BJT Differential Amplifier

[kahei]

In a BJT Differential amplifier, how to find the maximum and minimum values of the common-mode input voltage? Beta and the resistors are given.

 

[turin]

Doesn't that depend on the input circuit? I mean, that is an input to the amplifier. All the amplifier itself can do is to partially reject the common mode input voltage that is given to it.

 

[Mene]

The maximum and minimum values of the common-mode input voltage in a BJT Differential amplifier can be found by taking into account the beta value of the transistors and the resistors used in the circuit. The common-mode input voltage refers to the voltage that is applied to both inputs of the differential amplifier. It is important to note that the common-mode voltage should be kept within a certain range to ensure proper functioning of the amplifier.

To find the maximum and minimum values of the common-mode input voltage, we can use the following equation:

Vcm(max) = Vcc - (Vbe/Q1 + Vbe/Q2)/(1 + R1/R2)

Vcm(min) = Vcc - (Vbe/Q1 + Vbe/Q2)/(1 + R1/R2)

Where:
Vcm(max) is the maximum common-mode input voltage
Vcm(min) is the minimum common-mode input voltage
Vcc is the supply voltage
Vbe is the base-emitter voltage of the transistors
Q1 and Q2 are the transistors in the differential amplifier
R1 and R2 are the resistors in the circuit

The above equation takes into account the voltage drops across the base-emitter junctions of the transistors, which can vary depending on the beta value of the transistors. The resistors R1 and R2 also affect the common-mode input voltage, as they form a voltage divider network.

Therefore, to find the maximum and minimum values of the common-mode input voltage, we need to know the supply voltage, beta value of the transistors, and the values of the resistors used in the circuit. By plugging in these values into the equation, we can determine the range of common-mode input voltage that is acceptable for the differential amplifier to function properly.

In conclusion, the maximum and minimum values of the common-mode input voltage can be found by taking into account the supply voltage, beta value of the transistors, and the resistors used in a BJT Differential amplifier. It is important to keep the common-mode input voltage within this range to ensure proper operation of the amplifier.