Special episode 6: ADS power amplifier design using Smith chart to verify the rationality of input and output matching
Input matching and output matching are very important in RF design, especially in RF power amplifier design.
When designing an RF power amplifier, the bandwidth of the power amplifier can be roughly determined by observing the S-parameter performance of the input or output match.
1. Appropriate input matching
The frequency is 2.4Ghz
, assuming that the appropriate source impedance is 9.375-j19.090 ohms obtained through source pulling at this time ( if you don’t know about source pulling and load pulling, read the previous episode 5: Load pulling and source pulling in ADS power amplifier design ):
the next step is to use the Smith chart to design the matching circuit. This time, use the SmithChart control to design the matching circuit: 9.090) In the Smith chart control, also write the conjugate 9.375+j19.090 ohm of the impedance obtained by source traction : use the Smith chart for design, and perform simulation observation after the design is completed:
Here, modify the impedance of the load end to the standard impedance of 50 ohms, as shown below:
Perform the simulation again, observe the result **(S22)**, and find that the impedance point at 2.4G has fallen into the setting area of the previous source pull:
2. Appropriate output matching
假设此前通过负载牵引得出最佳负载阻抗为19.733+j*11.344欧姆：
下一步需要使用Smith圆图设计匹配电路，这次使用SmithChart控件进行匹配电路的设计（左边阻抗写入负载牵引所得阻抗的共轭19.733-j*11.344欧姆，右边端口写入50欧姆标准微带线）：
点击Smith控件，设置输入阻抗为负载牵引所得阻抗19.733+j*11.344欧姆，设置输入源类型为Input Impedance：
点击圆图进行设计，设计完成后进行仿真：
将输入阻抗修改为50欧姆，再次进行仿真，发现S11已经落入了之前负载牵引所得的高效率区域：
