May 2012

SAW filters for automotive applications

Well-packaged telematics

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Motor vehicles are being equipped with more and more telematics applications. Miniaturized EPCOS SAW filters qualified to AEC-Q200 are key components for these. The product portfolio now also includes filters in a chip-sized SAW package (CSSP®) with a footprint of only
1.4 × 1.1 mm2.

Telematics is becoming increasingly important for road transport and thus also in on-board automotive systems. The list of technologies linking telecommunications and IT is growing continuously for both passenger cars and utility vehicles. They include classical satellite-based navigation using systems such as GPS, Galileo, Glonass and mobile phones as well as mobile-phone supported traffic guidance systems and Internet access inclusive of local services. But also WLAN, emergency call systems such as eCall for use in the event of an accident, vehicle fleet management, car-to-X communications and toll systems.


The overwhelming majority of telematics functions in cars have so far been limited to devices that can only receive information such as GPS. With the additional use of mobile phones, however, more and more devices are being used that are capable of both transmission and reception. Application-specific SAW filters from EPCOS in various package sizes qualified to AEC-Q200 are particularly well suited for such purposes.

Reliability and miniaturization in one
Up until now, compromises were often unavoidable in SAW filters for telematics or mobile-phone based applications in cars: they used either compact package sizes of the kind typical for mobile phone technology, or else highly reliable rugged variants meeting the requirements of the automotive industry.


SAW filters from EPCOS in the CSSP package with dimensions of 1.4 × 1.1 mm2 can now meet the required high reliability and qualification to AEC-Q200 that are already available for those with dimensions of 3.0 × 3.0 mm2. SAW components in the CSSP package have already been an established standard in mobile phone technology for many years. Compromises between reliability and miniaturization thus belong to the past (Figure 1).


The new EPCOS SAW filters for automotive electronics applications are the first worldwide in the miniaturized package size 1.4 × 1.1 mm2 qualified to AEC-Q200. The product range of these qualified and space-saving SAW filters is being continuously extended in line with customer requirements.

Figure 1: Demands of the automotive industry on SAW filters

State-of-the-art design processes for the new EPCOS SAW filters for automotive electronics applications combine miniaturization and reliability. These EPCOS products are qualified to AEC-Q200.

High demands on robustness
The humidity test (85 °C/85 % relative humidity, 1000 h), the rapid temperature cycling test (1000 cycles −40 to +85 or +125 °C) and the operating temperatures of up to 125 °C stipulated by the AEC-Q200 standard represent a particular challenge for the reliability of the components. In order to meet this challenge, the design of these SAW filters had to be specially adapted to meet these demands. This is their key difference from SAW filters that are not qualified to AEC-Q200.

Availability for many years
EPCOS SAW filters for automotive electronics are distinguished by the fact they remain available for a very long time. This corresponds to the long product cycles of the applications in which these filters are used, thus satisfying the rigorous requirements of the automotive industry. SAW filters are adapted to the electrical requirements of the widely used ICs. Customized AEC-Q200-qualified EPCOS SAW filters are thus available that facilitate the design work of customers on their products.

Extensive range for satellite-based navigation systems
Up to now, satellite-based navigation systems were used principally to determine locations, such as in vehicle fleet management or tracking systems as well as acting as pilots for specific destinations. A wide range of AEC-Q200-qualified SAW filter components (single and diplexer) for satellite-based navigation systems using GPS, Galileo and Glonass is now available from EPCOS. Their package sizes range from 3.0 × 3.0 mm2 to 1.4 × 1.1 mm2, and various center frequencies, insertion attenuations and useful bandwidths are offered. EPCOS will naturally also develop suitable filters for the Chinese satellite navigation system COMPASS. Table 1 shows a selection from the current product range.

Table 1: AEC-Q200-qualified EPCOS SAW filters for satellite-based navigation

ApplicationDescriptionfc
[MHz]
Usable bandwidth
[MHz]
Insertion attenuation
[dB]
TypePackage size
[mm2]
GPSfilter1575.422.41.3B3520

3.0 × 3.0

GPSfilter1575.422.03.2B3521

3.0 × 3.0

GPSfilter1575.422.01.6B3522

3.0 × 3.0

Glonassfilter1601.50172.5B3529

3.0 × 3.0

GPS/Galileo/Glonassfilter1588.00562B3913

3.0 × 3.0

GPS/Galileo/Glonassfilter1585.50411.9B3519

3.0 × 3.0

GPS/Galileo/Glonassfilter1586.00421.9B3517

3.0 × 3.0

GPS/Galileofilter1575.423.01.0B43001.4 × 1.1
GPS/Galileo/Glonassfilter1588.6634.471.5B43101.4 × 1.1
GPS/Galileo/Glonassdiplexer1575.42
1601.50
10
10
3.8
3.6
B35183.0 × 2.5
GPS/SDARSdiplexer1575.42
2332.50
6
25
1.2
1.4
B39203.0 × 3.0

All listed filters and diplexers have unbalanced inputs and outputs of 50 Ω. Many filters are also available in versions with unbalanced inputs of 50 Ω and balanced outputs of 100 Ω.

Extended applications of mobile communications technology
When mobile phones first entered cars, their uses were limited to telephony via a hands-free setup. Now, these devices are increasingly being used to access the Internet on the road to contact local services or augment satellite-based navigation. A significant and increasingly important function is navigation responding to the momentary traffic situation. It determines how many mobile phone subscribers are logged into a cell and at what speed they are moving. The more such subscribers present in a cell and the slower they are moving, the denser the traffic or else a traffic jam has built up.


Another combined option for satellite-based navigation and mobile phones is offered by emergency call systems – such as eCall – that are used in the event of an accident or breakdown. This intelligent emergency call system determines the position of the vehicle via satellite and sets up a data and voice link to an emergency call center via the mobile communications network. Vehicle fleet management and the German toll system, for example, also operate with satellite-based navigation and mobile communications technology. The frequency ranges they use depend on the regions in which they operate.


An extensive range of AEC-Q200-qualified EPCOS SAW filters (single and diplexer) is also available in package sizes of 3.0 × 3.0 mm2 down to 1.4 × 1.1 mm2 with various center frequencies, insertion losses and useful bandwidths for the typical frequency bands. A selection from the current product range is shown in Table 2.

Table 2: AEC-Q200-qualified EPCOS SAW filters for mobile-communications-based applications

Band

Receive

path RX

Transceive

path TX

Descrip-

tion

fc
[MHz]

Usable

band-

width

[MHz]

Insertion

atten-

uation
[dB]

Type

Package

size [mm2]

Band IRX
TX
filter2140.0
1950.0
60
60
1.6
2.3
B4302
B4309

1.4 × 1.1

Band II GSM1900RX
TX
filter1960.0
1880.0
60
58.75
1.7
2.7
B4305
B4315

1.4 × 1.1

Band IIIRXfilter1842.5751.8B4306

1.4 × 1.1

Band V GSM850RX
TX
RX diversity
filter881.5
836.5
881.5
25
25
25
1.2
1.7
1.9
B4303
B4311
B4314

1.4 × 1.1

Band VIII GSM900RXfilter942.5351.5B4304

1.4 × 1.1

Band V GSM850
Band VIII GSM900
RX
RX
2in1 filter881.5
942.5
25
35
1.1
1.1
B4380

1.5 × 1.1

Band III GSM1800
Band II GSM1900
RX
RX
2in1 filter1842.5
1960.0
75
60
1.3
1.4
B4381

1.5 × 1.1

All the listed RX filters and 2in1 components have unbalanced inputs of 50 Ω and balanced outputs of 150 Ω. All listed TX and RX diversity filters have unbalanced inputs and outputs of 50 Ω.

Internet in the car
WLAN systems operating in the 2.4 GHz frequency range are used for Internet access in cars. Some of them receive mobile phone signals via their external antenna and convert them into WLAN frequencies. This allows passengers to use the Internet with high reliability. WLAN antennas are also used in the external antennas to permit Internet access in hot spots. The B3912 SAW filter (fc=2448.5 MHz) from EPCOS for applications in automotive electronics was developed specifically for WLAN frequencies (Figure 2).

Figure 2: Attenuation curve of the EPCOS B3912 filter

Another application sector for WLAN will be car-to-X communications: either car-to-car communications that permit networking between vehicles, or car-to-infrastructure communications that set up links between vehicles and systems such as traffic lights. These systems will probably operate in the 5.9 GHz frequency range and will also control the traffic flow at crossings more effectively and thus avoid accidents. Ongoing field trials by the automotive industry will show whether this frequency is suitable or whether its range is too short. A system of this kind called the Intelligent Traffic System (ITS) is currently being set up in Japan: it operates with a frequency of around 760 MHz and is designed to control the efficiency of traffic flows.

In future, duplexers to AEC-Q200 too
Intensive work is also taking place on duplexers qualified to AEC-Q200 for various mobile phone frequencies in package size 2.0 × 1.6 mm2. They are expected to be available as engineering samples in mid-2012.


The EPCOS product range for these applications will be continuously expanded in order to meet the requirements of both customers and IC manufacturers.

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