**7.2.1 Test setup for noise level measurement**

The system platform noise under investigation is first analyzed by noise floor measurement system. The complete PNS (platform noise measuring system) is composed of shielded box, pre-amplifier, spectrum analyzer, and EUT (Laptop computer). The noise level measuring system and setup for frequency domain is shown in Figure 52.

Fig. 52. Setup for antenna port noise level measurement.

Since the CAMERA or CMOS camera module is most adopted to the popular mobile devices like cellular phone or Netbook, we hence focus on EMI analysis of the built-in camera module by application of IEC 61967-2[1].

### **7.2.2 Test setup for TEM cell measurement[11]**

The test setup for TEM cell method in this study is shown in Figure 53. One end of the TEM cell is terminated with a 50 Ω resistance terminator, and the other end is connected to spectrum analyzer via pre-amplifier.

Fig. 53. TEM cell setup for IC or module EMI test.

There are two PCBs with module under test on it and are marked as 1 and 2 shown in Figure 54 and Figure 55. The tested boards for Webcam DUT are driven by USB with clock frequency 48 MHz, and the grounding connection between camera chip and PCB is utilized with wire bonding. The function of module and inner PCB routine for both boards under test are identical except for different number of bonding wires connecting to ground, there are more grounding wires for No. 2 PCB than No.1. The purpose of this measurement is to investigate the effect of multi-point grounding scheme to EMI level. Since the bonding wire is equivalent to inductance, we expect to reduce ground bounce and hence the EMI emission by parallel connection of multiple grounding wires. The connection between camera module and testing board is shown in Figure 56.

The experimental procedure for EMI test using TEM cell is following:


Fig. 54. Physical PCB with CAMERA module marked as NO.1.

Fig. 55. Physical PCB with CAMERA module marked as NO.2.

216 Wireless Communications and Networks – Recent Advances

There are two PCBs with module under test on it and are marked as 1 and 2 shown in Figure 54 and Figure 55. The tested boards for Webcam DUT are driven by USB with clock frequency 48 MHz, and the grounding connection between camera chip and PCB is utilized with wire bonding. The function of module and inner PCB routine for both boards under test are identical except for different number of bonding wires connecting to ground, there are more grounding wires for No. 2 PCB than No.1. The purpose of this measurement is to investigate the effect of multi-point grounding scheme to EMI level. Since the bonding wire is equivalent to inductance, we expect to reduce ground bounce and hence the EMI emission by parallel connection of multiple grounding wires. The connection between camera module

1. Connect the pre-amplifier (if needed) in front of spectrum analyzer at one end, and

2. Define or identify the four side of TEM cell to place the DUT oriented along all four

3. Set the measurement frequency range of spectrum analyzer from 150 kHz to 1 GHz. 4. Set the resolution bandwidth of spectrum analyzer around 9 to 10 kHz, and video bandwidth as more than three times of resolution bandwidth to meet the IEC standard

Fig. 53. TEM cell setup for IC or module EMI test.

and testing board is shown in Figure 56.

specification[12].

connect a 50Ω terminator at the other end.

The experimental procedure for EMI test using TEM cell is following:

Fig. 54. Physical PCB with CAMERA module marked as NO.1.

directions and measure EMI one for each time as shown in Figure 57.

Fig. 56. Physical camera connected to testing board.

There were two operation modes for camera module to be analyzed on EMI measurement. The first mode simulates the cellular phone activating the camera module for video communication. In the case of first mode, the camera is simply turned on for full function but does not execute the video file transferring from capturing camera to store on hard disc or memory card. However, the second mode simulates the cellular phone activating the camera module for video recording. In the case of the second mode, the camera is not only activated for full function but also execute the video file transferring from capturing camera to store on hard disc or memory card. The measured results for both operation modes are shown in Table 8 and 9 respectively. Compare the measured results for both operational mode, we can observe the occurring EMI phenomena during video file transferring from capturing camera to storage device. It can be used to find that if the more functions IC executes, would the severe EMI noise be generated or not.

Fig. 57. Definition of 4 directions for TEM cell test orientation.


Table 8. Maximum EMI level with corresponding PCB orientation and frequency for video communications mode (mode 1).


Table 9. Maximum EMI level with corresponding PCB orientation and frequency for video file transfer mode (mode 2).
