Question 1

In the label dBm,the m at the end of dBm designates the millivolt reference.

Accepted Answer

The "m" in dBm stands for milliwatt, indicating that the power level is referenced to 1 milliwatt.

Question 2

To prevent oscillations,most op amp circuits include an RC lag circuit that rolls off the voltage gain.

Accepted Answer

The RC lag circuit is used to limit the bandwidth of the circuit and prevent oscillations. This is accomplished by rolling off the gain at high frequencies, which prevents the circuit from amplifying noise and other unwanted signals.

Question 3

A fast and simple method to test the frequency response of an amplifier is
A) by using sine-wave testing.
B) by using square-wave testing.
C) by measuring dc voltages.
D) by measuring resistance values.

Accepted Answer

Square-wave testing is a fast and simple method to test the frequency response of an amplifier. When a square wave is applied to the input of an amplifier, the output should ideally also be a square wave if the amplifier has a good frequency response. Deviations from the ideal square shape at the output can indicate issues with the amplifier's response to different frequencies. This method is quicker and simpler compared to sine-wave testing, which requires testing at many different frequencies to fully understand the amplifier's frequency response.

Question 4

A common-emitter amplifier that uses coupling and bypass capacitors is an example of a dc amplifier.

Accepted Answer

A common-emitter amplifier that uses coupling and bypass capacitors is an example of an AC-coupled amplifier. It blocks the DC component of the input signal, allowing only the AC component to pass through the amplifier for amplification.

Question 5

Impedance matching in communication systems is used because it produces maximum power transfer.

Accepted Answer

Impedance matching is used in communication systems to minimize signal reflection and attenuation, resulting in maximum power transfer between devices.

Question 6

Each time the ordinary power gain decreases by a factor of 2,the decibel power gain decreases by 3 dB.

Accepted Answer

This statement is true according to the formula for converting power gain to decibel power gain - for each reduction by a factor of 2 in power gain, the decibel power gain decreases by 3 dB.

Question 7

The frequency response of an ac amplifier shows decreased voltage gain at low frequencies because of the effects of capacitive reactances.

Accepted Answer

Capacitive reactances have an inverse relationship with frequency, meaning that as the frequency decreases, the capacitive reactance increases. This causes the signal to have a harder time passing through the capacitor, resulting in decreased voltage gain at low frequencies.

Question 8

In a dc amplifier,all the frequencies from zero up to the cutoff frequency is referred to as the
A) roll off.
B) maximum band.
C) notch frequencies.
D) bandwidth.

Accepted Answer

The frequencies from zero up to the cutoff frequency in a DC amplifier are referred to as the bandwidth. Therefore, option D is the correct choice. Options A, B, and C are incorrect as they do not accurately describe this frequency range in a DC amplifier.

Question 9

The frequencies at which the voltage gain equals 0.707 of its maximum value are called the half-power frequencies.

Accepted Answer

This statement is true. The frequencies at which the voltage gain equals 0.707 or -3dB of its maximum value are called the half-power frequencies. This is commonly used in frequency response analysis and design of filters.

Question 10

A designer can use direct coupling between amplifier stages in order to amplify down to zero hertz.

Accepted Answer

Direct coupling (also known as DC coupling) allows the signal to pass directly from one amplifier stage to the next without any capacitive or inductive coupling, thus enabling the amplification of signals down to zero hertz (DC signals).

Question 11

A Bode plot is a graph that uses decibels and provides more information about the amplifier's response outside the midband.

Accepted Answer

A Bode plot is a graph that uses logarithmic scales for frequency and amplitude, typically in decibels, to show the gain, phase shift, and other characteristics of a circuit or system over a wide range of frequencies. It provides more information about the amplifier's response outside the midband, including the high and low frequency roll-off, frequency response, and stability.

Question 12

In music,the word octave refers to eight times the frequency.

Accepted Answer

An octave in music refers to the interval between one musical pitch and another with double its frequency, not eight times.

Question 13

The frequency response of an amplifier is the graph of its gain versus the frequency.

Accepted Answer

The frequency response of an amplifier is indeed the graph of its gain (or output amplitude) versus the frequency. This is an important characteristic of any amplifier or other electronic system that can affect the signal processing or transmission. The frequency response can show how well the system operates over a range of frequencies or how it amplifies, attenuates, or distorts specific frequency components in the input signal.

Question 14

The Miller effect has useful applications because
A) it creates virtual capacitors that are much larger than the feedback capacitor.
B) it creates virtual resistors that are much larger than the load resistor.
C) it creates additional gain without adding amplifiers.
D) it makes coupling capacitors appear smaller than they actually are.

Accepted Answer

The Miller effect creates virtual capacitors that are much larger than the feedback capacitor, which can be useful in amplifier design and can improve frequency response.

Question 15

When an op amp includes one dominant bypass capacitor that rolls off the voltage gain at a rate of 20 dB per decade,it means the op amp is
A) operating as an open-loop.
B) externally compensated.
C) internally compensated.
D) operating as a closed-loop.

Accepted Answer

An op amp with one dominant bypass capacitor that rolls off the voltage gain at a rate of 20 dB per decade is internally compensated. This is because internal compensation is achieved using a dominant pole in the frequency response, where a single capacitor is used to set the pole frequency. This dominant pole limits the bandwidth of the op amp and makes it stable when used in a closed-loop configuration.

Question 16

The total voltage gain of a two-stage cascaded amplifier is the sum of the individual voltage gains.

Accepted Answer

The total voltage gain of a two-stage cascaded amplifier is the product of the individual voltage gains, not the sum.

Question 17

The charging and discharging of a capacitor produce a lag in the output voltage of an RC bypass circuit.

Accepted Answer

This is because capacitors take time to charge and discharge, thus creating a lag in the output voltage of an RC bypass circuit. This lag is commonly referred to as the time constant, which is determined by the values of the resistance and capacitance in the circuit.

Question 18

Most amplifiers are now being built using
A) BJTs.
B) MOSFETs.
C) power amps.
D) op amps.

Accepted Answer

The answer of Most amplifiers are now being built using
A)...

Question 19

Decibel power gain is often used on data sheets to specify the power gain of devices.

Accepted Answer

Decibel power gain is a common way to specify the power gain of devices on data sheets. This value is often provided in units of dB, which can be easily converted to a power amplification ratio.

Question 20

The total decibel voltage gain of two cascaded stages equals the sum of the individual decibel voltage gains.

Accepted Answer

The decibel voltage gain is a logarithmic scale, so the individual gains of each stage can be added together to determine the overall gain in decibels.

Quiz 14: Frequency Effects