The document discusses the importance of combining large-signal and small-signal measurements using a vector network analyzer for characterizing amplifiers and assessing stability. It outlines practical setups, measurement techniques, and the impact of spurious and interference signals, emphasizing the value of s-parameters in analyzing amplifier behavior. Conclusions highlight the simplicity of using a Rohde & Schwarz network analyzer for achieving comprehensive insights into both small-signal and large-signal conditions.

1. Spurious and Stability Analysis
under Large-Signal Conditions
using your Vector Network
Analyser
An application of ICE
June 2012

2. Outline
● Why combining Large-Signal and Small-Signal Measurements
● Block Diagram
● Practical Setup
● S-parameters
● Stability Criteria
● Large-Signal Measurements
● References and Acknowledgements
● Conclusions
© NMDG 2012 2

3. Why combining Large-Signal and Small-Signal Measurements
How to quantify impact from … ? SPURIOUS SIGNALS
INTERFERENCE
S-parameters, usually measured under small-signal conditions, provide
● good insight in the linear behaviour of a amplifiers
● provide insight in the stability of the amplifier
S-parameters, measured under large-signal conditions, provide
● good insight in what happens with spurious signals and interference signals
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4. Why combining Large-Signal and Small-Signal Measurements
Under different large signal conditions … what about … ? STABILITY
ZS
ZL
S-parameters, usually measured under small-signal conditions, provide
● good insight in the linear behaviour of a amplifiers
● provide insight in the stability of the amplifier
S-parameters, measured under large-signal conditions, provide
● provide insight in the stability of the amplifier as conditions change
© NMDG 2012 4

5. Block Diagram
Measure at large-signal frequency grid and
at small-signal frequency grid, sweeping source 2
Network Analyzer Receivers
Large Signal ` (*) (*)
Conditions
ZS
f0 DUT
External RF source 1 ZL
or
VNA RF source 1 “Measure S-par” 50 Ohm
Large Signal
(depends on VNA)
Conditions
VNA couplers
or VNA RF source 2
external (low-loss) couplers [similar to S-par measurement]
Absolute Calibration Planes
(*) Other configurations possible, e.g. position couplers, use of splitters,
depending on power requirements
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6. © NMDG 2012 6

7. Practical Setup
Bias
External RF Source 1
ICE
Using VNA couplers
Termination
FET Gate bias: -1.2 V (class A)
Drain bias: 4 V
Increasing input power and different terminations
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8. “Channel” capability of the ZVA 24
Using Rohde&Schwarz ZVA capability to configure different “channels”
Each channel has his own specific hardware configuration
measured data
The Rohde&Schwarz ZVA switches fast from channel to channel
ZVA24 Display
Large-Signal Measurements
Small-Signal Measurements
© NMDG 2012 8

9. S-parameters under different large-signal conditions
S11
dB
S12 NO RF signal
dB
0 dBm (load)
freq GHz
5 dBm (load)
2 4 6 8 10
 15 5 dBm (open)
1
 20
2
3
 25
4
freq GHz
2 4 6 8 10
5
S21 S22
dB dB
20
30
10
20
freq GHz
2 4 6 8 10
10
 10
freq GHz
2 4 6 8 10
 20
 10
 30
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10. Stability K-Factor and Determinant
Abs U
Determinant
Abs U
Kfact
1.0
1.0 0.8
0.6
0.5
0.4
freq GHz 0.2
2 4 6 8 10
freq GHz
2 4 6 8 10
 0.5
NO RF signal
Stability Conditions 0 dBm (load)
5 dBm (load)
∣K∣1 and ∣∣1 5 dBm (open)
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11. Input and Output Stability Circles
Input Output 5 dBm (load / open)
NO RF signal
0 dBm (load)
X1.0
R0
X1.0
R0
X0.5 X2.0 X0.5 X2.0
R0.5
R0.5 R1.0
R2.0
R1.0
Stable X0
R2.0
X0.5 X2.0
X1.0
X0
5 dBm (load / open)
Stable NO RF signal
X0.5 X2.0
X1.0
0 dBm (load)
Frequency: 4.2 GHz
© NMDG 2012 11

12. Large-Signal Conditions while measuring S-parameters
v2t 
v1t  Amp  V
Amp  V
time ns 8
0.5 1.0 1.5 2.0
0 dBm (load)
 0.5 6
5 dBm (load)
5 dBm (open)
 1.0
4
 1.5
2
 2.0
time ns
i2t 
0.5 1.0 1.5 2.0
i1t  Amp A
Amp A
0.010 0.25
0.20
0.005
0.15
time ns
0.5 1.0 1.5 2.0
0.10
 0.005 0.05
time ns
 0.010 0.5 1.0 1.5 2.0
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13. References and Acknowledgements
● “A New Characterization Technique of “Four Hot S-parameters” for the
Study of Nonlinear Parametric Behaviors of Microwave Devices”, T.
Gasseling, D. Barataud, et alii, 2003 IEEE MTT-S Digest, p. 1663
● Thanks to Rohde & Schwarz for providing the R&S ZVA network analyzer
equipment and the support around the network analyzer
● Thanks to Focus Microwaves for providing the tuners and the good
cooperation
© NMDG 2012 13

14. Conclusions
● It is straightforward with a Rohde & Schwarz network analyzer to measure
the small-signal behaviour while applying and measuring the large-signal
conditions
● With the S-parameters it is possible to get better insight when spurious
signals are applied to the component or interference signals are picked up,
e.g. RF front-end picking up signals
● The S-parameters result in different stability criteria. This is evenly important
as the large-signal performance, designing active circuits, like amplifiers
For more information info@nmdg.be
www.nmdg.be
© NMDG 2012 14