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Linear and Nonlinear Compact Transistor Modeling

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Maury and AMCAD complete the cycle from Pulsed-IV and S-Parameters, to Linear and Nonlinear Compact Transistor Models, and Harmonic Load Pull for model validation !

Introduction


Amplifier designers have been making use of modern transistor models since their first appearance in the mid-1970s. Models have allowed engineers to create advanced designs with first-pass success, without the need for multiple prototypes and design iterations. But with so many different modeling techniques, how does one select which one to use?

Compact transistor models, based on measured IV and S-parameters, allow designers to shift focus from transistor designs to circuit designs. Extracted from quasi-isothermal pulsed IV and pulsed S-parameter data and validated with load-pull characterization, compact transistor models contain a reduced set of parameters. Unlike other model types, compact models take into account complex phenomena, such as electro-thermal and trapping effects. For simulations under nonlinear operating conditions, responses to complex modulated signals (such as EVM or ACPR) are accurately predicted as low-frequency and high-frequency memory effects are taken into account. Compact transistor models are ideal for die-level applications, as developing such a model from IV and S-parameters is straightforward and relatively quick.

 



Typical Pulsed IV Curve Traces

Press Release


Maury Microwave And AMCAD Engineering Announce A Development And Distribution Partnership For Advanced Measurement and Modeling Software and Pulsed IV Systems +

Cables and Assemblies of Cables React Quickly with Great Results

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The RF is cable is a cable that offers easy use. The RF cable can slide into the socket and pulled out easily. There are other versions or types of RF cables too. These types can include screwing up the cable and so on. The type of the screw may be more secure, but it is also of difficult use and not convenient. The best point in using the RF cable is to have a cable that is not so expensive. These are affordable cables. There are qualities of certain nature in affordable prices too.   There are the other forms of cables too. There are also the assemblies of cables.  There is the RF Cable assembly, the Microwave Cable assembly or a phaseflex cable assembly. The RF Cable assembly, the Microwave cable assembly or a phaseflex cable assembly is made by making an assembly of the wires.

The assembly of wires can be made according to specific designs and so on. The design diagram or the plan to make the RF Cable assembly, the Microwave cable assembly or a phaseflex cable assembly is made according to the specifications required or needed. The RF Cable assembly, the Microwave cable assembly or a phaseflex cable assembly may be different kinds, but the basic structure of design is usually the same. The cables are arranged and cut according to the size that is needed. These are then joined together and the lose metal ends are connected. These are then assembled on a board to make an assembly. Finally the assembly is sleeved to protect it. These assemblies are also designed for safety purposes and also for the ease in use that they provide. Moreover the cost and the time of installing are also saved.

The working and performance can be checked through a test board. The VNA cables are also a kind that is reliable and accurate kind of cables. VNA Cables needs to be reliable and accurate. There is no way they are not so. The reason is this that the VNA needs to give reliable and perfect results. The VNA Cables are designed for this main purpose. The Phase Stable Cable is also the kind that needs to be as accurate and good performance giver as can be. The phase stable cable, for the stability of the phase needs to be heat resistant and flexible too. These qualities are in good quality Phase Stable Cables.

Cables and Connections are Co-related to Each with Maximum Outputs to Generate

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An RF cable is an option for cable that caters to a variety of connection use. Only where there is no option to use an RF cable is available, other sorts may be used. It is used for connecting the aerial to the TV and an RF cable is used to attach gadgets to gadgets, for example a TV with a VCR. A cheaper quality may be used for this purpose. For other purposes, a better quality must be preferred. The RF Cable assembly, the Microwave cable assembly or a phaseflex cable assembly can also be used for the specified purpose. There are at times demanding conditions of the task at hand or where The RF Cable Assembly, the Microwave cable assembly or a phaseflex cable assembly is required. There may be a need for flexing and there may be several levels of temperatures that The RF Cable assembly, the Microwave cable assembly or a phaseflex cable assembly would have to hold. In these cases a good manufacture is the best option. There are many manufacturers available for the manufacturing and assembling of these so many kinds of cables. There are manufacturers giving all kinds of guarantees.

The various claims however are to be taken logically and objectively. After all it is a matter of spending money and an investment you don’t want to get into again and again. The consistency in performance is the achievement that should be seen. The product with more consistency is the one that may be called as more reliable too. For example if the use of a gadget requires frequent connecting and disconnecting, the wires and assemblies should be strong enough. The cables need to be reliable. For some gadgets and works, these requirements are increased. For example in the case of VNA, the VNA Cable has to be so. The differences in results of ordinary and customized VNA cables are obvious. This has been tested and verified numerous times. Using high performance VNA Cable can show a major shift in results obtained.  Another kind may be the phase stable cable. This kind i.e. phase stable cable requires to be as much in line with the same requirements as of any good reliable and stable cable.

The unstable cable has damaging effects of systems, system performance and on the measurements. The accuracy of measurement cannot be guaranteed by low performance cables. So the phase stable cables must be of a good quality for accuracy.

A SUB 1 W LOAD-PULL QUARTER-WAVE PREMATCHING NETWORK BASED ON A TWO-TIER TRL CALIBRATION

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Transistors used for cellular and PCS infrastructure applications are required to amplify signals with a peak-to-average ratio that can exceed 13 dB, resulting in a peak envelope power (PEP) approaching 1 kW. This PEP requirement is a consequence of simultaneous amplification of multiple digitally modulated carriers with a time-varying envelope and requires a load resistance in the neighborhood of 0.3 W. Present load-pull technologies based on mechanical tuners is limited to approximately 1 W at cellular and PCS frequencies, which renders these systems incapable of characterizing transistors under these conditions. Quarter-wave prematching networks have been developed to transform the source- and load-pull domains to lower impedance. A variety of techniques have been used to characterize these quarter-wave networks, including standard vector network analyzer (VNA) error correction. This article presents a further refinement of this characterization technique, which is based on a twotier calibration using 7mm and microstrip thru-reflectline (TRL) calibrations.
RF power amplifiers deployed with first-generation cellular base stations were based on cavity combiners and class C-operated silicon bipolar junction transistors for final-stage devices. Up to 10 independent carriers, each constituting one user typically was combined prior to feeding the antenna. This architecture, coupled with the constant envelope property of FM, virtually eliminated the need for linear transistor operation. However, the linearity requirements placed on transistor performance for second- and third-generation wireless base stations are much more demanding. Wireless service providers require that base stations occupy as little volume as possible and, with the adoption of digital modulation; many carrier signals now have a timevarying envelope. The first requirement implies the elimination of the cavity combiner, thereby requiring simultaneous amplification of several carriers. The second requirement implies that quasilinear class AB amplification be used to maintain the integrity of the modulation envelope.
These changes have drastically changed the way in which high power transistors are characterized. Simultaneous amplification of several carriers, each with a time-varying envelope, results in a peak-toaverage ratio that can exceed 13 dB, leading to a PEP demand approaching 1 kW. At the standard 26 V base station supply voltage, a load resistance in the neighborhood of 0.1 W  is required for generating closed load-pull contours of power, gain, poweradded efficiency and adjacent-channel power rejection.

Present high power load-pull technology is based on either active fundamental re-injection or mechanical tuners1-4. Although in principle an active load-pull system can present an arbitrary load impedance, the architecture of these systems is not amenable to generating the extremely high power necessary to emulate a sub 1 W load at 1 kW PEP. The current state of the art in mechanical tuners is limited in resistance to approximately 1 W, although narrowband systems can go lower5. To overcome the limitation posed by mechanical tuners, many researchers have adopted quarter-wave prematching networks to transform the tuner impedance to lower impedance. With this approach, it is possible to present a sub 1 W resistance necessary for high power transistor characterization.

Traditional Noise Parameter Measurements

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A traditional noise parameter measurement setup, it includes a vector network analyzer (VNA) and a separate noise figure analyzer. For s-parameter measurements, the tuner is set to 50 ohms, and the two RF switches connect the device under test (DUT) to the VNA. For noise measurements, the switches connect the noise source to the DUT input and the noise receiver to the DUT output. An optional load tuner (not shown) is sometimes used when the DUT is highly reflective, to reduce sensitivity to error.

The tuner is pre-characterized at every frequency independently. This means that there is a unique set of tuner positions for each frequency, ensuring a good spread of source impedance points at every frequency. The tuner can be characterized separately, or as part of an in-situ system calibration. The advantage of doing it separately is that the same tuner file can be used for a long time, and then a hybrid in-situ calibration can quickly get the remaining s-parameter blocks.

The in-situ system calibration normally uses two VNA calibrations: a 2-port calibration at the DUT reference planes, and a 1-port s22 calibration at the noise source reference plane. By subtracting error terms, the 2-port x-parameters from the noise source to the DUT can then be determined. If the optional load tuner is used, then a 1-port s11 calibration at the noise receiver reference plane is also used to determine the 2-port s-parameters from the DUT to the noise receiver.

A hybrid in-situ calibration uses tuner data that is already characterized. The same VNA calibrations are still used to determine the 2-port s-parameters from the noise source to the DUT plane, which are then de-embedded to remove the tuner s-parameters. The result will be s-parameter blocks that include everything except the tuner.

After the system TRL calibration, the traditional noise receiver calibration and DUT noise parameter measurement are both done one frequency at a time[3][4]. This is because the noise parameter extraction involves complex math that is sensitive to small errors, and the pattern of source impedance points is important to get well-conditioned data[2]. Measuring one frequency at a time solves this by allowing the impedance pattern to be selected in an optimal manner for each frequency.

Pulsed IV testing to precisely measure the RF Devices

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There are various methods characterizing the devices working on the signal networks using RF and other frequencies. Pulsed IV is one of the methods used for testing the devices working on electronic signals like as microwave and RF frequencies.  This can be applied to test and specify the characteristics of the DUT after carrying out the calibration process carefully.

The testing procedure that uses the Pulsed (IV) current has become more prevalent these days for evaluating performance of the semiconductor devices. This process of testing uses pulse sources that is supplying a current pulse to the device under test and do the measurements with pulse measurement device. The technique of Pulsed IV measurement is used mainly on the large signal analysis.

This method is useful and effective over the other methods as it is cost effective and don’t give negative effects like as self heating and transient trapped charges. The factors like as self heating and trapped charges can be producing misleading results of the tests. The pulsed IV testing process delivers the accurate data on the devices needed to improvise the devices. This is best suitable to measure the test results in RF devices like as the transistors, switched and amplifiers relating to nonlinear responses.

There are two types of test methods used for testing in the pulsed environment; i.e. pulsed IV sweeps and transient (single pulse) testing method. If the DUT is associated with the double channels including pulse source and a pulse measurement system the results can be recoreded easily. This makes it very cost effective.

The results produced under different biased conditions for the Pulsed IV measurement sweeps carried out in pulsed system can be easily compared with the results produced in DC tests. The graphs of the curves produced by showing drain voltage VD and drain current ID behavior under different bias conditions are similar to that of the pulsed testing.

The basics of the pulsed IV testing are set to provide the pulses with non-zero value for both gate and drain voltage, often referred to as the operating point or quiescent (q) point. This technique is very useful for condition and based on the applicability of the low-duty-cycle pulse to the DUT. This helps in avoiding the self-heating and carrier-trapping effects that can deviate the exact results. The method of  load pull testing is used to support the test results of overall measurements carried for a device.

The pulse width that is used in this technique ranges from milliseconds to nanoseconds.  The selection of the pulse widths depends upon the DUT, materials and test parameters. The standard source-measure units (SMUs) are usually used to measure the results on millisecond pulse widths. The shorter pulses (microseconds to nanoseconds) are generally more effective for avoiding self heating and charge-trapping effects. Therefore, short-pulse pulsed I-V testing of RF transistors generally allows the creation of more useful models.

THEORY OF LOAD AND SOURCE PULL MEASUREMENT

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Load pull consists of varying or “pulling” the load impedance seen by a device-under-test (DUT) while measuring the performance of the DUT. Source pull is the same as load pull except that the source impedance is changed instead of the load impedance.

Load and source pull is used to measure a DUT in actual operating conditions. This method is important for largesignal, nonlinear devices where the operating point may change with power level or tuning. Load or source pull is not usually needed for linear devices, where performance with any load can be predicted from small signal x-parameters.

Calibrating to measure output power and gain consists of measuring the available input power at the power source reference plane and the coupling value of the directional coupler. If the coupler had perfect directivity, then coupling could be measured with only a short at the source power reference plane. However, finite directivity causes the apparent reflection to vary with reflection-phase, so a more accurate coupling value is found by taking the average of both short and open measurements. This minimizes directivity errors, although good coupler directivity is still important for the best accuracy.

Once the available input power and coupling are known, the output power, transducer gain, and power gain can all be measured with any combination of source or load impedance. Output power is the power delivered to the load. Transducer gain is the ratio of delivered output power to available input power. Power gain is the ratio of delivered output power to delivered input power.

The objective of the measurement is to get the power and gain values at the DUT reference planes. Although the tuners are very low loss, bias tees and other components may be included as part of the “ stub tuner” characterization, so the loss must be considered. To get the output power at the DUT reference plane, the dissipative loss of the load tuner is added to the raw measured output power. To get the available input power at the DUT reference plane, the dissipative loss of the source tuner is subtracted from the calibrated available input power. To get the delivered input power at the DUT input reference plane, the reflected power at the source is subtracted from the calibrated available power at the source. The dissipative loss of the source tuner is then subtracted from the result to shift from the source power reference plane to the DUT input reference plane.