OpenStax_CNX

You are here: Home » Content » Lectures on Analog Electronics » AE_Lecture11_Part2_Radio-Frequency Oscillators

Inside Collection (Course):

Course by: Bijay_Kumar Sharma. E-mail the author

Module by: Bijay_Kumar Sharma. E-mail the author

Summary: AE_Lecture11_Part2 describes the Radio-Frequency Oscillators.

AE_LECTURE 11_Part2.

Part 2 deals with RF Oscillators.

Section 1. Class of RF OSCILLATORS

(100kHz- 1000kHz:Medium Wave RF & 1MHz-30MHz:Short Wave RF;

30MHz-70MHz: Amateur Band for HAM Radio practitioners;

70MHz-300MHz: Very High Frequency (VHF) Band for FM and TV transmissions;

300MHz-800MHz: Ultra High Frequency(UHF) Band for Police Communication;

1GHz-100GHz: Microwaves for satellite communication;

Terra Hz(0.4µm-100µm): Optical Fiber Communication)

LC oscillators are RF oscillators.

Figure 1. Parallel Resonance Circuit or Tank Circuit.

Figure 2. Circuit Diagram of a Tank Circuit driven by a constant current source.

Parallel resonance circuit is known as tank Circuit.

Resonance frequency=ωo=

Figure 3. Magnitude of the reactance of a tank circuit vs frequency.

At ω=

;

When quality factor Q of the tank circuit =∞, the circuit is purely reactive and there is no dissipation.

When quality factor Q is finite say 1000 then an equivalent RP comes in parallel with the tank circuit. RP accounts for the losses

For a finite quality factor tank circuit, the effective impedance is a pure resistance RP at resonance frequency.

Hence

Frequency response of the tank circuit is :

Figure4. The peak response of a tank circuit for various quality factors.

At Q=∞, spike response.

At Q=finite, peak response.

As Q falls, sharpness of the peak response is lost.

Section 1.1. GENERALIZED LC OSCILLATOR.

Figure 5. Block Diagram of generalized LC Oscillator

Where

Therefore:

Examining the feedback network in Figure 8:

Feed back voltage

If loop gain=1∟0˚

This identity can be true only if

Subs(4) & (5) in (3)

Starting condition is

This means

are same kind of reactance and is of opposite kind of reactance.

Table 1. Different possible configurations of a generalized LC Oscillator.

 Z 1 Z 2 Z 3 Type of Oscillator 1 L L C Hartley Oscillator 2 C C L Colpitts Oscillator

Content actions

PDF | EPUB (?)

What is an EPUB file?

EPUB is an electronic book format that can be read on a variety of mobile devices.

PDF | EPUB (?)

What is an EPUB file?

EPUB is an electronic book format that can be read on a variety of mobile devices.

Collection to:

My Favorites (?)

'My Favorites' is a special kind of lens which you can use to bookmark modules and collections. 'My Favorites' can only be seen by you, and collections saved in 'My Favorites' can remember the last module you were on. You need an account to use 'My Favorites'.

| A lens I own (?)

Definition of a lens

Lenses

A lens is a custom view of the content in the repository. You can think of it as a fancy kind of list that will let you see content through the eyes of organizations and people you trust.

What is in a lens?

Lens makers point to materials (modules and collections), creating a guide that includes their own comments and descriptive tags about the content.

Who can create a lens?

Any individual member, a community, or a respected organization.

What are tags?

Tags are descriptors added by lens makers to help label content, attaching a vocabulary that is meaningful in the context of the lens.

| External bookmarks

Module to:

My Favorites (?)

'My Favorites' is a special kind of lens which you can use to bookmark modules and collections. 'My Favorites' can only be seen by you, and collections saved in 'My Favorites' can remember the last module you were on. You need an account to use 'My Favorites'.

| A lens I own (?)

Definition of a lens

Lenses

A lens is a custom view of the content in the repository. You can think of it as a fancy kind of list that will let you see content through the eyes of organizations and people you trust.

What is in a lens?

Lens makers point to materials (modules and collections), creating a guide that includes their own comments and descriptive tags about the content.

Who can create a lens?

Any individual member, a community, or a respected organization.

What are tags?

Tags are descriptors added by lens makers to help label content, attaching a vocabulary that is meaningful in the context of the lens.

| External bookmarks