Seek clarifications on load pulling technique

Could some electronics guru please help clarify the following. I am a bit rusty on load pulling. I am currently working on some ideas and testing them with SPICE.

Suppose that a RF transistor( e.g. BFU520) is configured as a single stage RF amplifier, with a simple voltage divider base biasing network, a collector resistor, and DC blocking capacitors at the base and collector. The source resistor is set at 50.0 Ohm, and the load resistor is varied. The RMS input and output power(in Watts) is measured for each value of the variable load resistor. The input signal frequency is set to 500 MHz.

Now suppose that using this configration and SPICE transient analysis, the input power is deliveed to the load when the variable load has a value of 150 Ohm.

Now the questions:

  1. The output impedance of the transistor is approximately 150 Ohm at 500 MHz. Is this correct ?

2, Is it safe to state that at 500 MHz, the input impedance is 50 Ohm, for the given configuration.

  1. The BFU520 datasheet provides S parameters, and it is possible to compute the Zin, Zout from S11, S22, S12 and S21. But it is not clear if the supplied S parameters are small signal or large signal. Spice transient analysis is large signal, so is the supplied SPICE device model, so if the supplied S parameters ought to be latge signal, but there is no clear indication.

All hints, suggesyions are welcome. Thanks in advance.

Reply to
amal banerjee
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On a sunny day (Sat, 31 Aug 2019 21:16:38 -0700 (PDT)) it happened amal banerjee wrote in :

Buy the transistor, build the circuit, test it.

This has 2 advantages over using spice:

1) you are sure you have reality. 2) you actually have a working circuit you can use.

As a bonus it will likely save you money and time, as when you build your spice circuit later it may not work.

At 500 MHz things like PCB layout, wire length, parasitic capacitances, etc already become very important. Building a circuit will manifest those mysterious effects that spice won't.

RF spice is a bit like Hollywood movies about space travel and aliens. It looks real, but... It iS MosTlY DeSIGneD tO seLL MoRE COmpUteRS

Reply to
Jan Panteltje

I totally agree with what you say. However, high frequency parasitic (capacitive, inductive) effects can be simulated in ordinary Spice(HSpice, Ngspice in my case) by, e.g., having a very low value non-ideal inductor in-between the terminals of two components. In fact, the SPICE device models of most RF transistors include terminal inductances, etc., I have tested these in the past, and the differences in the results is significant. The problem is that the values selected for the components of the non-ideal capacitors etc., are educated guesses, not the real ones.

Reply to
amal banerjee

Post your proposed circuit! Your written description leaves out a lot of specifics.

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Reply to
Cursitor Doom

I would be happy to supply the text SPICE netlist. Is that what you are looking for > Please specify. Plain text descriptions are often vague, I admit.

Reply to
amal banerjee

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