Chapter 10 Solid State
In determining gain, an amplifier can be thought of as a...
"Black box"
What points on the frequency response curve are the upper and lower frequency limits?
0.707 times it's max gain
The ratio of a decibel:
1.26 1.26/1 100/79.4
A typical resistance value for a transistor is...
100,000 ohms
What is the bandwidth of a frequency response curve?
2,000Hz to 20,000 Hz
Common base amplifier
A BJT with both the input and output signals connected to the base.
A common collector circuit is also known as
A emitter follower circuit, because output is taken from the emitter.
On a characteristics curve, the operating point or quiescent (Q) point, is established on...
A load line.
Base-emitter impedance:
A low resistance value and is the input impedance of the common-emitter amplifier.
cascade amplifier:
A series of connected amplifiers in which the the output to one amplifier is connected to the input of another. (10x10=100)
What are the four main classes of amplifier operation?
A,B,AB, and C
Common-collector circuit operation:
Almost identical to a common-emitter circuit, however the output voltage for the circuit is is equal to the input voltage minus voltage drop from base to to emitter of the transistor.
Total Harmonic Distortion (THD)
Amplifier distortion, expressed as a percentage such as 0.05% THD. Lower the %, higher quality of amplifier.
Linear amplifier:
Amplifier that increases the and maintains the the exact duplicate of an input signal. In other words the output signal is the same as the input signal, but larger.
For a signal transfer to occur with minimal loss...
An amplifier should have extremely high input impedance and extremely low output impedance.
Common Emitter Amplifier signal
An input signal must be applied to make an amplifier change from static (rest) condition to a dynamic condition (normal operation)
Grounded emitter circuit:
Another word for common emitter circuit because the emitter is connected to ground.
Distortion:
Any undesirable change in a signal. Stereo amplifiers are linear so that music can be duplicated with the least amount of distortion.
Class A amplifiers are used...
As audio amplifiers where true reproduction of the waveform is demanded.
Phase inversion:
As input signal increases, output signal decreases. 180 degree phase shift
Common-emitter amplifier:
BJT with both output and input signals connected to the emitter.
Common Collector Amplifier
BJT with both the input and output signals connected to the collector.
Beta is the change in...
Base current
Beta definition:
Beta (transistor current gain) is the maximum gain possible for for a single stage (one transistor) amplifier circuit.
Alpha equals:
Change in collector current/ change in emitter current
3 basic types of transistor amplifiers:
Common-emitter, common-base, common-collector
Where is the input signal applied to in a common-base amplifier?
Directly to the emitter. Emitter current controls collector current.
Common-collector circuit has the ability to pass signals in______ direction
Either
Alpha is the change in...
Emitter current
What graph shows the bandwidth for a given amplifier?
Frequency response curve
Formula for gain:
Gain= output/input
For many amplifiers, gain is in the...
Hundreds or thousands
In a controls system, transistor AC amplifiers are used:
Increase small signal currents and voltages so that they can do useful work.
Common Collector Amplifier impedance
Input impedance is high (100,000ohm) and output is low (1,000 ohm or less).
Common Collector circuit
Input signal is applied between the collector-base junction, but output is taken from collector-emitter circuit
Common emitter circuit operation
Input signal is positive, output signal is negative, phase inversion.
Common base circuit operation:
Input signal positive, output signal positive
Input Impedance
Is the loading effect an amplifier presents to an incoming signal.
A common collector circuit is often used as an....
Isolation amplifier, because of its high input impedance.
Wide bandwidth:
Large range of frequencies over which an amplifier operates.
Bel
Larger unit then a decibel and was originally used to show loss of signal in 2 miles of telephone wire.
Amplifier gain for a particular transistor should always be_____ then the Beta of the single transistor in the circuit.
Less
Class A amplifiers are also called:
Linear amplifiers
Class AB Operation
Located between class A and B amplifiers on load line. Collector current flows more than half input signal, but less than full.
Class C operation:
Located closest to cutoff. Collector current flows for less than half the input signal. Found in radio frequency transmitters.
Class B operation:
Located near lower end of load line close to cutoff. Reproduces 180 degrees of input signal, collector current only flows half the the input signal. Used mostly with a pair of transistors.
Common-emitter amplifier impedance:
Low base-emitter impedance is the input and a high collector-emitter impedance is the output.
Common-base amplifier impedance:
Low input impedance (100ohms) and high output impedance (100,000ohms)
Maximum ratings of transistors
Must not be exceeded under normal operating conditions. Max ratings include voltage, current, power dissipation, and temperature.
Half power point:
Point on a frequency-response curve where the power output is one half the maximum value.
Impedance matching:
Process of setting the input impedance of a load equal to the output impedance of a signal source. Must be used when connecting devices to an amplifier, such as a antenna, microphone, and speakers.
Amplification:
Process of taking small signal and making it larger.
What is the primary purpose of an amplifier?
Produce gain.
The common base circuit is _____ used
Rarely
Current gain:
Ratio of output current to input current.
Power gain:
Ratio of output power to input power.
In a common base amplifier circuit, the base is the:
Reference point and the ground.
Beta refers to...
Refers to transistors as a single device, doesn't refer to the whole amplifier circuit containing a transistor.
Transistor specification sheets
Shows characteristics of semiconductors, including max ratings, mechanical data, heat sinking Info, and characteristics curve.
How is signal passed through a Common emitter amplifier?
Signal enters the amplifier through the input circuit and exits through the output circuit.
Signal change due to cutoff:
Signal may be clipped or distorted. May be used in circuits such as a radio transmitter circuit.
Narrow bandwidth:
Small range of frequencies over which an amplifier operates.
The large ratio of output impedance to input impedance makes it possible for...
The amplifier to produce a large voltage gain.
Mathematically bandwidth is expressed by:
The difference between upper half-power frequency and the lower half-power frequency.
Amplitude:
The distance a sine wave travels from its x-axis to its peak. The greater the amplitude, the louder the sound.
How is signal passed through a common base amplifier?
The input signal is applied to the emitter-base junction and and then output signal is taken from the collector-base junction.
Output impedance:
The loading effect an amplifier presents to another device.
Bandwidth
The range of frequencies over which an amplifier is maximum and relatively constant.
Voltage gain:
The ratio of output voltage to input voltage. V gain= Rms out/Rms in
What could happen when an operating point is located too close to saturation?
The signal may be clipped or distorted.
Operating points: distortion of the signal would result in...
The signal reaching saturation or cutoff. A signal swing should be set so that the signal never reaches cutoff or saturation.
What are preamplifiers?
They accept low-level audio signals, such as those from microphones and turntables, and amplify them to medium-level audio signals that are sent to amplifiers.
What is a common collector circuit often used for?
To couple high impedance sources to low impedance loads. Performs the same basic function as a impedance-matching transformer.
T/F: amplifiers are designed to operate within a given frequency range
True
Decibel (dB)
Unit of measure used to express the intensity of sound.
Class A operation:
Well above the cutoff condition of an amplifier. Collector current flows during entire input signal. Output duplicates the input, and increases its amplitude.
Signal change due to saturation and cutoff
When Input signal is too large, clipping and distortion may occur on both ends (alternations) of the signal.
The load line is where the transistor is biased...
When no signal is applied to the input.
Gain:
ratio of the amplitude of an output signal to the amplitude of an input signal.
