A universal integrated circuit RF noise filtering capability measurement method

Liu Nan School of Optoelectronics Information

and Communication Engineering

Beijing Information Science & Technology University

Beijing, China liunan@bistu.edu.cn

Wu Yao School of Optoelectronics Information

and Communication Engineering

Beijing Information Science & Technology University

Beijing, China wuyao391@163.com

Kang Feng Yuan

School of Optoelectronics Information and Communication

Engineering Beijing Information Science &

Technology University Beijing, China

kangfengyuan@yahoo.com.cn

Abstract—Generally, the measurement of radio frequency (RF) noise filtering capability is a necessary part in the design of integrated circuit productions. In this paper, the authors propose a universal integrated circuit RF noise filtering capability measurement method—RF anechoic chamber. During the test, we put the integrated circuit in anechoic chamber, which provides a controllable RF signal electrical level, standing for the interface intensity when the integrated circuit works. By measure the results from voltmeter, we get the RF noise filtering capability of the integrated circuit. This novel measurement method is useful for selecting IC method and helpful to get a suitable integrated circuit which could resist the RF noise.

Keywords-RF; anechoic chamber; integrated circuit

I. INTRODUCTION With the development of the mobile communication

industry, GSM mobile phones could be seen everywhere, which leads to a constant increase of RF noises we don’t need. If electronic circuits don’t have the ability to resist RF noises, these RF noises would leads to distortion of the results. To make sure of the reliable work of electronic circuits, the measurement of RF noise filtering capability is a necessary part in the design of production. This paper introduces a universal integrated circuit RF noise filtering capability measurement method—RF anechoic chamber, describes its component, and gives a realistic example.

At present, the majority of nest telephone systems adapt the TDMA (Time Division Multiple Address), which modulates 217Hz frequency carrier with passes/breaks the impulse modulation. Integrated circuit (IC) which is easily disturbed by RF signals could demodulate the carrier, resulting in 217Hz signal and its higher harmonic wave component. Since the vast majority of signals are in voice band (300Hz-3400Hz) , users would hear unwanted noises. In conclusion, bad IC could demodulate RF signals from nest telephones, bringing about low frequency noise[1].

To survey the quality of products, we need to put the circuit under a certain RF environment, which equals to the environment when the circuit normally works[2]. This paper

provides a RF measurement anechoic chamber[3,4], giving a controllable RF field, to test integrated circuit RF noise filtering capability.

II. TEST SCHEME

A. Measurement circuit We compared a double operational amplifier (MAX4232)

with another competitive product (X).

Figure 1. Measurement circuit of double operational amplifier

Fund Support: The paper by the BISTU Fund in 2011 to support (NO 5026010918.)

2495978-1-4577-0321-8/11/$26.00 ©2011 IEEE

Figure 1 gives the circuit connection, where each operational amplifier is designed as alternating current amplifier. When there is no alternating current input, the output is 1.5V (VCC=3V). While inverting input via a 1.5 link short circuit to ground, this simulates the antenna. Antenna would select and demodulate RF signals under working frequency[5]. We could get the noise filtering capability of the circuit by measuring the voltage of the output port.

B. Measurement device system

Figure 2. Measurement device system of noise filtering capability

Figure 2 introduces the measurement device system. The RF measurement device of Maxim produces the RF filed which noise filtering capability measurement needs. RF anechoic chamber has a shielded chamber, which possesses ports to power supply and monitor. The measurement device system consists of:

1. Signal generator: 8kHz-3GHz

2. RF power amplifier (PA): 800MHz-1GHz, 20W

3. Power meter: 25MHz-1GHz

4. Anechoic chamber

5. Field intensity indicator

6. Computer

7. Voltmeter

Signal generator produces the RF modulated signal, and sends the signal to RF power amplifier. Then the signal is measured by a directional coupler which connects with the power meter and monitors the PA output. The computer could control the frequency, kind of modulation, modulation percentage, power output and the RF filed we need by regulating the signal generator. And the field is radiated in anechoic chamber via antenna. The field is symmetrical, consistent and repetitive.

The typical case of nest telephone filed is almost 60V/m (4 cm from telephone antenna). The field would be lower away

from telephone. For instance, the field is 25V/m when 10cm from telephone antenna. So we need a symmetrical field of 60V/m to simulate the realistic RF environment. The RF signal we adopted the sine signal which varies from 800MHz to 1GHz, modulated by 1kHz voice frequency signal, and the modulation percentage is 100%.

III. MEASUREMENT RESULTS

Figure 3. Measurement results.

The results are according to the figure 3. While RF frequency varies from 800MHz to 1GHz, in symmetrical field of 60V/m, the average output of MAX4232 is -66dBV. By contrast, the average output of X is -18dBV, and output is -86dBV when there is no RF signal.

So the change of MAX4232 is only -20dBV, meaning that RF noises make the output of MAX4232 vary from -86dBV to -66dBV, while the change of X is -18dBV. In a word, MAX4232 is much better than X in restraining RF noises.

TABLE I. OUTPUT RESULTS

Frequency

/MHz

Output/dBV Output of MAX4232

Change of MAX4232

Output of X

Change of X

800 -60.00 0.00 -5.00 0.00

860 -65.00 -5.00 -25.00 -20.00

920 -65.00 0.00 -23.00 -2.00

980 -70.00 -5.00 -20 -3.00

IV. CONCLUSION The experiment indicates that device X has a poor ability

to restrain RF noise (-18dBV), so X could not work normally when close to telephones or other RF sources. Apparently MAX4232 is a better choice for voice processing usage, such as earphone amplifies and microphone amplifies.

To insure the products' quality of work under RF environment, measurement of integrated circuit RF noise filtering capability is a step IC producer must consider[6,7,8,9,10]. Measurement device system of noise filtering capability

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provides an economical, flexible and precise method to measure the filtering capability of electronic circuits.

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Zheng Junqi, “EMC design and analysis of testing cases ” Beijing,electron industry press,2006,12

[2]

Li shunyang, “EMC design and measurement technology” Beijing, China standard press,2009

[3]

Wang kailong, Li zhengjun, Chen shufeng, the application of GTEM in EMC measurement, space electronic technology, 1996

[4]

Zhou Yu, “Anechoic chamber and EMC test,” Beijing University of Posts and Telecommunications, 2008.

[5]

Ma Ning, Chen li, “The resistance design of RF circuit,” modern radar. [6]

He Wei, “Principle and application of EMC,” Beijing Qinghua university press, 2008.

[7]

Heinrich Hollmann. Relexionsarme Trichter-und Rechtecka-mmern fur Antennenmesungen. NTZ. 1972(12):545-553.

[8]

IEC 61000 4 6:2006, Electromagnetic compatibility(EMC)-Part4-6:Testing and measurement techniques-Immunity to conducted disturbances induced by radio frequency fields[S].

[9]

Zhou Huizhong. The EMC Consideration about the Designing of RF Receiver. Electronics Quality, 2010(9)

[10]

Chen Ying-mei, Li Zhi-qun, Wang Zhi-gong, Jing Yong-kang, Zhang Li, Design of an L1 band low noise single-chip GPS receiver in 0.18 m CMOS technology, The Journal of China Universities of Posts and Telecommunications,2010,17(3).

______________________________________________________________ About the author: Liu Nan: 1959-6, F, Beijing Information Science & Technology University, associate professor, engaged in the electronic information and communication engineering teaching and research. liunan@bistu.edu.cn

. Address: Beijing 9716 mailbox, (Optical Information and Communication Engineering) Zip: 100101

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