Mixed-Signal VLSI Design Course Code: EE719 Department: Electrical Engineering Lecture 20: February 19, 2018 Instructor Name: M. Shojaei Baghini E-Mail ID: mshojaei@ee.iitb.ac.in 1
2 2 Module 27 Histogram (Code Density Test) for Measuring DNL/INL of ADC Reference • Chapter 5, the Data Conversion Handbook, Analog Devices, 2005. IIT-Bombay Lecture 20 M. Shojaei Baghini
3 3 Basic Concept • Collecting many digitized samples for a desirable shape of input signal • A slow triangular waveform which exceeds the full scale range provides equal distribution of the input samples. • Number of occurrences for each code is a measure of DNL for that code. If DNL is zero there will be equal number of occurrences for each code. IIT-Bombay Lecture 20 M. Shojaei Baghini
4 4 Measuring DNL and INL – Histogram Method Automated measurement • Almost independent of internal noise of ADC due to • averaging over many samples Input waveform (triangular or sinusoid input?) • Amplitude? Frequency? • Periodic triangular waveform generator (more than FS range) IIT-Bombay Lecture 20 M. Shojaei Baghini
5 5 Procedure Triangular waveform generator N-bit (more than FS range) Total number of samples for codes 1 to 2 N -2: M T (0 and 2 N -1 are • not included.) h(n): Measured number of hits for code # n • Ideal value of h(n) = M T /(2 N -2) • DNL of code n (in LSB unit) = !"#$%& ((*) ,-.%& ((*) − 1 • Condition on the frequency of triangular input • What about the first and last code, offset and gain error? • What about monotonicity? (linked to distortion and hence FFT is • also necessary.) IIT-Bombay Lecture 20 M. Shojaei Baghini
6 6 Example Histogram for a Triangular Input IIT-Bombay Lecture 20 M. Shojaei Baghini
7 7 Derivation of DNL from the Histogram IIT-Bombay Lecture 20 M. Shojaei Baghini
8 8 Derivation of INL from DNL IIT-Bombay Lecture 20 M. Shojaei Baghini
9 9 Requirements Number of collected samples and duration of • DNL/INL simulation/measurement depends on the desirable measurement accuracy. Enough number of analog samples per code for ADC • simulation. Slow varying ramp. • M: Number of samples per code ⇒ Total required number of samples excluding overhead = 2 N × M Measurement time = 2 N × M × T s × K • IIT-Bombay Lecture 20 M. Shojaei Baghini
10 10 Module 28 Limitations of the Triangular Input for Measuring DNL/INL of ADC using Histogram Method Reference • Chapter 5, the Data Conversion Handbook, Analog Devices, 2005. IIT-Bombay Lecture 20 M. Shojaei Baghini
11 11 Histogram Method Periodic waveform generator (more than FS range) IIT-Bombay Lecture 20 M. Shojaei Baghini
12 12 Discussion Around the Triangular Input Generation of the input? A high resolution fast settling • DAC? Accuracy of the measurement can be verified by • repeating the measurements several times. What about linearity of the triangular input? • Remember such input signal is not even single tone and filtering should not add to the non-linearity. Why not to use a single-tone input with high linearity • and high SNR? IIT-Bombay Lecture 20 M. Shojaei Baghini
13 13 Single-tone Input Ideal value of h(n) • = p(n) × M T DNL of code n • (in LSB unit) = !"#$%& ((*) ,-.%& ((*) − 1 𝑞 𝑜 = 1 𝜌 sin 89 𝑜𝑊 𝐺𝑇 2 𝑂 ×𝐵 − sin 89 (𝑜 − 1)𝑊 𝐺𝑇 2 𝑂 ×𝐵 IIT-Bombay Lecture 20 M. Shojaei Baghini
14 14 End of Lecture 20 IIT-Bombay Lecture 20 M. Shojaei Baghini
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