tailieunhanh - Nonlinear Microwave Circuit Design phần 4

Một giải pháp đơn giản bao gồm các mạch kết hợp, trước đó là, trở kháng biến áp, giữa DUT và bộ chỉnh, giải pháp này cho phép một độ chính xác tốt hơn trong khu vực được chuyển đổi. cung cấp năng lượng đầu vào tương ứng cao hơn được cung cấp, không có cải tiến phù hợp với thu được. | 108 NONLINEAR MODELS In the third one the device is biased at many points along the curve at each point the differential small-signal conductance is measured by a microwave admittance measurement. In practice small-signal S-parameter measurements are performed and the reflection coefficients are converted to admittances. The small-signal conductance corresponds to the tangent of the fast measurement performed from that bias point Figure . This is easily seen by considering the measurement set-up for large-signal fast measurements and comparing it to a standard vector network analyser. Once the smallsignal conductance is evaluated for all bias points the current curve is computed by integration with respect to voltage. Let us now discuss the three measurements. The DC curve must be used for the simulation of slow or constant phenomena as the DC bias or rectified voltages and currents the low-frequency second-order intermodulation signal in multi-tone systems or the down-converted phase-noise in oscillators when their frequency is very low below approximately 100 KHz . The pulsed curves must be used for the simulation of microwave large signals in this case the curve must be measured from the same quiescent point as that of the large-signal operation. This is however in general not predictable since it includes rectified terms see Chapter 1 the model must then include the curves measured from all quiescent points and must be able to adjust to the actual quiescent point obtained in the analysis. The curve obtained by the integration of the small-signal measurements finally is not physically correct and should never be used. Unfortunately this is a popular method to extract nonlinear models because it is also the most practical and traditional from the point of view of both instrumentation and extraction procedure. A complete measurement set-up for DC small-signal and pulsed S-parameter measurement has been demonstrated 63 allowing consistent modelling however it