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EVA-M8

TCXO-to-crystal migration guide

Application note

Abstract

This document provides options and guidelines for migrating the EVA-M8Q TCXO-based SiP module
to EVA-M8M crystal-based SiP module. The application note als
GNSS performance and other possible hardware/firmware concerns.

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EVA-M8 - Application note

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Document information

Title EVA-M8

Subtitle TCXO-to-crystal migration guide

Document type Application note

Document number UBX-20052988

Revision and date R02 11-Feb-2021

Disclosure restriction C1-Public

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EVA-M8 - Application note

Contents

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

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

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

2. Migration guideline ............................................................................................................................... 5

2.1 EVA-M8 (Q/M) comparison ....................................................................................................................... 5

2.2 RF design ...................................................................................................................................................... 5

2.3 Power requirements ................................................................................................................................... 6

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

2.5 VCC_IO monitor ........................................................................................................................................... 7

2.6 Temperature ................................................................................................................................................ 7

2.7 Performance ................................................................................................................................................. 8

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

Road test performance analysis ....................................................................................................11

3. Conclusion ............................................................................................................................................. 17

Related documentation ........................................................................................................................... 18

Revision history .......................................................................................................................................... 18

Contact .......................................................................................................................................................... 19

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EVA-M8 - Application note

1. Introduction

This application note describes the migration procedure from EVA-M8Q to EVA-M8M.

The EVA-M8Q uses a TCXO, while the EVA-M8M 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 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.

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EVA-M8 - Application note

recommended.

mandatory.

Flash FW SPG 3.01

Flash FW SPG 3.01

OTP config.

VCC_IO monitor HIGH

VCC_IO monitor LOW

2. Migration guideline

2.1 EVA-M8 (Q/M) comparison

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

Field Parameter EVA-M8Q EVA-M8M

HW Oscillator TCXO Crystal

RTC derived from osc. Not possible Possible

Interface config. Same Same

Pinout Same Same

RF design Front-end With passive antenna, an external LNA is

Out of band immunity Same Same

Temp. Storage temp. °(C) Max +85 Max +105

Thermal isolation

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

Supply current (mA)

SW backup current (mA) 2 0.02 0.02

HW backup current (mA) 2 0.015 0.015

Sensitivity
(GPS&GLO)

SW Firmware ROM SPG 3.01 /

Dynamic Tracking (dBm) -167 -164

TTFF (sec)

1

2

3

Optional Recommended

22 23

Same

With passive antenna, an external LNA is

Same

ROM SPG 3.01 /

Table 1: EVA-M8Q to EVA-M8M migration comparison (default mode: GPS & GLONASS including QZSS, SBAS)

☞ When migrating to crystal-based EVA-M8M 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 RF design

For designs without an external LNA or using a passive antenna, it is mandatory to include an external
LNA before the EVA-M8M module during the migration redesign, especially for those applications
under difficult GNSS visibility or poor reception. If, in addition, strong out-of-band jammers are close
to the GNSS antenna (for example, a cellular antenna), an additional SAW filter in front of the LNA
might be needed.

Applications with an active antenna or a present external LNA are exempt of RF front-end redesign.

Refer to the EVA-M8 Hardware Integration Manual [1] for more information about passive antenna
designs and recommended LNA/SAW components.

1

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

2

Single crystal feature disabled. Voltage supply = 3.0 V.

3

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

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EVA-M8 - Application note

2.3 Power requirements

Crystal-based EVA-M8M allows a wider voltage supply range. This is due to the lower voltage required
by the crystal. Nevertheless, products have overlapping operational voltage ranges and similar
current consumption when using the RTC crystal.

The table below shows the expected current drawn of EVA-M8M and EVA-M8Q. More information is
available in the EVA-M8 Data Sheet [2].

Parameter Symbol Conditions Module Typ

Max. supply current

4

Average
supply current

Backup battery
current

7

Iccp All 67 mA

6

VCC_IO =

VCC = 3 V

VCC_IO =
VCC = 3 V

VCC_IO =
VCC = 3 V

HW Backup mode,
VCC_IO =

EVA-M8M 25 19 mA

EVA-M8Q 26 20 mA

EVA-M8M 22 17 mA

EVA-M8Q 23 18 mA

EVA-M8M 5.3 4.7 mA

EVA-M8Q 6.2 5.7 mA

All 15 µA

5

Icc Acquisition

Icc Tracking

(Continuous mode)

Icc Tracking

(Power Save mode / 1
Hz)

I_BCKP

using the RTC crystal

VCC = 0 V

I_BCKP

using the 26 MHz
XTO in “single
crystal” operation

SW Backup current I_SWBCKP

using the RTC crystal

HW Backup mode,
VCC_IO =
VCC = 0 V

SW Backup mode,
VCC_IO =

EVA-M8M 100 µA

EVA-M8Q N/A8

All 20 µA

VCC = 3 V

I_SWBCKP

using the 26 MHz
XTO in “single
crystal” operation

SW Backup mode,
VCC_IO =
VCC = 3 V

EVA-M8M 105 µA

EVA-M8Q N/A9

Table 2: EVA-M8Q to EVA-M8M power requirements

GPS &
GLONASS

Typ

GPS / QZSS /SBAS

Max Units

2.4 Real-time clock (RTC)

In EVA-M8Q designs without RTC, the TCXO-to-crystal migration offers the option to enable the EVA­M8M’s single crystal feature, which uses the crystal as RTC. The single crystal feature will increase
the hardware and software backup currents, but will considerably reduce hot and warm start times.

☞ Note that the single crystal mode increases the back-up current consumption 5 times, which

is a sensitive factor for battery-powered devices.

For more information about the single crystal feature, see EVA-8M / EVA-M8M Hardware Integration
Manual [1].

4

Use this figure to dimension maximum current capability of power supply. Measurement of this parameter with 1 Hz bandwidth.

5

Simulated constellation of 8 satellites is used. All signals are at -130 dBm. VCC= 3 V.

6

Average current from start-up until the first fix.

7

Use this figure to determine required battery capacity.

8

Not applicable, feature not supported.

9

Not applicable, feature not supported.

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