Waveform Generators Questions and Answers

Answer: B

The correct matching is a-iv, b-iii, c-i, d-ii.

• (a) Active filters are built from R-C networks with an op-amp (iv).
• (b) Multivibrators produce a pulse or pulse train (iii).
• (c) A Schmitt trigger is a comparator with positive feedback, which gives it hysteresis, printed 'Hysteris' (i).
• (d) A voltage regulator provides a steady dc output (ii).

The other codes put hysteresis or the dc output against the wrong circuit.

Answer: C

The key gives a clipper.

A triangular wave can be shaped into a near-sinusoid with a diode shaping network, which is a clipper with several break points. As the triangle rises, successive diodes conduct and progressively reduce the slope of the output, so the straight sides are bent into curves and the sharp peaks are rounded off, approximating a sine wave. Function generators use this method.

A clamper only shifts the DC level of a waveform without changing its shape. A rectifier removes one polarity. An integrator turns a triangle into a series of parabolic segments, which is still not a sine wave and does not round the peaks in the required way.

Answer: A

An astable multivibrator can be used as a voltage-to-frequency converter.

An astable circuit switches back and forth continuously as a timing capacitor charges and discharges between two thresholds. If the charging current, or the threshold, is set by a control voltage, the time per cycle changes with that voltage, so the output frequency becomes a function of the input voltage. This is how a 555 timer with its control pin driven, or a VCO such as the 566, works as a V/F converter.

A crystal oscillator is designed for a fixed, very stable frequency and resists being pulled. A Schmitt trigger converts a level into a clean switching edge but does not oscillate by itself, and a CE amplifier amplifies; neither produces a frequency proportional to voltage.

Answer: C

The IC used for V to F conversion among these is the 566.

The LM566 (NE566) is a voltage-controlled oscillator: the frequency of its square and triangular outputs is set by an external RC and varies linearly with a control voltage. A voltage-controlled oscillator is in effect a voltage-to-frequency converter, and the 566 is the standard textbook example.

The 741 is a general-purpose operational amplifier. The 7400 is a TTL quad two-input NAND gate. The 723 is an adjustable voltage regulator. None of them converts a voltage to a frequency.