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True Differential Measurements – Characterization of Balanced Devices White Paper
Chris Scholz, Ph.D 11.2013
White Paper
Abstract This white paper provides an overview of both the virtual and true differential measurement methods. Examples are shown in both modeling theory and actual measurements of when the true differential method will provide a more accurate result versus the virtual method.
Table of Contents Abstract. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2
Virtual Differential Method Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3
Introducing the True Differential Method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4
Theoretical Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5
Measurement Verification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6 Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Rohde & Schwarz True Differential Measurements – Characterization of Balanced Devices
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1 Introduction Differential devices are used in a wide variety of applications, including almost all modern high-speed signals running on serial ports and computers. This includes hard drives, PCI express, USB – almost all of the modern standards are differential today. In addition, many components use differential or balanced designs including amplifiers, mixers, filters, and PCBs. The advantages of differential designs are many, including: J J J J
Noise immunity Reduced power consumption Less crosstalk Higher integration density
Differential devices however, also require special measurement capabilities. Traditionally a Vector Network analyzer (VNA) has been used to stimulate the device with an unbalanced signal and then mathematically transform the wave quantities into balanced S-parameters, essentially producing a “virtual” differential measurement. The virtual method can work well, but when active devices are driven into their nonlinear region the “virtual” method is no longer sufficient. Rohde & Schwarz has developed a method that more accurately evaluates the performance of differential devices. This method, referred to as “True Differential”, utilizes multiple coherent sources to stimulate the device with actual or “true” differential signals. For the first time devices can be tested more accurately using a true differential stimulus. This white paper provides an overview of both the virtual and true differential measurement methods. Examples are shown in both modeling theory and actual measurements of when the true differential method will provide a more accurate result versus the virtual method.
Rohde & Schwarz True Differential Measurements – Characterization of Balanced Devices
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2 Virtual Differential Method Overview Traditionally, when two-port (balanced) components were characterized with network analyzers, they used balanced (singleended) S-parameter results to mathematically calculate differential S-parameters with the set-up shown in Figure 1. This method uses only one source and measures the device as an unbalanced (single-ended) device, instead of stimulating it with a differential signal.
Figure 1 Traditional differential measurements switched a single source between the ports and mathematically created virtual differential measured results.
A signal or incident wave is applied at Port 1 (now a single-ended port) at every frequency point and the output signal (wave quantity) is measured at Port 3 (Figure 2a). The reflected wave is also measured at Port 1 as it is a single-ended port. The incident wave is next applied to Port 3 (reflected wave measured at Port 3) and the output is measured at Port 1. Therefore, when using the virtual differential measurement method the balanced/differential device would be measured as single-ended. This process is repeated for Ports 2/4 and 4/2 respectively, and in total 16 single-ended S-parameters (S11 to S44) are measured (Figure 2a). Next virtual transformers are created and virtual differential ports that correspond to the differential mode of the device on the test are generated (Figure 2b). Using the virtual transformer one can mathematically construct the differential response or the common mode response. The resulting calculation provides mixed mode S-parameters (Figure 2c). The virtual method works well when measuring passive circuitry such as transmission or high-speed data lines. It also works well when measuring RF power transistors and amplifiers as long as they are operating under drive conditions in which their performance remains linear. For devices exhibiting nonlinear characteristics, single-ended Port 1 and single-ended Port 2 are never simultaneously stimulated so the device is never driven the way it would be in actual operation. For example, a differential amplifier might reach its 1-dB compression point at an incorrect drive level, due to the transistor’s incorrectly characterized gain characteristics. However, the virtual method has until recently been the only one offered by network analyzer manufacturers for making these measurements because (among other challenges) it was extremely difficult to control the magnitude and phase of the two signal sources.
Rohde & Schwarz True Differential Measurements – Characterization of Balanced Devices
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Figure 2 Creating virtual differential measured results.
Figure 2a 16 single-ended S-parameters are measured
Differential-mode (ideally matched) → 100 Ω ( = 2*Z0 ) Common-mode (ideally matched) → 25 Ω ( = 0,5*Z0 ) Figure 2b Virtual transformers are used to generate logical ports
Naming Convention: S mode res., mode stim., port res., port stim. Figure 2c Mixed mode S-parameters are calculated
Rohde & Schwarz True Differential Measurements – Characterization of Balanced Devices
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3 Introducing the True Differential Method So what would be required to build a true differential measurement system? First we need to have two coherent sources. The two sources need to be phase coherent so that we can generate a reliable common mode or differential mode stimulus signal. While dual source measurements are not uncommon, such as in IP3 (third order intercept) measurements, the challenge of keeping the two sources phase coherent had not been addressed before. With coherent sources we can generate two out-ofphase signals or in-phase signals and inject them into the device at the same time, just like your device would be operating in the real world. The VNA would then measure the response to the true differential stimulus in the way the device would actually see it. The method developed by Rohde & Schwarz allows active RF and microwave differential components, such as amplifiers, to be stimulated with actual differential signals at frequencies as high as 67 GHz. This differential-mode signal then stimulates the device, and mixed-mode S-parameters are then directly calculated from the ratios of the error-corrected differential or commonmode wave quantities. Figure 3 shows how the true differential method works. A generator that generates two signals that are 180° out-of-phase, or in-phase for the common mode measurement, and injects them into the device. The power waves are measured the same as with the virtual differential method. However, for true differential measurements, the power waves are a response to a true differential stimulus. So you get the same description, the same values, the same A1s and same B1s, but their response is due to a different stimulus.
Figure 3 The true differential technique stimulates the device with two phase coherent signals simultaneously.
Rohde & Schwarz True Differential Measurements – Characterization of Balanced Devices
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The ability to produce two test signals – each with 0/180° of phase shift and independent of time or temperature variations – is significant because maintaining phase stability was one of the primary reasons why true differential measurement could not be achieved in the past. The R&S method is based on vector-corrected wave quantities and uses a patented technique to control the magnitude and phase of two or more internal sources. The sources generate two signals identical in magnitude and phase-shifted 0° or 180°, with phase uncertainty below 1° (Figure 4). R&S also offers solutions for multiport testing, with up eight phase coherent sources. This would allow for more than just two lanes at the same time, allowing the measurement of crosstalk. In addition, once the two measurement channels have been configured, a device can be evaluated simultaneously in both virtual and true differential modes. This can provide a great deal of insight into both of the measurement processes. The results may be viewed in real time, on the same plot, and often reveal the sometimes vast differences between the results. Finally, there are new measurements that can be performed with phase coherent sources that are not possible with the virtual mode. Test engineers may produce “non-standard” conditions that provide greater insight into device performance by conducting amplitude and phase imbalance sweeps. In the amplitude imbalance sweep, the instrument generates a balanced signal at one of its ports and the amplitude of one signal component may be varied based on the user-defined power sweep range. For the phase imbalance sweep, the instrument generates a balanced signal at one of its ports, and the relative phase of the two signal components may be varied according to the selected phase range.
Figure 4 R&S VNA’s equipped with option K6 make coherent signals of arbitrary phase and amplitude imbalance possible.
Rohde & Schwarz True Differential Measurements – Characterization of Balanced Devices
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4 Theoretical Verification Let’s look at a model based analysis using a simple bipolar differential amplifier with a few biasing resistors (Figure 5a). Using MATLAB to perform our analytical calculations we can compare the techniques by stimulating the amplifier with single-ended or differential and looking at the virtual and true differential results. The key variable to evaluate the two methods is the common-mode rejection ratio (CMRR). The CMRR of a differential amplifier (or other device) is the ratio between differential mode and common mode voltage gain: CMRR = Sdd21/Scc21 While an ideal differential amplifier would have infinite CMRR; this is not achievable in practice. A high CMRR is required when a differential signal must be amplified in the presence of a possibly large common-mode input. The CMRR is a very important specification, as it indicates how much of the common-mode signal will appear in your measurement and is key in reducing noise on transmission lines. In Figure 5b we show the feedback terms that will be varied in the evaluation of our model (a1, afb). By adjusting the afb term, or the feedback gain, one can set the CMMR of the device. In this model the afb can be adjusted to tune the CMMR from 0 to 30 dB. The results of the analysis are shown in Figure 6. The modeling shows that depending on the input power we can get a significant difference between the virtual excitation and the true differential excitation of the device.
< Figure 5a Amplifier model
Figure 5 Model of simple bipolar differential amplifier used for MATLAB analysis
Figure 5b Adjusting afb allows tuning of the CMMR from 0 to 30 dB
Rohde & Schwarz True Differential Measurements – Characterization of Balanced Devices
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Figure 6a No shared feedback (CMRR → 0)
Figure 6b Current sourced differential pair (CMRR →∞)
Figure 6 Increasing the input power under varying CMMR shows a significant difference between the virtual excitation and the true differential excitation results.
Rohde & Schwarz True Differential Measurements – Characterization of Balanced Devices
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5 Measurement Verification Next the bipolar differential amplifier was fabricated with the feedback term, Rε able to have values of 0 and 27 Ω. This enabled the CMRR of the differential amplifier to range between 0 and 16 dB depending on what resistor was used (Figure 7).
Figure 7 The fabricated bipolar differential amplifier enabled the CMRR to be at 0 dB or 16 dB by changing the feedback resistor.
Figure 8 shows the measured results of the differential amplifier for the two resistor values for both virtual and true differential measurements. Note that the results provide a very similar match to our theoretical predictions. In Figure 9 we can see very good correlation between the modeled and measured behavior as we vary the feedback factor. The difference between the virtual and true differential methods shows up to 3 dB difference depending on how hard the device is driven and the level of CMMR.
Rohde & Schwarz True Differential Measurements – Characterization of Balanced Devices
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Figure 8 Measured results of virtual and true differential techniques at both CMMR=0 and 16 dB.
Figure 9 Good correlation between the modeled and measured shows up to 3db difference between virtual and true differential depending on how hard the device is driven and the level of CMMR.
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6 Summary For the testing of passive components and other devices operating in their linear region, either the virtual or true differential method will deliver an accurate measurement. At both the theoretical and measurement level we showed the results of the two methods diverging when devices moved into their nonlinear region. As more and more differential RF amplifiers, RFICs, and interconnects are used in mobile communication devices (CMOS power amplifiers and transceivers, for example) choosing the correct method becomes more critical. The ability of true differential measurements to more accurately measure active device performance allows manufacturers of components, subsystems, and systems to create products that achieve excellent results under their anticipated operating conditions. Through its ability to correctly evaluate the performance of active devices when operating in their nonlinear region, true differential measurement capability enabled through Rohde & Schwarz VNAs will be increasingly important in the future. They allow virtual and true differential measurements to be conducted and the results displayed simultaneously to give designers insight into the performance of their devices and circuits. The process is simple, requires minimal operational intervention, requires no difference in calibration techniques, and is accomplished very quickly.
Rohde & Schwarz True Differential Measurements – Characterization of Balanced Devices
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About Rohde & Schwarz Rohde & Schwarz is an independent group of companies specializing in electronics. It is a leading supplier of solutions in the fields of test and measurement, broadcasting, radiomonitoring and radiolocation, as well as secure communications. Established more than 75 years ago, Rohde & Schwarz has a global presence and a dedicated service network in over 70 countries. Company headquarters are in Munich, Germany. J Environmental commitment J Energy-efficient products J Continuous improvement in environmental sustainability J ISO 14001-certified environmental management system Regional Contacts North America 1-888-TEST-RSA (1-888-837-8772) [email protected] Latin America +1 410-910-7988 [email protected] Europe, Africa, Middle East +49 89 4129 123 45 [email protected] Asia/Pacific +65 65 13 04 88 [email protected] Rohde & Schwarz® is a registered trademark of Rohde & Schwarz GmbH & Co. KG; Trade names are trademarks of the owners.
Rohde & Schwarz USA, Inc. 6821 Benjamin Franklin Drive Columbia, MD 21046 1-888-837-8772 www.rohde-schwarz.us
Chris Scholz, Ph.D 11.2013
White Paper
Abstract This white paper provides an overview of both the virtual and true differential measurement methods. Examples are shown in both modeling theory and actual measurements of when the true differential method will provide a more accurate result versus the virtual method.
Table of Contents Abstract. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2
Virtual Differential Method Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3
Introducing the True Differential Method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4
Theoretical Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5
Measurement Verification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6 Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Rohde & Schwarz True Differential Measurements – Characterization of Balanced Devices
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1 Introduction Differential devices are used in a wide variety of applications, including almost all modern high-speed signals running on serial ports and computers. This includes hard drives, PCI express, USB – almost all of the modern standards are differential today. In addition, many components use differential or balanced designs including amplifiers, mixers, filters, and PCBs. The advantages of differential designs are many, including: J J J J
Noise immunity Reduced power consumption Less crosstalk Higher integration density
Differential devices however, also require special measurement capabilities. Traditionally a Vector Network analyzer (VNA) has been used to stimulate the device with an unbalanced signal and then mathematically transform the wave quantities into balanced S-parameters, essentially producing a “virtual” differential measurement. The virtual method can work well, but when active devices are driven into their nonlinear region the “virtual” method is no longer sufficient. Rohde & Schwarz has developed a method that more accurately evaluates the performance of differential devices. This method, referred to as “True Differential”, utilizes multiple coherent sources to stimulate the device with actual or “true” differential signals. For the first time devices can be tested more accurately using a true differential stimulus. This white paper provides an overview of both the virtual and true differential measurement methods. Examples are shown in both modeling theory and actual measurements of when the true differential method will provide a more accurate result versus the virtual method.
Rohde & Schwarz True Differential Measurements – Characterization of Balanced Devices
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2 Virtual Differential Method Overview Traditionally, when two-port (balanced) components were characterized with network analyzers, they used balanced (singleended) S-parameter results to mathematically calculate differential S-parameters with the set-up shown in Figure 1. This method uses only one source and measures the device as an unbalanced (single-ended) device, instead of stimulating it with a differential signal.
Figure 1 Traditional differential measurements switched a single source between the ports and mathematically created virtual differential measured results.
A signal or incident wave is applied at Port 1 (now a single-ended port) at every frequency point and the output signal (wave quantity) is measured at Port 3 (Figure 2a). The reflected wave is also measured at Port 1 as it is a single-ended port. The incident wave is next applied to Port 3 (reflected wave measured at Port 3) and the output is measured at Port 1. Therefore, when using the virtual differential measurement method the balanced/differential device would be measured as single-ended. This process is repeated for Ports 2/4 and 4/2 respectively, and in total 16 single-ended S-parameters (S11 to S44) are measured (Figure 2a). Next virtual transformers are created and virtual differential ports that correspond to the differential mode of the device on the test are generated (Figure 2b). Using the virtual transformer one can mathematically construct the differential response or the common mode response. The resulting calculation provides mixed mode S-parameters (Figure 2c). The virtual method works well when measuring passive circuitry such as transmission or high-speed data lines. It also works well when measuring RF power transistors and amplifiers as long as they are operating under drive conditions in which their performance remains linear. For devices exhibiting nonlinear characteristics, single-ended Port 1 and single-ended Port 2 are never simultaneously stimulated so the device is never driven the way it would be in actual operation. For example, a differential amplifier might reach its 1-dB compression point at an incorrect drive level, due to the transistor’s incorrectly characterized gain characteristics. However, the virtual method has until recently been the only one offered by network analyzer manufacturers for making these measurements because (among other challenges) it was extremely difficult to control the magnitude and phase of the two signal sources.
Rohde & Schwarz True Differential Measurements – Characterization of Balanced Devices
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Figure 2 Creating virtual differential measured results.
Figure 2a 16 single-ended S-parameters are measured
Differential-mode (ideally matched) → 100 Ω ( = 2*Z0 ) Common-mode (ideally matched) → 25 Ω ( = 0,5*Z0 ) Figure 2b Virtual transformers are used to generate logical ports
Naming Convention: S mode res., mode stim., port res., port stim. Figure 2c Mixed mode S-parameters are calculated
Rohde & Schwarz True Differential Measurements – Characterization of Balanced Devices
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3 Introducing the True Differential Method So what would be required to build a true differential measurement system? First we need to have two coherent sources. The two sources need to be phase coherent so that we can generate a reliable common mode or differential mode stimulus signal. While dual source measurements are not uncommon, such as in IP3 (third order intercept) measurements, the challenge of keeping the two sources phase coherent had not been addressed before. With coherent sources we can generate two out-ofphase signals or in-phase signals and inject them into the device at the same time, just like your device would be operating in the real world. The VNA would then measure the response to the true differential stimulus in the way the device would actually see it. The method developed by Rohde & Schwarz allows active RF and microwave differential components, such as amplifiers, to be stimulated with actual differential signals at frequencies as high as 67 GHz. This differential-mode signal then stimulates the device, and mixed-mode S-parameters are then directly calculated from the ratios of the error-corrected differential or commonmode wave quantities. Figure 3 shows how the true differential method works. A generator that generates two signals that are 180° out-of-phase, or in-phase for the common mode measurement, and injects them into the device. The power waves are measured the same as with the virtual differential method. However, for true differential measurements, the power waves are a response to a true differential stimulus. So you get the same description, the same values, the same A1s and same B1s, but their response is due to a different stimulus.
Figure 3 The true differential technique stimulates the device with two phase coherent signals simultaneously.
Rohde & Schwarz True Differential Measurements – Characterization of Balanced Devices
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The ability to produce two test signals – each with 0/180° of phase shift and independent of time or temperature variations – is significant because maintaining phase stability was one of the primary reasons why true differential measurement could not be achieved in the past. The R&S method is based on vector-corrected wave quantities and uses a patented technique to control the magnitude and phase of two or more internal sources. The sources generate two signals identical in magnitude and phase-shifted 0° or 180°, with phase uncertainty below 1° (Figure 4). R&S also offers solutions for multiport testing, with up eight phase coherent sources. This would allow for more than just two lanes at the same time, allowing the measurement of crosstalk. In addition, once the two measurement channels have been configured, a device can be evaluated simultaneously in both virtual and true differential modes. This can provide a great deal of insight into both of the measurement processes. The results may be viewed in real time, on the same plot, and often reveal the sometimes vast differences between the results. Finally, there are new measurements that can be performed with phase coherent sources that are not possible with the virtual mode. Test engineers may produce “non-standard” conditions that provide greater insight into device performance by conducting amplitude and phase imbalance sweeps. In the amplitude imbalance sweep, the instrument generates a balanced signal at one of its ports and the amplitude of one signal component may be varied based on the user-defined power sweep range. For the phase imbalance sweep, the instrument generates a balanced signal at one of its ports, and the relative phase of the two signal components may be varied according to the selected phase range.
Figure 4 R&S VNA’s equipped with option K6 make coherent signals of arbitrary phase and amplitude imbalance possible.
Rohde & Schwarz True Differential Measurements – Characterization of Balanced Devices
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4 Theoretical Verification Let’s look at a model based analysis using a simple bipolar differential amplifier with a few biasing resistors (Figure 5a). Using MATLAB to perform our analytical calculations we can compare the techniques by stimulating the amplifier with single-ended or differential and looking at the virtual and true differential results. The key variable to evaluate the two methods is the common-mode rejection ratio (CMRR). The CMRR of a differential amplifier (or other device) is the ratio between differential mode and common mode voltage gain: CMRR = Sdd21/Scc21 While an ideal differential amplifier would have infinite CMRR; this is not achievable in practice. A high CMRR is required when a differential signal must be amplified in the presence of a possibly large common-mode input. The CMRR is a very important specification, as it indicates how much of the common-mode signal will appear in your measurement and is key in reducing noise on transmission lines. In Figure 5b we show the feedback terms that will be varied in the evaluation of our model (a1, afb). By adjusting the afb term, or the feedback gain, one can set the CMMR of the device. In this model the afb can be adjusted to tune the CMMR from 0 to 30 dB. The results of the analysis are shown in Figure 6. The modeling shows that depending on the input power we can get a significant difference between the virtual excitation and the true differential excitation of the device.
< Figure 5a Amplifier model
Figure 5 Model of simple bipolar differential amplifier used for MATLAB analysis
Figure 5b Adjusting afb allows tuning of the CMMR from 0 to 30 dB
Rohde & Schwarz True Differential Measurements – Characterization of Balanced Devices
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Figure 6a No shared feedback (CMRR → 0)
Figure 6b Current sourced differential pair (CMRR →∞)
Figure 6 Increasing the input power under varying CMMR shows a significant difference between the virtual excitation and the true differential excitation results.
Rohde & Schwarz True Differential Measurements – Characterization of Balanced Devices
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5 Measurement Verification Next the bipolar differential amplifier was fabricated with the feedback term, Rε able to have values of 0 and 27 Ω. This enabled the CMRR of the differential amplifier to range between 0 and 16 dB depending on what resistor was used (Figure 7).
Figure 7 The fabricated bipolar differential amplifier enabled the CMRR to be at 0 dB or 16 dB by changing the feedback resistor.
Figure 8 shows the measured results of the differential amplifier for the two resistor values for both virtual and true differential measurements. Note that the results provide a very similar match to our theoretical predictions. In Figure 9 we can see very good correlation between the modeled and measured behavior as we vary the feedback factor. The difference between the virtual and true differential methods shows up to 3 dB difference depending on how hard the device is driven and the level of CMMR.
Rohde & Schwarz True Differential Measurements – Characterization of Balanced Devices
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Figure 8 Measured results of virtual and true differential techniques at both CMMR=0 and 16 dB.
Figure 9 Good correlation between the modeled and measured shows up to 3db difference between virtual and true differential depending on how hard the device is driven and the level of CMMR.
Rohde & Schwarz True Differential Measurements – Characterization of Balanced Devices
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6 Summary For the testing of passive components and other devices operating in their linear region, either the virtual or true differential method will deliver an accurate measurement. At both the theoretical and measurement level we showed the results of the two methods diverging when devices moved into their nonlinear region. As more and more differential RF amplifiers, RFICs, and interconnects are used in mobile communication devices (CMOS power amplifiers and transceivers, for example) choosing the correct method becomes more critical. The ability of true differential measurements to more accurately measure active device performance allows manufacturers of components, subsystems, and systems to create products that achieve excellent results under their anticipated operating conditions. Through its ability to correctly evaluate the performance of active devices when operating in their nonlinear region, true differential measurement capability enabled through Rohde & Schwarz VNAs will be increasingly important in the future. They allow virtual and true differential measurements to be conducted and the results displayed simultaneously to give designers insight into the performance of their devices and circuits. The process is simple, requires minimal operational intervention, requires no difference in calibration techniques, and is accomplished very quickly.
Rohde & Schwarz True Differential Measurements – Characterization of Balanced Devices
12
About Rohde & Schwarz Rohde & Schwarz is an independent group of companies specializing in electronics. It is a leading supplier of solutions in the fields of test and measurement, broadcasting, radiomonitoring and radiolocation, as well as secure communications. Established more than 75 years ago, Rohde & Schwarz has a global presence and a dedicated service network in over 70 countries. Company headquarters are in Munich, Germany. J Environmental commitment J Energy-efficient products J Continuous improvement in environmental sustainability J ISO 14001-certified environmental management system Regional Contacts North America 1-888-TEST-RSA (1-888-837-8772) [email protected] Latin America +1 410-910-7988 [email protected] Europe, Africa, Middle East +49 89 4129 123 45 [email protected] Asia/Pacific +65 65 13 04 88 [email protected] Rohde & Schwarz® is a registered trademark of Rohde & Schwarz GmbH & Co. KG; Trade names are trademarks of the owners.
Rohde & Schwarz USA, Inc. 6821 Benjamin Franklin Drive Columbia, MD 21046 1-888-837-8772 www.rohde-schwarz.us
