AN2438 Freescale Semiconductor / Motorola, AN2438 Datasheet
AN2438
Related parts for AN2438
AN2438 Summary of contents
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... Freescale Semiconductor, Inc. Application Note AN2438/D 2/2003 ADC Definitions and Specifications By: J. Feddeler and Bill Lucas 8/16 Bit Division Systems Engineering Austin, Texas Introduction This application note will help users of analog-to-digital converters (ADC) understand common terminologies used in the electronics industry to define ADC operation and performance. There are many terms and parameters used to define the performance of ADC’ ...
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... Freescale Semiconductor, Inc. AN2438/D • • • • ADC Transfer The ADC converts an input voltage to a corresponding digital code. The curve Curves describing this behavior is the Actual Transfer Function. The Ideal Transfer Function represents this behavior assuming the ADC is perfectly linear, or that a given change in input voltage will create the same change in conversion code regardless of the input’ ...
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... V V REFH REFL REFH Input Voltage in LSB Figure 1. Quantization Graphs ADC Definitions and Specifications Go to: www.freescale.com AN2438/D Quantization Error (EQ) and Method ) in this case is from 0LSB this case is Q ½ Compensated Ideal TF LSB Quantization Conversion Error $7 (±½ ) ...
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... Freescale Semiconductor, Inc. AN2438/D Adjusted Transfer Function ½LSB Comp. Adjusted TF Conversion $ Zero-Scale Error The Adjusted Transfer Function is then quantized in the same method as the Ideal Transfer Function. The Adjusted Code Width is therefore: ACW = [(V The Adjusted Transfer Function is then: Code = (V Best-Fit Transfer Function ½ ...
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... Adjusted Transfer $1 Function (+) Zero-Scale Error REFH Input Voltage in LSB Figure 2. Endpoints Error Graph ADC Definitions and Specifications Go to: www.freescale.com AN2438/D Zero-Scale Error and Full-Scale Error x)[ICW(i)] Offset and Gain Error (+) Gain Error Conversion $7 Adjusted Straight-Line $6 Trans Func Ideal S.L. Transfer ...
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... Freescale Semiconductor, Inc. AN2438/D Offset and Gain Error Zero-Scale Errors and Full-Scale Errors can be used to calculate Offset and Gain Errors. These terms are used to define the performance on many industry-standard ADC’s but the definitions used vary and can be misleading or inconsistent. • ...
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... DNL = -1 Code $ missing $ REFH REFH REFL Input Voltage in LSB ADC Definitions and Specifications Go to: www.freescale.com AN2438/D Differential Non-Linearity (DNL) Non-Monotonicity Conversion $7 $6 DNL = +1 Code $2 is converted after $ ...
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... Freescale Semiconductor, Inc. AN2438/D Related to DNL are two critical figures of merit used in defining ADC operation. These are: • • Some literature suggests that a DNL of greater than 1.0 LSB may indicate non- monotonicity. Non-monotonicity is usually accompanied by large, positive DNL (>1.0 LSB), although a non-monotonic situation can be coincident with a DNL of less than 1 ...
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... Code Error is the error between the ideal code and the current code. This is the only figure of merit that measures by the quantized output instead of voltage. The code error is the Total Unadjusted in LSB, rounded to the nearest integer. ADC Definitions and Specifications Go to: www.freescale.com AN2438/D Integral Non-Linearity (INL) Code Error Conversion $7 Code Error ...
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... Freescale Semiconductor, Inc. AN2438/D Power Supply Noise Error Power Supply Noise Error (ENS) is the difference in conversion caused by power supply noise (on the V Power Supply Noise Errors are caused by: • • • Power Supply Noise Error is ultimately inherent in any ADC design reduced in the design phase by the use of differential, cascaded circuits (increases PSRR), reducing parasitics (increase PSDR), and matching parasitics on the input and reference paths (increases DPSDR) ...
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... SSAD capacitor near source, low resistive impedance and no choke). This increases the Reference Coupling Ratio, reducing differential noise. ADC Definitions and Specifications Go to: www.freescale.com AN2438/D Input to Reference Differential Noise Error ) relative to the other. Input Noise ) that will be coupled onto the REFH ...
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... Freescale Semiconductor, Inc. AN2438/D • • • Noise Error Mechanism Regardless of the type of noise (Power Supply Noise or Input to Reference Differential Noise), the error mechanism is the same. While the DC-average of most noise is zero (primarily due to the power supply which sources the reference or input), the short-term average is non-zero as shown in The amount of error depends on the magnitude and decay rate of the noise relative to the width of the sample or compare window ...
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... If the waveform is predictable, the maximum noise error (therefore, the number of cycles required to average it out) can be reduced. This type ADC Definitions and Specifications Go to: www.freescale.com AN2438/D Synchronous Noise Offset Error Figure 5, occurs Figure 5) of this ...
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... Freescale Semiconductor, Inc. AN2438/D • • Input Leakage Offset Error (E There is an additional source of input error that is often overlooked but can be extremely significant. Leakage on the Analog input pin or on the PC board can cause a voltage drop across the resistive portion of the Analog Input Source. ...
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... ADC’s comparator input. Few 10b ADC architectures are compatible with this method (full-RDAC SAR architectures can use this type of acquisition but are usually limited to about 7b of accuracy). ADC Definitions and Specifications Go to: www.freescale.com AN2438/D Acquisition Error (EAQ) ) can IN 15 ...
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... Freescale Semiconductor, Inc. AN2438/D Acquisition Time (Sample and Hold) and Error Calculations A number of steps are required during an analog-to-digital conversion. When an analog-to-digital conversion begins, one channel select switch is closed, allowing the sample and hold capacitor (C switch is then opened. The charge applied to the sample and hold capacitor is then converted into a digital representation by the successive approximation register ...
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... AIN (>10 kΩ) are possible if a large provided between samples. In order to AS ADC Definitions and Specifications Go to: www.freescale.com AN2438/D ) — This is the frequency ATDCLK ) — This is the frequency that a given ) — This is the difference SAMP ) — This is the difference between AIN ...
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... Freescale Semiconductor, Inc. AN2438/D ∆V SAMP 10 kΩ. The maximum value of 10 kΩ for R the worst case condition of maximum ∆V Summary of Specification Parameters The following terms and simplified definitions will be used to describe Motorola’s future ADC’s: • • • • ...
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... Differential Non-Linearity (DNL) — The difference between the Current Code Width and the Ideal Code Width. Endpoint INL — Integral Non-Linearity. ADC Definitions and Specifications Go to: www.freescale.com AN2438/D Common ADC Terminology ) — The real portion of the Analog AIN and the IN ...
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... Freescale Semiconductor, Inc. AN2438/D • • • • • • • • • • • • • • • • • • 20 For More Information On This Product, Full-Scale Conversion — The maximum code output by the ADC, typically $3FF for a 10b ADC. ...
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... V . REFL ½LSB Compensated Quantization — Technique in which the ideal transfer function’s first transition voltage is shifted to cause the first transition voltage at ½LSB instead of 1LSB. ADC Definitions and Specifications Go to: www.freescale.com AN2438/D Conclusion . SSAD while maintaining a minimum DDAD . REFL ...
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... Motorola and the Stylized M Logo are registered in the U.S. Patent and Trademark Office. digital dna is a trademark of Motorola, Inc. All other product or service names are the property of their respective owners. Motorola, Inc Equal Opportunity/Affirmative Action Employer. © Motorola, Inc. 2002 AN2438/D Rev. 0 2/2003 Go to: www.freescale.com ...