![]() Simulate the circuit to verify your result and adjust the values of capacitors if necessary. Calculate C B, C C, C E to have f L = 500 Hz.Simulate the circuit to verify your result and adjust the value of C F if necessary. Calculate the value of C F to have f H = 5 kHz.Remember that the equation gives you the radian frequency and you need to convert to Hz. Calculate f H using the equation from the High Frequency Response section and compare it with the simulation result obtained in Step 3. Determine C π, C μ, and r b of the transistor from the simulated operating point data.Using LTspice, find the higher 3 dB frequency (f H) while C F = 0.Also provide the circuit schematic with dc bias points annotated. Submit all necessary simulation plots showing that the specifications are satisfied. Verify your results using the LTspice ® circuit simulator. ![]() Show all your calculations, design procedure, and final component values.Thus, if we assume that the common emitter amplifier is properly characterized by these dominant low and high frequency poles, then the frequency response of the amplifier can be approximated by:Īssuming C B = C C = C E = 1 farad and C F = C Π = C μ = 0, and, using a 2N3904 transistor, design a common emitter amplifier with the following specifications: The higher 3 dB frequency (ω H) can be derived as: At high frequencies, C B, C C, and C E can be replaced with short circuits since their impedance becomes very small compared to R S, R L, and R E. Using short-circuit time constant analysis, the lower 3 dB frequency (ω L) can be found as:įigure 3 shows the high frequency, small signal equivalent circuit of the amplifier. R B is the parallel combination of R B1 and R B2. Note that C F is ignored since it is assumed that its impedance at these frequencies is very high. Low Frequency Responseįigure 2 shows the low frequency, small signal equivalent circuit of the amplifier. Miller capacitor C F is a small capacitance that will be used to control the high frequency 3 dB response of the amplifier. Capacitor C E is an ac bypass capacitor used to establish a low frequency ac ground at the emitter of Q1. Capacitors C B and C C are used to block the amplifier dc bias point from the input and output (ac coupling). The schematic of a typical common emitter amplifier is shown in Figure 1. The objective of this activity is to investigate the frequency response of the common emitter amplifier configuration using an NPN BJT transistor. These transistors are available in package styles TO-92, SOT23, SOT223 with different prefixes.ADALM2000 Activity: Frequency Response of a Common-Emitter BJT Amplifier The 2N3904 (NPN) and 2N3906 (PNP) are complementary transistor pairs. Top view or PCB layout view is shown in the lower right corner. Part numbers Pinout of 2N3904 in TO-92 package. The complementary PNP transistor is 2N3906. It is a 200 mA, 40 V, 625 mW transistor with a transition frequency of 300 MHz, with a minimum beta, or current gain, of 100 at a collector current of 10 mA.Įlectrically similar devices, such as the MMBT3904, are available in a variety of small through-hole and surface-mount packages, including TO-92, SOT-23, and SOT-223, with package-dependent thermal ratings from 625 milliwatts to 1 watt. Some manufacturers mark "EBC" on the molded part, but all are required to have those connections for a part which is a "2N3904". When looking at the flat side with the leads pointed downward, the three wires emerging from the bottom are connected to, from left to right, the emitter, the base and the collector. This transistor is a low-cost device, widely available and sufficiently robust to be of use by experimenters and electronics hobbyists. The construction of the 2N3904 and 2N3906 in the 1960s represented a significant performance and cost improvement, with the plastic TO-92 case replacing metal cans. Both types were registered by Motorola Semiconductor in the mid-1960s.ĭevice packaging and specifications It is complementary to the 2N3906 PNP transistor. It is designed for low current and power, medium voltage, and can operate at moderately high speeds. The 2N3904 is a common NPN bipolar junction transistor used for general-purpose low-power amplifying or switching applications. A 2N3904 in a TO-92 package on a breadboard (lower left) The pinout from left to right is: Emitter, Base, Collector. Common NPN bipolar junction transistor A 2N3904 made by Motorola.
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