In the diagram above:

• The initial input voltage is +10mV.
• The offset voltage of the op amp is adjusted to zero.
• The op amp is internally compensated to be stable at unity gain closed loop.
• Assume the transistor's beta is very large.

Questions:

1. What, approximately, is the voltage at the output of the circuit?
2. If the input voltage is increased to +100mV (i.e., by a factor of 10 times), how does the output voltage change, and why?
3. What mathematical function relates the output voltage to the input voltage?
4. Is the circuit stable under all conditions of positive input voltage?

(To answer these questions, you do not need to know the value of R.)

Answer