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Unit 6: Active Filters and Wave Shaping Circuits - Practice Quiz

ECE226 — Analog Electronic Devices And Circuits 60 Questions
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1 An active filter uses which of the following components in addition to resistors and capacitors?

Introduction to active filters Easy
A. Only inductors
B. Active devices like op-amps
C. Only transformers
D. Only diodes

2 Which type of filter allows frequencies below a certain cutoff to pass and attenuates higher frequencies?

Introduction to active filters Easy
A. High pass filter
B. All pass filter
C. Band reject filter
D. Low pass filter

3 What is the roll-off rate of a first order low pass Butterworth filter?

First order low pass Butterworth filter Easy
A. dB/decade
B. dB/decade
C. dB/decade
D. dB/decade

4 The cutoff frequency of a first order low pass filter with resistance and capacitance is given by:

First order low pass Butterworth filter Easy
A.
B.
C.
D.

5 A first order high pass Butterworth filter passes which frequencies?

First order high pass Butterworth filter Easy
A. Only the cutoff frequency
B. Frequencies below the cutoff
C. All frequencies equally
D. Frequencies above the cutoff

6 In a high pass filter, the positions of R and C are interchanged compared to which filter?

First order high pass Butterworth filter Easy
A. All pass filter
B. Low pass filter
C. Band reject filter
D. Notch filter

7 A band pass filter allows which range of frequencies to pass?

Band pass filter Easy
A. Frequencies between two cutoff points
B. Only very high frequencies
C. All frequencies uniformly
D. Only very low frequencies

8 A band pass filter can be constructed by cascading which two filters?

Band pass filter Easy
A. Two high pass filters
B. A low pass and a high pass filter
C. Two all pass filters
D. Two low pass filters

9 A band reject filter is also commonly known as a:

Band reject filter Easy
A. Buffer filter
B. Pass filter
C. Notch filter
D. All pass filter

10 What does a band reject filter do to a specific band of frequencies?

Band reject filter Easy
A. Passes them unchanged
B. Amplifies them
C. Delays them only
D. Attenuates them

11 What is the primary function of an all pass filter?

All pass filter Easy
A. To block high frequencies
B. To reject a band of frequencies
C. To change phase without changing amplitude
D. To amplify all frequencies

12 The magnitude of the gain of an ideal all pass filter across all frequencies is:

All pass filter Easy
A. Decreasing
B. Increasing
C. Zero
D. Constant

13 A square wave generator using an op-amp is essentially a type of:

Square wave generator Easy
A. Monostable multivibrator
B. Bistable multivibrator
C. Linear amplifier
D. Astable multivibrator

14 The output of a square wave generator switches between which two levels?

Square wave generator Easy
A. Positive and negative saturation
B. Zero and infinity
C. Only positive values
D. Only negative values

15 A triangular wave generator is typically formed by combining a square wave generator with a:

Triangular wave generator Easy
A. Comparator only
B. Differentiator
C. Rectifier
D. Integrator

16 How does a sawtooth waveform differ from a triangular waveform?

Sawtooth wave generator Easy
A. It is a pure sine wave
B. It has equal rise and fall times
C. It has no rising edge
D. It has unequal rise and fall times

17 In a voltage controlled oscillator (VCO), the output frequency depends on the:

Voltage controlled oscillator Easy
A. Output load resistance
B. Supply current only
C. Ambient temperature only
D. Input control voltage

18 How many pins does a standard 555 timer IC have?

555 timer pin configuration and operating modes Easy
A. 8
B. 6
C. 10
D. 14

19 Which mode of the 555 timer produces a continuous train of pulses without any external trigger?

555 timer pin configuration and operating modes Easy
A. Comparator mode
B. Bistable mode
C. Monostable mode
D. Astable mode

20 Which of the following is a recent trend in electronics aimed at reducing device size?

recent trends in electronics Easy
A. Increasing vacuum tube usage
B. Higher power resistors only
C. VLSI and nanoelectronics
D. Larger discrete components

21 An active filter uses op-amps along with resistors and capacitors instead of inductors. What is the primary advantage of avoiding inductors in the audio frequency range?

Introduction to active filters Medium
A. Inductors require an external DC bias to operate
B. Inductors are bulky, expensive, and non-ideal at low frequencies
C. Inductors always introduce a fixed phase shift
D. Inductors cannot pass AC signals at all

22 A first order low pass Butterworth filter has and . What is its cutoff frequency ?

First order low pass Butterworth filter Medium
A.
B.
C.
D.

23 The roll-off rate of a first order low pass Butterworth filter beyond the cutoff frequency is:

First order low pass Butterworth filter Medium
A.
B.
C.
D.

24 In a first order high pass Butterworth filter, at frequencies well below the cutoff frequency the gain magnitude:

First order high pass Butterworth filter Medium
A. Rises at as frequency falls
B. Decreases at as frequency falls
C. Equals times the maximum gain
D. Remains constant at the passband gain

25 A high pass Butterworth filter is designed for a cutoff of using . What resistor value is required?

First order high pass Butterworth filter Medium
A.
B.
C.
D.

26 A wide band pass filter is realized by cascading a low pass and a high pass section. For proper operation, the relationship between the low pass cutoff and high pass cutoff must be:

Band pass filter Medium
A.
B. exactly
C.
D.

27 A band pass filter has a center frequency of and a bandwidth of . What is its quality factor ?

Band pass filter Medium
A.
B.
C.
D.

28 A band reject (notch) filter is commonly used in instrumentation to:

Band reject filter Medium
A. Eliminate power line interference
B. Pass only a single narrow band of frequencies
C. Provide constant phase shift
D. Boost all frequencies uniformly

29 A wide band reject filter is typically constructed by combining a low pass and high pass filter using a:

Band reject filter Medium
A. Single voltage follower stage
B. Summing amplifier at the outputs
C. Series RC differentiator
D. Wien bridge network

30 An all pass filter has a constant magnitude response over all frequencies. Its primary purpose is to:

All pass filter Medium
A. Attenuate high frequencies only
B. Block the DC component of a signal
C. Provide voltage gain that rises with frequency
D. Introduce a controlled, frequency-dependent phase shift

31 For a first order all pass filter, as the input frequency increases from to , the output phase shift varies over a range of approximately:

All pass filter Medium
A. to
B. to
C. to
D. to

32 In an op-amp astable (square wave) multivibrator, the frequency of oscillation depends on the RC time constant and the feedback ratio . Which change will increase the output frequency?

Square wave generator Medium
A. Increasing the supply voltage
B. Increasing the timing capacitor
C. Increasing the load resistance
D. Decreasing the timing resistor

33 In an op-amp square wave generator, the capacitor voltage charges and discharges between two threshold levels set by the:

Square wave generator Medium
A. Positive feedback voltage divider
B. Input bias current
C. Negative feedback capacitor only
D. Output saturation current

34 A triangular wave generator is typically built by cascading which two circuits?

Triangular wave generator Medium
A. Two integrators in series
B. A differentiator followed by a comparator
C. A rectifier followed by a filter
D. A square wave (comparator) followed by an integrator

35 In a triangular wave generator, the amplitude of the triangular output can be increased by:

Triangular wave generator Medium
A. Reducing the op-amp supply voltage
B. Increasing the integrator feedback capacitor
C. Increasing the integrator input resistor or decreasing the comparator feedback ratio
D. Increasing the frequency of oscillation

36 How does a sawtooth waveform differ from a triangular waveform?

Sawtooth wave generator Medium
A. A sawtooth has no DC content ever
B. A sawtooth is a pure sinusoid
C. A sawtooth has unequal rise and fall times (asymmetric)
D. A sawtooth has equal rise and fall slopes

37 In a Voltage Controlled Oscillator (VCO), the output frequency is a function of the:

Voltage controlled oscillator Medium
A. Applied DC control voltage
B. Supply ripple frequency
C. Ambient temperature only
D. Output load current

38 The IC 566 VCO produces which two synchronized output waveforms?

Voltage controlled oscillator Medium
A. Sine wave and sawtooth wave
B. Pulse train and sinusoid
C. Square wave and triangular wave
D. Square wave and sine wave

39 In a 555 timer operating in astable mode with resistors and capacitor , the frequency is given by . If , , and , the frequency is approximately:

555 timer pin configuration and operating modes Medium
A.
B.
C.
D.

40 In the monostable mode of a 555 timer, the width of the output pulse is given by . For a output pulse using , the required resistance is approximately:

555 timer pin configuration and operating modes Medium
A.
B.
C.
D.

41 A designer claims an active filter can achieve a roll-off steeper than dB/decade per pole using only a single op-amp and passive RC networks. Which statement best analyzes the fundamental limitation?

Introduction to active filters Hard
A. A single RC pole can yield dB/decade if the op-amp is configured for positive feedback
B. The op-amp gain-bandwidth product alone determines the achievable roll-off slope independent of the RC network
C. The roll-off slope is set solely by the op-amp slew rate and is unrelated to the number of poles
D. Each independent RC pole contributes exactly dB/decade; steeper slopes require cascading more poles regardless of the op-amp

42 A first-order low-pass Butterworth filter has and in its RC section, with a passband gain of . What is the gain magnitude (in dB) at the cutoff frequency?

First order low pass Butterworth filter Hard
A. dB
B. dB
C. dB
D. dB

43 In a first-order high-pass Butterworth filter, the transfer function magnitude is . At what frequency ratio does the output reach of the passband gain ?

First order high pass Butterworth filter Hard
A.
B.
C.
D.

44 A wide band-pass filter is formed by cascading a high-pass stage ( Hz) with a low-pass stage ( kHz). What is the quality factor of this band-pass filter?

Band pass filter Hard
A.
B.
C.
D.

45 A narrow-band multiple-feedback band-pass filter must have kHz and . If the design requires the gain at resonance , what problem arises and how is it typically managed?

Band pass filter Hard
A. The gain becomes negative and the filter oscillates, requiring a series limiting resistor
B. The bandwidth becomes zero, forcing use of a switched-capacitor topology
C. Required midband gain becomes , so the design constraint must be satisfied to keep resistor values realizable
D. The gain drops to , so extra gain stages must be cascaded to compensate

46 A notch (band-reject) filter built from a twin-T network has a theoretical notch depth of infinity. In practice the achievable notch depth is limited primarily by which factor?

Band reject filter Hard
A. The supply voltage available to the op-amp
B. The input signal amplitude relative to the noise floor
C. Mismatch and tolerance of the twin-T's R and C components
D. The op-amp slew rate at the notch frequency

47 A band-reject filter is realized by summing the outputs of a low-pass ( Hz) and a high-pass ( kHz) filter. What is the essential requirement for this to behave as a proper wide band-reject filter?

Band reject filter Hard
A. The low-pass and high-pass gains must be equal and opposite in sign
B. of the high-pass must be greater than of the low-pass so the stopband lies between them
C. must equal so the outputs cancel completely at one frequency
D. The two filters must share the same cutoff and a common feedback capacitor

48 A first-order all-pass filter provides a phase shift that varies with frequency while keeping magnitude constant. For a lag-type all-pass with time constant , at what is the output phase shift relative to input?

All pass filter Hard
A.
B.
C.
D.

49 Which statement correctly distinguishes the pole-zero placement of an ideal all-pass filter in the s-plane?

All pass filter Hard
A. Poles and zeros coincide, cancelling to give unity transfer at all frequencies
B. All poles are at infinity while zeros are at the origin
C. Zeros lie on the axis while poles lie at the origin
D. Poles and zeros are mirror images about the axis, giving flat magnitude but nonzero phase

50 An op-amp astable (square wave) multivibrator uses feedback fraction . If , the oscillation period is . What is for , ?

Square wave generator Hard
A. ms
B. ms
C. ms
D. ms

51 In an op-amp square wave generator, the output amplitude is clamped to . If back-to-back Zener diodes ( V, V) are added at the output, what is the new peak-to-peak output amplitude?

Square wave generator Hard
A. V
B. V
C. V
D. V

52 A triangular wave generator uses a comparator followed by an integrator. If the square wave has amplitude V, integrator , , and the comparator threshold ratio gives a triangle peak of V at kHz, what determines the triangle peak amplitude?

Triangular wave generator Hard
A. The ratio in the comparator feedback network, times
B. The integrator time constant alone
C. The Zener voltage of the output clamp only
D. The op-amp slew rate divided by the frequency

53 In a triangular wave generator, the output frequency is (with the integrator constant). If the triangle amplitude must be increased while keeping frequency constant, which adjustment achieves this?

Triangular wave generator Hard
A. Increase the supply voltage which raises only
B. Increase and correspondingly increase to hold fixed
C. Decrease to raise the comparator threshold
D. Increase only so the integration is slower

54 A sawtooth generator differs from a triangular generator mainly because its rising and falling ramps have unequal slopes. In an op-amp integrator-based sawtooth, how is this asymmetry most commonly introduced?

Sawtooth wave generator Hard
A. By clamping only the positive output peak with a Zener
B. By using two integrators in series with matched capacitors
C. By increasing the comparator hysteresis symmetrically
D. By steering charge and discharge through different resistances using a diode, making rise and fall time constants unequal

55 For the 566 VCO, output frequency is . Given V, V, , , find .

Voltage controlled oscillator Hard
A. kHz
B. kHz
C. kHz
D. kHz

56 In an IC 566 VCO, the datasheet recommends the control voltage stay in the range . What is the analytical reason for the lower bound?

Voltage controlled oscillator Hard
A. Below the output amplitude exceeds the supply rail
B. Below the timing capacitor cannot discharge
C. Below the internal current sources saturate and the frequency-vs-voltage linearity degrades
D. Below the oscillator switches to monostable mode

57 A 555 in astable mode uses , , . What is the duty cycle of the output?

555 timer pin configuration and operating modes Hard
A.
B.
C.
D.

58 A 555 monostable is triggered while its output is still HIGH from a previous trigger. What happens, and which pin governs this behaviour?

555 timer pin configuration and operating modes Hard
A. The pulse width doubles because pin 6 latches the second trigger
B. The pulse is not restarted or extended; retriggering is ignored until the timing completes because trigger (pin 2) only acts when output is low
C. The output immediately resets to low via pin 4
D. The control voltage on pin 5 forces a new longer pulse

59 The control voltage pin (pin 5) of a 555 is normally at . If an external voltage of is applied to pin 5 in astable mode, what is the effect on timing?

555 timer pin configuration and operating modes Hard
A. Both threshold and trigger levels shift, changing the charge/discharge intervals and thus the output frequency
B. The timer stops oscillating and latches high
C. Only the output amplitude changes while frequency stays constant
D. The discharge transistor is disabled, doubling the period

60 Modern switched-capacitor (SC) filters replace physical resistors with switched capacitors clocked at frequency . What is the key analytical advantage over classic RC active filters?

recent trends in electronics Hard
A. They operate without any clock, purely from the input signal
B. The cutoff frequency tracks and the capacitor ratio, giving precise, tunable, IC-integrable filters independent of absolute component values
C. They eliminate the need for any op-amp in the signal path
D. They provide infinite roll-off with a single pole
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