Module 4: Op-amps Flashcards
Assuming a square-wave input, draw the output of this circuit. What is it called?
Integrator circuit
Assuming a square-wave input, sketch the output of this circuit. What is it called?
Differentiator; voltage spike whenever input changes
Assuming a sine wave input, sketch the output of this circuit. What is it called? What is its purpose, and what is a major drawback?
Logarithmic op-amp
Used for multiplication; heavily tempertaure dependant!
How might one eliminate the log op-amp’s dependance on temperature? Sketch an example circuit.
The double transistor eliminates the temperature dependance.
What is a bode plot?
The plot of the frequency response of a system, with gain and frequency on either axis, both on a logarithmic scale.
What is a transfer function, and how does it differ from the gain?
A function relating the output of a system (e.g. a filter) to its input.
What is the signficance of ‘order’ in filters (e.g. 1st order vs 7th order system)?
Higher order filters are constructed by increasing the number of storage elements (e.g., capacitors, inductors). In other words, the more reactive components, the higher the order of filter. The higher the order, the steeper the frequency response.
What is the difference between an active and a passive filter?
Passive filters are made of passive components (e.g. resistors, inductors, capacitors and transformers).
Active filters have made of active components (e.g. voltage amplifier), and have some power gain.
What is ‘Sallen-Key’?
‘Sallen-key’ is a form of electronic filter toplogy (i.e. format in which components are connected) used in 2nd order filter systems.
What is the ‘slew-rate’?
The maximum rate at which the output voltage can change with a change in the input voltage.
How would one practically express errors for this circuit?
Output offset voltage (~CMRR) is found on the data sheet - e.g. +/- 5mV
Bias current, also found on the data sheet, might be 0.5uAish.
What is the relationship between the input and output voltage for an ideal logarithmic amplifier?
V(out) = K log V(in)
What makes an logarithmic amplifier logarithmic?
The relationship between IC abd VBE in a transistor is logarithmic
Draw the circuit diagram for a simple logarithmic amplifier, and its output voltage assuming:
IC = ISeqV(BE) / kT
Vout = kT / q ln Vin / IsR1
What are some ideal characteristics for a filter?
- constant gain (in the passband)
- linear rate of change of phase
