Question

For the amplifier shown determine the value of the bias current (Ib) and input offset current (Io) respectively.

(a) Ib = IB1 + IB2

Answer 1

To determine the bias current (Ib) and input offset current (Io) for an amplifier, let's address the formulas provided:

1. Bias Current (Ib):

The total bias current (Ib) in a differential amplifier is the sum of the individual bias currents of the two transistors.

The equation for the bias current is:

Ib=IB1+IB2I_b = I_{B1} + I_{B2}Ib​=IB1​+IB2​

where:

• IB1I_{B1}IB1​ is the bias current of the first transistor (Q1).
• IB2I_{B2}IB2​ is the bias current of the second transistor (Q2).

2. Input Offset Current (Io):

The input offset current (Io) is defined as the difference between the bias currents of the two transistors. It is the imbalance between the bias currents of the two input transistors of the differential amplifier.

The equation for the input offset current is:

Io=∣IB1−IB2∣I_o = |I_{B1} - I_{B2}|Io​=∣IB1​−IB2​∣

where:

• IB1I_{B1}IB1​ is the bias current of the first transistor.
• IB2I_{B2}IB2​ is the bias current of the second transistor.

Summary:

• Bias Current (Ib) = IB1+IB2I_{B1} + I_{B2}IB1​+IB2​
• Input Offset Current (Io) = ∣IB1−IB2∣|I_{B1} - I_{B2}|∣IB1​−IB2​∣

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