What is DC biasing? If in terms of how a device is supplied with electricity, it is a method of providing a fixed value of either voltage or current.For instance, a power supply gives a constant value of voltage or current. A parametric analyzer sweep a value, and it is used to obtain the DC transfer function. Now, nothing prevent people using an SMU to bias a circuit (i.e.use it as power supply). If instead of sweeping a voltage (or current) have the SMU set to deliver a fixed value. A SMU provides a voltage and current,it is controlled in a way that you can sweep either. So SMU can be used as a DC supply or to characterize device in DC. From diodes prospective, biasing accounts for: Externally applying a diode a DC voltage source, which is presented by a battery, there will be a pn junction potential formed internally. Thus the current is conducted only in one direction, but blocked in the opposite direction. This is how forward-biased and reverse-biased de_ned.[11] From BJTs prospective, bias-ing means externally providing each terminal with a constant voltage value by externally connecting to a DC voltage source which can be batteries or DC power supplies. Because BJT has three terminals, its DC supply voltages are normally indicated as: VEE, VBB and VCC. ..Figure 8.1: A transistor is characterized by the relationships between currents and voltages at both input and output. The Input Characteristics is the IV characteristics curves that are measured at the emitter base junction.Iin = f(Vin). The Output Characteristics is the IV characteristic curves that are measured at the base collector junction.A SMU provides a voltage and current, it is controlled in a way that you can sweep between specified values. So it can be used as a DC supply or to characterize device in DC. indicated as: VE, VB and VC, respectively. Two junctions voltages VEB and VBC are formed by its three terminals VE VB VC, respectively. For the former junction VEB, forward-biased (VEB > 0) is always needed in order to switch on the device. But for the later junction VBC, both forward-biased (VBC > 0) and reverse-biased (VBC < 0) are possible. The two biasing conditions will result in two complete di_erent operation modes. One is the saturation mode,which is used in digital electronics. The other is the active mode, used in analogue electronics. When VBC is forward-biased(VBC > 0), BJT is used as a switch in digital electronics. When VBC is reverse-biased (VBC < 0), BJT is functioning as an ampli_er in analogue electronics. [11]The established constant values at BJTs three terminals are named as: the bias point or the quiescent point (Q-point) or the DC operating point. The Q-point can be further stabilized against and temperature by replacing the Bias Schemes, such as : voltage divider bias , emitter feedback bias, current source bias...etc. The position of the DC voltage level decides if the waveform of the AC signal that fed in the input port can expand its fully swing( amplification) without being clipped the output port. To put it simply, when a BJT is biased, regardless its operation modes, all its threes terminals are provided with constant values of voltages and currents.[11] From amplifiers prospective, it does not matter what is inside the black box. What does matter is the connection outside the black box.[37] "Biasing" refers to all the external power supply networks or circuits arrangement that connected to its input and output ports to ensure the constant (V, I) levels. Figure 8.2: The _gure on the top left is the input characteristics, which plots IB versus VBE with a constant VCE. Where IB is an exponential function of VBE.The input bias point Qin(VBE, IB) is determined from the intersection between the input load line and the input characteristics. The figure on the top right is the output characteristics, which plots IC versus VCE with IB as the varing parameter. The output bias point Qout(VCE, IC) is determined. The output bias point Qout (VCE, IC) is the intersection between the output load line and the output characteristics. The two schematics below are for DC biasing BJT in CE con_guration. In the measurement of output characteristics, instead of forcing a voltage source VBB to the base, a current source IB is employed. The replacement in the bias current source at the base is to prevent the self-heating effects. 65
Figure 8.3: The graphic analysis of determining the Q-point of the input loop is presented here. Two plots are involved during the analysis process. One is the input characteristics from the the CE con_guration of BJT, which plots the relationship between IB and VBE with a constant VCE. The other is the load line, which is governed from the KVL around the input loop. Both plots intersects at the statics input operating point Qin(VBEQ; IBQ).
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（德国之声中文网）莫名其妙、遮遮掩掩、"官僚怪兽"、漫无头绪：对管理外国劳工移民德国的众多法规，社民党议会党团内政发言人布尔卡德· 利施卡（Burkhard Lischka）找不出好的形容词。对既非欧盟公民，也非难民，而是到德国来工作的外国人，德国有50种不同的居留许可。利施卡评价说："即便法律系毕业，也没法闹明白。"
"一场噩梦"，哈妮·尤素福（ Hani Yousuf ）谈起和德国当局打交道的经历时这样说道。这位巴基斯坦记者生活在卡拉奇。在接受德国之声电话采访时，她越说越生气。6年前，她向德国当局递交了到德国工作半年的签证申请。德国使馆工作人员既不愿提供帮助，也不灵活机动，而且"非常不礼貌"，哈妮·尤素福这样说道。虽然她最后获得了签证，但这一切留下了不愉快的记忆。有了这次经历之后，她没什么兴趣再来德国工作了。"除非是提供特别好的条件"，哈妮·尤素福补充道，"否则我宁愿去加拿大，在那里，技术移民会受到相应的对待。"
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