Question

6.    Answer the following questions:

a.    What is the difference between Op-Amp circuit and Comparator circuit?

b.    Discuss some of the issues with this Op-Amp oscillations and explain the voltage swing and cause of potential failure of this circuit.

c.     What makes the comparator circuit oscillate and more ideal for the applications?

d.    Describe the operation of the comparator oscillator circuit and explain the difference in inverting and non-inverting waveforms of the comparator

e.    What is the significance of using comparator circuit to achieve sinusoidal oscillations?

Answer 1

a>output of the opamp can either linearly change with the applied voltage or gets saturated to +VCC( Vsat) or -Vcc (-Vsat)when the applied voltage exceeds certain value.Thus the output can be optimized to operate in either the linear zone(when feedback is negative) or saturation zone(when there is no feedback or when the feedback is positive.)

Comparator circuit can only operate in saturation zone irrespective of the applied voltage.

b> In open loop configaration the OPAMP acts as a voltage comparator.When the non-inverting terminal voltage is more than the inverting terminal voltage OPAMP goes to +Vsat else it goes to -Vsat. As the output voltage of the OPAMP can never cross the +_Vsat voltage so it gets saturated to +_Vsat in healthy condition.

(Exception: suppose the OPAMP is given 100 V supply but the bais voltage is +_15V that means whatever feedback might be(even in case of negative feedback) the output voltage cannot exceed +_15V).

If some shortcircuit occurs,however the OPAMP voltage becomes more than the +_Vcc then that is a faulty device.

c>when using opamps as comparators, responsiveness will be much worse due to the phase compensation capacitance included in opamps. Hence caution is recommended when replacing comparators with opamps.

d>d>