Part 1 of this deck discusses Digital Modulation and Part 2 focuses on Digital Demodulation. By Analog Devices, Inc.

1. The World Leader in High-Performance Signal Processing Solutions
FUNDAMENTALS OF THE RF
TRANSMISSION AND RECEPTION
OF
DIGITAL SIGNALS

2. The World Leader in High-Performance Signal Processing Solutions
Part 1: Digital Modulation
2

3. Transmitting Bits
Bit Stream
1 1 -1 1 1 -1 -1 -1 1 1 Bits
Divide into
1 1 -1 1 1 -1 -1 -1 1 1 Symbols
(2 bits per Symbol)
-135° 45° Assign Phase
45° 135° -45°
to Symbols
135° 45°
Modulate
Phases on to
Carrier
-135° -45°
3

4. Practical Digital Modulation using an IQ Modulator
Filtered Bit Stream
I IN
0
LO RF OUT
LO (from PLL) 90
Q IN
Filtered Bit Stream Looks like Amplitude Modulation (AM) but this signal is
indeed phase modulated. Why the amplitude variations?
 Phase Splitter separates LO from PLL into “Quadrature” components of
equal amplitude but 90 degrees out of phase
 Filtered bit streams from a dual DAC drive the I and Q inputs which are
multiplied with the quadrature LOs
 The outputs of the two multipliers are combined to yield the modulated
carrier
 This modulation coding scheme is called Quadrature Phase Shift Keying
(QPSK)
4

5. IQ Modulation in the Frequency Domain
I IN 3 dB BW=Symbol Rate
0
LO RF OUT
FLO 90
FLO
Q IN
3 dB BW=Symbol Rate/2
 I and Q baseband signals are mixed up to an IF or to RF. Modulated
carrier bandwidth is twice the baseband bandwidth
5

6. Other Digital Phase Modulation Schemes
m=2, n=1 m=4, n=2 m=8, n=3
BPSK – 1 bit/symbol QPSK- 2 bits/symbol 8-PSK – 3 bits/symbol
m=16, n=4
m=64, n=8
64 QAM – 6 bits/symbol
16 QAM – 4 bits/symbol
 By allowing more I and Q levels (beyond -1 and +1), we can implement higher order QAM
modulation schemes.
 Higher Order Modulation Schemes → Higher Data Rate.
 But Symbols are closer together → Requires higher Signal-to-Noise Ratio for demodulation
 Increasing “Symbol Rate” increases data rate but widens Spectrum
6

7. Error Vector Magnitude - EVM
Q Magnitude Error (I/Q error mag)
{
Actual M
∑ Z (k ) − R(k )
2
Signal EVM = k =1
M
Unit = %
2
∑ R(k )
k =1
φ Ideal (Reference) Signal
Phase Error (I/Q error phase)
I
 Noise and Imperfections in transmit and receive signal chains result in
demodulated voltages which are displaced from their ideal location.
 Error Vector Magnitude expresses this dislocation
 Large EVM will result in Symbol Errors and degraded Bit Error Rate
 Higher Order Modulation Schemes → Symbols Closer Together → EVM More
Critical
7

8. The Imperfect IQ Modulator Gain
Imbalance
IQ MOD (G1,G2,G3,G4)
IIN Vofs1 Degrades
G3 EVM
Imbalance G1
In Phase 0
Splitter Vn
89.5
Degrades
EVM G2
Q IN Vofs2 Noise risks
G4 violation of
Offset emissions
Voltages LOIN regulations
Cause LO
Leakage to
RFOUT
8

9. Dealing with IQ Modulator Imperfections
 DAC incorporates Gain, Phase and Offset Voltage adjustment
functions
 DAC and IQ Modulator have matching bias levels (0.5 V), permitting a
glue-less interface with no level shifting requirements
 Modulator correction functions can also be performed in the digital
domain
9

10. How Distortion Impacts Transmitters
Marker 1 [T1] RBW 30 kHz RF Att 20 dB
Ref Lvl -10.73 dBm VBW 300 kHz
-10 dBm 99.48897796 MHz SWT 84 ms Unit dBm
1
-10
1 [T1] -10.73 dBm
A
99.48897796 MHz
-20
CH PWR 8.11 dBm
ACP Up -58.77 dB
-30 ACP Low -59.27 dB
ACLR=58 dBc -40
1RM Adjacent
-50
Channel
-60 Leakage
-70
Ratio
Caused
-80
By poor IMD
-90
C0
C0
cl1
-100 cl1
cu1
cu1
-110
Center 100 MHz 3 MHz/ Span 30 MHz
Date: 24.FEB.2006 12:00:50
 No Blockers to worry about in Transmitter.
 But excessive distortion creates Spectral Leakage into adjacent
channels
 Distortion can be caused by any component in the signal chain,
not just the modulator
10

11. Marker 1 [T1] RBW 10 kHz RF Att 0 dB
Ref Lvl -79.38 dBm VBW 100 kHz
-30 dBm 1.95950000 GHz SWT 370 ms Unit dBm
-30
1 [T1] -79.38 dBm
A
1.95950000 GHz
-40
CH PWR -53.44 dBm
ACP Up -41.74 dB
-50 ACP Low -41.71 dB
-60
1AVG 1RM
-70
1
-80
-90
-100 ADJACENT MAIN ADJACENT
CHANNEL CHANNEL CHANNEL
-110
C0
C0
cl1
-120 cl1
cu1
cu1
-130
Center 1.96 GHz 1.46848 MHz/ Span 14.6848 MHz
11
Date: 9.NOV.2009 18:36:37

12. Marker 1 [T1] RBW 10 kHz RF Att 0 dB
Ref Lvl -60.22 dBm VBW 100 kHz
-30 dBm 1.95950000 GHz SWT 370 ms Unit dBm
-30
1 [T1] -60.22 dBm
A
1.95950000 GHz
-40
CH PWR -35.08 dBm
ACP Up -60.05 dB
-50 ACP Low -60.01 dB
1
-60
1AVG 1RM
-70
-80
-90
-100 ADJACENT MAIN ADJACENT
CHANNEL CHANNEL CHANNEL
-110
C0
C0
cl1
-120 cl1
cu1
cu1
-130
Center 1.96 GHz 1.46848 MHz/ Span 14.6848 MHz
12
Date: 9.NOV.2009 18:33:38

13. Marker 1 [T1] RBW 10 kHz RF Att 0 dB
Ref Lvl -33.52 dBm VBW 100 kHz
-30 dBm 1.95950000 GHz SWT 370 ms Unit dBm
-30 1
1 [T1] -33.52 dBm
A
1.95950000 GHz
-40
CH PWR -8.92 dBm
ACP Up -68.55 dB
-50 ACP Low -71.69 dB
-60
1AVG 1RM
-70
-80
-90
-100 ADJACENT MAIN ADJACENT
CHANNEL CHANNEL CHANNEL
-110
C0
C0
cl1
-120 cl1
cu1
cu1
-130
Center 1.96 GHz 1.46848 MHz/ Span 14.6848 MHz
13
Date: 9.NOV.2009 18:10:08

14. Marker 1 [T1] RBW 10 kHz RF Att 0 dB
Ref Lvl -42.87 dBm VBW 100 kHz
-30 dBm 1.95950000 GHz SWT 370 ms Unit dBm
-30
1 [T1] -42.87 dBm
A
1.95950000 GHz
-40 1 CH PWR -17.67 dBm
ACP Up -73.47 dB
-50 ACP Low -74.75 dB
-60
1AVG 1RM
-70
-80
-90
-100
-110
C0
C0
cl1
-120 cl1
cu1
cu1
-130
Center 1.96 GHz 1.46848 MHz/ Span 14.6848 MHz
14
Date: 9.NOV.2009 18:12:07

15. Marker 1 [T1] RBW 10 kHz RF Att 0 dB
Ref Lvl -36.78 dBm VBW 100 kHz
-30 dBm 1.95950000 GHz SWT 370 ms Unit dBm
-30
1 1 [T1] -36.78 dBm
A
1.95950000 GHz
-40
CH PWR -11.53 dBm
ACP Up -72.85 dB
-50 ACP Low -74.71 dB
-60
1AVG 1RM
-70
-80
-90
-100
-110
C0
C0
cl1
-120 cl1
cu1
cu1
-130
Center 1.96 GHz 1.46848 MHz/ Span 14.6848 MHz
15
Date: 9.NOV.2009 19:14:23

16. Marker 1 [T1] RBW 10 kHz RF Att 0 dB
Ref Lvl -33.52 dBm VBW 100 kHz
-30 dBm 1.95950000 GHz SWT 370 ms Unit dBm
-30 1
1 [T1] -33.52 dBm
A
1.95950000 GHz
-40
CH PWR -8.92 dBm
ACP Up -68.55 dB
-50 ACP Low -71.69 dB
-60
1AVG 1RM
-70
-80
-90
-100
-110
C0
C0
cl1
-120 cl1
cu1
cu1
-130
Center 1.96 GHz 1.46848 MHz/ Span 14.6848 MHz
16
Date: 9.NOV.2009 18:10:08

17. What is happening here?
50
*
Intercept
SLOPE=1 of
0 Fundamentals
Fundamentals and
*
* *
Intermods
* * IMD(dBc)
(IP3)
-50 SLOPE=3
*
-100 *
* Intermods
*
*
-150
-20 -10 0 10 20 30 40 50
 OIP3 Intercept(dBm) = PFUND – (IMD/2)
 Knowing the OIP3 allows you to calculate Intermodulation Distortion
(IMD) at any power level
17  Many devices do not follow this rule

18. Striking a Balance
Poor SNR Excessive Distortion
Marker 1 [T1] RBW 10 kHz RF Att 0 dB
Marker 1 [T1] RBW 10 kHz RF Att 0 dB
Ref Lvl -33.52 dBm VBW 100 kHz
Ref Lvl -79.38 dBm VBW 100 kHz
-30 dBm 1.95950000 GHz SWT 370 ms Unit dBm
-30 dBm 1.95950000 GHz SWT 370 ms Unit dBm
-30 1
-30
1 [T1] -79.38 dBm 1 [T1] -33.52 dBm
A
A
1.95950000 GHz 1.95950000 GHz
-40 -40
CH PWR -53.44 dBm CH PWR -8.92 dBm
ACP Up -41.74 dB ACP Up -68.55 dB
-50 ACP Low -41.71 dB -50 ACP Low -71.69 dB
-60 -60
1AVG 1RM 1AVG 1RM
-70 -70
1
-80 -80
-90
-90
-100
-100
-110
C0 -110
C0 C0
cl1 C0
-120 cl1 cl1
cu1 -120 cl1
cu1 cu1
-130
cu1
Center 1.96 GHz 1.46848 MHz/ Span 14.6848 MHz -130
Center 1.96 GHz 1.46848 MHz/ Span 14.6848 MHz
Date: 9.NOV.2009 18:36:37
Date: 9.NOV.2009 18:10:08
 We need to set our gains and levels so that we can strike a balance
between SNR and Distortion
 This is why our customers simultaneously demand low noise and
low distortion
 Gain is generally distributed throughout the channel to achieve
this goal
18

19. Last Word on Distortion…..
Marker 1 [T1] RBW 10 kHz RF Att 0 dB
Ref Lvl -42.87 dBm VBW 100 kHz
-30 dBm 1.95950000 GHz SWT 370 ms Unit dBm
•During an IP3 -30
1 [T1] -42.87 dBm
A
sweep, at a certain -40 1
1.95950000 GHz
CH PWR -17.67 dBm
power level, the ACP Up -73.47 dB
power of the IMD -50 ACP Low -74.75 dB
tones will be equal -60
to the noise power 1AVG 1RM
in a defined -70
Spurious
bandwidth. The SNR -80
Free
at this point is the
Dynamic
SFDR of the
-90
Range
component -100
•Don’t mix this up
-110
with the SFDR of an C0
C0
cl1
ADC or DAC -120 cl1
cu1
cu1
-130
Center 1.96 GHz 1.46848 MHz/ Span 14.6848 MHz
SFDR = (2/3)(IIP3-NF-10log(kTB))
Date: 9.NOV.2009 18:12:07
19

20. Key IQ Modulator Specifications
 Input IP3 (IIP3): Same as OIP3 but referred to input:
Intermodulating Blockers can create IMD products that fall
on the desired signal
 Noise Figure
 IP2: Figure of Merit for Second order Intermodulation
Distortion. Poor IP2 can intermodulate with the desired
signal and produce dc offsets
 LO Quadrature accuracy: Affects EVM/BER of recovered data
20

21. I/Q Modulator Key specifications
Part Freq LO Sideband Noise P1dB OIP3 Specs P/N Isy
Desc Vs(V) Package
Number (MHz) (dBm) (dBc) (dBm/Hz) (dBm) (dBm) @ (MHz) dBc/Hz (mA)
5.1×6.4
AD8345 140-1000 Low Power I/Q Mod -42 -42 -154.5 2.5 25 800 N/A 2.7-5.5 65
TSSOP-16
5.1×6.4
AD8346 800-2500 Low Power I/Q Mod -42 -36 -147 -3 20 1900 N/A 2.7-5.5 45
TSSOP-16
5.1x6.4
AD8349 700-2700 Low Power I/Q Mod -45 -35 -155 7.6 21 900 N/A 4.75-5.5 135
TSSOP-16
7X7
ADF9010 840-960 IQ Mod & Int-N PLL -40 -46 -158 10 24 900 -83 3.15-3.45 360
LFCSP-48
4×4
ADL5370 300-1000 Narrowband IQ Mod -50 -41 -160 11.0 24 450 N/A 4.75-5.25 205
LFCSP-24
4×4
ADL5371 500-1500 Narrowband IQ Mod -50 -55 -158.6 14.4 27 900 N/A 4.75-5.25 175
LFCSP-24
4×4
ADL5372 1500-2500 Narrowband IQ Mod -45 -45 -158 14.2 27 1900 N/A 4.75-5.25 165
LFCSP-24
4x4
ADL5373 2300-3000 Narrowband IQ Mod -32 -57 -157.1 13.8 26 2500 N/A 4.75-5.25 174
LFCSP-24
4×4
ADL5374 3000-4000 Narrowband IQ Mod -32.8 -50 -159.6 12.0 22.8 3500 N/A 4.75-5.25 173
LFCSP-24
4×4
ADL5375 400-6000 IQ Mod w Output Disable -46.2 -52.1 -160 9.4 26.8 900 N/A 4.75-5.25 200
LFCSP-24
4×4
ADL5385 50-2200 2XLO Broadband IQ Mod -46 -50 -159 11.0 26 350 N/A 4.75-5.5 215
LFCSP-24
6×6
ADL5386 50-2200 2XLO IQ Mod & VVA&AGC -38 -46 -160 11.1 25 350 N/A 4.75-5.5 230
LFCSP-40
6x6
ADRF6701 750-1100 IQ Mod & Frac-N PLL&VCO -45 -40 -158 14 29 900 -93 4.75-5.25 260
LFCSP-40
6x6
ADRF6702 1550-2150 IQ Mod & Frac-N PLL&VCO -40 -33 -158 14 26 1800 -90 4.75-5.25 260
LFCSP-40
6x6
ADRF6703 2100-2600 IQ Mod & Frac-N PLL&VCO -40 -40 -158 15 33 2200 -93 4.75-5.5 260
LFCSP-40
6x6
ADRF6704 2500-2900 IQ Mod & Frac-N PLL&VCO -41 -40 -158 15 31 2600 -92 4.75-5.5 260
LFCSP-40
8X8
ADRF6750 950-1575 IQ Mod & Frac-N PLL&VCO -45 -45 -157 8.5 21 1200 -93 4.75-5.25 310
LFCSP-56
21

22. The World Leader in High-Performance Signal Processing Solutions
Part 2: Digital Demodulation
22

23. Recovering Data from a Digitally Modulated Carrier
Iout
0
VREF
90
Qout
70 MHz
VREF
Comparators
(real systems use Dual ADCs)
70 MHz
Sine Wave
 Reverse process to IQ Modulation
 IQ Demodulator extracts phase (and amplitude) information from
the modulated signal and presents it in XY (or IQ) format.
 Apply I and Q outputs to an ADC or Comparator and bits can be
recovered.
23

24. Critical IQ Demodulator Specs – LO to RF Leakage
-60dBm
-30dBm(~20mVp-p)
-40dBm
FLO
ω
A B C
LNA ADC
-70dBm
Leakage
Desired
0dBm Assume,
ω
Gain from A to C =30dB
FLO LO to RF leakage ~ 60dB
•If some of the LO leaks to the RF input, it mixes
(multiplies) with itself in the mixer generating unwanted dc
offsets on top of the recovered baseband data stream
24

25. What is causing the poor quality of
this demodulated Constellation?
Symbol
Decision
Threshold
If the symbol lands
on the edge or outside
of the box, bit errors
will occur
 Very poor LO Quadrature Phase Split (in DMOD)
 Dc Offset of the complete constellation (probably LO to RF Leakage)
 Noise has enlarged the footprint of the constellation points (poor Receiver
Noise Figure)
25

26. Reading the Demodulated Constellation
 Signal Compression (signal chain is being over driven)

27. Key IQ DMOD Specifications
 Input IP3 (IIP3): Same as OIP3 but referred to input:
Intermodulating Blockers can create IMD products that fall
on the desired signal
 Noise Figure
 IP2: Figure of Merit for Second order Intermodulation
Distortion. Poor IP2 can intermodulate with the desired
signal and produce dc offsets
 LO Quadrature accuracy: Affects EVM/BER of recovered data
27

28. IQ Demodulators
VGA IQ Quadrature Noise
Freq P1dB IIP3 Specs Isy VS
Part No. Range 3dB BW Error Figure Package
(MHz) (dBm) (dBm) @(MHz) (mA) (V)
(dB) (MHz) (dB/deg) (dBm)
9.7x6.4
AD8347 800-2700 70 65 0.3/1º -2 +11.5 11 1900 64 2.7-5.5
TSSOP-28
9.7x6.4
AD8348 50-1000 44 125 0.25/0.5º +13 +28 10.75 380 48 2.7-5.5
TSSOP-28
4X4
ADL5382 700-2700 N/A 370 0.05/0.2º 14.4 30.5 15.6 1900 220 4.75-5.25
LFCSP-24
4X4
ADL5387 50-2000 N/A 240 0.05/0.2º +13 +31 12 140 180 5
LFCSP-24
4X4
ADL5380 400-6000 N/A 390 0.07/0.25º 11.6 27.8 11.7 1900 245 5
LFCSP-24
8X8
ADRF6850 100-1000 60 300 0.1/0.5º 12 22.5 11 800 350 3.15-3.45
LFCSP-56
28

29. Application Example – Complete Direct Conversion Receiver
 Direct Conversion
Receiver has no IFs and
no IF Filters
 Variable gain after IQ
DMOD is used to
optimize the peak-to-
peak swing of the signal
for the ADCs
29

30. Receiver EVM vs Input power
using ADF4350 PLL/VCO as LO source
-10
-15
Modulation Error Rate-
using ADF4350
-20 PLL/VCO as LO
source
MER-dB
-25
-30
-35
-40
-90 -80 -70 -60 -50 -40 -30 -20
Input Power (dBm)
30

31. An IQ DMOD-based Receiver
 Filtersand Amplifiers amplify signal and remove out-of-band
blockers
 Variable gain after IQ DMOD is used to optimize the peak-to-peak
swing of the signal for the ADCs
 When the input frequency to the IQ Modulator is also the receive
frequency, we have a Direct Conversion Receiver (Zero IF)
31

32. AD8348 IQ Demodulator with Integrated VGA
 Built-in VGA has 45 dB of gain control range
 VGA will still require external circuitry to implement AGC
32