Introduction

Calibration

PA Power Management IC

TX Timing Optimization

RF Power Amplifier

RF Connector

VCO

Supply Voltage

I/Q Signal

Power Management IC

Common GND

By Criterion 4

Introduction

By Criterion 5

ACPR(Adjacent Channel Power Ratio)

nn For many of the current and future transmissionstandards(GSM, CDMA, TD-SCDMA, WCDMA, and LTE),ACPR (sometimes also termed adjacent channelleakage ratio-ACLR) is an important test parameter forcharacterizing the distortion of subsystems and thelikelihood that a given system may cause interferencewith a neighboring radio[32].

By Criterion 6

ORFS(Output Radio Frequency Spectrum)

nn In GSM, As part of the out-of-channel measurements,the ACPR is defined by two measurements: spectrumdue to modulation and wideband noise, and spectrumdue to switching. These two measurements are usuallygrouped together and referred to as output RFspectrum (ORFS)[34].

By Criterion 7

ORFS due to Modulation

nn The modulation process in a transmitter causescontinuous wave carriers to spread spectrally. Thespectrum due to modulation and wideband noisemeasurement is used to ensure that the modulationprocess does not cause excessive spread. This wouldcause interference to adjacent channel users[34].

With max PCL,why is the

carrier powermerely 22 dBm?

With max PCL,why is the

carrier powermerely 22 dBm?

By Criterion 8

ORFS due to Modulation

nn The analyzer is tuned to a spot frequency and thentime-gated across 50% ~ 90% part of the modulatedburst to avoid training sequence[34].

nn Besides, spectral components that result from theeffect of bursting do NOT appear because the rampsare gated out[34].

By Criterion 9

ORFS due to Switching

nn GSM/EDGE transmitters ramp RF power rapidly due toburst mode. If RF power is ramped too quickly,undesirable spectral components exist in thetransmission. Users operating on different frequencies,especially those close to the channel of interest, willexperience significant interference[34].

By Criterion 10

ORFS due to Switching

nn In this case, no time gating is used, so power from boththe ramping and modulation processes affect themeasurement[34].

nn Nevertheless, because ORFS due to switching level islarger than modulation level, the effect of rampingdominates the spectrum due to switchingmeasurements[34].

By Criterion 11

Calibration

By Criterion 12

DPD

nn DPD(Digital Predistortion) is applied to linearize the PAto improve the linearity in the linear region and increasethe linear region by compensating the compressionwith an inverse function[39].

nn As shown below, DPD can be used to lower spectralregrowth to improve both ACLR and ORFS aswell[1,41,66].

By Criterion 13

GMSK and 8PSK

nn GMSK is a constant-envelope modulation, but 8PSK isNOT[59].

nn Thus, 8PSK has larger PAPR than GMSK. In otherwords, 8PSK has more strict linearity than GMSK[61].

Average Power

Peak Power

Time

Power

Average Power

Peak Power

Time

Power

By Criterion 14

GMSK and 8PSK

nn With the identical output power, 8PSK has worse ORFS-SW than GMSK[62].

nn Thus, Pre-distortion calibration helps EDGE 850/900ORFS-SW margin, not ORFS-MOD[12].

By Criterion 15

Path Delay for EDGE

nn A source of distortion is a delay that might occurbetween the amplitude and phase path[42,74].

By Criterion 16

Path Delay for EDGE

nn The existence of two separate waveform paths couldlead to different signal delays on the phase path andthe envelope path, affecting the EDGE waveformquality[1,42].

nn As shown below, the larger the delay is, the worse theORFS due to modulation and EVM will be[42].

By Criterion 17

Path Delay for EDGE

nn Hence, while calibration, the chipset solution allows fordelays to be added to either path to make sure that thephase and envelope paths remain in sync to improveORFS due to modulation[1,9].

By Criterion 18

Path Delay for EDGE

nn Path Delay Cal Tree is as below[9]:

By Criterion 19

Path Delay for EDGE

nn The best-case delay is determined by finding the delayvalue resulting in the lowest ORFS due to themodulation measurement at +400 kHz and -400 kHz[1,9].

By Criterion 20

Path Delay for EDGE

nn As shown below, the figure shows a 8PSK modulationspectrum for various values of delay mismatch. With adelay mismatch more than 30ns, the spectrum fails.And the spectrum passes with a delay mismatch lessthan 30ns[54].

By Criterion 21

PA PowerManagement IC

By Criterion 22

QFE2101

nn The main QFE2101 functional blocks are[4]:uuAPT buck converter – essentially a programmable buck

converter, or switched-mode power supply (SMPS).

uuBypass switch – routes battery or primary phone power(VPH_PWR) directly to the PA(s).

uuGSM switches – bypass switches (or optional extra GSMcapacitor switch).

ll Bypass – a separate bypass switch for GSM with a very lowresistance that connects the GSM PA directly to battery.

ll GSM capacitor switch – C_GSM pin should be connected to primaryphone power (VPH_PWR); utilize this switch as the third bypassswitch to further reduce the IR drop.

By Criterion 23

QFE2101

By Criterion 24

QFE2101

nn To switch-in extra load capacitance at the VPA node(C_GSM to capacitor only) during GSM Tx. This optioncan be used to improve the margin for GSMORFS/RxBN due to less IR drop, and APT mode insteadof bypass mode.[2-4].

By Criterion 25

TX TimingOptimization

By Criterion 26

Ramping Profile

nn Effect of different Ramp timing on SwitchingTransients[44].

By Criterion 27

Ramping Profile

nn Nevertheless, there is a trade-off between GSM PvT andGSM ORFS due to switching @400kHz with high PCL[6].

nn Hence, tune ramping profile to pass PVT and ORFSspecification simultaneously[6,8].

By Criterion 28

GSM RF Timing Adjustment

nn In general, there are six types of GSM RF timingadjustment, as shown below[10]:

By Criterion 29

GSM RF Timing Adjustment

By Criterion 30

GSM RF Timing Adjustment

nn pa_en_start/stop_offset_adj:The PA enable signalstart/stop time adjustment value can be altered to movethe rising edge of the PA enable signal forward orbackward to get the optimal configuration[9].

nn pa_start/stop_offset_adj :The PA turn-on/off timeadjustment value can be altered to adjust the risingedge of the TDMA Tx power burst[9].

nn ant_timing_start/stop_offset_adj : The antennaselect control signal start/stop time adjustment valuecan be altered to move the falling edge of antennaselect control signal forward or backward relative to thePA enable signal falling edge to get the optimalconfiguration[9].

By Criterion 31

PA ON Timing[9]

By Criterion 32

PA OFF Timing[9]

By Criterion 33

PA Ramp Up Timing[9]

By Criterion 34

PA Ramp Down Timing[9]

By Criterion 35

Antenna ON Timing[9]

By Criterion 36

Antenna OFF Timing[9]

By Criterion 37

Potential Issues of Improper Tx Timing

nn In addition to PvT and ORFS, Improper Tx timing valuemay cause improper power in certain hardwareboards[9].

nn For MIPI PA device, PA ON signal is expected earlierthan the PA range signal, since PA ON script sets PA tothe lowest gain state and overrides the settings in thePA range script[9].

By Criterion 38

Potential Issues of Improper Tx Timing

nn If PA ON is later than PA range timing, the power will belower than expected; e.g. Max Tx power is merely ~20dBm[9]

nn The error message can be observed in QXDM log[9].

By Criterion 39

Potential Issues of Improper Tx Timing

nn And the improper power may cause EDGE calibration orregistration failure in certain hardware boards[9]

nn Failed to calibrate GSM850 due to improper PA timingapplied[9].

nn Failed to calibrate GSM900 per improper PA timingapplied[9].

By Criterion 40

Potential Issues of Improper Tx Timing

nn In the case, PCS1900, there is ORFS issue at lowtemperature, and which is independent of PCL.

nn Nevertheless, the issue was NOT observed in DCS1800.

By Criterion 41

Potential Issues of Improper Tx Timing

nn First, we did NOT observe this issue in FTM(FactoryTest Mode). In other words, the issue disappearswithout RX operation.

nn Second, we did NOT observe this issue at transceiveroutput, as shown below :

By Criterion 42

Potential Issues of Improper Tx Timing

nn Because there are merely two blocks(transceiver andPAMiD) in TX chain, so we conclude that this issue isrelated to PAMiD[74], especially ASM timing.

By Criterion 43

Potential Issues of Improper Tx Timing

nn There are two statuses for TX mode while RX isoperating :

uuDisable Status(Default) :uu Isolation Status:

RX OFFRX ON

ASM_TX OFF

ASM_TX ON

Level

Time

RX OFFRX ON

ASM_TX OFF

ASM_TX ON

Level

Time

ASM

RX

TXPA

ASM

RX

TXPA

RX OFFRX ON

ASM_TX ON

Level

Time

RX OFFRX ON

ASM_TX ON

Level

Time

By Criterion 44

Potential Issues of Improper Tx Timing

nn For disable status, when switching to Tx state underlow temperature, it may take up to 100 µS for the switchto be fully operational and RF compliant. That’s to say,there will be delay in TX timing while switching from TXOFF to TX ON[28].

nn As mentioned earlier, the antenna select control signalstart/stop time affects ORFS performance. That’s whyORFS fails.

RX OFFRX ON

ASM_TX OFF

ASM_TX ONLevel

Time

RX OFFRX ON

ASM_TX OFF

ASM_TX ONLevel

Time

By Criterion 45

Potential Issues of Improper Tx Timing

nn For isolation status, TX is still ON while RX is ON, butTX port will shunt to ground while RX is ON. That’s whyit’s called “isolation” status.

nn Because TX is always ON, there will be NO delay in TXtiming while switching from TX OFF to TX ON. Hencethe issue passes after introducing Isolation Status.

RX OFFRX ON

ASM_TX ON

Level

Time

RX OFFRX ON

ASM_TX ON

Level

Time

ASM

RX

TXPA

ASM

RX

TXPA

By Criterion 46

Potential Issues of Improper Tx Timing

nn Besides, DCS1800 RX path is different from PCS1900RX path. Chances are that PCS1900 takes longer timeswitching from RX port to TX port than DCS1800, so wedid NOT observe this issue in DCS1800.

RX OFFRX ON

Level

Time

ASM_TX OFF

ASM_TX ON

ASM_TX OFF

ASM_TX ON

PCS

DCS

RX OFFRX ON

Level

Time

ASM_TX OFF

ASM_TX ON

ASM_TX OFF

ASM_TX ON

PCS

DCS

By Criterion 47

RF Power Amplifier

By Criterion 48

Linearity

nn As mentioned above, ORFS is just the concept of ACLR.And the formula of ACLR is :

ACLR = 2(Pin - OIP3 + G)+C, where C is correction coefficient

nn Hence, the better the linearity is, the better the ORFSdue to switching will be[45,46].

By Criterion 49

Temperature

nn In general, the higher the temperature is, the worse theOIP3 will be[47].

nn Thus, chances are that high temperature leads to worseORFS due to switching[15].

By Criterion 50

Layout

nn Thus, the GND vias should be as numerous as possibleto spread the heat[48,63].

By Criterion 51

Temperature

nn As shown below, the lower the temperature is, thehigher the gain will be[47].

nn Thus, with constant Pin, lower temperature leads tohigher Pout[49].

By Criterion 52

Temperature

nn As shown below, the larger Pout is, the worse the ACLRwill be.

nn That’s to say, chances are that low temperature leads tolow ORFS due to switching margin[43].

By Criterion 53

Temperature Compensation

nn Hence, we have to do temperature compensation tomake Pout identical under all temperatures.

nn By doing this, the Pout under low temperature will notbe too high, thereby improving ORFS due to switchingunder low temperature.

By Criterion 54

Temperature Compensation

nn Nevertheless, with temperature compensation, theORFS due to switching under high temperature mayaggravate more.

By Criterion 55

Temperature Compensation

nn As mentioned earlier, high temperature aggravateslinearity, thereby degrading ORFS due to switching.

nn With TC(Temperature Compensation), the Pout underhigh temperature becomes larger. With worse linearityand larger Pout, that’s why ORFS due to switchingunder high temperature may aggravate more with TC.

By Criterion 56

Ramping Profile Adjustment

nn Hence, with TC, adjust the ramping profile under hightemperature to improve ORFS due to switching becausePower versus time (PVT) variation is one of the mostimportant features for describing electrothermalperformance of RF power amplifiers (PAs)[51,52].

By Criterion 57

PA Output Matching Network Adjustment

nn Besides, adjust PA output matching network to improvelinearity and lower noise floor, thereby improving ORFSdue to switching and RxBN under high temperaturewith TC[6].

By Criterion 58

PA Output Matching Network Adjustment

nn As mentioned earlier, 8PSK has more strict linearitythan GMSK. In other words, if ORFS issue is related toPA linearity, the symptom should be:

By Criterion 59

PA Input Matching Adjustment

nn As shown below, the PA input matching networks isDA’s(Driver Amplifier) load-pull as well.

nn In other words, good ORFS@PA input leads to goodORFS@PA output[50,53].

nn Hence, to optimize PA input matching network can beused to improve ORFS as well.

By Criterion 60

PA Post loss

nn According to the following formula :

with constant target power, larger PA post loss leads tolarger PA output power, thereby aggravating ORFS-SW@ +- 400 kHz, even though PA’s output impedance isclose to 50Ω[11].

Target Power = PA Output Power – PA Post loss

nn Thus, minimize the PA post loss to have moreheadroom in Tx power. Because LB has larger maxpower than HB, headroom equal to 0.7 dB from 32.5dBm(i.e. 33.2 dBm) is preferred[11].

By Criterion 61

Stability

nn In the case, LB EDGE ORFS test fails in bothmodulation/switching spectrum when PCL is set <10(High Power Mode), and passes when PCL is set ≥11(Low Power Mode)[11].

By Criterion 62

Stability

nn Firstly, the best ORFS due to modulation result wasfound to be only approximately -43 dB, even aftertuning the path delay, but it can reach -60 dB[11].

ORFS-MO Before After-400KHz -43.1158 dB < -60 dB+400KHz -43.0755 dB < -60 dB

ORFS-MO Before After-400KHz -43.1158 dB < -60 dB+400KHz -43.0755 dB < -60 dB

nn Besides, many spurs are found(shown as yellow tracesin the graph), according to the analysis, the PA isoscillating[11].

By Criterion 63

Stability

nn According to the K-factor definition, the stabilitydepends on S-parameter[56]. Chances are that thecomponents marked as red circle affect theS-parameter and stability of QFE2320, therebyoscillating[11]

nn Because the issue occurs in LB, the componentsmarked as red circle must be changed to removeoscillation[11].

By Criterion 64

Stability

nn Therefore, after tuning the path delay and changing theBOM, LB EDGE ORFS margin is sufficient for allPCL[11].

By Criterion 65

Switch Point

nn For this case, EDGE LB ORFS fails at PCL8, PCL12, andPCL16.

nn As mentioned above, If failure is at maximum powerand improves as power is reduced, the issue is likelydue to linearity. Thus, it fails at PCL8 but passes atPCL9 ~ PCL11[10,16].

PCL 8 9 10 11Result Fail Pass Pass PassPCL 12 13 14 15

Result Fail Pass Pass PassPCL 16 17 18 19

Result Fail Pass Pass Pass

By Criterion 66

Switch Point

nn In general, there is hysteresis from the switching pointwhere the PA rises from a lower gain to a higher gain,and vice versa to avoid the PA oscillating at theswitching point[64].

nn In other words, as illustrated below, for EDGE single-slot, 19 dBm(PCL12) can be achieved by high gainmode or mid gain mode; 11 dBm(PCL16) can beachieved by mid gain mode or low gain mode.

By Criterion 67

Switch Point

nn Hence, as illustrated below, if 11 dBm is achieved bylow gain mode, the PA will be in saturation region,thereby degrading linearity and aggravating ORFS.So is 19 dBm(PCL 12).

nn In order to solve this issue, make these output power @switch points be in proper gain mode to be in linearregion[16].

By Criterion 68

RF Connector

By Criterion 69

Material issue

nn If the connector is abnormal, the antenna matchingnetwork may alter PA’s output impedance, therebyaggravating ORFS.

nn Besides, abnormal connector leads to leakage. And asshown below, with constant target power(e.g. LB 32.5dBm or HB 29.5 dBm), the larger the leakage is, thelarger the PA output power will be, thereby aggravatingORFS.

By Criterion

Layout issue

nn In the case, it is very difficult to pull load impedance to50 Ω for the common path[11].

nn Hence, ORFS due to switchingperformance is not good enough.

By Criterion

Layout issue

nn Because the signal pad size of the RF connector is verylarge(0.6 mm × 0.7 mm). According to simulation, ifusing L9 as RF GND, it introduces serious mismatching.

nn Thus, areas under the pads of the RF connector in L9,L8, and L7 should be cut out, and set L6 as thereference GND, to get better impedance[11].

Signal Pad

GND Pad

L9 L8 L7 L6

Impedance 14 Ω 32 Ω 44 Ω 53 Ω

By Criterion 72

VCO

By Criterion 73

VCO Pulling

nn In the case, GSM ORFS (modulation and switching) isobserved to be failing by about 5−6 dB on quad-bandGSM some channels at high power level(LB: PCL5; HB: PCL0)[30].

nn The max power at connector can be 34 dBm for LB, and31 dBm for HB. Besides, the PA’s load-pull is close to50Ω for both LB and HB. In other words, the issue isNOT related to PA linearity.

By Criterion 74

VCO Pulling

nn As shown below, the issue can be solved with SPDT.

By Criterion 75

VCO Pulling

nn Without SPDT, the issue is root caused too high Txpower during GSM operation leaking into FBRx paththrough front-end coupler and later coupling into TXquadrature up-converter of transceiver[16,17,30,72].

By Criterion 76

VCO Pulling

nn An SPDT (with bypass option) is recommended at frontend, as shown here to isolate GSM Tx power fromleaking into FBRx path[17,30].

nn Since FBRx is not operational in GSM mode. FBRX onlyworks in 3G/4G mode. So this switch (SPDT) does notimpact GSM operation[16,30].

nn Two possible implementations during GSM operationare shown here[30]:

By Criterion 77

VCO Pulling

nn In the case, as shown below, ORFS-MO passes if wepress the shielding can, and it fails without press.

By Criterion 78

VCO Pulling

nn As shown below, PA will couple TX signal onto theshielding can. In other words, there will be residual TXsignal on the shielding can.

nn With good grounding, the residual TX signal will flow toGND completely. Without good grounding, the shieldingcan will reflect the residual TX signal.

By Criterion 79

VCO Pulling

nn Thus, with press, the residual TX signal flows to GNDcompletely due to good grounding.

nn If possible, don’t put PA and transceiver in the sameshielding area to avoid VCO pulling.

By Criterion 80

VCO Pulling

nn As mentioned earlier, the PA input matching networks isDA’s(Driver Amplifier) load-pull as well.

nn Besides, for Direct-Conversion transmitter architecture,the RF frequency is the same as LO. So if PA inputmatching is not close to 50Ω, the reflection due to poorS11 may interfere VCO, thereby aggravating ORFS-MO.

By Criterion 81

VCO Pulling

nn In the case, the relationship between ORFS-MO andASM is as below :

Antenna Switch ModuleVendor A

(With Original RX Matching)Vendor B

(With Original RX Matching)Vendor B

(With New RX Matching)

Pass Fail Pass

By Criterion 82

VCO Pulling

nn If we set TX port as Port 1, and RX port as Port 2, S21 isjust the isolation between TX port and RX port, asshown below :

nn Hence, the isolation depends on TX matching, RXmatching, and ASM.

By Criterion 83

VCO Pulling

nn Therefore, vendor B ASM degrades isolation, andORFS-MO fails.

nn With vendor B ASM, we introduce new RX matching,and isolation improves, thereby improving ORFS-MO.

nn As shown below, the isolation affects VCO pullingthrough RX path.

By Criterion 84

Keep Out Area

nn Besides, keep-out areas on PCB layer 1 are required toavoid sensitive on-chip components such as VCO[73].

By Criterion 85

Keep Out Area

nn Otherwise, the parasitic effect aggravates phase noise,thereby degrading ORFS-MO[10].

nn In general, check the LO phase noise at 400 kHz offset,it should be better than -118 dBc/Hz[10].

By Criterion 86

Supply Voltage

By Criterion 87

IR Drop

nn IR drop refers to a voltage drop that appears at theresistive component of any impedance. This voltagedrop across any resistance is the product of current (I)passing through resistance and resistance value (R).

nn If there is IR drop issue in the supply voltage of any TXchain blocks, such as transceiver, PA, and ASM, the TXperformance including ORFS will aggravate[24].

By Criterion 88

IR Drop

nn In the case, LB GSM ORFS-MO fails for high powermode In low temperature.

nn We found the ORFS-MO issue appears not only inconnector, but also in transceiver output. As mentionedabove, poor ORFS performance in PA input leads toworse ORFS performance in PA output.

By Criterion 89

IR Drop

nn Thus, there are three possible factors relatedtransceiver: Layout, supply voltage, and material issue.

nn After changing the BOM for transceiver supply voltage,the issue is solved.

By Criterion 90

IR Drop

nn As mentioned above, low temperature makes gainincrease. Higher gain leads to higher Icc, therebyincreasing IR drop.

nn In addition, with max PCL, low band has larger outputpower than high band. So the issue occurred in LBinstead of HB[57].

LB 14 dBmHB 11 dBm

By Criterion 91

IR Drop

nn As shown below, power is getting lower as supplyvoltage drops[11]. In other words, the lower the supplyvoltage is, the lower power will be.

By Criterion 92

IR Drop

nn In other words, with constant target power(e.g. LB 32.5dBm or HB 29.5 dBm), the larger the IR drop is, thelarger PA output power and current consumption(i.e. Icc)will be, thereby aggravating ORFS-SW performance.

IR drop

PA Output Power& Icc

IR drop

PA Output Power& Icc

By Criterion 93

IR Drop

nn Besides, as shown below, the larger the temperature is,the larger the resistance including chip resistor or tracewill be, thereby increasing IR drop.

By Criterion 94

IR Drop

nn As mentioned above, with TC(TemperatureCompensation), the Pout under high temperaturebecomes larger. With worse linearity and larger Pout,that’s why ORFS due to switching under hightemperature may aggravate more with TC.

nn Thus, with TC and IR drop, ORFS-SW aggravates morein high temperature.

By Criterion 95

Decoupling Capacitor

nn Due to burst mode characteristic, GSM PA is being ONand OFF all the time. As shown below, while PA is ON,there will be unwanted 20KHz signal riding on DC,which is just ripple. Any supply disturbances caused byon/off activities could directly convert to ORFSissue[10].

By Criterion 96

Decoupling Capacitor

nn As shown below, larger decoupling capacitor can helpimprove spectral regrowth, thereby improving ORFS[31].

By Criterion 97

Decoupling Capacitor

nn Besides, the decoupling capacitor should be as closeto PA as possible. Otherwise, PA supply transientcurrent may leak into other ICs, and transient currentfrom other ICs may leak into GSM PA, therebyaggravating ORFS performance[10].

By Criterion 98

Decoupling Capacitor

nn Besides, the supply voltage of LO is important as well.

nn As shown below, change C3115 from 220nF to 4.7uF,ORFS-MO at 1.6 MHz offset improves.

By Criterion 99

Decoupling Capacitor

nn The lower ESL is, the wider capacitive range will be.nn The lower ESR is, the lower ripple will be

By Criterion 100

Decoupling Capacitor

nn The path the noise flows inside 3-terminal capacitor isshorter than which inside 2-terminal capacitor. That’s tosay, the 3-terminal capacitor has lower ESL and ESR.

By Criterion 101

Decoupling Capacitor

nn Compared to multiple capacitors, the 3-terminalcapacitor has better noise suppression, and it doesn’thave anti-resonance issue. Besides, the 3-terminalcapacitor can save PCB area due to lesscomponents[75].

By Criterion 102

Star Routing

nn Use star routing from battery to PMIC and PA. Besides,the branch point should be as close to battery aspossible[10].

nn As shown below, the length of coupling path 2 isshorter than coupling path 1, so the noise from GSM PAmay leak to PMIC. That’s why branch point should beclose to battery.

By Criterion 103

Star Routing

nn In the case, at high power level of GSM low bands,ORFS modulation performance is marginal, especiallyat the 400 kHz offset.

nn The issue is dependent on PCL. It disappears at lowpower level such as PCL19. Chances are that the issueis related to PA linearity, so we checked transceiveroutput performance to eliminate the influence of PA.

By Criterion 104

Star Routing

nn The issue already appears at transceiver output, sothere are three possibilities : material, layout, andvoltage supply.

nn With an external voltage supply, the issue improved.

By Criterion 105

Star Routing

nn Due to burst mode characteristic, GSM PA has strongtransient current. That’s why the issue disappears atlow power level because low power level leads to lowtransient current. And that’s why the issue appears athigh power level of GSM low bands because PCL5 ofLB (33 dBm) is larger than PCL0 of HB(30 dBm).

nn As shown below, the coupling path :GSM PA => PMIC => transceiver

By Criterion 106

Star Routing

nn In the case, as shown below, ORFS modulationperformance fails when monitor is ON, but performanceis good when monitor is OFF.

nn Besides, the issue appears at GSM quad-band,especially at the 400 kHz offset. And the issue isindependent on power level.

By Criterion 107

Star Routing

nn This is because backlight driver IC has strong transientcurrent as well. That’s why the issue disappears whenmonitor is OFF.

nn As shown below,Coupling path 1 : Backlight driver IC => PACoupling path 2 :Backlight driver IC => PMIC => Transceiver

By Criterion 108

Star Routing

nn Thus, increase the decoupling capacitor and powerinductor value for Backlight driver IC, and theperformance improved.

By Criterion 109

Star Routing

nn Similarly, use star routing from PMIC to VBATT pin andVcc_GSM pin of GSM PA separately, and the branchpoint should be as close to PMIC as possible.

nn At least, the branch point should NOT be close to GSMPA, as shown below :

By Criterion 110

Star Routing

nn If the branch point is close to GSM PA, make theVPH_PWR common part(marked as pink) and separatepart(marked as green) on different layer. As shownbelow, the coupling path(marked as yellow) has highimpedance to avoid noise coupling between the 2 pins.

By Criterion 111

High Frequency Noise

nn In the case, as shown below, ORFS-MO passes if wepress the PA shielding can, and it fails without press.Besides, after removing shielding can, it passes as well.

nn PA and transceiver are in separate shielding area, sothe issue is NOT related to VCO pulling.

By Criterion 112

High Frequency Noise

nn As mentioned earlier, without good grounding, theshielding can will reflect the residual TX signal. Withpress, the residual TX signal flows to GND completelydue to good grounding.

nn In addition, no shielding can, no residual TX signal.That’s why the issue disappears after removingshielding can.

By Criterion 113

High Frequency Noise

nn Thus, the issue is due to that residual RF TX signalreflects to PA Vcc by shielding can. In terms of DCvoltage, RF signal is regarded as noise.

nn There’re usually large capacitor for decoupling andsmall capacitor for filtering high frequency noise. Forthe issue, we can modify small capacitor value to filterresidual RF TX signal.

By Criterion 114

I/Q Signal

By Criterion 115

XO Harmonics

nn In the case, on certain channels of GSM high bands,ORFS switching and modulation performance ismarginal, especially at the 400 kHz offset.

nn The most affected channels are DCS channel 599, 600,602, 791, 792, 794, and 795; and PCS channel 668.

By Criterion 116

XO Harmonics

nn As shown in the table below, these channels are all 90times 19.2 MHz approximately in terms of frequency. Inother words, these channel are related to XO harmonics.

nn Baseband chip has an internal issue related to XOharmonics coupling into TX I/Q lines that causedegradation of ORFS performance only in GSM highbands[13,14].

Band Channel Frequency 19.2 MHz * N599 1727.6 89.97916667600 1727.8 89.98958333602 1728.2 90.01041667791 1766 91.97916667792 1766.2 91.98958333794 1766.6 92.01041667795 1766.8 92.02083333

PCS 668 1741.4 90.69791667DCS

Band Channel Frequency 19.2 MHz * N599 1727.6 89.97916667600 1727.8 89.98958333602 1728.2 90.01041667791 1766 91.97916667792 1766.2 91.98958333794 1766.6 92.01041667795 1766.8 92.02083333

PCS 668 1741.4 90.69791667DCS

By Criterion 117

XO Harmonics

nn As shown above, the solution is to add series L andshunt C onto each of the TX_I/Q lines[63].

nn As the spur level is reduced, and therefore the ORFSmodulation is improved[63].

nn This LC filter can also help reduce the number ofexceptions for the GSM Rx band noise[63].

w/o solution w/ solution

By Criterion 118

XO Harmonics

nn The trace between transceiver and PMIC is rich in XOharmonics because it is XO reference clock.

nn Thus, we need to put a R-C filter to reject XO harmonicsand a DC block to reject DC offset.

nn Besides, we need to keep the trace away from I/Q signalto avoid ORFS issue.

By Criterion 119

XO Harmonics

nn The digital XO signal and the analog XO signal cancorrupt each other; the layout should provide isolationbetween them. Isolation is highly recommended [77].

nn As shown below, they are too close.

By Criterion 120

I/Q Imbalance

nn I/Q imbalance can be characterized by: a phasemismatch that can happen between the I and the Qcomponents of the local oscillator signals, whichbecomes not exactly 90 degrees, and an amplitudemismatch due to the gain difference of the mixers of theI and Q branches[70].

By Criterion 121

I/Q Imbalance

nn As shown below, I/Q imbalance aggravates image,thereby aggravating sideband suppression and ORFS-MO.

nn Thus, we need to adjust phase and amplitude offsetsbetween I and Q channel by means of calibration tolower image to improve ORFS-MO[69].

By Criterion 122

I/Q Imbalance

nn Besides, in terms of modulator, high temperatureaggravates sideband suppression as well, therebyaggravating ORFS-MO. So good thermal design oftransceiver is important[69].

nn This is especially important for direct up-conversiontransmitter because I/Q imbalance are the inherentshortcomings of it[69].

By Criterion 123

I/Q Imbalance

nn Ideally, the four traces on the IQ signal path from theDAC output to the modulator input should besymmetrical between the I channel and Q channel andbetween the positive side and negative side within achannel[69].

nn In reality, due to PCB layout, trace lengths are notperfectly matched. The mismatches cause the signal inone channel to be skewed from the other, and, therefore,result in IQ imbalance(both gain and phase)[69].

By Criterion 124

LO Leakage(Carrier Leakage)

nn Excessive DC offsets in I/Q channels cause high levelsof LO leakage, thereby aggravating ORFS-MO[69].

nn According to the formula shown below, the more theDC offsets in I/Q channels, the larger the LO leakagewill be[69].

= +

+

By Criterion 125

LO Leakage(Carrier Leakage)

nn Thus, we need to remove DC Offsets by means ofcalibration to lower LO leakage to improve ORFS-MO[69].

nn In terms of modulator, high temperature aggravatescarrier suppression as well, thereby aggravating ORFS-MO. So good thermal design of transceiver isimportant[69].

By Criterion 126

Power ManagementIC

By Criterion 127

Charging

nn In the case, when charging is enabled, GSM850, ch190,ORFS-MO failure (0.5 dB) is observed at 600 kHz offsetmeasurement[18].

By Criterion 128

Charging

nn For a 5 V DCP(Dedicated Charging Port) plug-in, thecharging frequency is set to 600 kHz.

nn Spur coupling path: PMIC buck switching (600 kHz)spurs leaking into the Vbatt and appears at the Tx-RFoutput through QET4101 and PA[18].

nn Hence, there will be +- 600 KHz offset ORFS-MO issuedue to 2nd order intermodulation mechanism.

By Criterion 129

Charging

nn Adding a Pi (π) filter on the VPH_PWR rail attenuatesthe charger spur by 20 dB and passes the GSM ORFSspecification[18].

nn As a workaround, the placeholder for the π filter shouldbe provided at the QET4101 input to attenuate spurcoupling from the PMIC charger and also a 0 Ω (0201package) placeholder at power supply line of PA(VCC1_PA) for noise filtering[18].

By Criterion 130

Charging

nn As shown below[18]:

By Criterion 131

SMPS

nn In the case, GSM ORFS modulation spectrumperiodicity jump in all bands and all power levels,especially the mid-power level[28].

nn IC NCP6335 is external SMPS(Switching Mode PowerSupply) to the MSM8X25Q core. The NCP6335 is themain interference source to ORFS[28,75-76].

By Criterion 132

SMPS

nn NCP6335 has PFM and PWMoperation for optimumincreased efficiency,The transition betweenPWM/PFM modes can occurAutomatically, that’s whyORFS-MO spectrumperiodicity jump[28].

nn Set NCP6335 to forced PWM,and ORFS-MO passed.

By Criterion 133

Common GND

By Criterion 134

Common GND

nn In the case, with all decoupling capacitor and bypasscapacitors, ORFS fails; without all decoupling capacitorand bypass capacitor, ORFS passes.

By Criterion 135

Common GND

nn This is because transient current and high frequencynoise may leak into PA Vcc through these capacitors bymeans of common GND on top layer.

By Criterion 136

Common GND

nn Thus, make these shunt capacitors GND pad separatefrom common GND on top layer(i.e. GND Island), andadd GND via as many as possible.

nn If GND island is bound by PCB area, at least, the GNDvia should be as many as possible.

By Criterion

Noise

137

Common GND

nn As mentioned above, we’re able to use Pi (π) filter toattenuate the noise. Nevertheless, the GND ofcapacitors should be separate. Otherwise, the noisemay bypass the capacitors through common ground,thereby aggravating filtering effect.