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