DEMOSENSE2GOLTOBO1 - INFINEON TECHNOLOGIES AG

Application Note Please read the Important Notice and Warnings at the end of this document Revision 1.1

www.infineon.com 2017-07-11

AN472

User's Guide to BGT24LTR11N16

24GHz Radar

About this document

Scope and purpose

This application note is intended to put flesh on the bones of BGT24LTR11N16’s datasheet.

The datasheet gives technical data and limits of the device itself but it is not explaining the device in greater

detail. This application note takes care of this issue.

The reader will find here:

 Discussion of all different building blocks

 How to operate the different blocks

 Additional measurement data showing behavior over temperature

Intended audience

Hardware engineers and software engineers working on designs with Infineon’s BGT24LTR11N16.

Table of Contents

About this document ......................................................................................................................................................................... 1

Table of Contents ............................................................................................................................................................................... 1

List of Figures ...................................................................................................................................................................................... 2

List of Tables ....................................................................................................................................................................................... 2

1 Introduction to BGT24LTR11 ................................................................................................................................. 3

2 Building Blocks ........................................................................................................................................................... 4

2.1 Transmitter .......................................................................................................................................................................... 4

2.2 Receiver ................................................................................................................................................................................. 5

2.3 Voltage Controlled Oscillator (VCO) .......................................................................................................................... 7

2.4 Proportional to Absolute Temperature (PTAT) Voltage Source ................................................................... 8

2.5 Frequency Divider ............................................................................................................................................................. 9

3 Evaluation Board ...................................................................................................................................................... 10

3.1 Schematic Diagram ......................................................................................................................................................... 10

3.1.1 Matching Structures ................................................................................................................................................. 11

3.2 Layout of Evaluation Board ......................................................................................................................................... 12

3.3 Layout Version improving TX to RX Isolation ..................................................................................................... 13

4 Controlling the VCO ................................................................................................................................................. 14

4.1 Controlling the VCO using V_PTAT ........................................................................................................................... 14

4.1.1 Controlling the VCO with the PTAT source in detail ................................................................................... 14

4.2 Controlling the VCO using a PLL ................................................................................................................................ 15

4.3 Controlling the VCO using a Software Based Open-Loop Concept .............................................................. 16

5 Authors ........................................................................................................................................................................ 17

Revision History ............................................................................................................................................................................... 17

Application Note 2 Revision 1.1

2017-07-11

User's Guide to BGT24LTR11N16

24GHz Radar

Table of Contents

List of Figures

Figure 1 BGT24LTR11N16 Block Diagram .......................................................................................................................... 3

Figure 2 TX output power vs. frequency and temperature ........................................................................................... 4

Figure 3 TX output power with VTUNE connected to V_PTAT .................................................................................... 5

Figure 4 Gain vs. frequency......................................................................................................................................................... 5

Figure 5 Noise figure vs. frequency ......................................................................................................................................... 6

Figure 6 Conversion gain vs. temperature ........................................................................................................................... 6

Figure 7 Noise figure vs. temperature .................................................................................................................................... 7

Figure 8 VCO frequency over tuning voltage and temperature ................................................................................... 7

Figure 9 VCO frequency over temperature, VCO controlled by PTAT voltage source ....................................... 8

Figure 10 Voltage generated by PTAT voltage source vs. temperature ...................................................................... 9

Figure 11 Schematic diagram .................................................................................................................................................... 10

Figure 12 Component placement ............................................................................................................................................. 10

Figure 13 Matching structures to be used on a Ro4350B substrate with a thickness of 0.254 mm ............ 11

Figure 14 Layout of evaluation board with description of pin headers .................................................................. 12

Figure 15 Layer stack .................................................................................................................................................................... 12

Figure 16 Adding compensation structures will increase TX to RX isolation ....................................................... 13

Figure 17 Compensation structures in detail. (Unit is mm) ......................................................................................... 13

Figure 18 Block diagram: Using V_PTAT to keep BGT24LTR11N16 in the ISM band ....................................... 14

Figure 19 Bock diagram: Controlling BGT24LTR11N16 with a PLL ......................................................................... 15

Figure 20 Block diagram: Controlling BGT24LTR11N16 with an Open-Loop concept ..................................... 16

List of Tables

Table 1 Enabling/disabling TX output ................................................................................................................................. 4

Table 2 Setting the divider ratio ............................................................................................................................................. 9

Table 3 Bill of materials ........................................................................................................................................................... 11

Table 4 13

Application Note 3 Revision 1.1

2017-07-11

Introduction to BGT24LTR11

User's Guide to BGT24LTR11N16

24GHz Radar

1 Introduction to BGT24LTR11

BGT24LTR11 is Silicon Germanium radar MMIC for signal generation and reception, operating in the

24.0 GHz to 24.25 GHz ISM band. It is based on a 24 GHz fundamental voltage controlled oscillator (VCO).

The device was designed with Doppler-radar applications in mind—as it is capable of keeping the transmit

signal inside the ISM band without any external PLL — and may also be used in other types of radar such as

FMCW or FSK.

A built-in voltage source delivers a VCO tuning voltage which is proportional to absolute temperature

(PTAT). When connected to the VCO tuning pin it compensates for the inherent frequency drift of the VCO

over temperature thus stabilizing the VCO within the ISM band eliminating the need for a

PLL/Microcontroller. An integrated 1:16 frequency divider also allows for external phase lock loop VCO

frequency stabilization.

The receiver section uses a low noise amplifier (LNA) in front of a quadrature homodyne down-conversion

mixer in order to provide excellent receiver sensitivity. Derived from the internal VCO signal, a RC-polyphase

filter (PPF) generates quadrature LO signals for the quadrature mixer. I/Q IF outputs are available through

single-ended terminals.

The device is manufactured in a 0.18 μm SiGe:C technology offering a cutoff frequency of 200 GHz. It is

packaged in a 16-pin leadless RoHS compliant TSNP package.

Figure 1 BGT24LTR11N16 Block Diagram

VCC

VEE

PTAT

20141208_BGT24LTR11_Block

Diagram_TX_ON.vsd

IFI IFQ

RFIN

f-Div

90°

0°

Polyphase

Filter

Balun

MPA

Balun

LNA

Balun

VEE

VTUNE V_PTATDIV VCC_PTATVCC_DIV R_TUNE

TX_EN

Application Note 4 Revision 1.1

2017-07-11

Building Blocks

User's Guide to BGT24LTR11N16

24GHz Radar

2 Building Blocks

2.1 Transmitter

BGT24LTR11N16 has a single-ended transmitter output TX (pin 11) with a typical output power of 6 dBm.

The transmitter’s output may be enabled and disabled by applying appropriate voltages to TX_ON (pin 5) as

shown in the table below.

Disabling the TX output will not save power as the output will be switched to an internal load while the rest

of the chip is still running. This is necessary in case one wants to implement a software controlled oscillator

(see section 4.3).

Table 1 Enabling/disabling TX output

Enable TX

Disable TX

Voltage at TX_ON > 2 V

Voltage at TX_ON < 0.8 V

Figure 2 TX output power vs. frequency and temperature

23200 23400 23600 23800 24000 24200 24400 24600 24800

TX Output Power [dBm]

VCO Frequency [MHz]

TX Output Power over VCO Frequency and Temperature

T=-40°C T=-20°C T=0°C T=25°C T=40°C T=60°C T=85°C

Application Note 5 Revision 1.1

2017-07-11

Building Blocks

User's Guide to BGT24LTR11N16

24GHz Radar

Figure 3 TX output power with VTUNE connected to V_PTAT

2.2 Receiver

The receiver consists of an LNA followed by quadrature direct-conversion mixer. Its input (RX, pin 3) is

single-ended. The voltage conversion gain is typically 20 dB with a single side-band noise figure of 10 dB.

Figure 4 Gain vs. frequency

-40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90

TX Output Power [dBm]

Temperature [°C]

TX Output Power over Temperature

24 24.05 24.1 24.15 24.2 24.25

Conversion Gain, G [dB]

RX Frequency [GHz]

Conversion Gain over RX Frequency and Temperature

T=-40°C T=-20°C T=0°C T=25°C T=40°C T=60°C T=85°C

Application Note 6 Revision 1.1

2017-07-11

Building Blocks

User's Guide to BGT24LTR11N16

24GHz Radar

Figure 5 Noise figure vs. frequency

Figure 6 Conversion gain vs. temperature

24 24.05 24.1 24.15 24.2 24.25

Noise Figure, NF [dB]

RX Frequency [GHz]

Noise Figure over RX Frequency and Temperature

T=-40°C T=-20°C T=0°C T=25°C T=40°C T=60°C T=85°C

-40 -20 0 20 40 60 80 100

Conversion Gain, G [dB]

Temperature [°C]

Conversion Gain over Rx Frequency and Temperature

Rx=24GHz Rx=24.05GHz Rx=24.1GHz Rx=24.15GHz Rx=24.2GHz Rx=24.25GHz

Application Note 7 Revision 1.1

2017-07-11

Building Blocks

User's Guide to BGT24LTR11N16

24GHz Radar

Figure 7 Noise figure vs. temperature

2.3 Voltage Controlled Oscillator (VCO)

Figure 8 VCO frequency over tuning voltage and temperature

-40 -20 0 20 40 60 80 100

Noise Figure, NF [dB]

Temperature [°C]

Noise Figure over Rx Frequency and Temperature

Rx=24GHz Rx=24.05GHz Rx=24.1GHz Rx=24.15GHz Rx=24.2GHz Rx=24.25GHz

23200

23400

23600

23800

24000

24200

24400

24600

24800

0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2

VCO Frequency [MHz]

V_Tune [V]

VCO Frequency over tuning voltage (V_Tune) and Temperature

T=-40°C T=-20°C T=0°C T=25°C T=40°C T=60°C T=85°C

Application Note 8 Revision 1.1

2017-07-11

Building Blocks

User's Guide to BGT24LTR11N16

24GHz Radar

Figure 9 VCO frequency over temperature, VCO controlled by PTAT voltage source

2.4 Proportional to Absolute Temperature (PTAT) Voltage Source

The PTAT voltage source generates a voltage VPTAT at the V_PTAT pin (pin 15) which is proportional to the

chip temperature. It is powered separate from VCC via the VCC_PTAT pin (pin 16).

The PTAT voltage source serves two purposes:

 Generating tuning voltage for the VCO in Doppler mode. See section 4.1.

 Temperature sensor measuring chip temperature.

The chip temperature Tchip can be calculated from VPTAT using the following equation:

Tchip / °C = 158.7 * (VPTAT / V) – 217.0 with VCC_PTAT = VCC =3.3 V and VCC_DIV open.

24100

24110

24120

24130

24140

24150

24160

24170

24180

-40 -20 0 20 40 60 80 100

VCO Frequency [MHz]

Temperature [°C]

VCO Frequency over Temperature controlling with V_Ptat

Application Note 9 Revision 1.1

2017-07-11

Building Blocks

User's Guide to BGT24LTR11N16

24GHz Radar

Figure 10 Voltage generated by PTAT voltage source vs. temperature

2.5 Frequency Divider

BGT24LTR11N16’s frequency divider has two divider rations, divide by 16 and divide by 8182 which result

in output frequencies of 1.5 GHZ and 3 MHz respectively.

Table 2 Setting the divider ratio

Divider ratio

Voltage at VCC_PTAT (pin 16)

< 0.8 V

8192

3.3 V

Setting the divider to a 3 MHz output will cause the PTAT to consume current. This ratio is usually used only

in case of a software controlled VCO and for this use cases a temperature sensor is required anyways to

check the validity of the used look-up table.

V_PTAT = 0.0063V*(Temp/°C) + 1.3669V

R² = 0.9986

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

-40 -20 0 20 40 60 80 100

V_PTAT [V]

Temperature [°C]

V_PTAT over Temperature

Application Note 10 Revision 1.1

2017-07-11

Evaluation Board

User's Guide to BGT24LTR11N16

24GHz Radar

3 Evaluation Board

3.1 Schematic Diagram

Figure 11 Schematic diagram

Figure 12 Component placement

Schematic_Evalboard_general.vsd

VCC

PTAT

IFI IFQ

RFIN

f-Div

90°

0°

Polyphase

Filter

Balun

MPA

Balun

LNA

Balun

VTUNE V_PTAT

DIV VCC_PTAT

VCC_DIV

R_TUNE

TX_ON

Vctrl

VCC

to VCC_PTAT

C1 R1

Application Note 11 Revision 1.1

2017-07-11

Evaluation Board

User's Guide to BGT24LTR11N16

24GHz Radar

Table 3 Bill of materials

Designation

Part type

Value

Package

Manufacturer

C1, C5, C8

Chip capacitor

1 µF

0402

Various

C2, C3, C6, C7, C9

DNP

0402

Chip resistor

16 kΩ

0402

Various

R2,R3

Chip resistor

0 Ω

0402

Various

Chip resistor

100 kΩ

0402

Various

Chip resistor

1 kΩ

0402

Various

p-MOSFET

BSS209PW

SOT-323

Infineon

IC1

Radar MMIC

BGT24LTR11N16

TSNP-16-9

Infineon

3.1.1 Matching Structures

Figure 13 Matching structures to be used on a Ro4350B substrate with a thickness of 0.254 mm

W50=520 um

TX RX

W50=520 um

12 43

W=600 um

L=1300um

W=1100um

L=1290um

W=600 um

L=1100um

W=1100um

L=1300um

W1=300 um

W2=600um

L=950um

Application Note 12 Revision 1.1

2017-07-11

Evaluation Board

User's Guide to BGT24LTR11N16

24GHz Radar

3.2 Layout of Evaluation Board

Figure 14 Layout of evaluation board with description of pin headers

Figure 15 Layer stack

Copper

35um

Blind-Vias Vias

Ro4350B, 0.254mm

FR4, 0.5mm

BGT24AT2_Cross_Section_View.vsd

FR4, 0.25mm

Application Note 13 Revision 1.1

2017-07-11

Evaluation Board

User's Guide to BGT24LTR11N16

24GHz Radar

3.3 Layout Version improving TX to RX Isolation

The isolation between the TX port and the RX port on the standard evaluation board is typically about 25 dB.

This isolation can be improved to 35dB by adding a grounded length of line at the ground pins next to the TX

output pin as shown in Figure 16. Details of the used compensation structures can be found in Figure 17.

Table 4

Standard evaluation PCB

PCB with compensation structures

TX to RX isolation / dB

Figure 16 Adding compensation structures will increase TX to RX isolation

Figure 17 Compensation structures in detail. (Unit is mm)

0.03

0.16

0.09

0.26

0.15

1.75

0.34

0.3x0.3mm²

Package Pad

Via to GND

Application Note 14 Revision 1.1

2017-07-11

Controlling the VCO

User's Guide to BGT24LTR11N16

24GHz Radar

4 Controlling the VCO

4.1 Controlling the VCO using V_PTAT

Figure 18 Block diagram: Using V_PTAT to keep BGT24LTR11N16 in the ISM band

Exact frequency control in Doppler radars in the 24 GHz ISM band is not really necessary for most

applications. If we assume the transmit frequency to be at the lower edge of the band while it is actually at

the upper edge the introduced error is only 0.8 %.

BGT24LTR11N16 was designed to keep its transmit frequency inside the ISM band without the need for a

dedicated frequency control circuit like a Phase Locked Loop (PLL) or a look-up table based control of

VTUNE.

To achieve this capacitor C5 is charged by V_PTAT while the rest of the chip is turned off to save power. Once

C5 is fully charged VCC_PTAT is disconnected while VCC is applied and VTUNE gets its voltage from C5.

There are two reasons for toggling VCC and VCC_PTAT. The first one is obvious: Turning off VCC and

VCC_PTAT reduces current consumption (45 mA and 1.5mA, respectively). The second reason for turning off

VCC_PTAT is that the PTAT source generates noise at its output when running and this noise on the tuning

voltage will degrade the signal to noise ratio (SNR) of the system. Of course for some short range this SNR

might still be acceptable.

4.1.1 Controlling the VCO with the PTAT source in detail

One duty-cycle works as follows:

1. TX_ON = 0 V. Disables TX output to prevent out of band emissions.

2. Vctrl = 3.3 V. This turns on the PTAT source (VCC_PTAT = 3.3 V) while VCC is disconnected from power

supply.

Schematic_Self_control1.vsd

VCC

PTAT

IFI IFQ

RFIN

f-Div

90°

0°

Polyphase

Filter

Balun

MPA

Balun

LNA

Balun

VTUNE V_PTAT

from Vctrl

R_TUNE

TX_ON

Vctrl

VCC

to VCC_PTAT

C5 R1

Application Note 15 Revision 1.1

2017-07-11

Controlling the VCO

User's Guide to BGT24LTR11N16

24GHz Radar

3. Wait for C5 to be charged. At the start-up of the system when the capacitor is fully discharged this will

require a longer time. During normal operation the capacitor is only slightly discharged and will be very

quickly recharged.

4. Vctrl = 0 V. Turns off PTAT and turns on the rest of the chip.

5. Wait for VCO to settle its frequency. Settling time of the VCO is maximum 100 ns.

6. TX_ON = 3.3 V. Enables TX output.

7. Sample IF frequency.

8. Goto 1.

Further reduction of the power consumption is possible by introducing a time frame when both VCC and

VCC_PTAT are disconnected. This would mean that VCC_PTAT needs to be disconnected from Vctrl and one

more GPIO pin needs to be available at the microcontroller in the system.

4.2 Controlling the VCO using a PLL

Figure 19 Bock diagram: Controlling BGT24LTR11N16 with a PLL

Controlling BGT24LTR11N16’s VCO with a RF Phase Locked Loop (PLL) is straight forward. The frequency

divider needs to be set to a ratio of 16 by connecting VCC_PTAT to GND. The 1.5 GHz can then be used to feed

the PLL, which in turns generates the tuning voltage.

Block-diagram_PL.vsd

VCC

PTAT

IFI IFQ

RFIN

f-Div

90°

0°

Polyphase

Filter

Balun

MPA

Balun

LNA

Balun

V_PTAT

R_TUNE

TX_ON

VCC

VCC_DIV

DIV

C1 VTUNE

PLL

VCC_PTAT

Application Note 16 Revision 1.1

2017-07-11

Controlling the VCO

User's Guide to BGT24LTR11N16

24GHz Radar

4.3 Controlling the VCO using a Software Based Open-Loop Concept

Figure 20 Block diagram: Controlling BGT24LTR11N16 with an Open-Loop concept

It is possible to control BGT24LTR11N16 using an Open-Loop concept, sometimes also called Software-Loop

concept. Figure 20 shows a block diagram on how to set-up the system.

 The frequency divider is set to an 8192 division ratio and fed to a Capture Compare Unit (CCU) of the

microcontroller to determine the frequency of the oscillator.

 The PTAT source is used as a chip temperature sensor and V_PTAT is fed to an ADC of the

microcontroller.

 The microcontroller’s DAC is used to generate the tuning voltage of the VCO.

 A GPIO port of the microcontroller enables / disables BGT24LTR11N16’s TX output.

Controlling BGT24LTR11N16 with an Open-Loop concept works as follows:

1. Disable TX output

2. Check the chip temperature

3. Generate a Look-Up Table (LUT) that gives the DAC values corresponding to different VCO frequencies.

Use this LUT for the modulation of the VCO.

4. Enable TX output

5. Generate transmit signal using DAC

6. Check chip temperature. If chip temperature changed goto 1 else goto 5

Block-diagram_software_loop.vsd

VCC

PTAT

IFI IFQ

RFIN

f-Div

90°

0°

Polyphase

Filter

Balun

MPA

Balun

LNA

Balun

V_PTAT

R_TUNE

VCC

TX_ON

VCC_DIV DIV

VTUNE

CCU

VCC

LUT DAC

MCU

Temperature

Application Note 17 Revision 1.1

2017-07-11

Authors

User's Guide to BGT24LTR11N16

24GHz Radar

5 Authors

Dietmar Stolz, Senior Staff Engineer of Business Unit “Radio Frequency and Sensors”

Revision History

Major changes since the last revision

Page or Reference

Description of change

12 f

Added section on improving TX to RX isolation

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ifx1owners.

Edition 2017-07-11

AN_472_2016_03_PL32_001

Published by

Infineon Technologies AG

81726 Munich, Germany

Do you have a question about this

document?

Email: erratum@infineon.com

Document reference

IMPORTANT NOTICE

The information contained in this application note

is given as a hint for the implementation of the

product only and shall in no event be regarded as

a description or warranty of a certain

functionality, condition or quality of the product.

Before implementation of the product, the

recipient of this application note must verify any

function and other technical information given

herein in the real application. Infineon

Technologies hereby disclaims any and all

warranties and liabilities of any kind (including

without limitation warranties of non-infringement

of intellectual property rights of any third party)

with respect to any and all information given in

this application note.

The data contained in this document is exclusively

intended for technically trained staff. It is the

responsibility of customer’s technical departments

to evaluate the suitability of the product for the

intended application and the completeness of the

product information given in this document with

respect to such application.

For further information on the product,

technology, delivery terms and conditions and

prices please contact your nearest Infineon

Technologies office (www.infineon.com).

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contain dangerous substances. For information on

the types in question please contact your nearest

Infineon Technologies office.

Except as otherwise explicitly approved by

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signed by authorized representatives of Infineon

Technologies, Infineon Technologies’ products

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failure of the product or any consequences of the

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