Calculating Load Impedance

[Pheezy]

Hey all,

I intend to calculate the impedance as indicated but I am unsure on how I would do this. The reason I need to calculate this impedance is because this is part of a bigger project where I am trying to match the source impedance with the load impedance and I will need to design a impedance matching circuit for it.

The source is a 50 ohm antenna and this connects directly to this circuit in the given image.



NOTE: The diodes are the BAT46WJ schottky diodes. Essentially its a rectifier with multiple stages.

Any help would be appreciated.

Cheers

 

[D.A.(Tony)Stewart]

Each capacitor appears Zc=1/(2pif*C) + ESR. the diodes are dynamic resistance and depend on size.

You wont be able to match the impedance because the coupling current and spacing loss makes the input impedance high and the closer you get, it can drop below 50 Ohms.

You are much better off using a step-down inductive coil antenna to boost the current that is resonant to the carrier f. using a very high Q LC step down transformer coil that is tapped like an autotransformer and acts as an antenna.

then the antenna looks a like a current transformer to magnetic flux.

 

[Pheezy]

Each capacitor appears Zc=1/(2pif*C) + ESR. the diodes are dynamic resistance and depend on size.

You wont be able to match the impedance because the coupling current and spacing loss makes the input impedance high and the closer you get, it can drop below 50 Ohms.

You are much better off using a step-down inductive coil antenna to boost the current that is resonant to the carrier f. using a very high Q LC step down transformer coil that is tapped like an autotransformer and acts as an antenna.

then the antenna looks a like a current transformer to magnetic flux.

Hi there,

Thank you for your reply. Unfortunately, your suggestion is beyond the scope of what I am doing. This is not a practical problem. I am just to mathematically calculate the impedance as seen by the input. Based on the value I get, I was simply going to calculate inductor/capacitor values for the impedance matching and simulate it.

In regards to the dynamic resistance of the diodes, is that just the resistance values found in the datasheet?

Regards

 

[BradtheRad]

To match impedance, you can also view it in terms of the amount of amperes travelling in the loop.

The smaller the current, the larger a Henry value you need, and the smaller a capacitor.

Dealing in raw mathematics, to calculate inductive reactance, the formula is:

XL = 2 Pi f L

You want XL to come out to 50, although it might be 25, or 100, depending on what other component you have in series or in parallel.

The inductor lagging is equal and opposite to the capacitor leading, so I believe you do not need to draw the parallelogram angles in this case.

Post #2 already stated the formula for capacitive reactance.

 

[simazafrani]

Hi...if u are using software...u can try to do S-parameter simulation/calculation...where u can find the load impedance using S11 (by plotting the smith chart)

 

[D.A.(Tony)Stewart]

If you don't have a load impedance , the steady state impedance is infinite. Since the voltage tripler stops charging when fully charged.

The lowest impedance at start is the ESR of the diodes and caps.

what happens in between works like a Capacitive transformer so more stages, draw more current on each cycle while charging.

Discharge depends on the series C and load resistance for dv/dt.

It is a fairly simple but non-linear problem.