At a glance of CE Configuration
In our previous blogs, we learn about common base configuration and common collector configuration of the transistor, so in our today’s blog we are going to learn about CE Configuration of the transistor, the Input Characteristics, and Output characteristics also The dynamic input resistance, and The dynamic Output Resistance, Difference between common base common collector and common emitter configuration.
Common emitter CE configuration
The below figure shows the construction of the common-emitter configuration, the fig. you can see that base is the input terminal. In contrast, the collector is the output terminal. As the name suggests, the emitter is common for both the input and output sides. Therefore the input is provided between the base and common emitter terminal. In contrast, the output is taken from the collector and common emitter terminal.
Common emitter configuration is also known as grounded emitter configuration because the emitter terminal is grounded. However, the common-emitter configuration is also referred to as a common emitter amplifier.
Among the three transistor configurations, the common emitter (CE) is the most widely used configuration.
The widest application of a common emitter amplifier is when a large current gain is needed.
VBE is the supply voltage between base and emitter, while VCE is the supply voltage between collector and emitter.
For common emitter configuration (CE), IB denotes the input or base current, and IC indicates the output or collector current.
The power gain of the common-emitter configuration is high
however, the common-emitter amplifier’s current gain and voltage gain are medium because the input and output impedance levels of the common-emitter configuration are medium.
To understand the behavior of the Common emitter configuration of the transistor, we need to study the input and output characteristics.
Input characteristics of CE Configuration
An input characteristic is a curve plotted between the base current IB and the base-emitter voltage VEB.
To draw the input characteristics of the common-emitter configuration, we need to take the current IB and emitter voltage VBE at the constant collector current.
The curve for common base configuration shows a similar nature to the forward bias characteristics of the PN junction diode.
Base current IB and emitter-base voltage VBE are proportional to each other; therefore, as the base current increases, the emitter-base voltage also increases. However, due to this, the input resistance of the common-emitter configuration is higher than the common base configuration comparatively.
The effect of change in VCE on the input characteristic is ignored because Change in VCE does not cause large deviation on the curves.
The dynamic input resistance
The dynamic input resistance for common emitter configuration is defined as the reciprocal of the slope of IB curves at constant VCE.
Dynamic input resistance gives the value of VBE and VCE,
It can be formulated as, ri = ∆ VBE / ∆ IB | at constant VCE.
Output characteristics
For the common emitter configuration, the curve of output characteristics is drawn between the collector current IC and collector-emitter voltage VCE when the base current IB is constant.
The output characteristics curve for the NPN transistor in a common emitter configuration is shown in the figure below.
The collector current increases slightly when the collector-emitter voltage VCE increases. The output resistance of the common-emitter configuration is less than the common base configuration.
The value of β of increases whenever the value of collector current IC increases with an increase in VCE at constant voltage IB.
The VCE and IC are directly proportional to each other hence when the VCE falls, we can see a rapid decrease in the value of IC.
The collector-base junction of the common-emitter configuration is always in the forward bias condition and works in the saturation region. The collector current becomes independent and free from input current IB in the saturation region.
In the active region, IC = β.IB, the current IC is not zero, and instead of that, it is equal to reverse leakage current ICEO.
The dynamic Output Resistanceof CE Configuration
The dynamic output resistance for common emitter configuration can be defined as the ratio of variation in collector-emitter voltage to the collector-emitter current.
Ro = ∆ VCE /∆ IC | at constant IB
The value of output resistance for common emitter configuration is more than that of common base configuration.
Difference between common base common collector and common emitter configuration.
| Characteristic | Common Base | Common Collector | Common Emitter |
|---|---|---|---|
| Input Impedance | Low (50 to 500 Ohms) | High (150 to 600 Kilo Ohms) | Medium (500 to 5000 Ohms) |
| Output Impedance | Very High ( 1 to 10 Mega Ohms) | Low (100 to 1000 Ohms) | High (50 to 500 Kilo Ohms) |
| Phase Shift | 0o | 0o | 180o |
| Voltage Gain | High | Low (equal to or less than 1) | Medium |
| Current Gain | Low (α< unity) | High (β = 99) | Medium (β = 98) |
| Power Gain | Low | Medium (equal to or less than 1) | Very high (37 dB) |
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