Inductor Guide

Inductors suited for the bias tee circuit of automotive cameras [wiring inductor room]

1. Introduction

Cameras installed on automobiles have become widespread recently for driver assistance and autonomous driving in the future. In some countries, the installation of cameras on new vehicle models is already mandatory for accident prevention. Since this trend is expected to become more extensive, there is increasing demand for more compact cameras to limit the effect on external appearance and passenger cabin space.

To make cameras compact, the components used in cameras are naturally being made smaller and with lower profiles; these components are progressively evaluated from different standpoints, as well. Among these are attempts to reduce the number of wire harnesses (modules that bundle multiple electric wires together for power supply and communicating signals). To date, the transmission of camera-captured images, camera control and the supply of power for cameras have been performed using separate wire harnesses. However, the increase in the number of wire harnesses used has also resulted in larger connectors being mounted on camera modules to connect them. One method of solving this problem is sending both signals and power on a single wire harness.

Although this method has many advantages, a way to eliminate the mutual influence of signals and power is required. Here, we describe the performance of inductors that are required when configuring a bias tee circuit (a circuit for separating AC and DC components), which is one such measure, and discuss some of the appropriate inductors for use in such applications.


2. Performance for consideration in bias tee circuits for automotive cameras

A bias tee circuit is sometimes designed as shown in Figure 1 to eliminate the mutual influence of signal and power circuits. Generally, a bias tee circuit comprises series connected capacitors to prevent the inflow of large DC current to the signal processing section of the circuit, and inductors to prevent signal components from entering the circuit for the power supply.

Here, we consider the characteristics of inductors required for automotive cameras, in particular. The signal components of an automotive camera contain not just a high-speed signal of several Gbps for sending captured images, but also a low-speed signal of several hundred kbps to several Mbps for control. To prevent these signal components from entering the power circuit, multiple inductors having differing characteristics are needed to ensure effectiveness over a wide frequency band. Figure 2 shows an example of combined inductor characteristics applied in a bias tee circuits. A combination of components achieves high impedance over a wide frequency band ranging from several MHz to several GHz.

Figure 1 Example of a bias tee circuit for an automotive camera
Figure 2 Example of combined inductor characteristics applied in a bias tee circuit

3. Suggested inductors: LQH32PZ series and LQW15CN series

Murata has made full use of proprietary materials technology and winding technique to commercialize compact inductors having low to high inductance. LQH32PZ series inductors have relatively high inductance, while the LQW15CN series inductors have relatively low inductance, and both have high self-resonance frequency. A combination of these components enables appropriate bias tee circuits to be configured.

The characteristics shown in Figure 2 above are a combination of the following three items:

The following shows the specifications of the LQH32PZ and LQW15CN series. As you can see, we have commercialized compact inductors with various characteristics, and bias tee circuits close to required performance can be configured by combining two or more components.


A lineup of various other wiring inductors is also available:


4. Conclusion

The LQH32PZ and LQW15CN series introduced here represent just one example of components suited for the bias tee circuit of automotive cameras. It is essential that bias tee circuits having sufficient characteristics for required frequency bands, combine components having various inductance values.


Product Engineering Section 2
Product Engineering Department
EMI Filter Division
Murata Manufacturing Co., Ltd.

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