An impedance matching is required to ensure that most of the power from the RF source is transmitted to the load. In a typical example of using Proc Ble / PSoc Ble, during transmission, PSoc Ble is the source, and the antenna is load. During receiving, the antenna is a source, and PSoc Ble is a load. When PSoc Ble and antenna
Impedance is not 50 ohms, they need to match 50 ohms. At the radio frequency, the measured impedance is changed from the distance from the load / source (when leaving the load / source, the impedance rotates the characteristic impedance rotation of the RF traces clockwise clockwise in the Smith circle). The figure below depicts the impedance changes in the length of the trace.
Smith circle depicting the length of the impedance
Therefore, the matching network also needs to change from the distance from the source / load. When the measured impedance is equal to the feature impedance, it does not change from the distance from the power / load. Therefore, the recommended technique is to match the complex source impedance to the feature impedance using a matching network close to the source and match the load impedance with the feature impedance using a matching network close to the load. This ensures that the matching network component value does not change as the trace length, as long as the source matching network is close to the source and the load matching network is kept close to the load.
For 2.4 GHz, most of the available devices match 50 ohm impedance. Therefore, Cypress uses and recommends the 50 ohm characteristic impedance of the RF line.
Any given impedance (except for short circuits and openings) can be matched to 50 ohms using two reactive passive components (inductance or capacitors). Although the inductance and capacitance can be obtained using RF short interception, they usually take up extra space in the PCB. Due to size limits, it is best to use capacitance and inductance to impedance matching.
Increasing a series inductor moves the impedance along a constant resistance circle in a constant resistance circle, as shown below. The inductance value required to move the electric anti-moving XL factor on the Smith Circle is given by the following formula:
Adding a series capacitor can cause impedance to move in the counterclockwise direction along the constant resistance circle. The capacitance value required to move the reactive moving XC factor on the Smith circle is
Adding a parallel inductor moves the impedance in the counterclockwise direction along a constant conductance. The inductance value required by mobile conductivity YL is
The addition of the parallel capacitor moves the impedance along the constant electrical conductive circle in the clockwise direction. The capacitance value required by YC mobile conductance is
The first step is to set the impedance to a circle of 50 ohms or a circle of 20-ms. The next step is to move the impedance to 50 ohms. With these basic information, you can use the Smith circle to design a matching circuit, and the method is to move the impedance to 50 ohmotes using capacitors and inductors.
Description Smith circle with impedance changes with reactance
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