u-blox CAM-M8 Application Note



M8Q module to

M8C module. The application note also explains the potential impact on GNSS

CAM-M8

TCXO-to-crystal migration guide

Application note

Abstract

This document provides options and guidelines for migrating TCXO-based CAM­crystal-based CAM­performance and other possible hardware/firmware concerns.

UBX- 21004953 - R01
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CAM-M8 - Application note

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Document information

Title CAM-M8

Subtitle

Document type

TCXO-to-crystal migration guide

Application note

Document number UBX- 21004953

Revision and date

R01 11-Feb-2021

Disclosure restriction C1-Public

UBX- 21004953 - R01 Document information Page 2 of 16
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CAM-M8 - Application note

Contents

Document information ................................................................................................................................ 2

Contents .......................................................................................................................................................... 3

1 Introduction ............................................................................................................................................. 4

2 Migration guidelines ............................................................................................................................. 5

2.1 CAM-M8(Q/C) comparison ........................................................................................................................ 5

2.2 Power requirements ................................................................................................................................... 5

2.3 Real-time clock (RTC) ................................................................................................................................. 6

2.4 Temperature ................................................................................................................................................ 7

2.5 RF front-end design and ground plane ................................................................................................... 7

2.6 Performance ................................................................................................................................................. 8

2.6.1 Startup sensitivity and TTFF ........................................................................................................... 8

2.6.2 Road test performance analysis ....................................................................................................10

3 Conclusion ............................................................................................................................................. 14

Related documentation ........................................................................................................................... 15

Revision history .......................................................................................................................................... 15

Contact .......................................................................................................................................................... 16

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CAM-M8 - Application note

1 Introduction

This application note describes the migration procedure from TCXO-based CAM-M8Q module to
crystal-based CAM-M8C module.

The CAM-M8Q uses a TCXO, while the CAM-M8C uses a crystal. This small difference in the internal
oscillator leads to some considerations described in this document. For example, the frequency
tolerance of the crystal is wider than that of TCXO. This means that the receiver must search over a
wider range of frequencies, which will extend the time-to-first-fix (TTFF) especially in weak signal
conditions.

In addition, the crystal’s frequency is highly sensitive to temperature-variant environments.
Therefore, the operating temperature, as well as the heat dissipating systems on the board need to
be taken into consideration.

Nevertheless, with proper adjustments and design guidelines, crystal-based GNSS receivers can
achieve very similar performance to a TCXO-based solution and are thus worth considering as an
alternative to many applications.

☞ This document is still under development. New or additional information (e.g. test data) might

be added in the future.

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CAM-M8 - Application note

Front-end

Same

Same

2 Migration guidelines

The CAM-M8Q and CAM-M8C have a different type of internal oscillator, and a different source for
real-time clock (RTC).

This section provides details on aspects that need consideration during CAM-M8Q to CAM-M8C
migration.

2.1 CAM-M8(Q/C) comparison

The table below summarizes the specifications to be considered during the migration.

Field Parameter CAM-M8Q CAM-M8C

HW Oscillator TCXO Crystal

RTC Yes Yes, but with a higher backup current

Interface config. Same Same

Pinout Same Same

RF design

Out-of-band immunity Same Same

Temp. Storage temp. (°C) Same Same

Thermal isolation

Power Req. Supply (Vcc & Vio) (V) [2.7 - 3.6] [1.65 - 3.6]

Supply current (mA)

SW backup current (µA) 2

HW backup current (µA) 2

Sensitivity
(GPS&GLO)

SW Firmware ROM SPG 3.01 ROM SPG 3.01

Table 1: CAM-M8Q to CAM-M8C migration comparison (default mode: GPS & GLONASS including QZSS, SBAS)

Dynamic Tracking (dBm) -167 -164

TTFF (sec)

1

2

3

Recommended Highly recommended

Same Same

30 105

15 100

Same

Same

☞ When migrating to crystal-based CAM-M8C module, make sure the receiver is not operated in

Galileo-only mode. Crystal variants are not suitable for Galileo-only operation due to worse
performance (TTFF, sensitivity).

2.2 Power requirements

The crystal-based CAM-M8C allows a wider voltage supply range. This is due to the lower voltage
required by the crystal. Nevertheless, the products have overlapping operational voltage ranges and
similar current consumption.

The table below shows the expected current draw of CAM-M8Q and CAM-M8C. More information is
available in the CAM-M8 Data Sheet [1].

1

Mainly for applications where the GNSS module is under thermal activity on the board.

2

Voltage supply = 3.0 V and single crystal feature enabled on CAM-M8C.

3

Cold and hot start under good GNSS visibility and using power levels of -130 dBm.

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