Guoli Qu

New model extraction for predicting distortion in HEMT and MESFET circuits

A new method is presented for extracting Taylor series coefficients directly from IM measurements for modeling IM distortion in HEMT and MESFET circuits. It is based on an improved model that uses better simplifying assumptions. The method gives a substantially more accurate characterization, especially in the saturation region, required for amplifier designs.

Intermodulation nulling in HEMT common source amplifiers

A new model of the second- and third-order intermodulation products from HEMT and MESFET small-signal amplifiers, resulting from nonlinear drain-source current has been proposed in our previous publications. Based on this model, intermodulation nulling conditions in terms of the Taylor series coefficients, hence in terms of bias, have been investigated. This paper now examines the load dependence of the second- and third-order intermodulation products in HEMT small-signal common source amplifiers. Intermodulation nulling conditions are proposed and validated. This is useful in designing a high performance amplifier by calculation of optimum load for minimum distortion and studying distortion generation as a function of circuit topology.

Analysis of intermodulation nulling in HEMTs

This paper examines intermodulation nulling generated by the nonlinear current voltage characteristics of HEMTs. The conditions for intermodulation cancellation in terms of the coefficients of a two-dimensional Taylors series expansion are established and verified with measurement and simulation. Second and third-order intermodulation cancellation can be assessed by simple examination of the transconductance characteristics of the device. This permits routine selection of optional bias after characterising the devices.

Modeling HEMT intermodulation distortion characteristics

The significance of the nonlinearity of HEMT capacitance models to the prediction of intermodulation is investigated. Three capacitance models, one linear and two with contrasting nonlinear behavior, are shown to exhibit almost identical performance. It is concluded that the nonlinearity of the low-frequency model is the dominant distortion generating component. Development of capacitance models with accurate high-order derivatives is unwarranted without an accurate dc model. Therefore, careful characterization of the drain current description is most important for the successful circuit simulation.

Intrinsic dependence of intermodulation distortion in HEMTs

This paper analyses the intrinsic (the Taylor series coefficients) dependence of intermodulation distortion in HEMT (high electron mobility transistors) amplifiers. This analysis is very helpful for understanding the bias dependence of IM distortion since it critically depends on the bias dependence of Taylor series coefficients.

Validation of a new nonlinear HEMT model by intermodulation characterization

A new HEMT model is presented. The second and third-order intermodulation products of HEMT amplifiers are investigated at low frequency (50 MHz) and high frequency (1 GHz) respectively. Simulations performed with SPICE agree well with measurements. The contribution of nonlinear capacitance to intermodulation distortion is investigated.

Intermodulation cancellation in HEMTs

This paper examines intermodulation (IM) minima generated by the nonlinear drain-source current characteristics of HEMTs. This investigation is based on a more accurate intermodulation distortion model recently proposed by Qu and Parker (see The Proc. of 14th Australian Microelectronics Conference, p. 70-5, Oct. 1997). The IM cancellation conditions in terms of the Taylor series coefficients are established and verified with measurement and simulation. Second and third-order intermodulation cancellation can be assessed by simple examination of the transconductance characteristics of the device. This permits routine selection of optional bias after characterising the devices.

Intermodulation Distortion Simulation with a New MOSFET Model

The second-and third-order intermodulation products of MOSFET amplifiers are investigated with a new MOSFET model, which has been implemented in SPICE3f4. Simulations performed with the new model agree well with measurements.

Measurement and simulation of IM distortion in high mobility transistors

This paper reports the characterisation of intermodulation (IM) distortion in high electron mobility transistors (HEMTs). The second- and third-order IM products in HEMT common-source amplifiers are measured and simulated comprehensively. The comparison of measured and simulated IM products as a function of gate-source voltage, drain-source voltage, input level as well as load impedance are reported. Excellent agreement between measurements and simulations is achieved.

S-parameter simulation with a new MOSFET model

This paper presents a new MOSFET model, which has been implemented in SPICE3f4 for verification and testing. The DC and S-parameters of a MOSFET are measured and simulated. Simulations performed with the new model agree well with measurements.