The common emitter circuit with voltage divider polarization is the most commonly used linear amplifier configuration as it is easy to polarized and easy to understand. The input signal is applied to the base terminal and the output signal is taken from the RL load resistance, which, as shown, the collector and the positive feed rail are connected between the VCC. Thus, the emitter is common to both input and output circuits. In addition to providing voltage amplification determined by the RL/RE ratio, the main feature of the Common Transmitter (CE) configuration is that it is an inverter amplifier that produces a phase reversal of 180° between input and output signals. To operate as a class A amplifier, the circuit is polarized so that the immobile current fed to the base positions the IB's collector terminal voltage at about half the feed voltage value. The ratio of R1 and R2 resistors is selected to ensure that the transistor is accurately polarized, providing maximum unspoiled output signal.
The common collector amplifier uses the single transistor in the common collector configuration, which the collector is common for both input and output circuits. The input signal is applied to the transistor base terminal and the output is taken from the emiter terminal as shown.
Since the output signal is received through the emitter resistance, RE collector resistance is not used, so the collector terminal is connected directly to the feed rail, VCC. This type of amplifier configuration is also known as a voltage tracker or, more commonly, an emitter tracker, as the output signal follows the input signal.
The main feature of the Common Collector (CC) configuration is that it is an amplifier that does not reverse, as the input signal passes directly from the base-emitter connection to the output. Therefore, the output is "intra-phase" with input. Therefore, it has a slightly less voltage gain than one.
As with the previous common emitter configuration, the transistor of the common collector amplifier is polarized up to half the feed voltage using a voltage dividing network to ensure good stabilization for DC operating conditions.
Phase Separator Configuration
If we combine the configuration of the common emitter with the configuration of the common collector amplifier and simultaneously receive outputs from both the collector and the emiter terminals, we can create a transistor circuit that produces two output signals of equal size. But these exits are inversely opposites. Phase Divider uses a single transistor to produce inverting and non-inverting outputs as shown.
We have previously said that the voltage gain of the common emitter amplifier is the ratio of RL to RE, that is, -RL/RE (minus sign indicates a reverse riser). If we were to synchronize these two rescindors as values (RL = RE), the voltage gain of the common emitter stage would be equal to -1 or +1.
As a common collector, the emitter tracker amplifier circuit naturally has a voltage gain that does not reverse close to one (+1), two output signals, one from the collector and the other from the emitter, will be equal in amplitude but outside 180°. This makes the lucrative transistor phase separator circuit very useful for providing complementary or anti-phase inputs to another amplifier stage, such as a class B propulsion-pulling power amplifier.
For proper operation, the voltage dividing network connected to the feed rail and soil must be selected to produce accurate stabilization of DC conditions for output voltage release from both collector and emitter terminals producing symmetrical outputs.
Phase Divider Example
A single transistor phase separator circuit is required to drive a push-pull power amplifier stage. Design a suitable circuit if the supply voltage is 9 volts, the Beta value of the NPN 2N3904 transistor used is 100, the motionless collector current is 1mA and the amplitude of the input signal is 1V peak. To prevent the distortion of the emitter terminal output signal, the polarization voltage of the emiter terminal must be greater than the maximum value of the input signal, in this case a peak of 1 volt. If we set the DC emitter terminal voltage to double the input value to ensure a distortion-free output oscillation, it will equal 2 volts. And, since it is set to 2 volts and the emitter current with the collector stagnant current passing through it is given as 1mA, the emitter resistance value RE is calculated as follows: In order for the voltage gain of the common emitter side of the phase separator circuit to be equal to -1, the collector load resistance must be equal to RL RE. That is, RL = RE = 2kΩ. Thus, the voltage falling along the collector load resistance is calculated as follows: VCC – VC – VCE – VE = 0, applying Kirchhoff's Voltage Law. Thus, 9 – 2 – 5 – 2 = 0. We would expect to see this because the current passing through RL = RE and both resistors is approximately the same value, so the I*R voltage drop in each resistance will be the same at 2.0 volts. This means that the DC front polarizing voltage for the inverted output (transmitter terminal) is 2.0 volts (0 + 2) and the DC front polarizing voltage for the inverter output (collector terminal) is 7.0 volts (9 – 2). In other words, the DC silent output voltages of the two outputs are of different values. Dc current gain of transistors is given in Beta, 100. Beta for a common emitter amplifier is the ratio of collector current to base current, that is; β = IC/IB, the value of the required base polarization current is calculated as follows: Then for a DC current gain of 100, the sedentary base current is given as IB(Q), 10uA. It is common practice to have the value of the stagnant current flowing from the resistance of the voltage dividing network from the base to the ground ten times greater than the base current (x10). Thus, the current passing through R2 will be 10*IB = 10*10uA = 100uA. The basic voltage is equal to the 0.7 volt forward voltage drop of VB, emitter voltage AND plus base-emitter pn-connection, that is: 2.0 + 0.7 = 2.7 volts. Therefore, the value of R2 is calculated as follows: since there is 10uA flowing from R2 to 100uA and flowing into the transistor base terminal, the voltage divider should follow that the network's top rescientator is flowing 110uA (100uA + 10uA). If the supply voltage is 9 volts and the base voltage of the transistors is 2.7 volts. The value of resistance R1 is calculated as follows: Thus, the voltage dividing network used for DC polarization of the separator circuit consists of R1 = 57.3kΩ and R2 = 27kΩ. Combining the values calculated above gives us the single transistor phase separator circuit:
Since a single transistor phase separator circuit produces two output versions of the input signal, it is an unverted version that is in the same phase as the input signal and a 180o phase inverted version of the input signal, both outputs of which have a similar amplitude. This will make the phase divider circuit ideal for use in propulsion or totem-pole-configured outputs for amplification or DC engine control. Consider the circuit below.
Since complementary outputs are received from the transistor's Q1 collector and transmittor, when the upper transistor Q2 is polarized forward and conductive in negative semi-cycle (due to inversion), the lower transistor Q3 IS OFF, so half of the negative waveform is transmitted to load resistance (RL). In the positive half cycle of the input waveform, the lower transistor Q3 is forward-oriented and conductive, while the upper transistor Q2 is OFF, while the positive half of the waveform is passed to load resistance, RL. Thus, at any given time, only one of the output transistors, Q2 or Q3, is polarized far enough, and the input signal transmits only one half of the waveform. The two output transistors combine both halves of the input signal to produce an inverted output waveform throughout the RL, altering transmission from one to the other as determined by Q1. Load resistance has a DC pre-receding voltage centered around the difference between RL, VC and VE. Resistance R5 is used to limit the maximum current flow.
In this tutorial, we found that by combining a common emitter circuit with a common collector circuit, we can create another type of single transistor circuit, which in reality is not an CE amplifier or a CC amplifier, but instead a phase separator circuit that produces two voltages. it is the same amplitude but in the opposite phase. Sometimes it is necessary to have two signals, both of which are equal in amplitude but 180° out of phase with each other, and there are different ways to create a dual-output phase separator circuit, including the use of differential amplifiers and operational amplifiers. However, single transistor phase separator circuit configuration is the easiest to build and understand. The single transistor phase separator circuit is biased to operate as a Class A amplifier with two complementary (inverted and unverted) outputs from the transistor's collector and transmitter terminals, respectively. For it to work correctly, the gain of each output must be set to 1, unit gain. Single transistor phase separator circuits are useful for driving Class B push-pull amplifiers, center-end transformer for inverters, or engine control outputs, such as when a transistor is ON and the other transistor is OFF.