TABLE OF CONTENTS In order to build a digital receiver, an amplifier chain containing several amplifiers with different gains, noise figures, and third-order intermodulation points is needed in front of the analog-to-digital converter (ADC). To calculate the performance, an amplifier chain can be treated as a single amplifier with a certain gain, noise figure, and third-order intermodulation point. One of the purposes of using amplifiers in front of the ADC is to match the input signal to an ADC. In general, the adding of amplifiers will improve the sensitivity of the receiver.
The main purpose of this chapter is to present an optimum way to match the radio frequency (RF) amplifier with the ADC. The word "optimum" means to obtain a certain sensitivity and dynamic range, desired by the designer, within the limits of the amplifier performance and the ADC. The important parameters for the ADC are the number of bits, maximum sampling frequency, and input power level. It is assumed that the performance of the ADC is ideal. The lower limit of the dynamic range is the noise level rather than the spur levels because the spur levels are difficult to predict, as discussed in the Chapter 6. This same approach can be used to design with nonideal ADCs. For nonideal ADCs, the lower limit of the dynamic range should be considered as limited by the spur's response rather than the noise level.
This chapter will first very briefly present the performance of an analog receiver and point out the...
