rf system architecture and budget analysis · pdf filerf system architecture and budget...

RF System Architecture and

Budget Analysis

Anurag Bhargava

Application Consultant

Agilent EEsof EDA

Agilent Technologies

Email: [email protected]

You Tube: www.youtube.com/user/BhargavaAnurag

Blog: http://abhargava.wordpress.com

Spectral Domain Techniques

RF Architecture Design

During RF architecture design engineers determine how many,

what type, parameters, and the order of stages required to meet

system specifications

Coupler

IL=2 dB

CPL=20 dB

DIR=30 dB

Z0=50 ohm

1

3

2

? or


The Architecture is Critical

• Architecture is the system foundation

• Poor architecture causes poor performance

• Poor architecture causes more design turns

• Poor architecture causes increased cost

• Poor architecture causes increased time to market


Traditional Method Limitations

• SPICE, linear, and harmonic balance simulators are designed

for components, not for complex system realization

• Programming spreadsheets is extremely difficult when image

noise, intermod filtering, mismatch effects and multiple paths

are considered

• Summary: traditional tools are ill-suited for analyzing RF

architectures


What is Required for RF Architecture Analysis?

Spur identification and resolution

• Identifying root causes is critical in systems with hundreds of leakage,

harmonic and intermod tones.

Noise analysis that considers the channel bandwidth

In-channel and out-of-channel intermodulation analysis

Accuracy: mismatch, phase, images, measured vs. ideal

models, etc.

Typical RF System

Copyright © 2012 Agilent Technologies

6

Antenna

TX Filter

Switch or Duplexer

RX Filter

LNA

TX Power Amplifer

Synthesizer or PLL Buffer Amp

Buffer Amp

Attenuator Mixer

Mixer

IF Filter IF Amp

Demodulator

IF Filter Modulator

Typical RF System


7

How do you determine what types of

stages to use, the order to place

them, and the parameters for each

block?

How would you respond to the following questions?

1. How do you currently determine what and where spurious and intermod products are being generated in the RF portions of you design?

2. How do you identify possible leakage paths in your design?

3. Does your current method of designing wideband systems include the effects of frequency dependencies of complex load impedance?

4. How do you access the impact of phase noise on noise figure?

5. How do you do budget analysis in the presence of modulated signals?

6. How do you compute noise figure of a path while other paths are actively connected to this path?


8

Why was Spectrasys Developed?


9

• RF Architecture (or Systems design) are the titles used during

the design stage where engineers determine what types of

stages (filters, amplifiers, mixers, etc), the ordering of these

stages in the design, and their parameters.

• Cascaded equations are used during this phase.

G1

nf1

OP1dB1

OIP31

G2

nf2

OP1dB2

OIP32

G3

nf3

OP1dB3

OIP33

𝐺 = 𝐺1 × 𝐺2 × 𝐺3

1

𝑂𝐼𝑃3𝑡𝑜𝑡𝑎𝑙=

1

𝑂𝐼𝑃31 × 𝐺2 × 𝐺3+

1

𝑂𝐼𝑃32 × 𝐺3+

1

𝑂𝐼𝑃33

1

𝑂𝑃1𝑑𝐵𝑡𝑜𝑡𝑎𝑙=

1

𝑂𝑃1𝑑𝐵1 × 𝐺2 × 𝐺3+

1

𝑂𝑃1𝑑𝐵2 × 𝐺3+

1

𝑂𝑃1𝑑𝐵3

𝑛𝑓𝑡𝑜𝑡𝑎𝑙 = 𝑛𝑓1 +𝑛𝑓2 − 1

𝐺1+

𝑛𝑓3 − 1

𝐺1 × 𝐺2

Why was Spectrasys Developed?: Continued


10

How do you use

cascaded equations on

this?

Why was Spectrasys Developed?: Continued


11

It would be nice if every

design was two port AND just

contained behavioral models.

But its not!


SPARCA

These needs led to the development of the SPARCA method,

an acronym for Signal Propagation And Root Cause Analysis.

• New method developed in 2002

• Based in the frequency domain

• Bilateral signal flow of all paths

• Magnitude and phase modeling (vector)

• Channel concepts integrated into the method


How SPARCA Works

Signal generation and propagation:

• All signal sources and noise sources propagate through all paths to all nodes

• Harmonic and intermod products are generated by non-linear models and

propagate to all nodes

Measurements:

• Power and noise are each is integrated across the channel bandwidth

• In-channel and adjacent channel measurements are calculated from the spectrums

at each node

Imperfections modeled:

• Devices are bilateral

• The true filtered and non-flat transfer function including phase is modeled

• Mismatch, reflections, and reverse propagation are accurately modeled


SPARCA Method

SPARCA does not replace other analysis methods (except

perhaps spreadsheets), it complements them. It is optimized for

RF architecture design.

Advantages • Identifies root causes

• Handles multiple paths

• More accurate than ideal model and scalar

methods

• Handles more signals & tones than other methods

• Handles channel concepts

• Integrates well with other software and lab tools


Example: Aviation Band Downconverter

The analyzer uses a tunable 1st LO to convert 500 KHz segments

of the aviation band to 0.95 to 1.45 MHz for baseband processing.

(1)

RF BPF

FLO=105 MHz

FHI=139 MHz

N=4

R=0.1 dB

RFAMP

G=?9 dB

NF=2 dB

OP1DB=15 dBm

R IL

RF Mixer

CL=8 dB

LO=7 dBm

LO ATTN

L=6 dB

(2)

IFAMP1

G=9 dB

NF=3 dB

OP1DB=25 dBm

IF BPF

FLO=21.45 MHz

FHI=22.45 MHz

IL=2 dB

IFAMP2

G=20 dB

NF=3 dB

OP1DB=30 dBm

R IL

Detector

CL=8 dB

LO=23 dBm

(3)

BASEBAND AMP

G=46 dB

NF=6 dB

OP1DB=36 dBm

(4)

RF: 108 to 136 MHz

LO: 86.3 to 114.3 MHz

BFO: 20.75 MHz

BASEBAND:

0.95 to 1.45 MHz

1 5 6

13

2

16 9 10 17

3

7 4


Simple Cascade Noise Figure

In this equation block, noise figure cascade

formula have been entered much like could

be programmed into a spreadsheet. This is

being done to illustrate the errors introduced

by spreadsheet system analysis.


Results of the Cascade Calculation

(1)

RF BPF

FLO=105 MHz

FHI=139 MHz

N=4

R=0.1 dB

RFAMP

G=?9 dB

NF=2 dB

OP1DB=15 dBm

R IL

RF Mixer

CL=8 dB

LO=7 dBm

LO ATTN

L=6 dB

(2)

IFAMP1

G=9 dB

NF=3 dB

OP1DB=25 dBm

IF BPF

FLO=21.45 MHz

FHI=22.45 MHz

IL=2 dB

IFAMP2

G=20 dB

NF=3 dB

OP1DB=30 dBm

R IL

Detector

CL=8 dB

LO=23 dBm

(3)

BASEBAND AMP

G=46 dB

NF=6 dB

OP1DB=36 dBm

(4)

RF: 108 to 136 MHz

LO: 86.3 to 114.3 MHz

BFO: 20.75 MHz

BASEBAND:

0.95 to 1.45 MHz

1 5 6

13

2

16 9 10 17

3

7 4

Here the block diagram of the downconverter

is repeated along with the resulting cascade

noise figure after each stage in the

downconverter. The resulting noise figure at

the baseband output is 5.28 dB.


Results by Spectral Propagation

Shown at the left is a level diagram in SPECTRASYS. This

level diagram depicts the cascade noise figure in red, the

stage noise figure in blue and the percentage noise figure in

green. Numeric cascade noise figure data after each stage is

also given in the final column in the table at the lower right.

Notice that the noise figure after the final amplifier computed

using SPARCA is 7.83 dB, rather than the 5.28 dB computed

using classical cascade NF equations. The popular and

classical formula is in error by 2.55 dB!


Source of Noise Figure Error

What is the source of this error?

• Mixer noise figure assumes noise only exists in the desired signal channel. In reality, noise exists in both the desired and image channel. Therefore, the true noise figure of a mixer is 3.01 dB higher than the specified noise figure.

Why not just specify the mixer noise figure 3 dB higher than is normally done?

• Because in a system with gain and an image filter preceding the mixer, the effective noise figure of the mixer approaches the specified value. In that case, using the higher noise figure would give the wrong result.

The fact of the matter is, accurate assessment of system noise figure requires noise propagation analysis. If the position of the input filter and the preamp are changed and the loss of the input filter was set to zero. Simple cascade analysis would predict the same noise figure for both systems. In reality, the difference with a 30 dB preamp with 8 dB noise figure is 2.7 dB. Approaching 3 dB. But look what happens when the noise figure of the preamp is reduced to 2 dB. The difference is then 1.4 dB. Again, accurate noise analysis requires noise propagation techniques.

In a similar way, spreadsheet analysis of intermodulation and dynamic range are also flawed.


Measurements

Different applications require different forms of output data. In

the next few slides, brief definitions and examples of

SPECTRASYS output data are provided.

There are over 85 built-in measurements.


Measurements: Gain & Signals in the Channel

Cascaded Gain

Cascaded Gain (All Signals)

Channel Frequency

Channel Power

Channel Power (Desired)

Gain

Gain (All Signals)

Total Node Power


Example: Gain & Signal Level Diagram C

F (M

Hz), D

BM

[CP

], DB

M[D

CP

]

-50

-20

10

40

70

100

130

DB

[GA

IN],

DB

[CG

AIN

]

-10

0

10

20

30

40

50

Node

1 5 6 16 9 10 17 7 8 4

Gain & Signal

R IL

R IL

DB[GAIN]

DB[CGAIN]

CF (MHz)

DBM[CP]

DBM[DCP]


Measurements: Noise

Added Noise

Carrier to Noise Ratio

Cascaded NF

Channel Noise Power

Image Channel Noise Power

Image Noise Rejection Ratio

Minimum Detectable Signal

Percent Noise Figure

Stage NF


Example: Noise

Short Video

Removed due to size of

the Video……


Intermodulation

Cascaded intermod equations are NOT used by SPECTRASYS. Just as with

noise, cascade intermod equations are flawed because they:

• Assume interfering signals are not filtered and maintain the same gain as the

desired signal through all cascaded stages

• Assume all stages are perfectly matched

• Assume two equal tones

• Assume infinite reverse isolation

Signal propagation generates intermod signals as they appear in real

systems. Signals are not limited to two tones. All intermods are propagated

through the system using the system transfer function. Consequently,

intermod measurements are accurate for filtered and non-ideal systems.


Measurements: Intermodulation & Compression

Cascaded Gain (3rd IM)

Channel Frequency (Tone)

Channel Power (Desired 3rd IM)

Channel Power (Tone)

Gain (3rd IM)

Gain (All Signals)

Percent 3rd IM

Stage Output 1 dB Compression

Stage Output 2nd IM

Stage Output 3rd IM

Stage Output Saturation Power

3rd Order Intercept (Input)

3rd Order Intercept (Output)

3rd IM Power (Propagated)

3rd IM Power (Generated)

3rd IM Power (Total)


Example: Intermodulation & Compression D

BM

[GIM

3P

], DB

[SD

R]

-200

-160

-120

-80

-40

0

40

80

120

160

200

DB

M[II

P3

], P

RIM

3

-30

-24

-18

-12

-6

0

6

12

18

24

30

Node

1 5 6 16 9 10 17 7 8 4

Intermodulation & Compression

R IL

R IL

DBM[IIP3]

DBM[GIM3P]

DB[SDR]

PRIM3


Measurements: Dynamic Range

Spurious Free Dynamic Range

Stage Dynamic Range


Example: Dynamic Range D

BM

[MD

S]

-150

-144

-138

-132

-126

-120

DB

[SF

DR

], D

BM

[IIP

3]

-30

0

30

60

90

120

Node

1 5 6 16 9 10 17 7 8 4

Dynamic Range

R IL

R IL

DB[SFDR]

DBM[IIP3]

DBM[MDS]


Measurements: Out of Channel

Adjacent Channel Power

Adjacent Channel Frequency

Channel Frequency (Offset)

Channel Power (Offset)

Image Frequency

Image Channel Noise Power

Image Noise Rejection Ratio

Mixer Image Channel Power

Mixer Image Rejection Ratio


Phase & Complex Models

The SPECTRASYS SPARCA simulator propagates signals using complex

multi-port transfer functions for the system.

• Phase data is retained and utilized

• Circuit models and schematics may be mixed with system models in the schematic

• The effects of mismatch are simulated

• Bilateral signal flow is simulated

(1)

COUPLER1_1

IL=1 dB

CPL=10 dB

[DIR=30 dB]

ATTN_VAR_1

IL=1 dB

L=?0.25 dB

RF_DELAY_1

T=0.27 ns

[Z0=50 Ω]

RF_PHASE_1

A=?10°

[Z0=50 Ω]

RFAMP_1

G=17 dB

NF=8 dB

OPSAT=50 dBm

COUPLER1_2

IL=0.5 dB

CPL=24 dB

[DIR=30 dB]

SPLIT2_1

[IL=3.1 dB]

ISO=100 dB

PH3=0°

RF_DELAY_2

T=0.53 ns

[Z0=50 Ω]

RF_PHASE_2

A=?10°

[Z0=50 Ω]

ATTN_VAR_2

IL=1 dB

L=?0.5 dB

RFAMP_2

G=38 dB

NF=8 dB

OPSAT=43 dBm

COUPLER1_3

IL=0.5 dB

CPL=10 dB

DIR=30 dB

(2)1

15

4

15

5

14

11 6

7

7

14

8 8

9

10

13 12

10

3

3

2


X-Parameter Models are Supported


The Link to ADS

Schematics can be exported to ADS for further simulation.

Digital / DSP & RF System Cosimulation

Modulation and Spectrasys (SystemVue)


36

The RF Link part is used in a

data flow schematic to point

to a Spectrasys schematic.

How RF Impairments affect Modulation Quality


37

Tunable Impairment List:

Gain Imbalance

Phase Imbalance

LO to RF Isolation

Noise Figure

Phase Noise

ADC (# of bits, clock, ref voltage)

Gain Imbalance effects on Constellation


38

Blue – Balanced Gain (Square)

Red – Imbalanced Gain

Phase Imbalance effects on Constellation


39

Blue – Balanced Phase (Square)

Red – Imbalanced Phase

LO to RF Isolation (DC Offset) effects on

Constellation


40

Blue – High Isolation (Square)

Red – Lower Isolation

The LO leaks into the RF and

appears as another RF input

signal

LO to RF Isolation (DC Offset) effects on

Constellation


41

Blue – High Isolation (Square)

Red – Lower Isolation

The RF can also leak into the

LO and this is used as another

LO signal

Noise effects on Constellation


42

Blue – No Noise (Square)

Red – Thermal and Phase Noise

Modulation Analysis Software (works with

Hardware)


43


Summary

A new system simulation technique referred to as Spectral

Propagation and Root Cause Analysis (SPARCA) offers a new

set of tools for the optimization of system architectures

• Improved accuracy over conventional cascade analysis

• Rapid root cause discovery using spectral component display at any node

• Wide set of built-in as well as user specified measurements

• Complex, bilateral and mismatch analysis

• Integration of other spectral domain simulation and synthesis tools

SPARCA is optimized for system architecture development and

saves multiple architecture and component design turns.

Looking Ahead..!!

Kindly send your requests on what we can cover in our future webinars to:

India:

Mukul Pareek

Marketing Engineer

Agilent Technologies India Pvt. Ltd

Email: [email protected]

Elsewhere:

Please contact your local Agilent representative.

Resources to help you..….

• Subscribe to the Blog: http://abhargava.wordpress.com to receive latest news, tips &

tricks on RF design and industry news..

• Subscribe to the You Tube Channel: www.youtube.com/user/BhargavaAnurag to

see various tutorial videos and learn the concepts better

• Agilent EEsof Home Page: www.eesof.com

• For software evaluation license or for any other queries:

– E-mail: [email protected]

– Toll Free Number: 1800-11-2929

http://abhargava.wordpress.com/

http://www.youtube.com/user/BhargavaAnurag

http://www.eesof.com/

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