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Can you explain me, whats the Common Base-Common Collector?, please

francis19

@copilot Can you explain me, whats the Common Base-Common Collector?, please

copilot

Certainly! The terms "Common Base" (CB) and "Common Collector" (CC), refer to specific configurations of bipolar junction transistors (BJTs). These configurations are primarily defined by which terminal of the transistor (base, collector, or emitter) is common to both the input and the output of the circuit. Let's delve into both configurations individually:

Common Base (CB) Configuration

Characteristic: In a Common Base configuration, the base of the BJT is common to both the input and the output circuits, effectively serving as the "ground" or reference point for the transistor. The emitter is connected to the input circuit, while the collector is connected to the output circuit.
Input Impedance: The CB configuration has a low input impedance because the input is applied between the emitter and the base.
Output Impedance: It has a high output impedance since the output is taken from the collector.
Voltage Gain: The CB configuration provides high voltage gain but no current gain. In fact, the current gain (alpha, (\alpha)) is less than 1, which means the output current is slightly less than the input current.
Application: It's commonly used in applications requiring high-frequency response such as RF amplifiers, because it has the least capacitance effect among the three configurations (CB, CE, CC), which makes it suitable for high-frequency operations.

Common Collector (CC) Configuration

Characteristic: In the Common Collector configuration, the collector terminal is common to both the input and the output. The input is given to the base, and the output is taken from the emitter. This configuration is also known as an Emitter Follower because the output voltage on the emitter follows the input voltage applied to the base.
Input Impedance: CC has a high input impedance, making it suitable for impedance matching applications.
Output Impedance: It has a low output impedance, allowing it to drive loads with high efficiency.
Voltage Gain: The voltage gain of a CC configuration is slightly less than 1. This means the output voltage is almost equal to the input voltage but slightly less because of voltage drops inside the transistor. However, it provides substantial current gain, meaning it can supply a larger output current to the load.
Application: Due to its impedance characteristics and current gain, it's often used in buffer circuits, impedance matching, and as a voltage follower circuit.

Both configurations serve different purposes in electronic circuits and are chosen based on the requirements of the application, such as impedance matching, voltage amplification, or frequency response.

francis19

ok, What would be the formulas to make the respective calculations in both cases?

copilot

To perform calculations for circuits using the Common Base (CB) and Common Collector (CC) configurations, you'll need to know a few key formulas relevant to each configuration. Let's go through them now.

Common Base (CB) Configuration Formulas

Voltage Gain ((A_v)): The voltage gain in a CB configuration is given by the formula:

$A_v = \frac{V_{out}}{V_{in}} = \frac{\Delta V_{C}}{\Delta V_{E}} \approx -\alpha \cdot \frac{R_C}{r_e}$

where:
- (V_{out}) is the output voltage at the collector,
- (V_{in}) is the input voltage at the emitter,
- (\Delta V_{C}) is the change in collector voltage,
- (\Delta V_{E}) is the change in emitter voltage,
- (\alpha) is the current gain of the transistor (typically close to 1),
- (R_C) is the load resistance connected in the collector,
- (r_e) is the dynamic emitter resistance, (\frac{26mV}{I_E}), with (I_E) being the emitter current.
Input Impedance ((Z_{in})):
$Z_{in} = r_e$
This highlights the low input impedance nature of the CB configuration.
Current Gain ((A_i)):
$A_i = -\alpha$
The current gain is less than 1, meaning the output current is slightly less than the input current.

Common Collector (CC) Configuration Formulas

Voltage Gain ((A_v)): The voltage gain of a CC configuration is less than 1 because it is a buffer/amplifier. The exact formula depends on the load resistance and the transistor parameters, but it's often approximated to be slightly less than 1 due to the internal voltage drops:
$A_v \approx 1$
The gain is unit-less since it is a ratio of the output voltage to the input voltage, both measured in volts.
Input Impedance ((Z_{in})):
$Z_{in} = (\beta + 1) \cdot (r_e + R_E)$
where (\beta) is the current gain of the transistor and (R_E) is the emitter resistance. This configuration has a high input impedance.
Output Impedance ((Z_{out})):
$Z_{out} \approx \frac{r_e + R_s}{\beta + 1}$
where (R_s) is the source (or signal) resistance. The CC configuration typically has low output impedance.
Current Gain ((A_i)): For a common collector, the current gain ((A_i)) can be quite high since the output current through the emitter is significantly larger than the input base current. It is approximately equal to the (\beta) of the transistor:
$A_i \approx \beta$

These formulas are essential for analyzing and designing circuits with CB and CC configurations, helping you calculate key parameters like gain and impedance that dictate how the circuit interacts with signals and other components.

Reviews

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Dear Bronze Interocitor

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