To form an amplifier configuration, we must provide a bias voltage to the transistor used, the bias circuit that is widely used is the FeedBack bias type (current feedback), this circuit is usually used to make the transistor work optimally.
The working voltage of the transistor is determined by adjusting the collector current value (IC) and the voltage between the collector-emitter (VCE), both of which are the main elements for creating good output characteristics.
The IC value is the coordinate axis (y), while the VCE voltage is the obscissa, the coordinates form the working point (Q), then:
- point Q in the middle of the load line forms class A
- working point at cut off forms class B
- the working points between the two form class AB.
In the bias circuit there is a collector current value, this value can be known from the information listed on the transistor body. For example, the information explains that the collector current is max, then only max current can pass through the transistor.
Saturation current is the max current, which can be determined by the installation of resistor components. The IC and VCE elements are mutually rectified or inverse.
Procedure
In forming an amplifier configuration using transistors, the collector must not be used as an input.
In the amplifier configuration, there is an additional ELCO component with the largest capacity used for grounding, this ELCO is called a storage condenser (bypass), its function is to divert the AC signal to GND / ground.
A small capacity capacitor connected as input is called a coupling capacitor. A medium capacity capacitor is used to connect the previous amplifier block to the next amplifier block.
The configuration names are taken from the placement of the capacitor (bypass) on an electrode (transistor leg):
- Common Emitter: where the base is the input, the collector is the output and the emitter is GND.
- Common Collector: where the base is the input, the emitter is the output and the collector is GND.
- Common Base: where the emitter is the input, the collector is the output and the base is GND.
1. Strengthening Formula in Configuration
Current Amplification (AI)
- Common Emitter (CE) = IC/IB, called ? (beta)
- Common Collector (CC) = IE/IB, called ? (gamma)
- Common Base (CB) = IC/IE, called ? (alpha)
Beta (?) c is the gain value in the Transistor data book.
Alpha, Beta, Gamma Relationship
GAMMA
IE / IE = (IC+IB) / IE
1 = (IC+IB) / IE
1 = ? + 1/?
1/? = 1 - ?
? = 1 / (1 - ?)
ALPHA
1/? = 1 - ?
? = ?/? - 1/?
? = (? - 1) / ?
BETA
IE/IC = (IC + IB) / IC
IE/IC = IC/IC + IB/ IC
IE/IC = 1 + IB/ IC
1 = IE/IC - IB/ IC
1 = IE/IC - IB/ IC
1 = 1/? - 1/?
1/? = 1/? - 1
1/? = 1/? - ?/?
1/? = (1- ?) / ?
? = ? / (1 - ?)
GAMMA
IE/IB = (IC + IB) / IB
IE/IB = IC / IB + IB / IB
IE/IB = IC / IB + 1
1 = IE/IB - IC / IB
1 = ? - ?
? = 1 - ?
2. COMMON EMITOR (Common Emitter)
Common Emitter Configuration
It is a transistor circuit where the input signal (VI) is connected between the base and emitter, the current amplified by the transistor produces a larger output signal. The Emitter Amplifier (VE) is an inverse amplifier where the output signal phase is the opposite of the input signal, adding voltage to the base will increase the base current which results in increasing IC. The increasing IC value causes an increase in the RL voltage which results in a decrease in the collector voltage.
The addition of (+) voltage on the base causes a reduction in the collector voltage, if the base voltage decreases IB and IC also decrease, so the collector voltage will increase. The output signal is the opposite of the input signal.
Properties of common emitter circuits:
- has low input impedance
- has a high output impedance
- high current amplification
- maximum power gain +- 50dB (deciBell)
Common emitter gain equation:
IC/IB = output/input3. COMMON BASE (Common Base)
Common Base Configuration
The common base circuit is very good for use in VHF amplifier circuits, for example in television sets. (Tunner).
Common base circuit properties:
- the current gain is less than 1
- low input impedance
- high output impedance
- 40 dB power gain
- high voltage gain
- has HF signal response
4. COMMON COLLECTOR (Cersama Collector)
Common Collector Configuration
It is a transistor circuit where the collector is connected directly to vcc, the input signal is connected to the base and the output is taken from the emitter leg, this circuit has special features including: the output impedance is very low, so it can be connected with a capacitor to the speaker.
Common collector circuit properties:
- high current amplification
- high input impedance
- low output impedance
- low power gain
- low voltage gain
- has an inverting signal/phase (+)
- input signal at the base and output at the emitter
5. Bipolar Transistor Configuration
Bipolar Transistor Configuration
Comparison Table of Bipolar Transistor Configuration Characteristics
Inverting Bipolar Transistor Configuration
Inverting Bipolar Transistor
Conclusion:
- Common emitter = power amplifier
- Common base = voltage amplifier
- Common collector = current amplifier