Chapter 0
Signals and amplifiers
Outline
• Signals
• Amplifiers and circuit models
1. Signals
• Signals contain information about a variety of things and activities
in our physical world.
• Examples:
Weather (air temperature, pressure, wind speed,…)
Voice
• Transducers: convert signals in physical world into electrical
signals (voltage or current).
1. Signals
• Frequency spectrum of signals
1. Signals
• Analog signals
• Digital signals
2. Amplifiers and circuit models
• Signal amplification: 𝑣 𝑡 = 𝐴 𝑣 (𝑡), where A is amplifier gain.
• Transfer characteristic of a linear amplifier
• Power gain and Current gain
• Gain in Decibels
2. Amplifiers and circuit models
• Gain in Decibels
2. Amplifiers and circuit models
• Amplifier power supplies
 Power delivered to the load is greater than the power drawn from the
signal source. What is the source of this additional power?
 Amplifiers needs DC power supplies for their operation.
Amplifier Power e iciency
𝑃
𝜂=
100%
𝑃
Where 𝑃 is Power of signal source, 𝑃 is power delivered to the load,
and 𝑃
is power dissipated in the amplifier circuit
2. Amplifiers and circuit models
• Amplifier Transfer Characteristic Amplifier Saturation
• Amplifier Frequency Characteristic
2. Amplifiers and circuit models
• Basic concepts
Circuit Models for Amplifiers
𝑨𝑽 : Voltage Amplifier
𝐴
𝑉
𝑉
𝐺
𝐼
𝑨𝑰 : Current Amplifier
𝑹𝒎: Transresistance Amplifier
𝑮𝒎 : Transconductance Amplifier
𝑅
𝐼
𝐴
2. Amplifiers and circuit models
• Voltage Amplifier
2. Amplifiers and circuit models
• Current Amplifier
2. Amplifiers and circuit models
• Transconductance Amplifier
2. Amplifiers and circuit models
• Transresistance Amplifier
2. Amplifiers and circuit models
• Typical parameters:
 Open-circuit voltage gain:
𝑣
𝐴 =
𝑣
 Voltage gain:
𝑣
𝐴 =
𝑣
 Short-circuit current gain:
𝑖
𝐴 =
𝑖
 Input resistance:
𝑉
𝑅 =
 Current gain:
𝐼
𝑖
 Input resistance without load:
𝐴 =
𝑉
𝑖
𝑅 =
𝐼
 Open-circuit overall voltage gain:
𝑣
𝐴 =
𝑣
 Overall voltage gain:
𝑣
𝐴 =
𝑣
 Output resistance:
𝑣
𝑅
=
𝑖
Overall voltage gain:
𝐴 =
𝑣
𝑣
=
𝑣
𝑣
∗
𝑣
𝑅
𝑅
=
∗
𝑣
𝑅 +𝑅 𝑅 +𝑅