Vicentiu I. Cojocaru

A 24GHz Low-Cost, Long-Range, Narrow-Band, Monopulse Radar Front End System for Automotive ACC Applications

This paper presents details and results of the development of a low-cost, narrow-band, long range radar (LRR) front end system at 24 GHz, intended for autonomous cruise control (ACC) and other medium and long-range automotive applications. The system uses a high directivity patch array Tx/Rx antenna and a low-cost, high sensitivity RF front end. The narrow band, pulse radar concept is well suited for the applications envisaged, avoiding at the same time some well known regulatory issues related with existing UWB short range systems. The accurate azimuth detection functionality has been implemented by employing a phase/amplitude comparison monopulse solution using a dual receive patch-array antenna. Key performances currently achieved with the new system include: range detection of up to 120 meters for regular car size targets, azimuth detection range of plusmn 8deg, with azimuth accuracy better than 0.3deg. The successful realization of such low-cost, long range radar system at 24 GHz could potentially lead to two important developments in the near future: the implementation of the new radar technologies into the lower class, high volume car market and challenging the dominance of the much more expensive ACC systems currently developed at 77 GHz.

Improved prediction of the intermodulation distortion characteristics of MESFETs and PHEMTs via a robust nonlinear device model

The paper investigates the intermodulation distortion (IMD) prediction capabilities of the COBRA model by analysing the first, second and third order derivatives of the drain I/V model and the gate Q/V model. The model is extracted simply from DC and small-signal S-parameter data, without the need for complex low-frequency (VHF) measurements of harmonic output levels under low-load conditions, as proposed in previous studies. The computed main I/V characteristic and its derivatives are shown to be continuous over the entire bias plane, and are proven to give better results than other models available. Results of two-tone large signal tests for the case of a 0.2 /spl mu/m PHEMT process are presented, showing excellent agreement between simulated and experimental third and fifth intermodulation products.

A Large-Signal Equivalent Circuit Model for Hyperabrupt P-N Junction Varactor Diodes

A large-signal equivalent circuit model is presented for a hyperabrupt p-n junction varactor diode (HJVD), suitable for nonlinear CAD and computer simulation. A new function is proposed to describe the nonlinear dependence of the junction capacitance on the applied voltage. Experimental measurements on several commercial devices are presented, showing excellent agreement with the model proposed, over a very wide range of applied voltages. A physical investigation of the doping profile of hyperabrupt p-n junctions is made and a method to determine the doping profile parameters for an assumed type of dopant distribution is presented. Finally, validation of the model is demonstrated in two particular applications.

Modelling the gate capacitances of MESFETs and HEMTs from low-frequency C-V measurements

A novel modelling technique is presented to describe the gate capacitance non-linearities of MESFETs and HEMTh. The method is based on a set of low-frequency C-V measurements and new empirical expression for the bias-dependent gate-to-source and gate-to-drain capacitances. Extraction of the model parameters follows a two-step curve-fitting procedure and the method is equally applicable to C-V data extracted from small-signal S-parameter measurements. The model is tested on a number of commercial devices, both MESFETs and HEMT, showing a better agreement with experimental data then previous models. Finally, the model proposed gives a very accurate description of the total gate capacitance at zero drain-to-source voltages and this leads to a simple and fast technique to determine the approximate doping profile of the active channel.

Scaleability of DC/AC non-linear dispersion models for microwave FETs

This paper addresses the issue of scaleability in circuit based models for FETs, emphasising for the first time the particularly difficult problems associated with the scaleability of DC/AC dispersion phenomena. Results of a study carried out on both MESFET and PHEMT foundry processes, show that while the differential DC/AC transconductance obeys straightforward scaling rules, the output conductance does not. An equivalent circuit based solution that incorporates a differential DC/AC dispersion modelling methodology is presented. The solution is compact, obeys the required conservation constraints and can account for the scaling inconsistencies observed in the output conductance.

Parasitic resistance extraction errors with implications for FET model accuracy around V/sub ds/=0

The accuracy of non-linear FET models around the origin in the V/sub gs/-V/sub ds/ bias plane, may be seriously affected by errors in the extracted values of the source and drain parasitic resistances. In this paper we present test results that prove how relatively small errors of this kind, which can be easily encountered when using conventional extraction techniques, can lead to large errors in the values extracted for some intrinsic parameters, and in particular for the two gate capacitances. The source of these errors is investigated and, as a solution, an improved extraction methodology is offered, which substantially reduces the risk of such errors.

Non-linear modelling of microwave PIN diode switches for harmonic and intermodulation distortion simulation

The paper presents for the first time a practical and relatively simple non-linear modeling solution for /spl mu/-wave PIN diodes for use in harmonic balance (HB) circuit simulators. It enables very good prediction performance of the very important harmonic and intermodulation characteristics of these devices when used in typical /spl mu/-wave switching applications. Accurate harmonic distortion measurements have been performed on a number of commercial surface mount PIN diodes, over a wide range of relevant bias conditions and RF power levels. Parasitic elements are first extracted from microwave S-parameter data. Separate non-linear circuit models are then used for the ON and OFF states of the PIN diodes, and these are directly optimized on the measured harmonic distortion data using a dedicated modeling platform developed within a commercial modeling software tool. The new models have been implemented and tested in a popular harmonic balance circuit simulator with very good results. The modeling solution described here can be also applied to other active devices for similar large-signal modeling problems.

24 GHz LTCC I/Q Mixer Using Packaged HEMTs

An I/Q active mixer in LTCC technology using packaged HEMTs as mixing devices is described. A mixer is designed for use in the 24 GHz automotive radar application. An on-tile buffer amplifier was added to compensate for the limited power available from the system oscillator. Careful choice of the type or topology for each of the passive circuits implemented resulted in an optimal mixer layout, so a very small size for a ceramic tile of 15times15times0.8 mm3 was achieved. The measured conversion gain of the mixer for a 0 dBm LO level was -6.7 dB for I and -5.2 dB for Q. The amplitude imbalance between I and Q signals resulting from the aggressive miniaturization of the quadrature coupler could be compensated in the DSP stages of the system at no additional cost. The measured I-Q phase imbalance was around 3 degrees. The measured return losses at mixer ports and LO-RF isolations are also very good.

Accurate Substrate-Related Packaged Transistor Modeling for 24GHz Circuit Design

S-parameter measurements of packaged transistors are performed in dedicated microwave test fixtures and they provide the S-parameters with respect to reference planes usually extending to the transistor capsule. Most packaged transistors have typically an extra piece/length of the metal leads extending further from those reference planes, underneath the capsule, to enable the connection of each of the leads with the encapsulated transistor die. During measurements in a common test fixture these extra metal pieces remain basically suspended in the air. When a transistor is placed on a microwave substrate the leads are usually resting on transmission lines printed on the top layer. As a result, the overall electrical conditions regarding the transistors leads and package will differ to those present in the test fixture. This paper presents results showing how severe the impact of these lead extensions can be in the case of a 24GHz 2-stage amplifier design. It is shown how the extra package lead lengths can be accurately modeled with S-parameter blocks generated with an EM simulator. The demonstrated modeling method can lead to significant reductions in the number of design cycles at 24 GHz

Planar Antenna Design for Long Range Radar Applications

This paper describes the design of a high gain planar antenna on lossy substrate for use in long range radar applications in the 24GHz ISM band. This is significant since most current vehicle radars operate in the 77GHz frequency band, but as technologies for lower frequencies are less, the system should be cheaper. The paper discusses requirement in the design evolution from prototype to integrated system and uses the overall radar cost as a design parameter. Lastly measured results are presented and an indication of how the design is incorporated into the overall system is given.