GPS Applications - RF & Protection Devices | Infineon Technologies

RF and Protect ion Devices

BGM781N11

Appl icat ion Note AN184 Revision: Rev. 1.2, 2011.12.21

Compact and High Performance Front-End Module for GPS Appl icat ions

Edition 2011.12.21

Published by Infineon Technologies AG 81726 Munich, Germany

© 2011 Infineon Technologies AG All Rights Reserved.

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Application Note AN184 Compact and High Performance Front-End Module for GPS

Applications

Application Note AN184, Rev. 1.2 2011.12.21 3 / 23

Application Note AN184

Revision History: 2011.12.21

Previous Revision: Rev. 1.1

Page Subjects (major changes since last revision)

4/10/11/12/13/14/15/18

Updated Gain, Input Return Loss, Output Return Loss and Reverse Isolation values and curves

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Last Trademarks Update 2009-10-19


Applications


1 BGM781N11 GPS Front-End Module for High Performance Integrated Solution

Features

Front-End Module for GPS including Pre-filter, LNA and Post-filter

High gain: 17.9dB

Low noise figure: 1.7dB

High selectivity: over 80dBc

Only two external parts

Power-off function

Supply voltage: 1.5V to 3.6V

RF output internally matched to 50Ω

8kV contact discharge ESD protection at input

Application

Global positioning systems (GPS)

BGM781N11 Topview

1.1 Introduction

Global Positioning System or GPS receiver, as we know, works on the reception of location based information

from satellite signals. However, the power levels of the satellite signals received, can be lower than -130 dBm.

This poses a challenge on the sensitivity of the GPS receiver. Along with this, the ever growing disturbing or

jamming signals in the adjacent cellular bands makes the design of the receiver front-end even more difficult.

The rapidly growing market for GPS systems is driving the design of advanced and high-performance GPS

receivers. A simple overview of the RF system in a mobile phone or other handheld devices is shown in Figure

1.

GPS receivers for mobile or handheld applications are always under the threat of high power cellular signals.

Due to the coexistence of GPS and Cellular services, there is a strong coupling of the DCS/PCS and Cellular

signals to the GPS receiver. The performance of a standard integrated GPS receiver chip cannot meet the

specifications required for the present systems. An external RF front-end is essential to achieve this required

performance. The most important prerequisites for the front-end of a GPS receiver are low noise figure and

sufficient amplification of the desired signal together with high attenuation of the jamming signals.


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Figure 1 RF System Overview: Mobile Phone


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1.2 Systems overview of a GPS receiver

Several configurations can be adopted for a GPS receiver chain. In all configurations, as mentioned earlier, a

RF front-end like BGM781N11 is placed between the antenna and the GPS receiver chip. Mobile/portable

devices as well personal navigation devices request decreasing form factor used by the implementation of the

GPS function in the devices. BGM781N11 supports the designers to minimize the area in the front-end area

used with all the. Such a configuration is shown in Figure 2. The BGM781N11 can also be used for the active

antenna module as shown in Figure 3.

Figure 2 Compact GPS system with fully integrated GPS FEM BGM781N11 for mobile/portable and personal navigation devices.

Figure 3 Active antenna module using GPS FE Module.

ESD Diode

BPF BPF GPS

Receiver IC

Embedded ANT

LNA

BGM781N11


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1.3 What is inside the BGM781N11?

The Infineon BGM781N11 is a GPS receiver Front-end module comprising of pre-Surface Acoustic Wave

(SAW) filter, LNA (Low Noise Amplifier) and post-SAW filter as shown in Figure 4. Traditionally, in the GPS

receiver design, the three devices have been used as three individual components. With their integration into

one single device, the BGM781N11 brings the designer the advantages of small PCB area, low cost, faster and

simpler design cycles and lower part count.

Figure 4 Inside the BGM781N11

1.3.1 Pre-SAW filter

The strong cellular signals can drive the LNA of the receiver into saturation. This is because the LNA is

optimized for GPS reception and hence the power handling capability is relatively low compared to the high

power mobile signals. To avoid this, a pre-filter is needed to filter out these out-of-band disturbances. The filter

however should not contribute considerable losses to the system, since it is the first device after the antenna in

the receiver chain, which will impact the noise figure of the receiver system significantly. A Surface Acoustic

Wave pre-filter is used in this module, which can strongly attenuate these parasitic effects of cellular phones.

The SAW filter used for the BGM781N11 introduces an insertion loss of only 1.0 dB in the passband. It has a

high input power capability and delivers high out-of-band rejection of about 34 dB in the 900 MHz and 1800

MHz cellular bands and +47 dBm Input IP3 with f1=1713 MHz and f2=1851 MHz.


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1.3.2 Low Noise Amplifier (LNA)

The LNA follows the pre-SAW filter in BGM781N11. The well-known Infineon device BGA715L7 is used for the

LNA. After suppressing the unwanted signals with the pre-SAW filter, the in-band signal needs to be amplified

in order to meet the sensitivity required to acquire GPS signals, which otherwise cannot be met with the

integrated LNA of the GPS receiver. The LNA used provides 20 dB gain and 0.6 dB noise figure, which defines

more or less the noise figure of the complete receiver chain succeeding it. The LNA is based upon Infineon

Technologies’ B7HFM 70 GHz fT Silicon-Germanium (SiGe:C) technology, allowing for a cost-effective solution

with excellent performance at low current consumption. The LNA features integrated on/off function that

enables low power consumption and increased stand-by time for GPS handsets. It includes active biasing and

also has a transfer characteristic with out-of-band rejection to a certain extent.

1.3.3 Post-SAW filter

With the present trend of designing state of the art GPS receivers, which are expected to work error free, a

further out-of-band rejection is required after the LNA to prevent the later stages from interfering signals. A

second filter is thus necessary to achieve these levels of rejection. In the present module, again a SAW filter is

used to serve this purpose. Compared to the pre-filter, the attenuation in the cellular bands is stronger in the

post-filter at the cost of a small degradation in the insertion loss. The post filter inserts only a low loss of 1.5 dB

and we achieve a further attenuation of the stop-band of more than 40 dB.

1.3.4 Pin Assignment of BGM781N11

Table 1 shows the pin definition and their function of BGM781N11.

Table 1 Pin Definition and Function

Pin No. Symbol Function

1 BG2 (optional) Postfilter Ground

2 PON Power On/Off

3 VCC Power Supply

4 n.c. Not Used

5 RFIN RF Input

6 BG1 Pre-Filter Ground

7 BO1 Pre-Filter Output

8 AI LNA Input

9 BIAS BIAS

10 RFOUT RF Output

11 GND Package Middle Islands Ground


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1.4 Application Schematic

The BGM781N11 is internally matched at the output to 50 Ohm. The LNA bias circuitry is also integrated on

chip. Therefore, only two external components are required in the application.

The application schematic is shown in Figure 5 and the function of the external passives is listed in Table 2.

Figure 5 Application circuit of the BGM781N11

RFin is the input of the pre-filter. The output of the pre-filter is connected to the LNA input via the inductor L1 for

a better noise matching. Inductor L2 is a RF choke for biasing the LNA. The output of the LNA is connected

internally to the post-SAW filter. One capacitor of 20pF is integrated on the Vcc pin to ground pin on the LNA

chip. Therefore no external capacitor is required on the Vcc pin. A capacitor C1 can be optionally used for the

filtering of DC voltages.

Table 2 Bill of Materials

Symbol Value Unit Size Manufacturer Comment

N1 BGM781N11 TSNP11-2 Infineon GPS Front-End Module

C1 1.0 µF 0402 various Supply Filtering (optional)

L1 3.6 nH 0402 muRata LQG15HS series, matching

L2 33 nH 0402 muRata LQG15HS series, biasing


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2 Measurement Results

Measurement results of the BGM781N11 are presented in this section. The measurements are performed on

the Infineon application board at room temperature. The performances of the BGM781N11 are here provided

for the voltage of 1.8V (Table 3) and 2.8V (Table 4). The data exclude PCB and SMA connector losses, unless

otherwise mentioned.

Table 3 Summary of Measurement Results1)

TA = 25 °C, VCC = 1.8 V, VPON,ON = 1.8 V, VPON,OFF = 0 V 1)

Parameter Symbol Value Unit Note/Test Condition

Frequency Freq 1.575 GHz

DC Voltage Vcc 1.8 V

DC Current ICC;ON 3.25 mA ON-Mode

ICC;OFF < 0.1 uA OFF-Mode

Power On Control Current

IPON;ON 5

uA ON-Mode, measured on VPON pin

IPON;OFF << 0.1 uA OFF-Mode

In-Band Parameters @1575.42 MHz

Gain2) G 17.9 dB

Noise Figure2) NF 1.7 dB Zs=50Ohm

Input Return Loss RLin 17 dB

Output Return Loss RLout 14 dB

Reverse Isolation 1/|S12|² 41 dB

Input P1dB IP1dB -14.2 dBm @1575.42MHz

Input IP3 IIP3 -5.5 dBm f1 = 1575.42 MHz, f2 = f1 +/- 1 MHz

Pin1=-30dBm; Pin2=-30dBm

Stability k >1 -- Unconditionally stable

Stopband Parameters

Rejection 900MHz3) Rej900M 92 dBc f = 806 MHz - 928 MHz



Input P1dB IP1dB900M 22 dBm @900MHz

Input P1dB IP1dB1800 25 dBm @1710MHz

Input IP3 IIP3QC +47 dBm f1=1713MHz, f2=1851MHz

Pin1=+10dBm; Pin2=+10dBm 1)

Measured on BGM781N11 application board including PCB losses (unless noted otherwise) 2)

PCB and connector losses subtracted, verified on AQL base 3)

Rejection is defined as following: [Gain at 1575.42 MHz] – [Attenuation@stopband frequency]


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Table 4 Summary of Measurement Results1)

TA = 25 °C, VCC = 2.8 V, VPON,ON = 2.8 V, VPON,OFF = 0 V 1)

Parameter Symbol Value Unit Note/Test Condition

Frequency Freq 1.575 GHz

DC Voltage Vcc 2.8 V

DC Current ICC;ON 3.35 mA ON-Mode

ICC;OFF < 0.1 uA OFF-Mode

Gain Switch Control Current

IPON;ON 11

uA ON-Mode

IPON;OFF << 0.1 uA OFF-Mode

In-Band Parameters @1575.42 MHz

Gain2) G 17.9 dB

Noise Figure2) NF 1.7 dB Zs=50Ohm

Input Return Loss RLin 15 dB

Output Return Loss RLout 14 dB

Reverse Isolation 1/|S12|² 41 dB

Input P1dB IP1dB -10.5 dBm @1575.42MHz

Input IP3 IIP3 -5.0 dBm f1 = 1575.42 MHz, f2 = f1 +/- 1 MHz

Pin1=-30dBm; Pin2=-30dBm

Stability k >1 -- Unconditionally stable

Stopband Parameters




Input P1dB IP1dB900M 23 dBm @900MHz

Input P1dB IP1dB1800 28 dBm @1710MHz

Input IP3 IIP3QC +48 dBm f1=1713MHz, f2=1851MHz

Pin1=+10dBm; Pin2=+10dBm 1)

Measured on BGM781N11 application board including PCB losses (unless noted otherwise) 2)

PCB and connector losses subtracted. 3)

Rejection is defined as following: [Gain at 1575.42 MHz] – [Attenuation@stopband frequency]


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2.1 BGM781N11 characteristics

The Graphs presented on this section show measured characteristics of the BGM781N11. The Gain brought by

the LNA BGM781N11 at GPS frequency +/-10 MHz is displayed on Figure 6. The noise figure measured in the

+/-10 MHz band with the center frequency of 1575MHz is shown in Figure 7. The out-of-band attenuation

observed in Figure 8 can suppress the jammer signals generated by mobile phones by 89dBc below the

desired GPS signal. Thus, the BGM781N11 integrated solution is not perturbated by other signals which could

degrade the received GPS signal information. The Figure 9, 10 and 11 shows that the circuit is well matched at

the GPS frequency with a minimum of 14dB return loss. The BGM781N11 is unconditionally stable (please see

Figure 12 and 13).

The change of voltage from 1.8V to 2.8V has no impact on the noise figure since the current stays constant.

Regarding the characteristics of linearity, the curves of measurement for the input compression point at 1dB are

measured at 1.8V and 2.8V. Using a higher voltage brings a better 1dB compression point. In the same manner

of the compression point, the 3rd

Intercept point will also increase when using a higher voltage (see Figure 14

and 15).

Figure 16 and 17 show the insertion gain and noise figure over the temperature. Gain variation over the

temperature range from -40°C to +85°C is 3.5dB and the variation of noise figure is 1.2dB.


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1550 1555 1560 1565 1570 1575 1580 1585 1590 1595 1600

Frequency (MHz)

Insertion Power Gain

0

5

10

15

20

1575.42 MHz17.9 dB

Figure 6 Wideband Insertion Power Gain Inband of the BGM781N11

Figure 7 Noise figure of BGM781N11 over +/-10MHz band measured at room temperature


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0 1000 2000 3000 4000 5000 6000

Frequency (MHz)

Transducer Insertion Gain Wideband

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

10

20

30

1813 MHz-59.9 dB

2450 MHz-52.1 dB1980 MHz

-56.6 dB

1710 MHz-64.6 dB

900 MHz-71.3 dB

1575 MHz17.9 dB

Figure 8 Wideband Insertion Power Gain incl. out-of-band attenuation of the BGM781N11

1550 1560 1570 1580 1590 1600

Frequency (MHz)

Input Matching

-20

-15

-10

-5

0

1575.42 MHz-15.31 dB

Figure 9 Input Matching of the BGM781N11


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1550 1560 1570 1580 1590 1600

Frequency (MHz)

Output Matching

-40

-30

-20

-10

0

1575.42 MHz-14.42 dB

Figure 10 Output Matching of the BGM781N11

1550 1560 1570 1580 1590 1600

Frequency (MHz)

Reverse Isolation

-55

-45

-35

1575.42 MHz-40.83 dB

Figure 11 Reverse Isolation of the BGM781N11


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0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

Frequency (MHz)

Stability K Factor

0

1

2

3

4

5

6

7

8

9

10

Figure 12 Stability K-Factor of the BGM781N11

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

Frequency (MHz)

Stability Mu factor

0

0.5

1

1.5

2

Mu2 factor

Mu1 factor

Figure 13 Stability Mu Factor of the BGM781N11


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Figure 14 Output 3rd

Intermodulation measurement at 1.8V of the BGM781N11

Figure 15 Output 3rd

Intermodulation measurement at 2.8V of the BGM781N11


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1550 1560 1570 1580 1590 1600

Frequency (MHz)

B63_S21

5

7

9

11

13

15

17

19

211575 MHz19.74 dB

1575 MHz16.01 dB

1575 MHz17.43 dB

1575 MHz17.91 dB

1575 MHz18.66 dB

DB(|S(2,1)|)

B63_m40deg

DB(|S(2,1)|)

B63_p00deg

DB(|S(2,1)|)

B63_p25deg

DB(|S(2,1)|)

B63_p40deg

DB(|S(2,1)|)

B63_p85deg

+40°C

+85°C

+25°C

0°C

-40°C

-40 °C

0 °C

+25 °C

+40 °C

+85 °C

Gain over Temperature

Ga

ino

(dB

)

Figure 16 Inband Insertion Power Gain at 1.8V and 2.8V of the BGM781N11 over temperature

Figure 17 Noise figure at 1.8V and 2.8V of the BGM781N11 over temperature


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2.2 Pre- and Post-Filter Characteristics of BGM781N11

Figure 18 and 19 show the broadband characteristics of the pre- and post-filters in BGM781N11.

The pre-filter in BGM781N11 shows an attenuation of 34dB in the 800/900MHz frequency band and of 40dB in

the 1800/1900 MHz band. At 2.4GHz, attenuation of more than 59dB is realized. The post-filter in BGM781N11

shows an attenuation of 51dB in the 800/900MHz frequency band and of 32dB in the 1800/1900 MHz band. At

2.4GHz, attenuation of more than 45dB is realized.

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Frequency (GHz)

S21_BGM781_Pre_filter

-80

-70

-60

-50

-40

-30

-20

-10

0

S2

1 (

dB

)

0.85 GHz-34.22 dB

1.8 GHz-40.85 dB

2.4 GHz-58.98 dB

1.575 GHz-1.131 dB

Figure 18 Pre-filter characteristics of the BGM781N11

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Frequency (GHz)

S21_BGM781_Post_Filter

-60

-50

-40

-30

-20

-10

0

S2

1 (

dB

)

1.8 GHz-41.89 dB

2.4 GHz-35.42 dB

0.85 GHz-51.61 dB

DB(|S(2,1)|)

Ref04_3_cal7_probe_20090504

Figure 19 Post-filter characteristics of the BGM781N11


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3 Evaluation Board and Layout Information

Figure 20 Photo picture of the BGM781N11 application board

Figure 21 Populated application board of BGM781N11


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Figure 22 PCB Layer Information


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Authors:

Anthony Thomas, Application Enigineer of Business Unit “RF and Protection Devices”

Dr. Chih-I Lin, Senior Staff Engineer of Technical Marketing of Business Unit “RF and Protection Devices”

w w w . i n f i n e o n . c o m

Published by Infineon Technologies AG AN184

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