Rf and if digitization in Radio Receivers: Theory, Concepts, and Examples

 

 

NTIA Report 96-328 

RF and IF Digitization in Radio Receivers: 

Theory, Concepts, and Examples

 

J.A. Wepman 

J.R. Hoffman 

 

 

 

U.S. DEPARTMENT OF COMMERCE 

March 1996 

Reissued February 2014 

NTIA Report 96-328 

RF and IF Digitization in Radio Receivers: 

Theory, Concepts, and Examples

 

J.A. Wepman 

J.R. Hoffman 

 

 

iii 

DISCLAIMER 

Certain commercial equipment, components, instruments, and materials are identified in this 

paper to provide some examples of current technology. In no case does such identification imply 

recommendation or endorsement by the National Telecommunications and Information 

Administration, nor does it imply that the material or equipment identified is necessarily the best 

available for the purpose. Furthermore, examples of technology identified in this paper are not 

intended to be all-inclusive; they represent only a sampling of what is available. 

 

 

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CONTENTS 

1 Introduction ...................................................................................................................................1

 

2 Analog-to-Digital Converters .......................................................................................................3

 

2.1 Sampling Methods and Analog Filtering ...............................................................................3

 

2.1.1 Sampling at Twice the Maximum Frequency ..............................................................3

 

2.1.2 Out-of-Band Energy .....................................................................................................4

 

2.1.3 Realizable Anti-Aliasing Filters ...................................................................................6

 

2.1.4 Oversampling ...............................................................................................................6

 

2.1.5 Quadrature Sampling ....................................................................................................7

 

2.1.6 Bandpass Sampling for Direct Downconversion .........................................................7

 

2.2 Effects of Quantization Noise, Distortion, and Receiver Noise ............................................8

 

2.3 Important Specifications ......................................................................................................10

 

2.3.1 Theoretical Signal-to-Noise Ratio Specifications ......................................................10

 

2.3.2 Practical Specifications for Real ADCs .....................................................................12

 

2.4 ADC Conversion Methods...................................................................................................15

 

2.5 ADC Performance vs. Sampling Rate .................................................................................24

 

3 Digital Signal-Processing Requirements and Limitations ..........................................................26

 

3.1 Processors ............................................................................................................................26

 

3.2 Real-Time Operation ...........................................................................................................28

 

3.3 Algorithms ...........................................................................................................................29

 

4 Potential Devices and Methods Useful in Radios Employing RF and IF Digitization ...............32

 

4.1 Quantization Techniques .....................................................................................................32

 

4.2 Nonlinear Devices for Amplitude Compression ..................................................................33

 

4.2.1 Log Amplifiers ...........................................................................................................33

 

4.2.2 Automatic Gain Control .............................................................................................35

 

4.3 Postdigitization Algorithms for Improving Spurious Free Dynamic Range .......................36

 

4.4 Sampling Downconverters ...................................................................................................37

 

4.5 Specialized Integrated Circuits ............................................................................................38

 

5 Examples of Radios Using RF or IF Digitization .......................................................................39

 

6 Summary and Recommendations ...............................................................................................43

 

7 References ...................................................................................................................................45

 

Appendix: Acronyms and Abbreviations.......................................................................................49