Find us at www.keysight.com Page 1

Creating an X-Parameter Model

PathWave RF Synthesis (Genesys) and

PathWave System Design (SystemVue)

How do you get an X-parameter model to use in PathWave RF Synthesis or

PathWave System Design? Some vendors will give you one; you can also measure

one yourself. But PathWave Advanced Design System (ADS) can turn a circuit

schematic into an X-Parameter file, too. Start with the schematic of the device or

system in PathWave Advanced Design System. Any number of ports is okay,

frequency translation is okay, and other circuit simulation conditions are okay.

Figure 1. Device under test (DUT) – a power amplifier

Find us at www.keysight.com Page 2

Figure 1 shows the DUT— a power amplifier— surrounded by special parts from the Simulation–

X_Param palette. These parts correlate to similar parts for a Harmonic Balance simulation.

•

The

XP_Source

acts like a

P_nTone

•

The

XP_Load

acts like a

Term

•

The

X-Parameters

controller is like an

Harmonic Balance

controller.

•

And finally, the

XP_Bias

is simply a

V_DC

All these parts have one thing in common: they can be swept. So when we extract a model from this test

bench we can do it over frequency, power, load impedance, bias voltage… and we can even apply

multiple tones to the input for an n-tone model.

In our example, the source is set (Figure 2) for a harmonic index of 1, which corresponds to: 1 * Freq[1] =

1.85 GHz. Additional tones can be added to this source, just like in a P_nTone. As seen in Figure 2, the

power level is swept from -40 to +10 dBm.

Figure 2. Example

The load in this example is set to a constant 50 ohms, but you can specify 1) a swept impedance, for a

load-pull measurement; and/or 2) a different impedance at each harmonic of the input signal.

The XP_Bias is set to +5 V and is applied to a third pin on the DUT. Therefore, our X-parameter model

will have three ports: the RF input, the RF output, and the Vdd pin. This will be important if we want to

monitor supply current in a power-added efficiency (PAE) simulation later on. This voltage can also be

swept to extract a model over bias.

Finally, the X-Parameters controller looks a lot like Harmonic Balance, with the added field Output

GMDIF file at the top of its dialog box (see below). This is the X-parameter file that will be generated after

we run the simulation.

It’s important to check this box and fill in this field with a file name. Other than this, the controller is set to

Freq[1] = 1.85 GHz with MaxOrder = 5, so we’ll capture up to 5th order harmonics and intermods in our

model.

After simulation, the X-parameter file is saved, and you can open it with a text editor.

The file header tells us the conditions under which the model was extracted. We see (Figure 3) the

number and frequency of the tones, the bias voltages, the power sweep values, etc.