CIRCUIT DIAGRAMS - 5 | EXPERIMENT NO. 7: DIFFERENTIAL AMPLIFIER AND BASIC OP-AMP GAIN STAGES | Analog Circuit Lab
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5 - CIRCUIT DIAGRAMS

Practice

Interactive Audio Lesson

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Understanding the BJT Differential Amplifier Diagram

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0:00
Teacher
Teacher

Welcome, everyone! Today, we're going to explore the BJT differential amplifier circuit diagram. Can anyone tell me what a differential amplifier does?

Student 1
Student 1

It amplifies the difference between two input signals.

Teacher
Teacher

Exactly! Now, in the diagram, we see two NPN transistors, Q1 and Q2. They are key components here. What do you think happens at their emitters?

Student 2
Student 2

They connect to a current source, right? To keep the current constant?

Teacher
Teacher

Correct! This current source allows it to amplify the difference between the input signals. Any idea what happens at the collectors?

Student 3
Student 3

That’s where we connect the output to measure the amplified signal!

Teacher
Teacher

Well done! Remember, in the diagram, we can use it to observe both single-ended and differential outputs. Let’s summarize: the key components are the transistors, the current source, and how they relate to input and output signals.

Analyzing Op-Amp Circuit Diagrams

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0:00
Teacher
Teacher

Next, let’s look at the Op-Amp configurations. Who can explain the difference between the inverting and non-inverting amplifiers?

Student 4
Student 4

In the inverting amplifier, the signal is applied to the inverting input and the output is 180 degrees out of phase.

Teacher
Teacher

Great point! And how does this differ in the non-inverting configuration?

Student 1
Student 1

For the non-inverting amplifier, the input connects to the non-inverting input, so the output is in phase with the input.

Teacher
Teacher

That’s correct! In terms of gain, can anyone remind me how we calculate it for these configurations?

Student 2
Student 2

For the inverting amplifier, the gain is -Rf/Rin, and for the non-inverting, it’s 1 + R1/R2.

Teacher
Teacher

Exactly! Both configurations have unique advantages, and the circuit diagrams help visualize their functionality. Remember, these diagrams are crucial for implementing electronics in real-world applications.

Connecting Inputs and Outputs

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0:00
Teacher
Teacher

Now let’s discuss what happens when we apply input signals to these amplifiers. Can anyone explain what a differential input signal looks like?

Student 3
Student 3

It's when we have two different voltages applied to the base of the transistors.

Teacher
Teacher

Correct! And in the BJT diagram, how are these inputs connected?

Student 4
Student 4

Vin1 connects to the base of Q1 and Vin2 to Q2. We also can use the common emitter node.

Teacher
Teacher

Exactly! It’s crucial to differentiate between differential inputs and common-mode inputs. Can you all remember what happens with common-mode signals?

Student 1
Student 1

Ideally, the output should be close to zero for a well-functioning differential amplifier!

Teacher
Teacher

Correct! That shows you’ve understood the concept of common-mode gain, which should be very low. This understanding helps in designing amplifiers for specific applications. Let’s recap how these signals are introduced into the circuits.

Introduction & Overview

Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.

Quick Overview

This section focuses on circuit diagrams for BJT differential amplifiers and operational amplifiers (Op-Amps), illustrating their configurations and functionalities.

Standard

In this section, we delve into the circuit diagrams of BJT differential amplifiers and Op-Amps, spotlighting their operational principles through illustrative figures. These diagrams expose the structure, connections, and behavior of the components used in creating differential and basic gain amplifier circuits.

Detailed

Circuit Diagrams

The section on circuit diagrams provides a visual representation of the BJT differential amplifier and operational amplifier (Op-Amp) configurations. Understanding these diagrams is crucial for designing and analyzing electronic circuits.

1. BJT Differential Amplifier

The circuit diagram of a BJT differential amplifier includes two matched NPN transistors (Q1 and Q2). These transistors are configured with a common emitter and a current source (or resistor approximation). The diagram shows:
- Collector Resistors (Rc1, Rc2): They are connected to the collector terminals of each transistor, allowing for output voltage measurement.
- Common Emitter Node: This is where the emitters of both transistors connect to a current source, crucial for maintaining constant current.
- Inputs and Outputs: It also illustrates how the differential input voltages (Vin1 and Vin2) connect to the bases, with outputs tapped from the collectors (Vout1, Vout2).

2. Op-Amp Configurations

The section presents circuit diagrams for both inverting and non-inverting amplifier setups using a general-purpose Op-Amp (e.g., LM741). Key features include:
- Inverting Amplifier: The input signal goes through a resistor to the inverting input, while the non-inverting input is grounded. The output connects via a feedback resistor which determines the voltage gain.
- Non-Inverting Amplifier: Here, the input signal is directly applied to the non-inverting terminal, with resistors controlling the feedback to define the gain without inverting the signal.

These diagrams serve as essential tools in learning how these vital components function in practical applications.

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BJT Differential Amplifier Diagram

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Figure 7.1: BJT Differential Amplifier with Current Source (or Resistor)

+Vcc (e.g., +12V or +15V DC)
|
Rc1 (Collector Resistor) Rc2 (Collector Resistor)
| |
C1 (Collector) ------------- C2 (Collector)
| /|\ | /|\
B1 (Base) --------------------- B2 (Base)
| \|/ | \|/
E1 (Emitter) ----- E2 (Emitter)
\ /
\ /
\ /
Common Emitter Node
|
R_E_CS (Resistor for Current Source approximation)
|
NPN Transistor (Q3) for Current Source Base Biasing
|
R_B_CS1 (Base Resistor 1 for Q3)
|
+---- Base of Q3 ---- Emitter of Q3 ----- Isource (to common Emitter)
|
R_B_CS2 (Base Resistor 2 for Q3)
|
-Vee (e.g., -12V or -15V DC)

Simpler Version (using large resistor for current source approximation):
+Vcc
|
Rc1 Rc2
| |
C1 ----------------- C2
| /|\ | /|\
Vin1 --- B1 | ------------- B2 --- Vin2
| \|/ | \|/
E1 ----- E2 (Common Emitter Node)
\ /
\ /
\ /
|
R_E (Large Emitter Resistor, e.g., 22k - 100k Ohm)
|
-Vee (e.g., -12V or -15V DC)

For Common Mode Input: Vin1 = Vin2 = Vic
For Differential Input: Vin1 = Vid/2, Vin2 = -Vid/2 (or apply Vid to Vin1 and ground Vin2 for single-ended differential input)
Outputs: Vout1 (at C1), Vout2 (at C2)

Detailed Explanation

This chunk describes the circuit diagram for a BJT differential amplifier, which is used to amplify the difference between two input signals. The diagram shows two configurations: one with a dedicated current source and another with a simple large resistor approximating the current source. The circuit consists of two NPN transistors (Q1 and Q2), with their emitters connected to a common emitter node. The collector resistors (Rc1 and Rc2) determine the output voltage drops, while the input signals (Vin1 and Vin2) are applied to the bases of the transistors.

Examples & Analogies

Think of this differential amplifier as a pair of ears that are trying to listen to sounds coming from two different directions (Vin1 and Vin2). Just like the ears can distinguish between a conversation (differential input) and background noise (common mode input), the circuit amplifies the difference while reducing unwanted noise.

Op-Amp Inverting Amplifier Diagram

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Figure 7.2: Op-Amp Inverting Amplifier

+Vcc (e.g., +15V)
|
Op-Amp (e.g., LM741)
Non-inverting Input (+) --- GND
|
+-- Rf (Feedback Resistor)
|
Inverting Input (-) ---+
|
+-- Rin (Input Resistor) --- Vin (Input Signal)
Output of Op-Amp (Vout) --- (Connected to Rf)
-Vcc (e.g., -15V)

Detailed Explanation

This section illustrates the circuit diagram for an inverting amplifier configuration using an operational amplifier. The input signal (Vin) is applied through a resistor (Rin) to the inverting input of the Op-Amp, while the non-inverting input is grounded. A feedback resistor (Rf) connects the output back to the inverting input. This setup allows the Op-Amp to produce an output that is an inverted version of the input, controlled by the ratio of the resistors Rin and Rf.

Examples & Analogies

Imagine you are holding a mirror in front of you that flips your image upside down (this represents the inverting amplifier). Just like how the mirror reflects a backward image, the Op-Amp inverts the input signal. If you smile (input signal), the image in the mirror appears to frown (inverted output). The resistors determine how dramatically this flipping occurs.

Op-Amp Non-Inverting Amplifier Diagram

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Figure 7.3: Op-Amp Non-Inverting Amplifier

+Vcc (e.g., +15V)
|
Op-Amp (e.g., LM741)
Non-inverting Input (+) --- Vin (Input Signal)
|
+-- R1 (Feedback Resistor)
|
Inverting Input (-) ---+
|
+-- R2 (Feedback Resistor)
|
GND
Output of Op-Amp (Vout) --- (Connected to R1)
-Vcc (e.g., -15V)

Detailed Explanation

This segment provides a circuit diagram for a non-inverting amplifier configuration with an Op-Amp. In this setup, the input signal is applied to the non-inverting input of the Op-Amp. The output is fed back to the inverting input through two resistors, R1 and R2. Unlike the inverting configuration, this circuit provides an amplified output that is in phase with the input signal, characterized by a gain that is determined by the resistor values.

Examples & Analogies

Imagine you are standing at the edge of a pool, shouting to a friend across the water. The sound waves travel directly to your friend without any flipping or inversion (as represented by the non-inverting amplifier). Just as your voice is heard clearly and directly, the Op-Amp outputs an amplified version of the input signal without inverting it, with the resistors determining how loud it gets.

Definitions & Key Concepts

Learn essential terms and foundational ideas that form the basis of the topic.

Key Concepts

  • Differential Amplifier: Amplifies the difference between two input signals.

  • Operational Amplifier: A versatile component used in amplifying, filtering, and many other applications.

  • Inverting Amplifier: Produces an output that is the inverted version of the input.

  • Non-Inverting Amplifier: Produces an output that is the same phase as the input.

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • Using a BJT differential amplifier to amplify small signals in sensor applications.

  • Applying a non-inverting amplifier to buffer a sensor output before processing.

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🎵 Rhymes Time

  • Differential to the max, signals in my tracks, amplify the difference, that's how it impacts!

📖 Fascinating Stories

  • Imagine a race between two cars—one for each input signal. The differential amplifier picks the faster car difference and amplifies that speed.

🧠 Other Memory Gems

  • D-A-M (Differential Amplifier Measures) difference: D for Differential, A for Amplification, M for Measurement.

🎯 Super Acronyms

RAGE (Resistors, Amplify, Gain, and Enhance) reminds you of the components involved in Op-Amps.

Flash Cards

Review key concepts with flashcards.

Glossary of Terms

Review the Definitions for terms.

  • Term: Differential Amplifier

    Definition:

    An amplifier that amplifies the difference between two input signals.

  • Term: Common Mode Rejection Ratio (CMRR)

    Definition:

    A measure of the ability of an amplifier to reject input signals common to both inputs.

  • Term: Operational Amplifier (OpAmp)

    Definition:

    A high-gain differential amplifier with a single-ended output, used in various circuits.

  • Term: Inverting Amplifier

    Definition:

    An amplifier configuration where the output signal is inverted relative to the input.

  • Term: NonInverting Amplifier

    Definition:

    An amplifier configuration where the output signal is in phase with the input.