The methodology for the measurement of the knee voltage and maximum collector current for the linear operation of bipolar transistors is described and demonstrated on the horizontal current bipolar transistor (HCBT). Both limits are determined by measuring loadlines at 1-dB compression point (P1dB), wherein the hard-limiting nonlinearity occurs only in the positive half-wave of the collector current. The boundary defines the knee voltage, maximum collector current, and the transition between the two in which the onset of the Kirk effect takes place. It is found that the maximum collector current boundary saturates at a constant value for higher collector–emitter voltages and that there are the optimum load impedance and bias point for the maximum output power in the linear regime. They are found for HCBT, which achieves the output power of 21.25 dBm (P1dB) at 2.4 GHz, with the maximum collector–emitter voltage set to the open-emitter breakdown voltage of 9 V.

中文翻译：

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双极晶体管射频线性工作面积的测量

在水平电流双极晶体管 (HCBT) 上描述和演示了双极晶体管线性操作的拐点电压和最大集电极电流的测量方法。这两个限制都是通过在 1-dB 压缩点 (P1dB) 测量负载线来确定的，其中硬限制非线性仅出现在集电极电流的正半波中。边界定义了拐点电压、最大集电极电流以及两者之间发生柯克效应的转变。结果表明，对于较高的集电极-发射极电压，最大集电极电流边界在恒定值处饱和，并且在线性状态下存在最大输出功率的最佳负载阻抗和偏置点。它们用于 HCBT，其输出功率为 21。