High Q in a flat package

TDK has developed a new series of multilayer ceramic inductors designed especially for RF circuits in smartphones and tablets. They are characterized by their high degree of miniaturization and extremely high Q factors.

Smartphones designed for LTE must serve ever more frequency bands for telephony and data transfer. At the same time, these devices and tablets offer a series of connectivity functions, including WLAN, Bluetooth, NFC, and GPS, as well as radio and TV reception. The number of inductors required for impedance matching and filtering increases in line with the numerous RF circuits used.

Although conventional wirewound inductors offer the high Q factors required for RF circuits, they cannot be manufactured in the required miniaturized sizes and with ultraflat insertion heights. In addition, the inductance values of these versions exhibit relatively high tolerances. For this reason, TDK has developed the MHQ0603P and MHQ1005P super high-Q series of multilayer ceramic inductors. The components of these new series have a footprint of only 0.65 mm × 0.35 mm and 1.00 mm × 0.50 mm, respectively. Thanks to these compact dimensions and their respective insertion heights of 0.6 mm and 0.35 mm, these multilayer inductors satisfy the miniaturization requirements. Thus, the new components are not only suited for use in discrete filter circuits, but they can also be integrated in complex front-end modules, for example.

Good performance thanks to highest Q values

A decisive factor for the use of inductors in RF circuits is their Q factor. This is the ratio of the DC resistance to the impedance at a defined frequency (Q = ωZ/R). The higher its value, the lower the attenuation of the RF signal. Especially in battery-powered equipment such as smartphones, and tablets, the attenuation must be minimized as far as possible so that the RF amplifier stages only need to supply minimal power and thus conserve the battery. Figure 1 shows the Q factors of the new series compared with those of existing products and wound inductors (3.9 nH types).

Q factors as a function of frequency

Figure 1:

Curves for the Q factors for 3.9 nH types of the TDK MHQ1005P and MHQ0603P series compared to existing types and equivalent wound inductors. It can be clearly seen that the new series offer the highest Q values over the entire frequency range.

Figure 2:

Curves for the Q factors for 3.9 nH types of the TDK MHQ1005P and MHQ0603P series compared to existing types and equivalent wound inductors. It can be clearly seen that the new series offer the highest Q values over the entire frequency range.

To reach the required high Q values, TDK uses new material design and process technologies for the MHQ0603P and MHQ1005P series as well as special dielectrics and electrode materials. A multilayer LTTC process offering maximum precision is also applied. Thanks to the combination of these technologies, Q values can be achieved that are 30 percent higher in the case of the new MHQ0603P series and 80 percent higher for the MHQ1005P series than for the previous multilayer inductors (MLG0603P and MLG1005S). Thus, a Q factor of 60 is achieved at 1000 MHz. This value is comparable to that of conventional wound inductors. Figure 2 compares the attenuation curves of 3.9 nH inductors.

Figure 3:

Attenuation curves in the Tx and Rx bands:
Thanks to its good Q values, the TDK MHQ1005P series has a lower attenuation than the predecessor version, especially in the Tx band.

Large product range with narrow tolerances

TDK MHQ series of multilayer ceramic inductors

Matching circuits in the RF range in particular require very narrowly toleranced components. This is the only way to ensure that attenuations and frequency fluctuations are kept as low as possible. This means that, in addition to high Q values and low tolerances, the rated values of the inductors used in such circuits must be maintained. For this reason, the MHQ0603P and MHQ1005P series from TDK in the range below 3.9 nH offer very small inductance steps with intervals of only 0.1 nH. These components permit a very precise adjustment of RF circuits and matching networks. For standard inductors, the tolerance is ±5 percent. TDK is now working to implement tolerance values of ±3 percent, corresponding to 0.1 nH for these inductors.

Key data for the TDK MHQ series of multilayer ceramic inductors