The most common amplifier configuration for an npn transistor is that of the common emitter amplifier circuit. Note the distinction between cs the configuration and c s the capacitor dont let this confuse you. In the previous introduction to the amplifier tutorial. Common emitter amplifier working principle and its. A generic commonemitter ce amplifier circuit is shown to the right this is a modified representation of figure 5. We will now begin the analysis of the three basic types of linear bjt smallsignal amplifiers. The ac voltage gain expression for the commonemitter amplifier is developed using the model circuit in figure 614. Generally we think of amplifiers as audio amplifiers in the radios, cd players and stereos we use around the home. A typical transistor have three terminal base, collector emitter. This type of biasing arrangement uses two resistors as a potential divider network across the supply with their center point supplying the required base bias voltage to the transistor. An ac smallsignal model for the er amplifier is shown below on the. Transistors amplifiers common emitter amplifier simplified l whats common ground in a common emitter amp. This circuit typically in cludes a voltage source attached through a capacitor a to voltage divider driving the amplifier input port, an emitter.
In the source resistor sr configuration, the ac input is applied at c g, the ac output is taken at c d and c s is omitted. To an ac signal this looks like the emitter is connected to ground. The circuit diagram of a commonemitter ce amplifier is shown in fig. Common collector cc, which is oftentimes called the emitter follower amplifier. The single stage common emitter amplifier circuit shown above uses what is commonly called voltage divider biasing. Common emitter amplifier department of electrical engineering, cet. One pnp power transistor or any other pnp transistor that can be used as an amplifier, for example, 2n36,2n4403. Ac analysis involves figuring out the voltage gain, the input impedance and the output impedance of the amplifier. Bjt amplifiers 6 chapter outline 61 amplifier operation 62 transistor ac models 63 the common emitter amplifier 64 the commoncollector amplifier 65 the commonbase amplifier 66 multistage amplifiers 67 the differential amplifier 68 troubleshooting device application chapter objectives describe amplifier operation discuss transistor models.
From the voltage waveforms for the ce circuit shown in fig. Analysis of the common emitter amplifier taking into account. Cb is used to couple the input signal to the input port of the amplifier. The reason for this can be seen from the fact that as the input voltage rises, so the current increases through the base circuit. Common emitter amplifier circuit elements and their functions. Dc solution a replace the capacitors with open circuits. Designing a common emitter amplifier school of engineering. The common emitter transistor amplifier is the only configuration that gives an inversion, 180, between the input and output signals. The emitter is connected tied to ground usually by a capacitor. This is analogous to the emitter resistor configuration of the bjt. In turn this increases the current thought the collector circuit, i. Because the emitter is grounded, even if sometimes via a resistor, this transistor configuration is referred to as a common emitter amplifier. A video showing how to do ac analysis of a common emitter amplifier.
The object is to solve for the smallsignal voltage gain, input resistance, and output resistance. Also, the transistor output resistance ro is shown to make the circuit as generic as possible. The common emitter amplifier circuit shown uses a voltage divider network to bias the transistors base and the common emitter configuration is a very popular. It is also named common emitter amplifier because the emitter of the transistor is common to both the input circuit. The common emitter amplifier circuit is shown below figure a. Bipolar junction transistors common emitter amplifier duration. What is the difference between a common base, a common. Amplifiers introduction amplifiers are used extensively in electronic circuits to make an electronic signal bigger without affecting it in any other way.