In the previous chapters, it was explained that the RF front end (RFFE) plays a major role in defining the receiver performance. It was demonstrated that the system carrier-to-noise ratio (CNR) performance is significantly dependent on the front-end input low-noise amplifier's (LNA's) NF. Furthermore, it was seen that there is an optimum matching for NF by an input matching transformer. It was demonstrated in Chapter 9 that the receiver's dynamic range is highly dependent on the RF chain line-up and the location of the automatic gain control (AGC) attenuator. (Further AGC analysis will be provided in Chapter 12.) Those factors affect the overall system performance and the link budget. Additionally, the topology of the video receiver defines its linearity and its distortion-free dynamic range. This section will focus on the design and tradeoffs of gain blocks and equalizers used as building blocks of a receiver. It will explain how to achieve good noise performances of gain and ripple. Gain block design is essential to achieving a receiver with high performance. Emphasis on noise analysis will be provided in Sec. 11.11 for various design cases and CMOS RF cases.
11.1 Noise Parameters of a Two-Port Device
Noise analysis of such two-port networks was investigated by several authors, and the results of those analyses are provided in Refs. [1â5,17]. Any linear noise hybrid network can be represented by a quiet network and two equivalent noise sources, en and in, at its input, as described in Fig. 11.1. The input signal is represented by the current source Is and its output impedance Ys = Gs + jBs. The dashed line is a virtual short for the calculation of the signal short current and noise short current in order to derive the signal-to-noise ratio (SNR). The method of calculation is by superposition, since this is a linear network. In superposition, current sources are left open, and voltage sources are shorted. The only remaining connected source to the network is the one being calculated. With the contributions of every source, they are summed as a full result. This is how to calculate the noise factor F for an active device, which is explained later.