Modulators and Demodulators

Introduction

The Filters - < filter type > and System - < device type > palettes contain two fundamentally different types of behavioral system models.

Filters , System - Amps & Mixers , and System - Mod/Demod can be classified as tops-down system models that support a tops-down system design flow where model behaviors are characterized by a small number of independent parameters such as frequency, power and load. They are often referred to as parameter-based behavioral models .

System - Data Models can be classified as bottoms-up system models that support a bottoms-up verification flow where model behaviors are extracted from a simulation (or measurement) of a transistor-level circuit. They are often referred to as data-based behavioral models .

The parameter-based behavioral models typically provide superior speed relative to the data-based behavioral models with both of these being vastly superior to a brute-force transistor-level simulation.

The data-based behavioral models typically provide superior accuracy relative to the parameter-based behavioral models as they capture actual behaviors of implemented circuit components and not just design specifications.

The differences between parameter - and data-based behavioral models justify a palette emphasis on flow (all data-based behavioral models grouped together) rather than functionality (all amplifiers, mixers, modulators, and demodulators grouped together) and resulted in the addition of a System - Data Models palette.

The use model for parameter-based behavioral models is to simply set a series of parameters prior to using the model. The use model for data-based behavioral models is slightly more involved. For a discussion, refer to Chapter 8, System Data Models.

The modulators and demodulators system model library contains time domain tuned modulators and tuned demodulators. Each component in this library is described following this introduction.

When using the System-Mod/Demod components in the Analog/RF schematic, it is important to note that terminating the component with a load resistance equivalent to the component output resistance will provide an output voltage that is half of the applied input voltage. Consider the Thevenin equivalent of the output of a Mod/Demod component.

In an Analog/RF schematic, the value for Vout will be 1/2 Vo when Output Resistance=Load Resistance. In general, Vout=Vo × Load Resistance/(Load Resistance + Output Resistance). Thus, this is the potential divider action. All of the components in the System-Mod/Demod library have this property except for N_StateDemod and PM_UnwrapDemodTuned. (These two components do not have an Rout parameter).

For a similar circuit in a DSP schematic, the effect of the potential divider on the output voltage will not be noticeable when the output resistance equals the load resistance. In this case, Vout equals Vo. For the DSP components, there is an additional factor of 2 at the output voltage to cancel the factor of 1/2 from the potential divider. For a description of the digital implementation of the modulators and demodulators, and the potential divider action, refer to Introduction: Timed, Modem Components in the Signal Processing component documentation.

Components