reference clock: application on sysol me and dragon fly

REFERENCE CLOCK: application on Sysol ME and Dragon Fly

VYn_ps12660CS - Philips Semiconductors Le Mans

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Introduction: Importance of the reference clock

• Reference clock: Motor of the mobile

• All mobile functions depend on it

• Bad reference clock’s performances means bad mobile’s performances

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Training Content:

• Reference clock presentation• Reference clock contents• Reference clock on Sysol ME• Reference clock working on Sysol ME• Reference clock performances to check• Problems linked to reference clock• Reference clock on Dragon Fly

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Training Content:

Reference clock presentationReference clock presentation• Reference clock contents• Reference clock on Sysol ME• Reference clock working on Sysol ME• Reference clock performances to check• Problems linked to reference clock• Reference clock on Dragon Fly

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REFERENCE CLOCK

PRESENTATION

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Heart of the mobile:

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• For Base-Band: - Clock for processor

- Generation of all clocks

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• For the Radio part: Reference clock for the synthetisers (PLL)

With Fout= N x Fref

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• In Sysol 2

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Frequency of the reference clock

• Fref = N x 13 MHz

• For ALL GSM mobiles

• 13000 kHz/48 = 270.833 kbits/s48 clock cycle = 1 time bit

12 clock cycle = 1 quarter bit (time unity in mobiles)

System clock must allow to have complete quarter bits. It is this with 3.25, 6.5, 13, 26 MHz

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Training Content:Reference clock presentationReference clock contentsReference clock contents• Discrete or integrated• Reference clock on Sysol ME• Reference clock working on Sysol ME• Reference clock performances to check• Problems linked to reference clock• Reference clock on Dragon Fly

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REFERENCE CLOCK

CONTENTS

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• Reference clock purpose:

Provide a sinusoidal signal with a stable frequency of Nx13 MHz:

No square waves generator

32 kHz of BB is not enough- Not enough stable- Can’t provide easily Nx13 MHz

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Use of a Crystal-based oscillator

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Description of a quartz

• The piezo electrical quartz crystal is deformed by the application of an electrical voltage. The crystal behaves like an electrical resonance circuit .

• Z: Quartz impedance with no load

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Oscillation conditions

• The quartz is not perfect. It has losses

Oscillations can not appear Losses must be compensated « Negative resistor » (amplifier) needed

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Let’s see electrical characteristics of a crystal

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• Crystal has others defaults:Tolerance on components value

Frequency initial adjustment: RefCal

Done on the production line

Frequency shift vs. temperature

Temperature compensation

Frequency shift with age

Frequency adjustment: AFC

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Crystal temperature deviation

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

14

16

18

20

-30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80

Temperature (°C)

Fre

qu

en

cy d

evia

tio

n (

pp

m)

Crystal L1

Crystal L2

416 Hz deviation

520 Hz deviation

156 Hz deviation

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Influence of V supply (Pushing)

Regulated supply

Influence of load (Pulling)

Load adjustment + Buffers

+ Frequency drift with time

Frequency enslavement: AFC

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Final overview of the clock

AFC

RefCal

Output BB

Output RF

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Discrete vs integrated clock

• Two ways to implement the clock:

Discrete. Each function is done with discrete components

Module. Reference clock is generated by a component containing all functions

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Module clock

Advantages

• Nber of components• Reduced bulkiness• Nber of supply• Nber of signals• Easy to implement

Disadvantages

• Cost (twice discrete’s)• No possible adaptation

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Discrete clock

Disadvantages

• Nber of components• Bulkiness• Nber of supply• Nber of signals• difficult to

implement• Technical limits

Advantages

• Cost (half module)• Possible adaptation

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• Discrete clock is limited to GPRS class 10, 2 Tx slots (due to PA heat)

• Synchronisation algorithm is common• Temperature compensation:

hardware way for discrete Integrated in the module

• Temperature and load compensation are made internally for the module: RefCal not needed.

• Consumption is a little bit important for module (~ 1 mA).

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Overview of a module clock

No RefCal

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Training Content:

Reference clock presentationReference clock contents

Reference clock on Sysol MEReference clock on Sysol ME• Reference clock working on Sysol ME• Reference clock performances to check• Problems linked to reference clock• Reference clock on Dragon Fly

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REFERENCE CLOCK ON SYSOL ME

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Topology of the 26MHz

• The topology of the 26MHz oscillator is from Pierce principle as follows.

Var

ica

p

Coarce AFC capacitors

UAA3536

Temperaturecompensation circuit

Crystal

3537

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Characteristics of the ref. clock on SSME• Frequency: 26 MHz

Radio: UAA3537. Need 26 MHz

BBand: OM6357-7 (50874-6): 26 MHz

• Quartz: NDK NX4025DA 26 MHz• Semi-integrated clock: Three blocks are in 3537:

- RF buffer

- BB buffer

- Negative resistance

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• Supply for the clock: not needed.

Negative resistance and buffers supplies are provided by 3537 with an internal regulator.

• Signals: 2 signals are needed:

AFC: provided by BB

Clkfdbx: provided by 3537

• RefCal signal is generated by a register of 3537.

(CAFC register)

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Crystal NX4025DA specifications

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VariableLoading

Quartz

Temperature

compensation

RF Buffer

BB Buffer

Negative resistanc

e

Clkfdbk from 3537

AFC: from BB

Internal regulator

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Training Content:

Reference clock presentationReference clock contentsReference clock on Sysol ME

Reference clock workingReference clock working on Sysol ME on Sysol ME• Reference clock performances to check• Problems linked to reference clock• Reference clock on Dragon Fly

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REFERENCE CLOCK

WORKING ON SYSOL ME

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Some hard parameters

• Magnitude of the clock:

Input of 3537: 670 mVpp

Provided by 3537: 1.2 Vpp• DC value: 1.2 V

3537 specifications.

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Input of 3537F=26 MHz(Refin pin)

Output of 3537F=26MHz

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Synchronisation with network

• Step 1: wake up of the 26 MHz 26 MHz is not the real frequency. Clock is not enslaved

• Step 2: Mobiles goes in Rx mode to receive the FCB DESPITE the clock is not at 26 MHz (FCB: Frequency Control Burst)

• Step 3: with FCB, mobile can correct its frequency error.

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After synchronisation with network• Regularly, mobile measures the frequency

error with FCB

Frequency Offset Information (FOI)• Software value, given by tracer or a

communication tester (CMD)• Coded with 16 bits (2 bytes). • Positive FOI value = negative frequency error. • Negative FOI value = positive frequency error.• Using FOI information, mobile adjusts AFC.

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• Using FOI information, mobile increases or decreases AFC.

• Since AFC is provided by AuxDAC2 on 50732, it can change only step by step.

Foi_step

How mobile adjusts AFC: FOI_STEP

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FOI_STEP Calculation • Take the specified minimum voltage range of

the AFC DAC defined by ΔV ( unit in V).

• The correction per LSB is derived by: ΔV/(2n) for a n bits DAC (unit in V).

• Then, the TCXO slope needs to be measured on a statistical quantity of units (> 30). The slope is expressed by S (unit in ppm/V).

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• FOI_STEPphy is equal to (ΔV x S x F)/ 2n (unit in Hz/LSB) Where F is the middle Rx RF frequency corresponding to the band used for the calculation 881.4 x 106 Hz for the GSM850 (channel 189).

942.4 x 106 Hz for the GSM900 (channel 62).

1842.6 x 106 Hz for the GSM1800 (channel 699).

1960 x 106 Hz for the GSM1900 (channel 661).

• The correction is: (FOI/ FOI_STEPphy) (unit in LSB)

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• BUT: a division between an integer and a real number is an inconvenient operation for soft

Parameter FOI_step

FOI_STEP = 216/(FOI_STEPphy) (unit LSB/Hz)

• Thus, we have:

[216/(FOI_STEPphy)] x [FOI / 216]=[FOI_STEP] x [FOI / 216]

Instead of: FOI / FOI_STEPphy

One multiplication better than a division

One division with an integer

One division between one integer and one real number

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• What will happen if initial frequency error is too important?

Mobile can not synchronize

Use of an Initial FOI (FOInit)

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• DSP has a Rx frequency window (+/- 25 kHz). It comes from DSP firmware.

• Mobile can synchronize only if frequency error is in this window

• FOI_Init put frequency error in the synchronization range

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Settings of this parameters

• REF_Cal, FOI_Init, FOI_Step are stored in EEPROM

• It is possible to see and change their value with TAT software

• Ref_Cal and FOI_Init are tuned for each mobile.

• Ref_Cal is first tuned, then Foi_Init.• FOI is a soft parameter. Value accessible only

with TRACER or Communication TESTER

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FoiStep:One per

bandRefCal Foi-Init:

Needs an HWL reset (init button)

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Values for Sysol ME (updated on W347)

• FOIinit: 2340 *• RefCal: 78 **• FOIstep GSM850: 8082• FOIstep GSM900: 7759• FOIstep GSM1800: 3856• FOIstep GSM1900: 3634* : Depends on layout, quartz, diode…

** : Statistical value

* & **: Defaults values – Tuned in production

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GSM standard requirements:

• In all bands, in normal conditions, frequency error must not be greater than 0.1 ppm

For GSM 850: 85 HzFor GSM 900: 90 HzFor DCS 1800: 180 HzFor PCS 1900: 190 Hz

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Training Content:Reference clock presentationReference clock contentsReference clock on Sysol MEReference clock working on Sysol ME

Reference clock performances to checkReference clock performances to check• Problems linked to reference clock• Reference clock on Dragon Fly

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REFERENCE CLOCK

PERFORMANCES TO CHECK

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List of measurements to check 26 MHz

• Frequency drift vs output power Current freq error when Pout goes from PCL high

to low and low to high

• Waveform• Wake-up time• DAC frequency correction• AFC linearity• Frequency drift with temperature• Spectrum

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• Wake up time with temperature:

Spec: 9 ms; meas: 1.09 ms• Spectrum (Refin pin):

spec: -20 dBc; meas: -37.6 dBc (H2)• Frequency drift with temperature (–30 to 70°):

Spec: +/- 7 ppm; Measured: +/- 2 ppm• Waveform:

Vpp = 1.25 V; Duty Cycle = 42 – 57 %

Some specs and measurements:

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Training Content:

Reference clock presentationReference clock contentsReference clock on Sysol MEReference clock working on Sysol MEReference clock performances to check

Problems linked to reference clockProblems linked to reference clock• Reference clock on Dragon Fly

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PROBLEMS LINKED TO 26

MHz

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Main problem: Frequency error

• 26 MHz: origin of all synthesized frequencies

• Frequency drift on 26 MHz means frequency drift on all synthesizers

degradation of frequency error

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Degradation also of other performances

Phase error

Training sequence loss

Problem of synchronisation

Sensitivity

DUE TO FREQUENCY ERROR

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Case of the sensitivity

• Sensitivity can be degraded by phase noise

• But also by the Ref Clock itself with the harmonics

GSM 850: H34 for channel 202

GSM 900: H36 for channel 5

• Concern mainly GSM 850 and GSM 900

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Training Content:Reference clock presentationReference clock contentsReference clock on Sysol MEReference clock working on Sysol MEReference clock performances to checkProblems linked to reference clock

Reference clock on Dragon FlyReference clock on Dragon Fly

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REFERENCE CLOCK ON

DRAGON FLY

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Characteristics of the ref. clock on Dragon Fly

• Frequency: 26 MHz

Radio: UAA3537. Need 26 MHz

BBand: PCF 5213 (SWIFT) 26 MHz

Internal divider in 3537 not used

• Integrated clock: Module END 3512A (NDK)

• Buffers for radio and BB still in 3537

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• Supply for the clock: 2.5 V, provided by an internal regulator in 3537

• Signals: 1 signal is now needed: AFC: provided by BB

Clkfdbx: no more used

• RefCal: not used

• Synchronization algorithm is identical

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Temp. Comp:Unused

Variable load:unused

Supply:Internal

regulator

Buffers

Module AFC

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Values for Dragon Fly (updated on W347)

• FOIinit: 2230 – Default value for Vafc=1.2V• RefCal: Unused• FOIstep GSM850: 11669• FOIstep GSM900: 10922• FOIstep GSM1800: 5601• FOIstep GSM1900: 5243

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Used module on Dragon Fly: END 3512A

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Input of 3537F=26 MHz(Refin pin)

Output of 3537F=26 MHz

(Clockout pin)

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CONCLUSION:CONCLUSION:COMPARISON WITH SYSOL 2COMPARISON WITH SYSOL 2

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• Since Sysol 2 clock is a module, it’s easier to compare with Dragon Fly.

• More integrated: On sysol 2: external and discrete buffer External supply by a regulator

INTEGRATED IN SYSOL ME AND DRAGON FLY.

Frequency change: 26 MHz instead of 13.

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QUESTIONS