InductorsMobile Phones -Power amp-

Power amplifiers (hereinafter abbreviated as PA), amplify the high frequency signal output from communication IC (RF-IC) to the required output, and supply it to an antenna.

Figure 1 shows an example of a PA circuit. Since it is difficult for a PA to satisfy the required output power in 1 step, a multistep configuration is generally used. Figure 1 shows a PA with a 2 step configuration. However, since the required output power differs by the communication method of mobile phones, it is necessary to change the configuration of the PA according to the corresponding communication method. For example, the required output power of the GSM is larger than the UMTS therefore, there are many cases where a 2 step configuration is used for the UMTS, and a 3 step configuration for the GSM.

This is to match the output impedance of the sending side circuit, and the input impedance of the receiving side circuit in the signal transmission path, and by matching the impedance, the power of the sending side can be transmitted to the receiving side at the maximum. Therefore, a matching circuit is also required for the input/output portion of a PA.
Although a capacitor and inductor are used in the matching circuit, confirm that there are sufficient characteristics (Q, self-resonant frequency, etc.) in the frequency band being used.
The component characteristics of Murata can be confirmed by the design support tool SimSurfing provided by our company.

The signal level of the input matching circuit is low, and there are many cases where the PA characteristics are not affected so much by the level of component Q. In order to respond to the recent requirements of the miniaturization of PAs, there are many cases where smaller inductors are selected as well.

Among Murata's inductors, the film typeLQP03TN_02 series (0.6 x 0.3mm) and the even smaller LQP02TQ_02 series/LQP02TN_02 series (0.4 x 0.2mm) LQP02TN series.

Figure 2 shows a graph of the Q comparison of the LQP02TQ_02/LQP02TN_02 and LQP03TN_02 (Every 6.8nH) .SimSurfing introduced previously, was used to display this graph.

The signal level of the output matching circuit is high, because the signal amplified by the PA passes through, and the PA characteristics are greatly affected by component Q. When the Q is higher, the gain of the PA in the RF inductor can also be increased, and the output current can be reduced. For this reason, select an RF inductor while adjusting the required gain, output current and etc.

Among Murata's inductors, the coil type LQW series has the highest Q, and highly efficient PA characteristics can be acquired by using the LQW series. The LQW04AN_00 series (0.8 x 0.4 mm) and LQW03AW_00 series (0.53 x 0.4 mm) with their small sizes and high Q are suitable for applications like these. In addition, if even smaller dimensions are required, the film-type LQP03HQ series (0.6 x 0.3 mm) with the highest Q in the 0603 package size is suitable.

Figures 3 and 4 show the graphs of the Q comparison of LQW03AW/LQW04AN/LQP03HQ (7.5nH) .

Furthermore, the choke coils inside the PA are sometimes written into the multilayer substrates; however these choke coils take up a large surface area of the PA, which sometimes hinders the efforts to reduce the dimensions of the PA themselves.

With a view to making it easier to achieve smaller dimensions for PA, Murata recommends the film-type LQP03TN_02 series (0.6 x 0.3 mm) at the initial stage where the current levels are low. At subsequent stages that require high current levels, we recommend the LQP03P series (0.6 x 0.3 mm), which supports high current levels and which was specifically commercialized for use in the choke coils of PA.
The LQW15C series (1.0 x 0.5 mm) is also recommended as a noise suppression product for the power supply line between the DC-DC converter and the PA.