A method to determine if the transistor can amplify the AC signal

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determine if the transistor amplification circuit has a way to amplify the AC signal:


There are three basic configurations of transistor amplification circuit: Co-injection set circuit, common collector circuit, common base circuit. Regardless of which application configuration amplification circuit is involved, it must be guaranteed to have AC amplification capability. The following trigger from three points, you can determine whether a transistor has AC amplification capability.

1. The transistor must have a suitable working point
The proper working point needs to be calculated quantitatively. Only the qualitative judgement of its capacity for AC amplification, the key to see if the transistor is to meet the positive deviation of the emitter, collector reverse bias. It is possible to have AC amplification capability, for NPN pipes, ube>0, ubc<0, for PnP pipes, ube<0, ubc>0.

2. Input signal UI cannot be short-connected
If the UI is shortened, the current is cut short. Can not be added to the transistor to zoom in. The UI is an AC signal. To see if it is short-connected is relative to the AC signal. Co-injection, the input signal of the common collector is entered from the B pole, so the two configuration circuit B can not AC ground, and the input signal of the common set circuit is entered from the E pole, so this configuration circuit e cannot be AC grounded. The UI is being shorted by AC. There are three cases
<1> Direct Wire Short connection
<2> capacitors with large capacitance short connection
<3> short-Connect by DC power supply

3. Output signal UO cannot be short-connected
Similarly, the output signal UO short connection also refers to the AC short. Even if the input signal is added to the transistor. The resulting alternating current is amplified, but the output signal is short-connected, and the load does not get an AC signal. Common-injection, common-base circuit output signal to the C-pole, so the two configuration circuit C can not AC grounding, the output signal of the common set circuit to the e-pole, so this configuration circuit e pole can not AC ground.

Based on the above three principles, we can analyze whether the following circuits can amplify the AC signal

(1) analysis from principle one (transistor with suitable working point)

Figure 5-bit PNP transistor, should be in the C-pole plus negative power supply, but the capacitance C1 DC power equivalent to open, it can not meet the transmission junction positive bias. All other circuits satisfy the first original. Picture 1 is for dual-supply operation, picture 3-bit PNP type, DC +UCC from E inflow, via transmit knot, RB, ground. Collector inverse bias.

(2) from the principle two analysis (UI cannot be short-connected)

Figure 1 is a DC power EB short Connection, figure 2 through the wire is the DC power UCC short connection, figure 4, the UI is capacitor C1 short.

(3) from the Principle one analysis (UO cannot be short-connected)

Figure 2, 4 output in the e-pole, for the common circuit, the remaining output in the C-pole, for the common Radio Road. Figure 6 is short-connected by a UCC via a wire.

A method to determine if the transistor can amplify the AC signal