Verify the characteristic frequency fT of the transistor using a high-frequency signal source and a 500 MHz bandwidth oscilloscope. Where fβ is approximately equal to 1.4 MHz. When the output signal amplitude drops by 3 dB (peak-to-peak value drops by half), record the output frequency fβ of the signal source, indicating the cut-off frequency of the transistor at the current working point.Īt 1 kHz, the AC OUT output peak-to-peak value is approximately 38 mV, and at 1.4 MHz, the AC OUT output peak-to-peak value is approximately 19.2 mV.Ĭalculate the characteristic frequency fT of the transistor using the gain-bandwidth product formula: Gradually increase the output frequency of the signal source from 1 kHz, and observe the amplitude of the AC OUT signal on the right side of the experimental board using the oscilloscope. Measure the transistor’s cut-off frequency fβ and calculate its characteristic frequency fT using the “gain-bandwidth product” method. When the effective value of the voltage between the two terminals of R1 measured by the oscilloscope is 50 mVrms, and since R1 = 100 kohms, Ib is approximately equal to 0.5 uA. Set the signal source output to a 1 kHz sine wave and change the output amplitude. Calculate the effective value of Ib current so that Ib is approximately equal to 0.5 uA. Set the signal source output to a 1 kHz sine wave, adjust the signal source output signal amplitude, and use oscilloscope channel 2 to test the voltage waveform between the two terminals of R1 (connect the banana head interface marked as Input). The h-parameters of the transistor reflect the small-signal AC characteristics of the transistor under certain fixed static conditions.Ĭonnect the signal generator output to the BNC interface on the left side of the experimental board’s AC IN, and connect the oscilloscope Channel 1 to the BNC interface on the right side of the experimental board’s AC OUT. Where Ib and Vbe are the input variables of the transistor, and Ic and Vce are the output variables. With a reasonable setting of the static operating point and an AC small signal input, the transistor can be equivalent to a linear two-port circuit, represented by AC components of current and voltage. Once the base current separates, the transistor will turn off, so this phase is called the cutoff region, and the VBE may be around 600mV. Moreover, the collector-emitter/collector-base terminals are capable of handling typical voltages of 40V and 60V respectively. This particular stage is referred to as the saturation region. When the 2N3904 NPN transistor is completely biased, it permits a maximum of 200mA to flow through two specific terminals, namely emitter and collector. Once the current supply is given to the base terminal, the transistor can be biased. The maximum current supply across the collector terminal is 200mA, so loads consuming more than 200mA cannot be connected via this transistor. The high gain value of the 2N3904 transistor is 300, which determines its amplification ability. Similarly, once a signal is given to the base pin, it will be forward biased. If the base pin is connected to the GND terminal, both the emitter and collector terminals are reverse biased or left open.
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