How much do you know about impedance matching?
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By connecting capacitors and inductors in series or in parallel, the tolerance and reactance of the transmission line can be changed, the impedance matching device can affect the power level, and devices with higher rated voltage levels need to be used to optimize antenna efficiency. Let's take a look at Qorvo's approach.
Figure 2 shows two antenna designs, Modes A and B. Next, we will describe how these design modes interact with impedance matching components of different voltage ratings. We will also show how to maximize the overall radiated efficiency by utilizing higher voltage rated components.
Figure 2
First, in Figure 3 we can see how antenna modes “A” and “B” are measured on the Smith Chart at low-band GSM frequencies. As shown, the antenna impedance is in the inductive region of the Smith Chart, so a series capacitor becomes the optimal matching solution. Therefore, our antenna matching solution will use a capacitor.
Figure 3.
In our example, we measured and compared two similar devices shown on the left side of Figure 4 as antenna impedance matching components. One is 55VRF (DEVICE55) and the other is 65VRF (DEVICE65). Each device consists of a programmable capacitor with 32 different capacitance states and an independent switchable switch.
Figure 4.
The state of each device is selected to achieve the maximum radiation efficiency of antenna mode A in the low-band frequency range. In addition, the selected device state should also meet the rated RF voltage requirements of each device: 55VRF for DEVICE55 and 65VRF for DEVICE65, as shown in the figure below. The devices were tested under GSM850/900 and LTE B12 (Band 12). The measurement graph (Figure 5 below) shows the antenna efficiency and frequency graph connected to these two devices.
Figure 5.
The above output measurements were made using antenna pattern “A” for DEVICE 55 and DEVICE 65. As shown, the efficiency is significantly affected at GSM850 and GSM900 Tx frequencies if the lower voltage 55 V device is used. To achieve higher efficiency at GSM850, GSM900 and B12 while maintaining voltage levels, the voltage of DEVICE65 should be selected as its efficiency will exceed that of DEVICE55.
To improve the response of DEVICE55, we tried to use the Mode “B” antenna design. The output measurement graph below shows Mode “A” using DEVICE65. For DEVICE55, we used Mode “B”. Although the use of Mode “B” antenna design at GSM frequencies can improve the performance of DEVICE55 solution, it is still not enough to meet the requirements of DEVICE65 components. As shown in Figure 6, the efficiency of DEVICE65 once again exceeds that of DEVICE55. This is because DEVICE65 can meet the higher RF voltage input impedance requirements.
Figure 6.
Furthermore, the efficiency achieved using mode "B" and DEVICE55 is not as high and not as wide as using mode "A" and DEVICE65, especially in the B12 frequency range. Although DEVICE55 improves when using mode "B", the efficiency is not as high as using mode "A" and DEVICE65.
In summary, high voltage on the antenna does have an impact on efficiency and performance. Our measurements confirm that in impedance matching applications with high RF voltages, devices with higher voltage ratings can achieve higher performance. In our example, we use two configurable tuners from Qorvo, each of which contains a switch and a programmable capacitor array (PAC), one device with a rated voltage of 55V and the other with a rated voltage of 65V. Components with higher voltage ratings provide antenna designers with more margin. This allows system designers to more effectively match the circuit to multiple antenna patterns and RF voltage scenarios without modifying the design layout structure.
Which impedance matching method is better? Let's discuss it together.
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提升卡
变色卡
千斤顶
What you said is so accurate. I understand impedance matching in seconds. Thank you.