I want to implement an RF Energy harvesting circuit at f=2.45GHz, I finished the design of rectenna however the efficiency is quite low 40%,
I 'd like to attach a DC-DC converter to maximize the output voltage hence the efficiency, but I think it will cause losses?
which DC-DC converter is the optimum and what is the type of transistor shall I use and what is the switched mode frequency if i will use the switched mode DC-DC converter?
Efficiency will be the multiplication of all efficiencies of antenna, matching network, rectifier and the proposed dc dc converter.
Is the 40% is the maximum efficiency that you get or a value that you get for a specific load? If it is the maximum, adding dc dc converter can't help. You need to optimize the RF system itself, i.e. lower loss diodes and/or matching network. If you need specific load and you are not working at the eta maximum, you can do so by inserting the dc c converter, which shall change the load of the rectifier and get to the desired operating point.
For an energy recovery RF circuit, the efficiency depend on the voltage and the technology used ie the power supply voltage, the power received at the source, in this case the matching is necessary for the adaptation as explained by(Esraa Ali), transistors with low threshold voltage can also be used.
Best regards
Thank you, everyone, for your notice support. I optimized the design for maximum power transfer (optimum impedance matching network used) as Esraa suggested so the maximum EM model simulated efficiency reaches up to 80% at -10dBm. It seems too good to me however the measured one is declined to less than half about 35%. All for the same load 5Kohm and frequency 2.45GHz.
Do anybody has any suggestion about what kind of the associated practical problems???
I might guess this difference is due to losses generated from fabrication imperfections, soldering, fluctuation of lumped elements' values,....etc
But the wondered thing is half DC output power reduction !!!!!!!!!!!!!
No, the circuit doesn't include DC-DC converter, just a matching circuit+voltage doubler rectifier (SMS7630 Schottky diode+Load (5.6K), That's all !!!
Yes, I'm using FR4 substrate 0.8mm thickness and 0.02 tangent loss.
reverse leakage? how can it affect the circuit and how can I eliminate such trouble?How can i take current reverse leakage into account during the simulation??
Reverse leakage (current) will affect the efficiency - leaking what already was rectified.
If your simulation incorporates only ideal diodes, the introduction of a serial resisor (to account for conductiin losses) and an anti-parallel diode + resistor will improve the prediction - at the same time lowering the expectance :)
Regards
The simulation includes the practical model provided by the manufacturer, all of the diode characteristics were obtained from SPICE model. Therefore, i think the reverse leakage current contributes to the efficiency degradation during the simulation phase.
If I would like to check the amount of leakage current in practice and in simulation, how can i inspect it
On the "component base", you can measure the I/V curve to get the reverse leakage current as well as the forward voltage.
In SPICE, you can do similat things to check for the accuracy of the model: attach the diode to a sawtooth voltage source and measure! I'm not sure whether SPICE has x/y plot capabilities - eventually you'll have to draw the I/V curve by hand.
According to my experience, SPICE models usually do not consider "parasitic effects" beyond 1st order. Thus you may find out the the differential resistance is considered but neither the variation of the forward voltage vs. forward current nor the reverse leakage. SPICE is great! - but it takes some effort to tweak the simulations to closer represent the reality. Eg. you can simulate a 30 V transistor at 1000 V without ruining it :)
Regards
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