end of the chapter.
The fourth chapter is an important one. The application and development of dither in
A/D converter are reviewed at first. Then we elucidate three kinds of dither and their
application. By analyzing the harmonic distortion of ideal quantizer, coherent sampling
and DNL of A/D converters, we investigate the effect of dither on A/D converter. We
reach the conclusion that dither can improve the harmonic distortion caused by
quantization, coherent sampling and DNL of A/D converters. We also explain the reason
of such improvement and give a list of several methods and circuits for dither generation.
The fifth chapter is concerning simulation of A/D converter. We probe into the
structure of high speed and resolution A/D converter at first. Based on the structure of
A/D converter, we set up a mathematics model of A/D converter and develop a
simulation software system for A/D converter. By using this system to determine the
effect of white noise, narrow-band dither and coherence sampling on A/D converter’s
specifications, we obtain the simulation results that dither can improve greatly the
harmonic distortion caused by quantization, coherent sampling and DNL of A/D
converters.
The design of high speed IF sampling is introduced in chapter six. This is also an
important point of the thesis. We firstly illustrate several high performance chips for IF
sampling and specially introduce AD6644. In order to use these chips perfectly, we
suggest many methods for coupling analog input signal and encoding clock signal. In
additional we introduce the circuit design of dither as well as coupling of dither. The
design of A/D converter’s I/O interface is also considered. Lastly, two kinds design of
evaluation board are mentioned and PCB consideration is included too.
The seventh chapter is the testing result of AD6644 evaluation boards. At the first
state, we introduce the test bench and test condition, and then the different testing results
under the different conditions. The testing results match the theoretical analysis and
simulation results. At last we explain and analyze the testing results.
In chapter eight, we interpret the numerical controlled oscillator (NCO) and digital
filter. By deducing the frequency response of FIR filter, we recommend the design
method of FIR filter. In the end, we set forth a special FIR filter which is often used in
digital down-converter ---Cascaded Integrator Comb FIR Filter (CIC filter).
The chapter nine presents the design of digital down-converter system. We first
compare several different digital receiver chips and then emphasis on AD6620 and
GC1012A, and we describe circuit design of digital down-converter board used in radar
system. At the same time, we introduce AD6620 digital receiver board and a digital FIR
filter design based on FPGA. Finally we give a scheme of digital down-converter system
based upon FPGA.
In tenth chapter, we introduce the test theory and test method by studying the
transfer function of I/Q demodulation, and deduce the formulas for calculating three basic
parameters for I/Q demodulation. We test our GC1012A digital down-converter system
by these formulas, and the testing results show that our system meets the design
requirement.
The final appendix is regard to other potential non-uniform quantization methods
employed in RF and IF digitization. Although these methods can’t be used in current IF
A/D converters, they may be found in the new generation of IF or RF ADCs, since they
can improve ADCs specifications magnificently, especially for SFDR.
