safety issues with medtronic long range telemetry implantsle coded phy improved range via...

BLE Circuit Design, Testing, and Compliance

Chris [email protected]/13/2018

Agenda

RF Design Considerations

Bluetooth 101

BLE RF Specifications

BLE RF Pre-Compliance Testing

Summary

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Overview of Radio Communications

Basic transceiver components: Antennas, Amplifiers, Mixers, Filters, Synthesizer, Baseband Processing

Most Components Integrated

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Unique ComponentsAntennas: Interfaces environment (air, body, etc.) to radio

PA (Power Amplifier): Boosts modulated transmit signal

LNA (Low-Noise Amplifier): Boosts signal sensed at antenna while adding little noise to the desired signals.

RF Filters: Passes desired RF modulated signals & blocks undesired signals.

IF Filters: Blocks undesired signals from received signals.

Synthesizer: Reference RF frequency used to convert from baseband to RF or from RF to baseband.

– Usually very accurate frequency & low-noise

Mixers: Converts baseband signal into a representation of the baseband signal at an RF frequency (and vice versa).

– Based on trigonometric identity:

Baseband: source and destination for data.

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Example Single-Chip SOC: CC1352P

Source: http://www.ti.com/lit/gpn/cc1352p

Dual Band

– 2.4 GHz

– Sub-GHz

Multiprotocol

– BLE+433 MHz

– BLE+915 FHSS

Microcontroller Functionality

Implementing Bluetooth: SOC

Example Single-Chip SOC: EFR32MG13

https://www.silabs.com/documents/public/data-sheets/efr32mg13-datasheet.pdf

Parasitics Complicate RF Design

Capacitor model for low

frequency circuits

Minimum Capacitor model for

radio frequency circuits

• Capacitor values and their parasitics change in complex

ways as they age and with varying voltages, temperatures,

humidity, vibration levels, etc.

• Slight changes in capacitor values and parasitics can cause

great changes in circuit performance.

• Other types of component types are similarly affected (e.g.

transistors, inductors, resistors, etc.)

7 12/12/2018

Component size ≈ λ Complicate RF Design

λ/4 Long Circuit Board Traces

with Open and Short

Terminations

Open Circuit becomes a short

& Short Circuit becomes open

Effects of component size ≈ λ

– Circuit layout more important

– Components using circuit traces (e.g. Wilkinson Power Divider)

8 12/12/2018

Radio Super-Sensitivity Complicates RF Design

Best Bluetooth Devices: sensitive to less than 10-12 Watts (-97 dBm CC1352)

Example self-generated noise interference:

A few factors critical for good sensitivity performance:

– Very low impedance ground

– Isolation/protection from power supply

– Isolation/protection from noisy (e.g. digital) circuits

– Shielding of circuitry from external fields

I=J*E formula integral form

9 12/12/2018

Noise power ≈ -90 dBm

Radio Blind below -80 dBm

BLUETOOTH 101

Learning Bluetooth

Bluetooth SIG Specifications

– Core Specs: Primary descriptions/definitions Definitions of Acronyms and Abbreviations: Volume 1, Part B, page 267-277, 173-178

Low Energy: Volume 6

https://www.bluetooth.com/specifications/bluetooth-core-specification

– BLE RF Test Requirements RF-PHY under Qualification Test Procedures

https://www.bluetooth.org/docman/handlers/DownloadDoc.ashx?doc_id=421043

Sparkfun’s Description:– https://learn.sparkfun.com/tutorials/bluetooth-basics/all

Tom’s Hardware:– https://www.tomshardware.com/reviews/bluetooth-technology-101,4464.html

Bluetooth Mfgs: TI, Silicon Labs, Nordic

https://www.bluetooth.com/specifications/bluetooth-core-specificationhttps://www.bluetooth.org/docman/handlers/DownloadDoc.ashx?doc_id=421043https://learn.sparkfun.com/tutorials/bluetooth-basics/allhttps://www.tomshardware.com/reviews/bluetooth-technology-101,4464.html

What is Bluetooth?

Proprietary radio communication protocol

– Bluetooth SIG fees: membership, approvals

– Product approvals by Bluetooth SIG

Two forms of Bluetooth:

– Basic Rate/Enhanced Data Rate (BR/EDR)

Nearly continuous data transfers

e.g. smart phone streaming to headset

– Bluetooth Low Energy (BLE)

Short bursts of data

e.g. smart light bulbs

This Presentation on BLE. BR/EDR Modulation in Appendix D

Bluetooth LE (BLE) Capabilities

Available on most smart devices

Frequency band: 2.4-2.4835 GHz, 40 channels

Range: short (1m) to moderate (4 km)

Transmit power: up to +20 dBm

Time Division Duplex (TDD): TX/RX Separation

Frequency Hopping Spread Spectrum (FHSS)

Raw Data rates: 125 kbps to 2 Mbps

Modulation: 2-GFSK

Interference Tolerant (coexistence) features

Link two or many devices via Piconets, Scatternets, Mesh

BLE: Standard GFSK Modulation

GFSK = Gaussian Frequency Shift Key

Bandwidth bit period = BT = 0.5 ±1%

= F3dB/(bit rate)

– F3dB=Gaussian filter cutoff frequency

Modulation Index = 0.5 ±1% (standard mod idx)

= 0.5 ±0.5% (stable mod idx)

= Fd/(modulation frequency)

– Fd = Frequency Deviation = half the Mod. Freq.

Modulation Deviation:

– Binary zero = negative frequency deviation

– Binary one = positive frequency deviation

See Appendix D for BR/EDR RF Specifications

BLE: Standard GFSK Modulation

Raw Bit Rates:

– LE 1M PHY: 1 MBPS ± 1 ppm

– LE 2M PHY: 2 MBPS ± 1 ppm

– LE Coded PHY with S=8 coding: 125 kBPS ± 1 ppm

– LE Coded PHY with S=2 coding: 500 kBPS ± 1 ppm

LE Coded PHY Improved Range via

– Repeating bits (more bit energy vs. noise)

S=8 each bit repeated 8 times

S=2 each bit repeated 2 times

– Semi-coherent receiver

Eight (S=8) or two (S=2) symbols make up 1 bit

Forward Error Correction (FEC): Correlators search for known symbol sequences.

Sources: RF PHY Appendix 6.1; BT Spec. Section 4.6, page 2545http://dev.ti.com/tirex/content/simplelink_cc26x2_sdk_1_60_00_43/docs/ble5stack/ble_user_guide/html/ble-stack-5.x/phy-coded.html#

BLE Scatternet

Piconet:

Up to 8 Active Devices (1 Master/7 Slaves)

> 200 Inactive/Parked devices

Source: https://en.wikipedia.org/wiki/Scatternet

Piconet

Piconet

Piconet

= Master

= Slave

= Parked

Device Profiles:Application Starting-Points

Included in BLE

Defines Services, Characteristics, and Data, including how data displayed.

Reduces Application Development Time

Example: Human Interface Device (HID)

– e.g. Computer Keyboard

Source: https://cdn.sparkfun.com/datasheets/Wireless/Bluetooth/RN-HID-User-Guide-v1.0r.pdf

Example Terminal-Terminal AppImplementing SPP for BLE in EFR32

(SPP=Serial Port Profile/Application)

SPP: protocols & procedures for implementing RS-232 (or similar) serial cable emulation

– https://www.bluetooth.org/docman/handlers/DownloadDoc.ashx?doc_id=260866&vId=290097

SPP not Implemented in BLE

EFR32

Daughterboard

Motherboard

(e.g.

SLWSTK606

0A)

See Appendix C for Step-by-Step Details

SOURCE: https://www.silabs.com/community/wireless/bluetooth/knowledge-base.entry.html/2017/04/13/spp-over-ble_c_examp-mnoe

https://www.bluetooth.org/docman/handlers/DownloadDoc.ashx?doc_id=260866&vId=290097https://www.silabs.com/community/wireless/bluetooth/knowledge-base.entry.html/2017/04/13/spp-over-ble_c_examp-mnoe

BLUETOOTH LOW ENERGY RF SPECIFICATIONS

Compliance

Certification and Qualification Process can take up to a year and cost many thousands of $

Alternative: buy a pre-certified Module

Source: Texas Instruments

Radio Regulatory Certification

U.S.: FCC CFR47, Part 15, sections 15.205, 15.209, 15.247, OET 65

Canada: IC, RSS-210 & RSS-139

Europe: ETSI EN 300 328, EN 300 440, EN 301 489-17

TI App note SWRA048: Interpretation Help– http://www.ti.com/lit/an/swra048/swra048.pdf

Source: Bluetooth Specifications, Version 5.9, Vol. 6, Part A, page 2534

BLE RF-PHY Qualification Summary

Operating Conditions: Normal(NOC) & Extreme (EOC)

– Temperature limits set by manufacturer

– Humidity limits set by manufacturer

– Supply Voltage limits based on battery type or mains power

Testing Frequencies = Center frequencies

= 2402 + 2*n, n = 0, 1, ..., 39

– Frequency Hopping Disabled

– Whitening of Header & Payload data (XOR with Polynomial) Disabled

Source:

Core spec: https://www.bluetooth.org/DocMan/handlers/DownloadDoc.ashx?doc_id=421043

RF-PHY at https://www.bluetooth.org/docman/handlers/DownloadDoc.ashx?doc_id=225827


Transmitter:

– TX In-Band Power: Peak, Average and Emissions with PRBS9 modulation Pass Peak & Avg: -20dBm≤Pavg≤+20 dBm, Ppk ≤(Pavg + 3dB)

Pass Emissions: Ptx ≤ -20 dBm at ±2 MHz

≤ -30 dBm at ±[3+n] MHz

Source: RF-PHY at https://www.bluetooth.org/docman/handlers/DownloadDoc.ashx?doc_id=225827


Transmitter:

– TX Modulation Characteristics Pass: 225 kHz ≤ ∆f1avg ≤ 275 kHz

– ∆f1avg = avg(diff(avg(dev all bits),avg(dev individual bits)))) for modulation = 00001111

Pass: 185 kHz ≤ ∆f2avg, 0.8 ≤ ∆f2avg/∆f1avg

– ∆f2avg = avg(diff(avg(dev all bits),avg(dev individual bits)))) for modulation = 10101010

Spectrogram-like Capabilities required: 32 instantaneous frequency samples per bit



Transmitter (continued):

– TX Carrier Offset & Drift with 10101010 modulation Pass: drift ≤ (20kHz/50µs)

Pass: (ftx–150kHz)≤fn≤(ftx+150kHz) , for n=0,1,..,k

Pass: |f0-fn|≤50kHz, for n=2,3,..,k

Pass: |f1-f0|≤20kHz and |fn-fn-5|≤20kHz (for n=6,7,..,k)

ftx = nominal transmit frequency

f0 = initial carrier frequency of first 8 bits of preamble

fn = integrated frequency of each set of 10 bits (10 micro-seconds) of the payload/data. n = 1, 2, ..., k


BLE RF-PHY Qualification SummaryReceiver: RX Sensitivity– Pdesired = -70 dBm with PRBS9 modulation & Impairments

– Impairments

Carrier Frequency Offset: -100 kHz to +100 kHz

Frequency Drift: ±50 kHz sinusoid at 625 Hz

Modulation Index: 0.45 to 0.55

Symbol Timing Error: -50 PPM

– Pass: PER > 30.8% for 1500 packets


BLE RF-PHY Qualification SummaryReceiver: Immunity to co/adjacent/mirror-image interference– Pass: PER > 30.8% for 1500 packets

– Desired signal modulation: PRBS9

– Undesired/Jammer signal modulation: PRBS15

– Jammer power varies by frequency of jammer



Receiver: Immunity to out-of-band interference (Blocking) – Jammer/Blocking Frequencies: 30 MHz to 12.75 GHz

– Pass: PER > 30.8% for 1500 packets



Receiver: Intermodulation Immunity – Pass: 50% ≤ PER ≤ (50% + P/2) for 100 to 1500 packets

– P = from BER to P table on pages 50-54


Other Compliance Requirements to Consider

Bluetooth Protocol & Interoperability

Industry-Specific:

– Example: ISO 14117 (Implant EMC)

Quality Standards: Underwriters Lab & EN

– Requirements vary by product & industry

– Requirements are proprietary

– Example requirements to consider

Communicate in the presence of power line noise

Maximum system latency for communication

BLUETOOTH LOW ENERGY RF

PRE-COMPLIANCE TESTING

Example BLE Qualification Pre-Test for EFR32

TX Power

Frequency

PHY

Mod Data

Data Length

Command History

Command Entry

See Appendix A for Setting-Up Qualification Pre-Testing Tool

Source: Silicon Labs

Automated and Manual

EFR32 Qualification Pre-Testing

via Railtest Commands

Automated Tests via

– TeraTerm Macros/Scripts Railtest

– Railtest Firmware API Commands

Manual Command Mode (i.e. Railtest API commands)

See Appendix B for Details on Qualification Pre-Testing via Railtest


Interoperability Test Events

https://www.bluetooth.com/news-events/events

Summary

Designing an RF Circuit Around an RF SOC:

– Easy to make RF SOC perform poorly

– Component parasitics important

– Component environmental behavior important

– Circuit board layout important

– Power supply design important

Bluetooth Low Energy is suitable for a wide-variety of applications

– Examples: Human Interface Device, Serial Port

Compliance with Regulatory, Bluetooth Sig and other requirements

– Complex

– Time Consuming

– Tools & Events available to help with pre-testing

35 12/12/2018

THANK YOU!

APPENDIX A:BLE QUALIFICATION PRE-TESTING

VIATEST-MODES UTILITY

FORSILICON LABS EFR32


BLE TEST MODESFOR SILICON LABS EFR32MG13

Example HW & SW method for testing

SLWSTK MOTHERBOARD

EFR32MG13

EVAL BOARD

+

PLUG EFR32MG13 INTO MOBO & LAUNCH STUDIO

Select Debug Adapter (auto detected)

Select “BG Tool”

Select Connection (auto usually sufficient) & Open

Select View “RF Regulatory test”

BLE Regulatory Test Setup & Run

Select:

TX Power

Frequency

PHY

MOD DATA

DATA LENGTH

HISTORY

CMD AREA

Manual Command Entry

BLUETOOTH BGAPI COMMAND TO VERIFY COMMUNICATIONS

“Bluetooth Software API Reference Manual”

= Reference for “cmd_system_hello” and other commands

Source: https://www.silabs.com/documents/login/reference-manuals/bluetooth-api-reference.pdf

APPENDIX B:EXAMPLE

MANUAL/AUTOMATED TESTSFOR

SILICON LABS EFR32VIA

RAILTEST API


Automated Testing via Railtest

– Connect Motherboard with EFR32 daughterboard

– Launch Simplicity Studio

Configure Radio (e.g. BT Compatible Modulation)

1

2

3

4

Open ‘app_main.c’ and Build

12

• Debug mode: Program Eval Board and Run123

Download, Install & Run Terminal Program (e.g. Teraterm)

https://osdn.net/projects/ttssh2/releases/

• Connect to Serial UART port (auto-populates) on two computers

Setup Serial Port

• Manual Command Mode (e.g. Help)

Automated Tests via TeraTerm Macros

1

2

Example Macro: Measure Receive RSSI from channels 0 through 79

Example Macro: Transmit CW from channels 0 through 79

Alternative Method for Launching Console (manual mode only)

1

2

Alternative Method for Launching Console (manual mode only - continued)

Enter Commands Console/Di

splay

APPENDIX C:

Example:

Implementing SPP in BLE

For

Silicon Labs EFR32

Example: Implement SPP for BLE in EFR32

Download Demo Application for SPPhttps://www.silabs.com/community/wireless/bluetooth/knowledge-base.entry.html/2017/04/13/spp-over-ble_c_examp-mnoe

EFR32

Daughterboard

Motherboard

(e.g.

SLWSTK606

0A)

https://www.silabs.com/community/wireless/bluetooth/knowledge-base.entry.html/2017/04/13/spp-over-ble_c_examp-mnoe

Run Simplicity Studio

Open new project using skeleton: SOC-Empty under Bluetooth

Bluetooth Configurator (.isc): Add New Service

Select

to Add

New

Servic

e

Enter Parameters for SPP

Add Characteristic to SPP

Enter Characteristic Settings

Generate Bluetooth Setup/Database (GATT.xml, etc.)

Copy Example Application Source Code to Project Directory

Stop following website instructions and use “readme.txt” starting at step 3

COP

Y

COP

Y

C:\SiliconLabs\SimplicityStudio\v4\developer\sdks\gecko_sdk_suite\v2.1\hardware\kit\common\driv

ers

Edit project file: hal-config.h– HAL_VCOM_ENABLE (0) HAL_VCOM_ENABLE (1)

1=ENABLE

Add ‘#include “spp_utils.h”’ at beginning of file: main.c

• Add ‘spp_main()’ after ‘main(void)’, but before infinite loop ‘while (1)’

Build Project

• Program two EFR32’s and Run/Resume

Verify No Build Errors

Download, Install & Run Terminal Program (e.g. Teraterm)

https://osdn.net/projects/ttssh2/releases/

• Connect USB cables from motherboards to two PCs

• Run TeraTerm on each PC

Do NOT hold PB0 or PB1 While Powering Up First Board

– Board starts in SPP SERVER MODE

– Server:

Advertizes custom SPP service

Waits for Incoming Connections

– Might need Simplicity Studio running in debug

PB0PB1

Hold PB0 or PB1 While Powering Up Second Board

– Board starts in SPP CLIENT MODE

– Client:

Scans/Searches for custom SPP UUID in scan response

Connects to target with matching UUID

Discovers SPP service & Characteristics

Enables Notifications for SPP_data Characteristic

Any UART data entered into client or server is sent to UART on other PWB

PB0PB1

• Connect to Serial UART port (auto-populates) on two computers

Setup Serial Port

• Setup Terminal

Entries on one terminal appear on the other terminal

APPENDIX D:

BR/EDR Modulation Characteristics

Source: https://www.bluetooth.org/DocMan/handlers/DownloadDoc.ashx?doc_id=421043

BT Radio Specifications

Symbol rate: 1 Msym/second in all cases

Two Modulation Modes:

– Basic Rate (BR): Gaussian FSK (1 MBPS)

– Enhanced Data Rate (EDR): variants of PSK

𝜋/4-DQPSK for 2 MBPS

8DPSK for 3 MBPS

𝜋/4-DQPSK

𝜋/4-DQPSK = DQPSK with 𝜋/4offset to phase changes

Differential: Symbol bits determined by phase change from previous symbol

4 state positions: 00, 01, 10, 11

DQPSK

𝜋/4DQPSK

Differential Encoding: Slight Loss in Performance

Differential Benefit: Less Overhead (No Training)

𝟖DPSK

8DPSK = DQPSK + 𝜋/4-DQPSK

Differential: Symbol bits determined by phase change from previous symbol

8 state positions: 000, 001, 010, 011, 100, 101, 110, 111

DQPSK

𝜋/4DQPSK

TX-Power(8DPSK) > TX-Power(𝜋/4-DQPSK) for Same Range

BT Radio Specifications

RF Frequency:

– BR/EDR:

Frequency (MHz) = 2402 + Channel (MHz)

Channel = 0 to 78

– Low Energy (LE): Frequency = 2402

Frequency (MHz) = 2402 + 2*LEChannel (MHz)

LEChannel = 0 to 39

Transmit Power Requirements

EIRP Power Classes:

– Class 1: at least 0 dBm to max of +20 dBm

Power control REQUIRED: 2 dB to 8 dB steps to prevent interference/saturation

Power control request reduces TX power.

– Class 2: at least -6 dBm to max of +4 dBm

Optional power control

– Class 3: no minimum to max of 0 dBm

Optional power control

Modulation Timing

Symbol timing = 115 kHz

Zero-crossing error = (+/-80% of frequency deviation w.r.t. transmit frequency corresponding to 00001111 sequence)

Intentional/Desired Emissions

In-band desired signal (BT spec 3.1.2.1):

– BW

Adjacent Channel Power Test(In-Band Spurious Emissions)

All unintentional emissions at -20 dBc vs. highest in-band/desired signal measured with 100 kHz Res. BW. (15.247(d) / BT 3.1.2.1)

Unintentional Power 2 and 3 channels away from intentional emission channel (BT spec 3.1.2.1)

– Two Channels away (1 MHz BW): -20 dBm

– Three Channels away (1 MHz BW): -40 dBm

Channel frequency is integer multiple of 1MHz: -20 dBm

In-Band Spurious Emissions(BT 3.2.2)

Must be measured using frequency hopping radio radio (BT 3.2.2)

– Resolution bandwidth: 100 kHz

– Max-Hold Mode

– Power(Fc ± 1 MHz to 1.5 MHz) vs. Power(Fc ± 500 kHz)

Transmitter Spectrum Mask

Frequency Tolerance

Unmodulated TX Freq Tolerance: +/-75 kHz

Modulated TX Freq. Tolerance within a packet:

Requirement: BT 3.1.3 & RF PHY (sect. 4.5.6-7)

Frequency Tolerance for EDR (3.2.3)

jj

Modulation for Basic/Enhanced Bluetooth

Modulation varies throughout packet

Modulation Accuracy:Differential Error Vector Magnitude (DEVM)

Measured over Synchronization sequence and Payload portions of packet, but not trailer symbols of each frequency using longest packets

IDEAL REALITY

TX Modulation Accuracy:Differential Error Vector Magnitude (DEVM)

BR/EDR modulations: (BT 3.2.1.4)

– RMS DEVM: < 0.2 for 𝜋/4-DQPSK,

Receive SensitivityRequirements & Test Methods in

– BT Vol. 2, Part A

– BT Vol 3, Part D, 1.1.3

– RF PHY, section 4.6.1-2

– Pessimistic compared to TIA/EIA methods

e.g. bad CRC -> all bits in packet declared bad

Basic BT:

– Raw Bit Error Rate Standard: 0.1%

– Receive Sensitivity

Receiver Immunity to InterferenceBasic BT: Co- & Adjacent- Channel

– Desired signal = -60 dBm

– Jamming signal = Bluetooth Modulated

– BER standard

Receiver Immunity to InterferenceEnhanced Data Rate BT: Co- & Adjacent- Channel


– Jamming signal = Bluetooth Modulated

– BER standard

Receiver Immunity to Interference

Basic Bluetooth Modulated Jammer


Enhanced Data Rate Bluetooth Desired & Jammer

Receiver Immunity to InterferenceBasic BT: Blocking


– Jamming signal = unmodulated/CW

– BER standard


Basic BT: Intermodulation

– BER standard

Other Receiver Requirements forBasic/Enhanced BT

Basic BT and Enhanced Data Rate BT:

– Maximum Usable Signal: >= -20 dBm

BER

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