Basic Electronics Ninth Edition Grob Schultz ©2002 The McGraw-Hill Companies

Basic Electronics Electronic Circuits 29 Ninth Edition CHAPTER ©2003 The McGraw-Hill Companies

Topics Covered in Chapter 29 Analog and Digital Signals Amplifier Gain Characteristics of Amplifier Circuits Oscillators and Multivibrators

Topics Covered in Chapter 29 (continued) Modulation Diode Rectifiers Troubleshooting the DC Supply Voltage

Types of Signals Analog signals have continuous variations in voltage or current level. Digital signals usually have only two levels.

Digital and Analog Signals 2 levels  levels Analog signal Digital signal

Amplification An amplifier circuit increases the amplitude of a signal. The gain of an amplifier is the ratio of output signal level to input signal level. The voltage gain of an amplifier is given by: Av = output voltage/input voltage The current gain of an amplifier is given by: Ai = output current/input current

Amplification (gain) Av = output voltage/input voltage Ai = output current/input current

Cascaded Amplifiers Amplifiers are said to be cascaded when the output of one amplifier is fed to the input of the next amplifier. The overall gain of cascaded amplifiers is equal to the product of the individual amplifier gain values.

Cascade Amplifiers VOUT VIN AV1 AV2 VOUT = AV1x AV2 x VIN

Active Components in Amplifiers Active components include: Transistors Integrated circuits Active components can increase signal levels. Active components require a power supply in addition to an input signal.

Passive Components in Amplifiers Resistors are used to provide IR voltage drops in amplifier circuits. Capacitors are used for signal coupling and bypass circuits. Inductors are used as chokes and transformers. Capacitors and inductors are combined in resonant circuits.

Transistor Amplifier IC IB IE

Oscillator Circuits An oscillator is an amplifier with positive feedback. No input signal is required. An oscillator generates an ac output when energized by a dc supply.

RF Feedback Oscillators Tuned circuits determine the operating frequency. A Hartley oscillator uses a tapped coil as an ac voltage divider for feedback. A Colpitts oscillator uses a capacitive voltage divider for feedback.

Transistor Colpitts Oscillator Tuned Circuit Positive Feedback

Multivibrators A multivibrator produces an output voltage that alternates between a HIGH and LOW level. An astable multivibrator produces a continuous train of pulses. A bistable multivibrator is stable at the HIGH or LOW state, but can be triggered to the opposite state.

Transistor Astable Multivibrator

Modulation Modulation is the process of modifying one signal according to the variations of another signal at a lower frequency. Amplitude modulation (AM) varies the amplitude of the RF carrier signal. Frequency modulation (FM) varies the frequency of the RF carrier signal.

Amplitude Modulation X 400 Hz 1 MHz X The instantaneous amplitude of the 1 MHz carrier is controlled by the 400 Hz input signal.

Frequency Modulation VCO 400 Hz VCO The instantaneous frequency of the voltage controlled oscillator (VCO) is determined by the 400 Hz input signal.

DC Power Supplies A dc power supply converts 60 Hz ac power to a dc level. The dc level from a power supply is needed as a source of power for amplifiers, oscillators, and other types of active circuits. A half-wave power supply uses only one-half of each ac waveform. A full-wave rectifier uses both alternations the input ac waveform.

Half-Wave Rectification Half-wave pulsating dc

Half-Wave Rectifier with Filter Filtered Pulsating dc