1C Flashcards
A transistor may be connected in three basic amplifier configurations:
- Common Emitter (CE) or Grounded Emitter
- Common Base (CB) or Grounded Base
- Common Collector (CC) or Emitter Follower or Grounded Collector
You can use the following steps to identify a transistor amplifier configuration:
Step 1. Identify the element to which the input signal is applied. The input is always
applied to the emitter or base, never the collector element.
Step 2. Identify the element from which the output signal is taken. There will
always be a load resistance in the output. The output is never taken from the base.
Step 3. The remaining element is the common element.
Apply these steps to identify the configurations shown in Figure 1-117A. If the input signal is applied to the base and the output signal is taken from the collector, the common element is the
emitter (not used for signal). Since the emitter is the remaining element, this transistor is connected in the ___ ___ (CE) configuration.
Common Emitter
Looking at Figure 1-117B, if the input is applied to the emitter and the output is taken from collector, then the common element is the base (not used for signal). This transistor is connected
in the ___ ___ (CB) configuration.
Common Base
Finally, looking at Figure 1-117C, if the input is applied to the base and output is taken from the emitter, the common element is the collector (not used for signal). This transistor is connected in the ___ ___ (CC) configuration.
Common Collector
____ is defined as the average DC voltage (or current) used to establish the operating point in transistor circuits for a static, or quiescent, condition.
Bias
___ ___ means the circuit is powered on, but there is no input signal (Figure 1-118A), so the transistor is in a fixed, non-varying condition. Figure 1-118B shows the transistor is outputting
a steady voltage.
Static condition
A circuit’s ability to take a small change input (voltage or current) and produce a larger change in output (voltage or current)
Amplification
The input is always applied to the emitter or the base; never the collector:
NIC =
Never In the Collector
The output is never taken from the base:
NOB =
Never Out of the Base
In the static, or quiescent, state, a transistor is deactivated, or has no input, but what do you call it when the device is activated, or its conditions do vary? The varying condition of an amplifier
circuit is called its ___ ___ or operating condition.
dynamic condition
This occurs whenever an input signal is applied to a device in a static condition.
dynamic condition/operating condition
In a silicon transistor, the nominal forward bias across the EB junction is approximately ___ V.
0.6V
The ___ is the controlling factor for transistor operation
bias
Figure 1-121A shows an NPN transistor with 0.6V of forward bias across the EB junction and 10V of reverse bias across the CB junction. Under these conditions, current will flow from the
emitter to the base and from the emitter to the collector. The ___ ___ ___ ___ indicates the relative magnitudes of current flow.
width of the arrows
An increase in forward bias results in a current ___
A decrease in bias will ___ current
increase
decrease
Earlier, two different batteries were used to provide VEE and VCC. These voltages can also be supplied by a single power source using a ___ ___ ___ (Figure 1-122).
voltage divider circuit
The single power source is usually referred to as ___. REB represents the resistance of the emitter-base junction. The positive side of the battery is connected to the collector, and the negative side of the battery is connected to the emitter, which is grounded.
Vcc
Connecting RD between the base of Q1 and VCC provides a complete path for current flow through the emitter-base (EB) junction. RD and REB form a simple voltage divider. Current through this voltage divider network develops voltages across RD and REB. This voltage divider arrangement ___ ___ the emitter-base junction. By RD developing 19.4 V, this leaves 0.6 V for the emitter-base voltage (bias).
forward biases
The ___ ___ for the collector-base (CB) junction is the difference between the base voltage (0.6V) and VCC (20V). This makes the collector 19.4V more positive than the base, reverse biasing
the CB junction.
reverse bias
Another way of looking at the reverse biased CB junction is to realize that the most positive potential of the circuit is on the ____, which is N-type material.
collector
In all transistor circuits, a resistor (RD) connected between VCC and the base is mandatory. This resistor is necessary to determine the ___ of the ___. It determines the amount of base current and the voltage dropped across the EB junction (bias).
bias of the transistor
In some circuits, a resistor (RB) may be placed in parallel with the EB junction to improve ___ ___ and aid in developing forward bias (Figure 1-123). Since voltages in parallel are common,
the voltage drop across RB will be 0.6V. In this illustration, RB is adjustable and can be used to change the bias of Q1 and the output of the amplifier.
circuit stability
Another necessary component in transistor circuits is a load resistance (RL). This resistor enables Q1 to develop an output. The load resistor is placed in series with the transistor. By properly biasing the transistor, it allows a specific amount of ___. This same current will flow through the series load resistor developing a voltage (10V). The transistor will drop the remaining voltage (10V).
current
There are numerous operation classes for amplifiers. The most common amplifier classes are those used to amplify ___.
audio
What are the four classes of amplifiers?
A
B
AB
C
The class of operation is determined by how many ___ of the input signal the amplifier conducts, or how long the amplifier works during
an input signal.
degrees
Three terms are used to describe the characteristics of amplifiers:
fidelity, efficiency, and distortion.
___ is defined as the degree to which a device accurately reproduces the signal applied to its input.
Fidelity
Resistor RL controls the gain for the circuit. The size of the resistor is directly ____ to gain.
proportional
Resistor RD develops the ___ ___ for operation of the transistor amplifier.
bias voltage
The ratio between the output signal power and the total input power
Efficiency
The result of changing a waveshape so that its amplitude is no longer proportional to the original amplitude
Distortion
Amplifiers can produce an output signal from all, or ___ ___ ___, of the input signal
just a portion
The following describes which class of amplifier?
An exact reproduction of the input at the output
Biased so collector current will flow for 360° of the input signal (conduct 100% of the time)
Highest fidelity
Lowest efficiency
Class A
The following describes which class of amplifier?
Some amplitude distortion
Biased so collector current flows more than 180°, less than 360°
of the input signal (conducts 51% to 99% of the time)
Average/good fidelity, poor efficiency
Class AB
All four classes of transistor amplifiers below are assuming you know the normal PN junction forward biasing operation is between .2V and .9V. So, remember to closely look at the ___ ___ and how that effects the reproduced wave on the output.
input signal
The Class A design is the most inefficient (always consuming power) and is used in ___ ___ ___, as well as in very high-end stereo systems.
low power applications
Class AB designs are the most widely used for ___ applications.
audio
The following describes which class of amplifier?
Amplitude distortion
Biased so collector current flows for 180 of the input signal(conduct 50% of the time)
Poor fidelity
Average/good efficiency
Class B
The following describes which class of amplifier?
Distortion on both alternations
Biased so collector current flows for less than 180° of the input signal (less than 50% of the time)
Lowest fidelity
Most efficient
Class C
Figure 1-29 shows an ___ ___, which is not a class of operation, but an amplifier stage. ___ is an amplitude distortion. If the input signal is applied to an amplifier too large, one alternation will drive the amplifier to saturation, and the other alternation will drive
the amplifier to cutoff. The output sine wave is chopped off at the top and bottom, resulting in a signal that is poor in fidelity and efficiency.
Overdriven Amplifier
High gain amplifiers become unstable, unpredictable and create distortion in the circuit. To reduce distortion and noise in an amplifier, the voltage gain (AV) is normally restricted to a gain of about ___.
10
To achieve the high gain needed, amplifiers are connected in series (or cascaded together) to form ___ ___.
cascade amplifiers
Coupling circuits join the ___ ___ connecting the output of one to the input of another.
amplifiers together
____ is the technical term for an amplifier’s output-to-input magnitude ratio.
Gain
In amplifiers, gain can be expressed in terms of:
voltage, current and/or power
The gain of any device is a ratio of the change in ___ to the change in ___ (in mathematical terms).
output
input
Looking at the schematic diagram in Figure 1-130, we can say that the change in the input is 0.7V and the change in output is almost 10V. Notice this amplifier’s output starts at 5V, but that can be ignored. What you want to look at is the change, which is almost 10V total (peak-to-peak). Using the gain formula, we divide the change in output (10V) by the change in input (0.7V). 10V/.7V =14.29, giving us an answer of 14. This answer is expressed only as a plain number and should not have any voltage value. Any gain that is more than ___ is an increase.
1
The following describes which kind of amplifier?
For this discussion on the CE Amplifier operation, refer back to Figure 1-13,1 if needed. In the static condition, the collector voltage (Vc) is 15V and the voltage drop across the collector load resistor (R3) is 10V. On the positive alternation of the input signal, base current will increase due to an increase in base voltage from .6V to .7V. The increase in IB causes IC to increase. The voltage across R3 increases from 10V to 15V. VC then decreases from 15V to 10V. Note that increasing IB, increases IC and decreases VC. The output signal varies at the same rate as the sine wave input, but the output signal is amplified. The output signal is 180° out of phase with the
input signal.
Common Emitter
The following describes which kind of amplifier?
A ___ ___ amplifier configuration is shown in Figure 1-132. Notice the input signal is applied to the emitter, and the output signal is taken from the collector. The base is the element that is common
to both the input and output. The collector waveform is an amplified reproduction of the positive input alternation. The input and output signals are in phase. Notice that the base is connected to
AC ground (a filter) through capacitor C1 and holds DC voltage at the base steady. The power supply voltage (VCC), R1, and R2 provide forward bias for the emitter-base junction. Resistor R4
develops the input signal, and the collector load resistor R3 allows the collector to ground voltage (VC) to change as transistor resistance changes, thus, developing the output signal across the transistor.
Common Base
The ___ ___ amplifier has high current and power gain. It also has excellent stability and frequency response. The amplifier’s voltage gain is always less than one (<1), but the current gain is >1.
Common Collector
The following is describing which type of amplifier?
As the positive alternation of the input signal is applied to the base of the NPN transistor, an increase in base and emitter currents occurs (forward bias increases). The increase in current through R3 causes a corresponding increase in its voltage drop. In other words, the output signal goes more positive with respect to ground. The negative alternation of the input signal causes base and emitter currents to decrease, causing the output to become less positive. The output signal voltage developed across R3 is controlled by a change in input signal, and the two signals are in phase.
Common Collector
Some heat sinks have ____ to dissipate heat into the surrounding air more rapidly. The heat produced at the junctions of the transistor transfers to the metal case of the transistor. Since
the heat sink makes direct contact with the metal case, the heat transfers to the heat sink, and then the air. This lowers the operating temperature at the junction of the transistor.
fins
The three-stage cascade amplifier shown in Figure 1-136
below uses a ____ between each stage.
coupling
FETs are similar in construction to BJTs. FETs have three terminals. They are ___, ___ and ___. These terminals correspond roughly to the emitter, the collector, and the base of the BJT.
Source (S), Drain (D), and Gate (G).
The ____ is the source, or entry point, of the current.
Source
The ___ is where the current leaves, or drains, from the FET.
Drain
The ___ terminal may be thought of as controlling the opening and closing of a physical gate.
Gate
Which FET is the following describing?
Simplest type
Three-terminal semiconductor devices
Used as electronically controlled switches, amplifiers, or voltage controlled resistors
Current does not have to cross through the PN junction
Junction FET (JFET)
Solid state relays are purely ___ and contain no moving parts.
electronic
A SSR contains a ___ ___ ___ in the primary circuit, which provides optical coupling to a photodiode array (PDA). The PDA connects to a switching device, typically two MOSFETs.
light emitting diode (LED)
When no voltage is applied to the LED, the MOSFETs are shut off, and no current flows in the secondary circuit. When voltage is applied to the LED, it shines on the PDA, which produces a
voltage between the MOSFET’s source and its gate. This causes the MOSFET to turn on allowing current to flow in the secondary circuit. A MOSFET cannot block current in both directions, so if
the secondary voltage is AC, ____ MOSFETs are arranged back-to-back with their source pin tied together. This allows the two MOSFETs to act as an open switch when no voltage is applied to
the LED and as a closed switch when voltage is applied to the LED.
two
