Chapter 3: Envelope Domain Methods for Behavioral Modeling

3.1 INTRODUCTION

In the past few decades, so much has been accomplished in the modeling and simulation techniques for analog RF and microwave circuits both at the semiconductor device modeling (BSIM, EKV, MM9, HICUM, and so forth) and simulation algorithms (transient, shooting transient, harmonic balance, and envelope transient) sides. This progress has led to powerful verification tools for RF and microwave that have allowed tremendous productivity gains for circuit designers in significantly decreasing the number of prototypes. Today an equivalent work is necessary at the system simulation level, and this is particularly urged by the design challenge of the modern RF SOC transmitters.

The idealized RF transmit-receive chain (TX/RX) diagram of Figure 3.1 shows the various functional blocs (PLL-based frequency synthesizers, IQ modulators, image/harmonic reject mixers, LNA, C & E class power amplifiers, base band filters, and ADC circuits) for which new and efficient modeling paradigms have to be worked out.

Figure 3.1: Ideal RF transmit-receive chain.

One of the basic issues in the behavioral model development resides in finding the good compromise between description accuracy and complexity of building up and executing the model. We must obtain the most accurate prediction of the bloc behavior under the two constraints that: (1) the extraction principle of the model should be simple enough to be affordable with common circuit simulation and/or measurement tools; and (2) the resulting model should use mathematical concepts that can be effectively implemented in common simulation tools.