Download ADC与DAC

ADC与DAC
衡量指标：
• 静态指标：DNL, INL;
•
动态指标：SNR, SINAD, THD ,ENOB,
IMD,etc.
动态指标（1）
• 静态指标反映的特点有限，主要是慢速变
化特性，也称之为DC传输特性，对于高速
D/A,A/D来说，更需要AC传输特性来表征，
反映不同频率信号的响应。
• 主要反映了D/A, A/D器件的高速工作情况下
的性能，诸如，VEDIO DAC, TXDAC，
TX ADC等，
动态指标（2）
• SNR: Signal to Noise Ratio
• SINAD: Signal to Noise And Distortion
Ratio
• THD: Total Harmonic Distortion
• ENOB: Effective Number Of Bits
• SFDR: Spurious-Free Dynamic Range
• Two-tone IMD……..
Magnitude
Frequency Domain Analysis
S
Fundamental
Signal
Spurious
Harmonics
H2
H3
H4
H5
Noise
Ft
(M)
Frequency
动态特性的测试方法（1）
• 对于DAC来说，相对简单一些，通过编程产
生单频信号，然后将输出的信号发送到频谱
分析仪。
数字源
DAC
频谱分析仪
动态特性的测试方法（2）
Clock
Source
Analog
Source
DUT n Digital
(ADC)bits Capture
Data
Processing
(FFT)
Sinusoidal Wave
Frequency Spectrum
RXADC 测试环境要求（1）
• Input signal requests：
1：Quality of signal：SNR, THD…….
2：Amplitude , frequency and common
voltage of signal .
3：four orthogonal differential signals；
RXADC 测试环境要求（2）
• How to select sample numbers ----coherent sampling
Fin / Fsample = Ncycle / Nrecord,
Fin : Periodic input signal
Fsample : Sampling frequency of the ADC
Ncycle : Integer number of cycles within
the sampling window
Nrecord : Number of data points in the
sampling window or FFT
Coherent sampling
Uncoherent sampling
Windowing
RXADC 测试环境要求（3）
• 在rxadc的测试中，
Fin= Ncycle * Fsample / Nrecord
Fin (kHz)
Fsamp (kHz) Nrecord
Ncycle
10.3819
40.1736
60.0347
270.833
270.833
270.833
23
89
133
600
600
600
RXADC 测试环境要求（4）
• Spectral leakage
sample sequence not meets coherent
sampling
• Windowing
minimizes spectral leakage
Window function
• Window types: Rectangular, Hamming ,
Hanning, Blackman ……
• How to select window function:
1: -3dB bandwidth ;
2: -6dB bandwidth
3: maximum side-lobe level
4: side-lobe roll-off rate
• Blackman windows ----single tone test
Windows function
Windows function
Calculation (1): FFT
• Ps = sum{Pf(m-k):1:Pf(m+k)};
• Pdc = sum{Pf(1:k)};
• Ph = sum{Ph(2:n)} ;
Ph(i)= sum{Ph(i-1:i+1)};
• Pn = sum(Pf) - Ps- Pdc – Ph;
• Signal bin 的选择：
Calculation (2): FFT
•
•
•
•
S/N
= 10* log(Ps/Pn);
SINAD = 10* log[Ps/(Pn+Ph)];
THD = 10* log(Ph/Ps);
SFDR = 10* log[Ps / Pmax.spurious
Level]；
• ENOB = (SINAD - 1.763)/ 6.02
Signal bin
S/N = 10* log(Ps/Pn);
=====
S’/N’ = 10* log[Ps(1+<>)/Pn(1-10%)]
= 10*log[10/9]+log(Ps/Pn)
= 0.46 + S/N
I/Q match
• An ideal sinusoidal I/Q signal pair :
y(t) = A exp(i(ωt + φ))
= A cos(ωt + φ) + i A sin(ωt + φ)
I/Q mismatch
• Amplitude mismatch α and phase
mismatch ε :
y(t) = A cos(ωt + φ) + i α A sin(ωt +
φ + ε)
= 0.5 (1 + α exp(i ε)) A exp(i(ωt +
φ)) + 0.5 (1 - α exp(-i ε)) A exp(-i(ωt + φ))
I/Q mismatch calculation
• Amplitude
α=20log(Iamp/Qamp);