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Balanced Device Characterization
Page 2
Outline
• Characteristics of Differential Topologies
• Measurement Alternatives
• Unbalanced and Balanced Performance Parameters
• Balanced Devices Design Methodology
• Measurement Example
• Conclusion
Page 3
Differential Device Topology
12
Unbalanced Device• Signals referenced to ground
Differential Device• Signals equal amplitude
and anti-phase• Also supports a common
mode (in-phase) signal• Virtual ground
1 2
Page 4
Performance Attributes of Differential Circuits
• Noise Immunity from:
– Power Supplies
– Digital Hash
– External EMI
• Minimize Radiation from Circuit
• Even-Order Harmonic Suppression
• RF Grounding Quality Less Critical
Page 5
Enablers
• Demand for Higher Performance, Lower Cost RF IC’s
• Improved RF Device Performance
• Higher Yield RF IC’s
• Improved RF Simulation Tools
• Increased IC Density
Page 6
Challenges
• Measurement Tools Are Mostly Unbalanced
• No Balanced VNA Calibration Standards
• No Balanced RF Connector Standards
• No Standard Reference Impedance (Z0) for Balanced Devices
Page 7
Outline
• Characteristics of Differential Topologies
• Measurement Alternatives
• Unbalanced and Balanced Performance Parameters
• Balanced Devices Design Methodology
• Measurement Example
• Conclusion
Page 8
Measurement Alternatives
1) DUT
Desired measurement reference plane
Calibration reference plane
balun balun
Balun only measuresdifferential mode and difficult to calibrate
Page 9
Measurement Alternatives
1) DUT
Desired measurement reference plane
Calibration reference plane
balun balunBalun only measuresdifferential mode and difficult to calibrate
2) DUTMultiport single endeds-parameters do notaddress balanced modes
Page 10
Measurement Alternatives
1) DUT
Desired measurement reference plane
Calibration reference plane
balun balunBalun only measuresdifferential mode and difficult to calibrate
2) DUT Multiport single endeds-parameters do notaddress balanced modes
3) DUT
Reference plane
Consider DUT to have balanced pairs by using mixed-modes-parameters
1 2
Page 11
Outline
• Characteristics of Differential Topologies
• Measurement Alternatives
• Unbalanced and Balanced Performance Parameters
• Balanced Devices Design Methodology
• Measurement Example
• Conclusion
Page 12
How Many Ports Does this Device Have?
Example: Balanced Amplifier
Page 13
Unbalanced and Balanced Devices
Port 1
Port 2
Port 3
Port 4
• Unbalanced: ports referenced to gnd (S-parameters)
Port 1 Port 2
• Balanced: ports are pairs (Mixed-Mode S-parameters)
Page 14
Single-Ended S-Parameters
Conventional S-Parameters Answer the Question …
what are the corresponding responsesresponses on all ports of the device?
If a single port of a device is stimulated,stimulated,
Page 15
Mixed-Mode S-Parameters
Mixed-Mode S-Parameters Answer the Question …
If a balanced port of a device is stimulatedstimulated with a common-mode or differential-mode signal,
what are the corresponding common-mode and differential-mode responsesresponses on all ports of the device?
Page 16
Port 1
Port 2
Port 3
Port 4
Single-Ended 4-Port
Single-Ended S-Parameter Review
Page 17
Single-Ended S-Matrix
44434241
34333231
24232221
14131211
SSSS
SSSS
SSSS
SSSS
Stimulus Ports
Response Ports
Page 18
Mixed-Mode S-Parameter Basics
Page 19
Mixed-Mode S-Parameter Basics
Page 20
Mixed-Mode S-Parameter Basics
Page 21
Mixed-Mode S-Parameter Basics
Page 22
Mixed-Mode S-Matrix
Naming Convention: Smode res., mode stim., port res., port stim.
22212221
12111211
22212221
12111211
CCCCCDCD
CCCCCDCD
DCDCDDDD
DCDCDDDD
SSSS
SSSS
SSSS
SSSS
Port 1 Port 1Port 2 Port 2
Differential-Mode Stimulus
Common-Mode Stimulus
Differential-Mode
Response
Port 1
Port 2
Port 1
Port 2
Common-Mode
Response
Page 23
Mixed-Mode S-Matrix: DD Quadrant
22212221
12111211
22212221
12111211
CCCCCDCD
CCCCCDCD
DCDCDDDD
DCDCDDDD
SSSS
SSSS
SSSS
SSSS
Input Reflection
Output ReflectionForward Transmission
Reverse Transmission
Describes Fundamental Performance in Pure Differential-Mode Operation
Page 24
Hybrid Network:• Divides Signals Differentially• Combines Signals Differentially
Conceptual View of DD Quadrant
Stimulus Response
Stimulus Response
Stimulus Response
Stimulus Response
Stimulus Response
Stimulus Response
Stimulus Response
Stimulus Response
Differential Divide/Combine
Differential Divide/In-Phase Combine
In-Phase Divide/Differential Combine
In-Phase Divide/Combine
Page 25
Mixed-Mode S-Matrix: CC QuadrantInput Reflection
Output ReflectionForward Transmission
Reverse Transmission
22212221
12111211
22212221
12111211
CCCCCDCD
CCCCCDCD
DCDCDDDD
DCDCDDDD
SSSS
SSSS
SSSS
SSSS
Describes Fundamental Performance in Pure Common-Mode Operation
Page 26
Conceptual View of CC Quadrant
Stimulus Response
Stimulus Response
Stimulus Response
Stimulus Response
Stimulus Response
Stimulus Response
Stimulus Response
Stimulus Response
Differential Divide/Combine
Differential Divide/In-Phase Combine
In-Phase Divide/Differential Combine
In-Phase Divide/Combine
Hybrid Network:• Divides Signals In-Phase• Combines Signals In-Phase
Page 27
Mixed-Mode S-Matrix: CD QuadrantInput Reflection
Output ReflectionForward Transmission
Reverse Transmission
• Describes Conversion of a Differential-Mode Stimulus to a Common-Mode Response
• Terms Are Ideally Equal to Zero with Perfect Symmetry• Related to the Generation of EMI
22212221
12111211
22212221
12111211
CCCCCDCD
CCCCCDCD
DCDCDDDD
DCDCDDDD
SSSS
SSSS
SSSS
SSSS
Page 28
Conceptual View of CD Quadrant
Stimulus Response
Stimulus Response
Stimulus Response
Stimulus Response
Stimulus Response
Stimulus Response
Stimulus Response
Stimulus Response
Differential Divide/Combine
Differential Divide/In-Phase Combine
In-Phase Divide/Differential Combine
In-Phase Divide/Combine
Network:• Divides Signals Differentially• Combines Signals In-Phase
Page 29
22212221
12111211
22212221
12111211
CCCCCDCD
CCCCCDCD
DCDCDDDD
DCDCDDDD
SSSS
SSSS
SSSS
SSSS
Mixed-Mode S-Matrix: DC QuadrantInput Reflection
Output ReflectionForward Transmission
Reverse Transmission
• Describes Conversion of a Common-Mode Stimulus to a Differential-Mode Response
• Terms Are Ideally Equal to Zero with Perfect Symmetry• Related to the Susceptibility to EMI
Page 30
Conceptual View of DC Quadrant
Stimulus Response
Stimulus Response
Stimulus Response
Stimulus Response
Stimulus Response
Stimulus Response
Stimulus Response
Stimulus Response
Differential Divide/Combine
Differential Divide/In-Phase Combine
In-Phase Divide/Differential Combine
In-Phase Divide/Combine
Network:• Divides Signals In-Phase• Combines Signals Differentially
Page 31
222221
222221
121211
CCCDCS
DCDDDS
SCSDSS
SSS
SSS
SSS
Differential Mode Stimulus
Single Ended
Stimulus
Common Mode
Stimulus
Port 2Port 1 Port 2
Port 1
Differential Mode Response
Common Mode Response
Single Ended Response
Port 2
Port 2
Port 1(unbalanced)
Port 2(balanced)
Differential ModeCommon Mode
Single-Ended
Three-Terminal Devices
Page 32
Outline
• Characteristics of Differential Topologies
• Measurement Alternatives
• Unbalanced and Balanced Performance Parameters
• Balanced Devices Design Methodology
• Measurement Example
• Conclusion
Page 33
What are the simultaneous conjugate input and output matching impedances of the following circuit?
Brain Teaser #1
Single-ended 2-port
Page 34
What are the simultaneous conjugate input and output matching impedances of the following circuit?
Brain Teaser #1: Answers
Single-ended 2-portwhere:
1
22 21
1
1
1
1
1I
2*
C
B
C
B
C
C
1
22 22
2
2
2
2
2O
2*
C
B
C
B
C
C
2211
2221 1 DSSB
2222
2112 1 DSSB
*22111 SDSC
*11222 SDSC
21122211 SSSSD
Well-documented relationship between simultaneous conjugate match and s-parameters.
Page 35
Brain Teaser #2
What are the simultaneous conjugate input and output matching impedances of the following circuit?
Differential 2-port
Page 36
Brain Teaser #2: Answers
What are the simultaneous conjugate input and output matching impedances of the following circuit?
Differential 2-port
where:
1
22 21
1
1
1
1
1I
2*
C
B
C
B
C
C
1
22 22
2
2
2
2
2O
2*
C
B
C
B
C
C
2211
2221 1 DSSB DDDD
2222
2112 1 DSSB DDDD
*22111 DDDD SDSC
*11222 DDDD SDSC
21122211 DDDDDDDD SSSSD
Reduce performance of differential circuit to a single mode of operation using mixed-mode s-parameters, and follow same procedure as single-ended 2-port.
Page 37
Simultaneous Conjugate Match: Single-Ended vs. Differential
Single-Ended 2-Port
where:
1
22 21
1
1
1
1
1I
2*
C
B
C
B
C
C
1
22 22
2
2
2
2
2O
2*
C
B
C
B
C
C
2211
2221 1 DSSB
2222
2112 1 DSSB
*22111 SDSC
*11222 SDSC
21122211 SSSSD
Differential 2-Port
where:
1
22 21
1
1
1
1
1I
2*
C
B
C
B
C
C
1
22 22
2
2
2
2
2O
2*
C
B
C
B
C
C
2211
2221 1 DSSB DDDD
2222
2112 1 DSSB DDDD
*22111 DDDD SDSC
*11222 DDDD SDSC
21122211 DDDDDDDD SSSSD
Page 38
Balanced Device Design Methodology
• Matching Example can be Also be Extended to Other Design Considerations (K, MAG, VSWR, Z, etc.)
• Reason is Parallel Approach to Parameter Derivation
• For Balanced Device, Use Identical Approach as Single-Ended Design
• Isolate Balanced Device to Specific Mode
– Substitute Parameters
– Example: (Snm SDDnm)
Page 39
Outline
• Characteristics of Differential Topologies
• Measurement Alternatives
• Unbalanced and Balanced Performance Parameters
• Balanced Devices Design Methodology
• Measurement Example
• Conclusion
Page 40
Port 1
Port 3
Port 2
Port 4
Single-Ended Representation(Conventional S-Parameters)
Balanced Representation(Mixed-Mode S-Parameters)
Port 1 Port 2
SAW Filter Measurement Example
Page 41
• Reference Z = 350 (all ports)
• Capacitive Component to Port Matches• Insertion Loss (14.5dB)• Input-Input Coupling• Output-Output Coupling
Port 1
Port 3
Port 2
Port 4
Single-Ended SAW Filter Performance
Page 42
Port 1 Port 2
Z 0 = 7
00
Differential StimulusCommon Response
Common StimulusDifferential Response
Z 0 = 1
75
Differential StimulusDifferential Response
Common StimulusCommon Response
• Reference Z depends on mode• Well-matched differentially• Reflective in common mode• Insertion Loss (8.9dB)• Mode conversion• Common Mode rejection (60dB)
Balanced SAW Filter Performance
Page 43
Outline
• Characteristics of Differential Topologies
• Measurement Alternatives
• Unbalanced and Balanced Performance Parameters
• Balanced Devices Design Methodology
• Measurement Example
• Conclusion
Page 44
• Better accuracy than measurements made with a Balun
• Uses existing Calibration standards
• Comprehensive characterization (D-D, C-C, D-C, C-D)
• Describes behavior in intended operating mode
– not misleading like Single-Ended data
• Insight into system performance considerations
Conclusions
