Post on 12-Mar-2023
IEEE802.15.4 (ZigBee) 2.4 GHz Sensitivity
IEEE Std 802.15.4 2.4 GHz Sensitivity spec. : < -85 dBm
Noise floor [dBm] - 173.8 + 10log(B.W.) - 173 8 + 10log(3 106) = -109 dBm - 173.8 + 10log(3 10 ) = -109 dBm
where B.W. = 3 MHz (99% B.W.)
SNR t t [dB] (when PER=10-2) SNRoutput [dB] (when PER=10 )= Eb / No [dB] – Rc / Rb (processing gain) [dB]
= 14 – 9.03 = 4.97 dB ( from modem simulation )( )
Sensitivity of receiver [dBm] = Noise floor + NFReceiver + SNRoutput < -85 dBm
NFReceiver < -85 +109 - 4.97 = 19.03 dBm
1
Sensitivity – Theoretical Limit
2 2
bb bi
EP Q Q SNR
Performance of an ideal coherent O-QPSK detector
N = 20 octets 8 bits/octet 2 2
b bito
P Q Q SNRN
[ / ]1 (1 ) 2 N bits packetb b bitPER P N P N Q SNR
N 20 octets 8 bits/octet= 160 [bits/packet]PER = 1% = 0.01
E
PG = 10log108= 9.03 dBQ(3.8) = 0.000072348 = 1/13822.0738
2
min
0.01 3.92 , 8.8dB 2
b
bit bito
EQ SNR SNRN N
10min
0.20 31 log
cchip bit
o
ESNR SNR PGN
dB
Sensitivity lower bound
Q(3.9) = 0.000048096 = 1/20791.6011
174 10log(3 ) 109NoiseP dBm MHz dBm
109 23P P S BN d mR
Sensitivity lower bound
109.23S Noise chipP P S BN d mR
802.15.4 reference sensitivity : -85 dBm
802.15.4 standard allows a max. implementation loss of “24 dB”
2
Sensitivity - Budget Implementation loss budget
RFPartLoss
RF/AnalogLoss
DigitalLoss
2dB 7dB 6dB+ + = 15dBLow-bit ADC (4-bit)
Carrier freq./timing errorLow-complexity detector
Low-power RF/Analog
Circuits
AntennaRF BPF
T/R switch ? o co p e y de ec oC cu s/ s c
Our target sensitivity : - 93 dBm
Radio NF = 2 + 7 = 9 dB
Detector min. Eb/No = 9 + 6 = 15 dB for 1 % PERSNR = Ec/No ~ 6 dB
3
Blocking Profile and Intermodulation of ZigBee- 55dBm- 55dBm
30dB
Single interference signal (relatively low traffic envisioned for the WPAN service)
- 85 dBm- 85 dBm
30dB
- 85 dBm Loose filter attenuation specification Loose image rejection specification Therefore, low-IF receiver may be
fo(Wanted channel)
fo + 5fo 5 fo + 10 fo + 15fo - 10fo - 15 [ MHz ]
Therefore, low IF receiver may be suitable for ZigBee receiver
N i t d l ti ifi ti i No intermodulation specification in IEEE802.15.4 Std 2.4 GHz band
dBmdBmdBm 38)93(55
dBmdBmdBmIIP 36)2/(553
4
Selectivity – Intermodulation (IM3) Not specified in IEEE 802.15.4 From interferer profile
SIG IM3 min marginP P SNR INTP
SIGPIM3 INT 33 2P P IIP
INT SIG /P P C I marginSNR
/ 30C I dB
+2CH +4CH
IM3Pmin marginSNR
+2 CH +4 CH
min3 SIG
3 margin/ orSNRIIP P C I 3 SIG / or
2 2IIP P C I
min3 INT
1 margin/ 362 2
SNRIIP P C I dBm2 2
5
Selectivity – Channel Select Filter (CSF) Interferer (blocker) profile
BW(SSB)
CSF requirement
-10dBc@5MHz-40 dBc@10MHzSNR > 5dB
( )1.5MHz
A low-power 3rd?/4th? order SNR 5dB+ margin
pcomplex BPF is sufficient for this application
6
Selectivity – LO Phase Noise Requirement-30 dB
C/I
0 dBc
5 MHz 10 MHz
LO phase noise mask
min
65dB 10dB5dB
10log BW margin [dBc/Hz]
f
PN C I SNR
p
-80dBc/Hz PN of a sub-mA CMOS LC VCO
-100 dBc/Hz
-112 dBc/Hz-6 dB/oct-110dBc/Hz
7.5MHz
2 4 1 3 [MHz] 10
7.5MHz
8
ZigBee ADC Requirementge ADC headroom ( ~ 3 dB )
Maximum level of desired signal
ic ra
ng
Max. power difference between desired signal and interferer without filter = 30 dB
( )
dyna
m
g
( for example, 0 dB when 30 dB of filter rejection )
AD
C d
Noise margin (~ 9 dB)Noise from A/D
Noise from receiver + KTB
# of bit /o filter DR [dB] / 6 02 42 / 6 02 7 bit
A
# of bit w/o filter = DR [dB] / 6.02 = 42 / 6.02 = 7 bit
# of bit with 30 dB rejection of filter = DR [dB] / 6.02 = 2 bit
I dditi # f bit d d d f
9
In addition, # of bit depends on modem performance
→ 4-bit ADC is enough
Error Vector Magnitude (1)
),( jj QI )~,~( jj QI
),( jj QI
2 2
2 2
( )I QEVM
I Q
For applications (like WCDMA) requiring a wide gain control range a severe For applications (like WCDMA) requiring a wide gain control range, a severe drawback of direct up-conversion transmitter is carrier leakage
Carrier leakage can violate EVM and power accuracy requirement and limitCarrier leakage can violate EVM and power accuracy requirement and limit channel control
ZigBee does not require a wide gain control range
10
ZigBee EVM < 35%Ref) G. Brenna et al, ‘A 2-GHz carrier leakage calibrated direct-conversion WCDMA transmitter in 0.13-m CMOS,’ JSSC, 2004
Error Vector Magnitude (2)EVM [%]
120EVM [%]
140
0.75
1
1.25
1.5
100
120
0 75
1
1.25
1.5
120
140
0
0.25
0.5
0.75
erro
r [ra
d]
60
80
0
0.25
0.5
0.75
erro
r [ra
d]
80
100
-0.75
-0.5
-0.25
Phas
e
40
-0.75
-0.5
-0.25
Phas
e e
40
60
-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5-1.5
-1.25
-1 20
-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5-1.5
-1.25
-1
N li d lit d [ 100%]
20
Normalized amplitude error [x100%] Normalized amplitude error [x100%]
22
2 CC AA
I-path : amplitude error and phase error I-path : amplitude error, Q-path : phase error
[%]1001)sin(cos)1(2
1
C
C
AAEVM [%]1002
)1sin(cos2
2
C
CC
A
AA
EVM
11
Amplitude error < 20%, Phase error <20°, Carrier leakage < -20 dBc for EVM <30% Therefore, direct up-conversion transmitter is suitable for ZigBee transmitter
Transmission PSD Mask
Transmit PSD limits
Frequency Relative limit Absolute limit
| f f | 3 5 MH 20 dB 30 dB| f – fc | > 3.5 MHz - 20 dB - 30 dBm
For both relative and absolute limit average spectral power shall be For both relative and absolute limit, average spectral power shall be measured using a 100 kHz resolution bandwidth.
For relative limit reference level shall be the highest average spectral For relative limit, reference level shall be the highest average spectral power measured within +/- 1 MHz of fc.
From this specification # bit of DAC and harmonic distortion in a transmitter From this specification, # bit of DAC and harmonic distortion in a transmitter can be estimated
4-bit DAC and 1st LPF are proper.
12
4 bit DAC and 1st LPF are proper.
Harmonic distortion < -30 dBc
Transmission PSD Mask (Cont.)101
Spectrum mask 101
Spectrum mask
10-2
10-1
100
Spect u as
10-2
10-1
100
Spectrum mask
10-4
10-3
10
10-4
10-3
10
Ideal ZigBee spectrum-8 -6 -4 -2 0 2 4 6 8
x 106
10-6
10-5
-8 -6 -4 -2 0 2 4 6 8
x 106
10-6
10-5
ZigBee spectrum after 4 bit DACIdeal ZigBee spectrum ZigBee spectrum after 4-bit DAC
10-1
100
101
10-3
10-2
10
4-bit DAC and 1st LPF are proper
Harmonic distortion < -30 dBc10-6
10-5
10-4
13
Harmonic distortion 30 dBc-8 -6 -4 -2 0 2 4 6 8
x 106
10
ZigBee spectrum after 4-bit DAC and 1st LPF (2 MHz B.W.)
BER Performances
0 01
0.10.1
1E-3
0.01
BER
-20 dBc of carrier leakage
0.01
BER
1E 5
1E-4
20 dBc of carrier leakage -25 dBc of carrier leakage -30 dBc of carrier leakage No carrier leakage
1E-3 Ideal ZigBee signal ZigBee signal through 4-bit DAC
and LPF with 3dB B.W. of 2 MHz
BER according to carrier leakage
0 2 4 6 81E-5
Eb/No [dB]0 1 2 3 4 5 6 7
1E-4
Eb/No [dB]
BER when 4 bit DAC and LPF BER according to carrier leakage BER when 4-bit DAC and LPF with 3 dB B.W. of 2 MHz is used
14
Summary
Rx
Low-IF receiver architecture
Target sensitivity : -93 dBm (variable)
NF < 7 dB, IIP3 > -30 dBm, Max handling power : -20 dBm, , g p
3th/4th variable gain complex bandpass filter
4-bit ADC4 bit ADC
Tx
Direct-up conversion architecture Direct up conversion architecture
Harmonic distortion < -30 dBc
1th/2nd LPF 1th/2nd LPF
4 bit DAC
Linear drive amplifier (class A class AB)
14
Linear drive amplifier (class A, class AB)