Model RF Objects Using Verilog-A

Overview

Verilog-A is a language for modeling the high-level behavior of analog components and networks. Verilog-A describes components mathematically, for fast and accurate simulation.

RF Toolbox™ software lets you export a Verilog-A description of your circuit. You can create a Verilog-A model of any passive RF component or network and use it as a behavioral model for transient analysis in a third-party circuit simulator. This capability is useful in signal integrity engineering. For example, you can import the measured four-port S-parameters of a backplane into the toolbox, export a Verilog-A model of the backplane to a circuit simulator, and use the model to determine the performance of your driver and receiver circuitry when they are communicating across the backplane.

Behavioral Modeling Using Verilog-A

The Verilog-A language is a high-level language that uses modules to describe the structure and behavior of analog systems and their components. A module is a programming building block that forms an executable specification of the system.

Verilog-A uses modules to capture high-level analog behavior of components and systems. Modules describe circuit behavior in terms of

Input and output nets characterized by predefined Verilog-A disciplines that describe the attributes of the nets.
Equations and module parameters that define the relationship between the input and output nets mathematically.

When you create a Verilog-A model of your circuit, the toolbox writes a Verilog-A module that specifies circuit's input and output nets and the mathematical equations that describe how the circuit operates on the input to produce the output.

Supported Verilog-A Models

RF Toolbox software lets you export a Verilog-A model of an rfmodel object. The toolbox provides one rfmodel object, rfmodel.rational, that you can use to represent any RF component or network for export to Verilog-A.

The rfmodel.rational object represents components as rational functions in pole-residue form, as described in the rfmodel.rational reference page. This representation can include complex poles and residues, which occur in complex-conjugate pairs.

The toolbox implements each rfmodel.rational object as a series of Laplace Transform S-domain filters in Verilog-A using the numerator-denominator form of the Laplace transform filter:

$H (s) = \frac{\sum_{k = 0}^{M} n_{k} s^{k}}{\sum_{k = 0}^{N} d_{k} s^{k}}$

where

M is the order of the numerator polynomial.
N is the order of the denominator polynomial.
n_k is the coefficient of the kth power of s in the numerator.
d_k is the coefficient of the kth power of s in the denominator.

The number of poles in the rational function is related to the number of Laplace transform filters in the Verilog-A module. However, there is not a one-to-one correspondence between the two. The difference arises because the toolbox combines each pair of complex-conjugate poles and the corresponding residues in the rational function to form a Laplace transform numerator and denominator with real coefficients. the toolbox converts the real poles of the rational function directly to a Laplace transform filter in numerator-denominator form.