Calibration Techniques in Nyquist A/D Converters (eBook)

Table of contents 7
List of abbreviations 11
List of symbols 13
Preface 17
1 Introduction 19
1.1 A/D conversion systems 19
1.2 Motivation and objectives 23
1.3 Layout of the book 23
2 Accuracy, speed and power relation 25
2.1 Introduction 25
2.2 IC-technology accuracy limitations 26
2.3 Speed and power 29
2.4 Maximum speed 31
2.5 CMOS technology trends 33
2.6 Conclusions 36
3 A/D converter architecture comparison 39
3.1 Introduction 39
3.2 Flash 40
3.3 Folding and interpolation 51
3.4 Two-step 56
3.5 Pipe-line 64
3.6 Successive approximation 72
3.7 Theoretical power consumption comparison 74
3.8 Conclusions 84
4 Enhancement techniques for two- step A/ D converters 85
4.1 Introduction 85
4.2 Error sources in a two-step architecture 85
4.3 Residue gain in two-step A/D converters 87
4.4 Offset calibration 93
4.5 Mixed-signal chopping and calibration 101
5 A 10-bit two-step ADC with analog online calibration 121
5.1 Introduction 121
5.2 Two-step architecture 123
5.3 Circuit design 128
5.4 Experimental results 135
5.5 Discussion 139
5.6 Conclusions 140
6 A 12-bit two-step ADC with mixed- signal chopping and calibration 141
6.1 Introduction 141
6.2 Two-step architecture 144
6.3 Mixed-signal chopping and calibration 151
6.4 Circuit design 154
6.5 Experimental results 159
6.6 Discussion 163
6.7 Conclusions 164
7 A low-power 16-bit three-step ADC for imaging applications 167
7.1 Introduction 167
7.2 Three-step architecture 169
7.3 Noise considerations 174
7.4 Mixed-signal chopping and calibration 176
7.5 Supply voltages 179
7.6 Experimental results 180
7.7 Discussion 185
7.8 Conclusions 186
8 Conclusions 187
Appendix A Static and dynamic accuracy requirements 191
A.1 Static error requirments 191
A.2 Dynamic error requirements 193
References 195
Index 207

Chapter 1 Introduction (p. 1)

1.1 A/D conversion systems

In modern systems, most of the signal processing is performed in the digital domain. Digital circuits have a lower sensitivity to noise and are less susceptible to fluctuations in supply and process variations. Unlike with analog circuits, signal processing in the digital domain offers greater programmability, error correction and storage possibilities.

They are found in many systems that require digital signal processing. This book focuses on A/D converters. A/D converters can be classified into two groups. There are A/D converters with a high accuracy and a low sample rate and A/D converters with a low accuracy and a high sample rate. This is illustrated in figure 1.1.

The first group includes sigma-delta converters for audio, signal transmission and instrumentation systems, while the second group includes video, camera and wide-band signal transmission systems. In order to increase the accuracy or the speed specifications of the A/D converters in both groups more power is required. The A/D converters from the second group of converters are dealt with in this book.

They are found in products like television sets, security cameras, medical imaging devices, instrumentation, etc. The sampling speed required for these applications is generally in excess of 25 MSample/s and the resolution is 10 bits or more. A few examples of these applications are shown in figure 1.2. The position of the A/D converter in such systems is shown in figure 1.3. In this figure, the signal is conditioned in the analog domain before it is applied to the A/D converter.

For example, the A/D converter converts the down-converted radio frequency (RF) antenna signal to the digital domain. In the case of fgure 1.3, the filtering and channel selection is performed in the analog domain. Another example is an analog video signal with an aspect ratio of 4:3, which is converted to the digital domain. In the digital domain a field memory and additional processing is used to resize the video signal to an aspect ratio of 16:9.

A D/A converter converts this signal back to the analog domain to be applied to a display [1]. Similar signal processing is required As shown in figure 1.3, the A/D converters form the connection between the ana- to convert a video signal with a 50 Hz frame rate to a video signal with a 100 Hz frame rate. The performance level should be such that the system is not affected by the imperfections of the data converter.

Its design is therefore extremely important. Because of the trend towards decreasing feature sizes on silicon, it is becoming cheaper to shift analog functions, such as amplifying, filtering and mixing, into the digital domain. This involves shifting the A/D converter towards the input of the system, an extreme example of this is shown in figure 1.4.

In order to shift the A/D converter towards the input of such systems, A/D converters are required with a greater dynamic range and higher sampling speeds because there is less analog signal conditioning.