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Application Note

How to select the right PoC Filter Inductors and Chip Beads for Automotive SerDes (LVDS) Transmission

Increased demand for comfort functions and higher performing Advanced Driver Assistance Systems (ADAS) are requiring faster in-vehicle transmission interfaces. For image transmission using SerDes (LVDS), PoC (Power over Coax) has become mainstream to reduce the weight of the wiring harness by transmitting signal and supplying power within a single coaxial cable. The evolution of cameras used in automobiles continues with increased current capacity and faster image transmission for higher resolution images, as well as heating functions to defog the camera lens.
This article presents examples of the use and effects of PoC filter inductors and chip beads.

What is PoC (Power over Coax)?

PoC (Power over Coax) is a transmission system that reduces the number of wires by simultaneously transmitting signals and DC power on a single coaxial cable.
In order to separate the DC power supply from the broadband signals, the system is characterized by the use of a DC-cutting capacitor on the signal line side and a filter inductor on the power supply line to prevent the inflow of broadband signals.
There are a number of communication standards led by IC manufacturers and standardization organizations as shown below, and the appropriate inductor must be selected to match the respective signal transmission speed and power supply.

Standard Official Name IC Supplier / Alliance
FPD-Link Flat Panel Display Link Texas Instruments
GMSL Gigabit Multimedia Serial Link Analog Devices (formerly Maxim Integrated)
GVIF Gigabit Video Inter Face Sony
CLL-BD Clockless Link-BD Rohm
HSMT High-Speed Media Transmission China Local SerDes Supplier
ASA-ML ASA Motion Link Automotive SerDes Alliance
MIPI A-PHY MIPI A-PHY Mobile Industry Processor Interface Alliance
Table 1: Major SerDes standards supporting PoC
PoC transfer system overview
Figure 1: PoC transfer system

PoC (Power Over Coax) for higher speed and power

Sensing devices such as cameras and radar equipment are becoming increasingly high-capacity, high-functionality, and multifunctional as sensing accuracy improves, requiring higher transmission speeds and more power. As a result, PoC filters are required to support higher transmission speeds, from approximately 1.5 Gbps to 10 Gbps or more, and higher supply power, from 1 W to 5 W.

Camera module for Autonomous-Driving / ADAS cabling
Figure 2: Camera module for Autonomous-Driving / ADAS

What is an inductor (coil) optimized for PoC filters?

Space is often restricted in automotive camera modules and other products, requiring miniaturization of the product and reduction of the mounting area. A typical filter consists of four inductors together with chip beads, but constraints can often limit the number of products on the mount. In order to reduce the number of inductors, a product that can maintain impedance frequency characteristics over a wide bandwidth is required. At the same time, this device must maintain its characteristics in high-temperature environments and operate at temperatures up to 150°C.

Example of a typical PoC filter configuration
Figure 3: Example of a typical PoC filter configuration

37% reduction in mounting area

Under the same conditions as the general PoC filter configuration example above, TDK's inductors for PoC filters can be realized with one inductor and two chip beads. This reduces the mounting area by 37%.

Filter 1 Filter 2 Filter 3 Filter 4 Rdc[Ω] Mounting
footprint[mm2]
Conventional
inductor
NLCV32T-100K-EFRD/2kΩ NLCV25T-4R7M-EFRD/2kΩ Chip Beads
MPZ1608S102ATD25
Chip Beads
MMZ1608Y152BTD25
2.09 24.95

-50%

-37%

Recommended by
TDK
ADL3225VT-100M-TL000 / 1.2kΩ Chip Beads
MPZ1608S102ATD25
Chip Beads
MMZ1608Y152BTD25
Not required 1.05 15.83

*Example: 4Gbps 300mA PoC filter

Table 2: TDK inductors recommended for PoC filter use

Impedance characteristics maintained over a wide bandwidth

Magnitude Power Control Signal Video Signal Frequency Conventional inductor
2 to 3 inductors are required for general power circuit inductors.
High ripple due to narrow high impedance bandwidth.
TDK's ADL inductor optimized for PoC filter
Low ripple due to wide high-impedance bandwidth
Figure 4: Effect of TDK inductors for PoC filter use

TDK inductors for PoC filters

As shown in the diagram (Figure 5) below, TDK offers a wide range of inductors for PoC filters that meet your usage conditions, such as allowable current and filter requirements.(See table below: "TDK inductors for PoC (Power over Coax) filter circuits") The MLJ1608-G series, which is compact and covers a high frequency bandwidth, contributes to a space saving filter design. The ADL series is a product that supports a wide bandwidth, and reduces the overall number of filter coils. The ADL4524VL and ADL8030VA series, which cover an even wider bandwidth, are currently under development. The ADL4532VK and ADL3225VF series are also under development for high current applications.

TDK inductors for PoC filters can be used to reduce the number of filters by one

* R1 to R3 may vary according to the combination of capacitors and chip beads. Please inquire for details.

Figure 5: Types of inductors for PoC filter use

TDK inductors for PoC (Power over Coax) filter circuits

With the increasing speed and sophistication of in-vehicle interfaces, PoC is being promoted in camera systems with SerDes transmission, etc. To separate broadband signals and power in PoC, a wide-band, high-impedance filter using an inductor is required. TDK has a diverse product line-up and can propose filter configurations to suit the current capacity and communication speed of the circuits used.
*Product names in red can be used in 125°C environments.
*The above figures are based on an operating ambient temperature of 105°C. For 125°C environments, the combination may vary, so please contact us for more information.

ADL4532VK

+

FLP5535

+

ADL4532VK

+

ADL3225VF

+
+

ADL3225VF

ADL4532VK

+

ADL3225VF

ADL8030

OR
+
PoC current (mA)
1600
1400
1200
1000
800
600
400
200
0
0
2
4
6
8
10
12
Bitrate (Gbps)

The solution map above is just an example.
We will propose the optimal solution based on your usage environment and requests.

Table 3: Solution Map

The above PoC filter combinations are examples of TDK products that are used as references by IC manufacturers or filter combinations recommended by TDK. For choosing the best PoC filter combination under other conditions, use the TDK PoC Selection Tool.

List of reference designs
by chipset

A list of TDK products listed in the reference design for each chipset is available for download in PDF format. Please fill out the form on the right and click the "Download" button.

For more information on reference combinations by IC manufacturer or examples of filter combinations tailored to your requirements, please contact us using the 'Contact Form' below.

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