RF Circuit Design, 2nd Edition

Chapter 6: Impedance Measurement

6.1 Introduction

As mentioned in Chapter 1, the task of a digital circuit block in a communication system is status transport or manipulation. The so-called status of a digital signal is characterized by “0” or “1.” Direct observation of the signal waveform, including voltage at a node or current flowing through a part, is the best way to judge the performance of the circuit block, including its sequence of digits, repetition frequency, voltage level, rise and fall time, jitter and stability, and so on. Therefore, the main test equipment to be used is the oscilloscope, since a digital circuit block is tested in the time domain.

On the contrary, the task of an RF circuit block in a communication system is power transport or manipulation. In order to ensure effective transport and manipulation of power, the input and output impedances of the RF block must be matched with the output impedance of the previous block and the input impedance of the following block, respectively. In addition, the frequency bandwidth of the block must also be taken care of. The observation of the impedance matching state, power intensification, or attenuation over the entire frequency bandwidth is the best way to judge the performance of the circuit block, including the genuineness of the product, noise, nonlinearity, and so on. Therefore, the main test equipment to be used is the network analyzer, since the testing of the RF circuit block is carried out in the frequency ...