+ − + − V$_{output}$ V$_{input}$ E B C R$_{load}$ + − + − V$_{output}$ V$_{input}$ Q$_{1}$ R$_{load}$ 5.0k Ω R$_{1}$100 Ω V$_{1}$ 15V V$_{input}$ 0.12V$_{pp}$ 0V$_{offset}$  2 kHz v (4) I0*V ( 5.2 ) 15.0 10.0 5.0 0.0 500.0 1000.0 0.0 −5.0 Time uS Common-emitter Common-collector Common-base Input: fairly high Output: fairly high Input: high Output: low Input: low Output: high Relatively large Always less than one Large Large Relatively large Relatively large Inverts phase Output same as input Output same as input Relatively large Relatively large Always less than one Type of Amplifier Impedance Voltage Gain Current Gain Power Gain Phase 11-24 Figure 11-54.  PN junction transistor amplifier characteristics.  A square wave is produce when there is a flow of electrons  for a set period that stops for a set amount of time and  A sine wave is produced by generators when a conductor  is rotated in a uniform magnetic field. The typical AC sine  wave is characterized by a gradual build-up and decline of  voltage in one direction, followed by a similar smooth build- up to peak voltage and decline to zero again in the opposite  direction. The value of the voltage at any given time in  the cycle can be calculated by taking the peak voltage and  multiplying it by the sine of the angle through which the  conductor has rotated.  [Figure 11-55] An oscillator known as a relaxation oscillator produces  another kind of wave form, a sawtooth wave. A slow rise from  zero to peak voltage is followed by a rapid drop-off of voltage  back to almost zero. Then it repeats.  [Figure 11-57]  In the  circuit, a capacitor slowly charges through a resistor. A neon  bulb is wired across the capacitor. When its ignition voltage  is reached, the bulb conducts. This short-circuits the charged  capacitor, which causes the voltage to drop to nearly zero  and the bulb goes out. Then, the voltage rises again as the  cycle repeats. Oscillators function to make AC from DC. They can produce  various waveforms as required by electronic circuits. There  are many different types of oscillators and oscillator circuits.  Some of the most common types are discussed below. then repeats. In DC current, this is simply pulsing DC.  [Figure 11-56]  This same wave form can be of opposite  polarities when passed through a transformer to produce AC.  Certain oscillators produce square waves. NOTE: There are many variations in circuit design. JFETs  and MOSFETS are also used in amplifier circuits, usually in  small signal amplifiers due to their low noise outputs. to flow from the collector to the emitter during both cycles  of the AC. A circuit for AC amplification is illustrated in  Figure 11-53  with a graph of the output voltage showing  the large increase produced. The common-base amplifier is  limited in its use since it does not increase current flow. This  makes it the least used configuration. However, it is used in  radio frequency amplification because of the low input Z.  Figure 11-54  summarizes the characteristics of the bipolar  amplifier circuits discussed above. Oscillator Circuits Figure 11-53.  In a common-base amplification circuit for AC (top),  output voltage amplitude is greatly increased in phase with the  input signal (bottom).  Figure 11-52.  A common-base amplifier circuit for DC current. 