ABCs of ADCs - Analog-to-Digital Converter Basics (PDF)

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Common Sources of Noise andDistortion• Inadequate Supply Bypassing• Inadequate V A - V DR * Supply Decoupling• Noisy Components/Conditioning Circuitry• Quantization• Clock• Output to Input Coupling* V DR (or DR V D ) is the supply for the output drivers28There are many sources of signal degradation in any analog signal chain and the circuitryassociated with an ADC has its share. Many of the problem areas mentioned here arecommon to any analog circuitry.ABCs of ADCs - Rev 3, June 2006Authored by: Nicholas “Nick” Gray28Copyright © 2003, 2004, 2006 National SemiconductorCorporationAll rights reserved
Inadequate Supply Bypassing• Noise Can Enter Via The Power Supply• Specified PSRR Is A D.C. Measurement• A.C. PSRR Worse Than D.C. PSRR• A.C. PSRR Degrades With Frequency29Digital circuitry typically causes a lot of noise on digital power lines. If the power source usedfor analog and/or mixed-signal devices is the same power source that is used for digitalcomponents, this noise can couple into the analog and mixed-signal components through theirsupply pins. To the extent that the analog or mixed-signal components exhibit good powersupply rejection, this will not affect the analog or mixed-signal components. However, PowerSupply Rejection Ratio (PSRR) degrades with increasing frequency. Furthermore, PSRR asexpressed on data sheets often refers to the difference in a single parameter (e.g., OffsetVoltage) with two different stable d.c. supply voltages. This says nothing about how well highfrequency noise on the supply source is rejected by the component.Noise rejection on the power supply is never quite as good as the d.c. PSRR described aboveand gets worse with increasing frequency.ABCs of ADCs - Rev 3, June 2006Authored by: Nicholas “Nick” Gray29Copyright © 2003, 2004, 2006 National SemiconductorCorporationAll rights reserved
Page 1 and 2: ABCs of ADCsAnalog-to-Digital Conve
Page 3 and 4: What Is an ADC?• Mixed-Signal Dev
Page 5 and 6: Least Significant Bit (LSB)andMost
Page 7 and 8: Quantization Error111Digital Output
Page 9 and 10: Offset Error111OUTPUT CODE110101100
Page 11 and 12: Gain Error (Full-Scale GainError)Ga
Page 13 and 14: DNL1111101010.3 LSB;DNL = -0.7Ideal
Page 15 and 16: Integral Non-Linearity (INL)orInteg
Page 17 and 18: Total Unadjusted Error101OUTPUT COD
Page 19 and 20: THD - Total HarmonicDistortionAnalo
Page 21 and 22: 1Signal-to-Noise and Distortion(SIN
Page 23 and 24: ENOB - Effective Number OfBits• E
Page 25 and 26: Input Dynamic RangeDynamic Range is
Page 27: Sources of Noiseand DistortionABCs
Page 31 and 32: V A - DR Decoupling• ADC Outputs
Page 33 and 34: Output to Input Coupling• Output
Page 35 and 36: Noisy Components/Circuitry• ADC I
Page 37 and 38: Clock Noise• Clock Can Add Noise
Page 39 and 40: Common Design Mistakes• Inadequat
Page 41 and 42: Noisy Components/Circuitry• ADC I
Page 43 and 44: Better Conditioning Circuitry22 220
Page 45 and 46: Resistor Pack Danger500*V REF +V RE
Page 47 and 48: Clock Noise• Clock Can Add Noise
Page 49 and 50: Excessive Clock Jitter (cont’d)No
Page 51 and 52: Treating the Clock LineAs a Trace
Page 53 and 54: A Better Reference CircuitLM4040-4.
Page 55 and 56: High Speed ADCs FromNational: 10-bi
Page 57 and 58: High Speed ADCs FromNational: 14 &
Page 59 and 60: Other General Purpose ADCsFrom Nati
Page 61 and 62: ADC Web Site• Site: www.national.
Page 63 and 64: Absolute Maximum Ratings - Voltages

ABCs of ADCs - Analog-to-Digital Converter Basics (PDF)

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