It has been found that the analytical extraction methods cannot be applied to the usual test structure of the switch high electron-mobility transistor (HEMT) with a large-value gate grounded resistor. The significant effect of the precise multicapacitive current path on switch model precision has also been found. The multicapacitive current path here is different from the seemingly similar hypothesis proposed for the distributed parasitic effects at high frequencies (eg, D-band). In fact, for switch based HEMT, it is important to distinguish between the capacitive current paths accurately even at relatively low frequencies. Due to the existing of the large gate resistance, the usual capacitance mix decreases the accuracy of the switch model significantly. Thus an analytical method has been developed to calculate parasitic capacitances (the capacitance to ground and the interelectrode capacitance) through full-wave electromagnetic analysis. For practical applications and further verification, the whole HEMT switch small-signal models and the direct extraction methods are presented. The simulated results fit well with the measurements up to 40 GHz. K E Y W O R D S electromagnetic analysis, high electron-mobility transistor, interelectrode parasitic capacitance, microwave switches, small-signal model 1 | INTRODUCTION In 1988, Dambrine et al.proposed an analytical way to extract FET small-signal equivalent circuit parameters. 1 All the parasitic parameters were analytically extracted by using cold-FET method. After de-embedding all the parasitic effects from the whole S parameters, the intrinsic parameters were calculated by analytical equations. 2 De-embedding methods, cold-FET techniques, and analytical equations 3 are used by lots of FET small-signal model extraction methods today. Note that Reference 1 also has some limitations, for example, the pinch-off intrinsic model used to determine the parasitic capacitance parameters tends to overestimate the value of the drain to ground capacitance (C pd ). The high positive gate bias condition used to determine the parasitic inductances and resistances have the potential to destroy the gate Schottky diode. 4 In addition, for high electron-mobility transistors (HEMTs), it is difficult to apply enough high gate bias to ignore the gate capacitance effect. 5,6 Many works are making improvements to meet the needs of new semiconductor technologies and new applications like high frequency applications. 7-11 The small-signal modeling is also the basis of the large-signal and noise modeling. [12][13][14] As stated above, lots of articles and effort has been dedicated to common-source FET small-signal modeling, but high-frequency switch FET small-signal modeling is still difficult. Very few works concern switch FET small-signal modeling. [15][16][17][18][19][20][21] Numerical solutions concern intrinsic effects only and are difficult to meet measured behavior. [15][16][17] The simplified equivalent circuits cannot capture full feature of the switch HEMT at high frequencies. 18,19...
The recent modernization of the livestock industry lags behind the scale of the livestock industry, particularly in indoor environmental monitoring. In particular, the H2S gas concentration in chicken coops affects the growth and reproductive capacity of the chickens and threatens their health. Therefore, the research and development of a low-cost, environmentally friendly sensor that can achieve on-line monitoring of H2S gas has a notably important practical significance. This paper reports the design of an H2S gas sensor, with selection of an electrochemical probe with high accuracy and wide measurement range using the relatively mature technology of electrochemical sensors. Although the probe of the sensor is the main factor that affects the sensor accuracy, the probe must be combined with a specifically designed signal condition circuit that can overcome the lack of an electrode to satisfy the requirements for the interconnection and matching between the output signal and the test instrument. Because the output current of the electrochemical electrode is small and likely to be disturbed by noise, we designed signal-conditioning modules. Through the signal-conditioning circuit, the output signal of the current electrode can be converted into a voltage and amplified. In addition, we designed a power control module because a bias voltage is necessary for the electrode. Finally, after the calibration experiment, the accurate concentration of H2S gas can be measured. Based on the experimental analysis, the sensor shows good linearity and selectivity, comparatively high sensitivity, perfect stability and an extremely long operating life of up to two years.
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