1
M
mmavm
isavmiavm
fEM
noiserms
ffXfXM
signalrms
• Effective number of bits (ENOB)
))2/(
(log)5.1(log2
1)(log 222 V
ASINADENOB
WhereA is the amplitude of the sine wave fitted to the outputV is the full-scale range of the ADC under test
Signal-to-noise and distortion ratio (SINAD) cont’
Summary Must follow