Electronic Design Automation

AWR Netlist

Q: How does AWR handle EM co-simulation in the netlist?

AWR uses an extracted model approach. You draw your layout (microstrip junction, via transition, or coupled-line filter) in the EM simulator (AXIEM for planar, Analyst for 3D). AWR runs the EM simulation to generate a multi-port S-parameter block, then automatically inserts that block into the circuit netlist as a SUBCKT. The rest of the circuit uses lumped or ideal models. This hybrid approach gives you EM accuracy at critical discontinuities without the computational cost of full-wave simulation on the entire design.

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An AWR Netlist is the text-based circuit description format used by Cadence AWR Design Environment (formerly Microwave Office) to define RF and microwave circuit topologies. It specifies component instance names, parameter values, port connections, and simulation directives that drive linear S-parameter, harmonic balance, and transient analyses of amplifiers, mixers, oscillators, and filter networks.

Category: Electronic Design Automation

Software: Cadence AWR Design Environment

File Formats: .emp, .sch, Touchstone (.snp)

Understanding AWR Netlists

Every RF circuit simulation starts with a netlist: a structured text file that tells the simulator what components exist, how they connect, and what analyses to run. In AWR Microwave Office, the graphical schematic editor generates this netlist automatically when you press "Analyze," but understanding the underlying netlist format is essential for scripting, automation, debugging convergence failures, and importing designs from other tools.

Netlist Structure

An AWR netlist organizes the circuit into several key sections:

Element definitions: Each component gets an instance name, a model type, and parameter values. For example, a microstrip line is defined by its width (W), length (L), substrate reference, and port assignments.
Port assignments: Unlike SPICE's node-based connectivity, AWR uses numbered ports. Port 1 on one element connects to Port 1 on the next element in the signal chain. This port-based model naturally represents the cascaded two-port networks that dominate RF design.
Subcircuits (SUBCKT): Complex blocks like vendor transistor models, EM-simulated layout extractions, or measured Touchstone data are wrapped in subcircuit definitions that can be instantiated multiple times.
Simulation directives: The netlist specifies frequency sweeps, power sweeps, harmonic orders for nonlinear simulation, and optimization goals.

AWR Netlist vs. Other EDA Formats

AWR Netlist:
An AWR Netlist is the text-based circuit description format used by Cadence AWR Design Environment (formerly Microwave Office) to define RF and microwave circuit topologies....

Key specifications:
1 W | 0.6 mm | 5.2 mm | 35 ps | 0 dB | 1 mW

Power: P(dBm) = 10log(P_mW), 0dBm = 1mW

Supported Analysis Types

Analysis	Netlist Directive	Use Case	Output
Linear (S-parameter)	FDOMAIN	Filter response, matching networks, passive circuits	S11, S21, group delay
Harmonic Balance	HBANALYSIS	PA compression, mixer intermod, oscillator startup	P1dB, IP3, phase noise
Load Pull	LPANALYSIS	Optimal load impedance for max PAE or power	Constant-power contours
Transient	TRAN	Pulsed radar waveforms, switch transients	Time-domain voltage/current
EM (AXIEM/Analyst)	EMEXTRACT	Microstrip discontinuities, via transitions, coupled lines	Multi-port S-parameter block

Key Equations

Decibel conversion:
Power: dB = 10log(P₂/P₁)
Voltage: dB = 20log(V₂/V₁)

dBm to watts:
P(W) = 10^{(dBm−30)/10}
0 dBm = 1 mW, +30 dBm = 1 W

Wavelength:
λ = c/f = 300/f(MHz) meters

Comparison

Aspect	AWR Netlist Spec	Typical Range	Impact	Design Note
Primary function	An AWR Netlist is the text-based circuit...	Application-dep.	Critical	Verify in sim
Operating range	Understanding AWR Netlists Every RF circ...	Application-dep.	Critical	Verify in sim
Performance	Netlist Structure An AWR netlist organiz...	Application-dep.	Critical	Verify in sim
Integration	For example, a microstrip line is define...	Application-dep.	Critical	Verify in sim
Trade-off	Port assignments: Unlike SPICE's node-ba...	Application-dep.	Critical	Verify in sim

Common Questions

Frequently Asked Questions

What is the difference between an AWR netlist and a SPICE netlist?

A SPICE netlist describes circuits using node-based connectivity (R1 node1 node2 100) and is designed for low-frequency analog simulation. An AWR netlist uses a port-based connectivity model better suited for RF work: components connect through named ports rather than shared nodes, making it natural to represent S-parameter blocks, transmission lines, and multi-port networks. AWR netlists also natively support frequency-domain simulation directives like harmonic balance sweeps and load-pull contours.

Can I import vendor S-parameter files into an AWR netlist?

Yes. AWR supports Touchstone files (.s1p, .s2p, .snp) directly as subcircuit models. You place a SUBCKT element and point it to the .s2p file from the component vendor. AWR also supports MDIF (Measurement Data Interchange Format) files for multi-dimensional data like gain vs. bias vs. temperature. This lets you simulate using actual measured S-parameters from the vendor's evaluation board rather than relying solely on compact models.

How does AWR handle EM co-simulation in the netlist?

AWR uses an extracted model approach. You draw your layout in the EM simulator (AXIEM for planar, Analyst for 3D). AWR runs the EM simulation to generate a multi-port S-parameter block, then automatically inserts that block into the circuit netlist as a SUBCKT. The rest of the circuit uses lumped or ideal models. This hybrid approach gives EM accuracy at critical discontinuities without full-wave simulation on the entire design.

Related Terms

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