Comparator Based Crystal Oscillator

Posted on Feb 6, 2014

Although a simple crystal oscillator may be built from one comparator of an LT1720/LT1721, this will suffer from a number of inherent shortcomings and design problems. Although the LT1720/LT1721 will give the correct logic output when one input is outside the common mode range, additional delays may occur when it is so operated, opening the possib

Click here to download the full size of the above Circuit.

ility of spurious operating modes. Therefore, the DC bias voltages at the inputs have to be set near the center of the LT1720/LT1721`s common mode range and a resistor is required to attenuate the feedback to the non-inverting input. Unfortunately, although the output duty cycle for this circuit is roughly 50%, it is affected by resistor tolerances and, to a lesser extent, by comparator offsets and timings. If a 50% duty cycle is required, the circuit shown here creates a pair of complementary outputs with a forced 50% duty cycle. Crystals are narrow-band elements, so the feedback to the non-inverting input is altered analogue version of the square-wave output. The crystal`s path provides resonant positive feedback and stable oscillation occurs. Changing the non-inverting reference level can vary the duty cycle. The 2k-680 resistor pair sets a bias point at the comparator + (Comparator IC1a) and (Comparator IC1b) input. At the complementary input of each comparator, the 2k-1. 8k-0. 1 µF path sets up an appropriate DC average level based on the output. IC1b creates a complementary output to IC1a by comparing the same two nodes with the opposite input. IC2 compares band-limited versions of the outputs and biases IC1a`s negative input. IC1a`s only degree of freedom to respond is variation of pulse width; hence the outputs are forced to 50% duty cycle. The circuit operates from 2. 7V to 6V. When scoping the oscillator output...

Leave Comment

characters left:

Related Circuits

Solar Panel Based Charger And Small LED Lamp

You can save on your electricity bills by switching to alternative sources of power. The photovoltaic module or solar panel described here is capable of delivering a power of 5 watts. At full...

AC Power filter and phone line filter (homemade circuit breaker)

What is a circuit breaker? When do I need an ac power line filter or a phone line filter; How do I design a noise filter; Can I build a homemade surge protection? The following circuit protection...

Audio Reproduction on HCS12 Microcontrollers with Pulse-Width Modulation (PWM) Capability

The HCS12 series of microcontrollers does not support dedicated internal digital-to-analogue conversion hardware, and thus external hardware, perhaps in the form of a digital-to-analogue conversion...

Brushless DC electric motor control by CPLD

The main area for application of brushless direct current motors (BLDC) is positioning

Car Door Keypad Using LIN

A car door differs from a calculator or a phone in that it makes sense to press more than one key at a time

FAN2001/2 Evaluation Board User Guide

The FAN2001/2 (datasheet) Evaluation Board is a compact circuit including either the FAN2001 MPX or the FAN2002 MPX in a 3x3 MLP package

FAN5607 Evaluation Board

The FAN5607 Evaluation Board is a compact circuit including the FAN5607 HMPX in a 4x4 MLP package and two 4.7uF capacitors which can provide stable input/output current for up to four of Fairchild...

Fundamentals of Transistor Oscillators

This chapter deals with the operation and circuitry of transistor oscillators. In general, these fall into two categories: the feedback (or vacuum tube equivalent) types, and the...

New Circuits

Zero consumption Anti-theft High power Code Switch for E-Bike Batteries

This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of....
Ultrasonic distance finder circuit

The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Simple Metal detector circuit with CD4030

Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
Fully automatic watering circuit for flower pots

Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....
Simple deep searching metal detector circuit

The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
Sub-Harmonic Bass Converter for Electric Guitars

The sub-harmonic bass generator is a sound producing unit for guitars. The sound it produces looks very much like that of the bass guitar. The octave generator is sometimes quite unusual since it does not produce any of the usual ways of coloring the sound,....
Echo Depth Sounding Sonar for Boats

In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
100W HiFi Audio Amplifier Circuit

This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
Plant-Pot Water Level Indicator Circuit

A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....

Create NOW your QR MENU for your Restaurant / Hotel / Bar / Caffe,

Comprehensive ordering/paying features. fully personalized to suit your Business.

Update Anytime! Easy and Simple!

Popular Circuits

Distortion Analyser

Total harmonic distortion (THD) measurements are one of the most commonly quoted in audio....

Biquad-audio-filter

This universal filter offers low-pass, high-pass, bandpass, band elimination, and all-pass...

PIC16F688 Based Digital Voltmeter with a PIC mictocontroller

This project describes how to make a digital voltmeter with a PIC microcontroller. A character...

Car Anti-Theft Wireless Alarm

This alarm circuit is an anti- theft wireless alarm can be used with any vehicle having 6- to...

uhf antenna amplifier booster

This UHF antenna amplifier circuit or UHF antenna booster circuit can be used to amplify or boost...

usb power socket with indicator

Today, almost all computers contain logic blocks for implementing a USB port. A USB port, in...

computer-circuits

This simple pc scope probe is nothing more than a fet follower. It has a high input impedance and...

50 MHz frequency counter voltage meter & SWR/PWR indicator

This is a successor of the PIC16C71 4-digit LED f-counter & V-meter. Some hard to find parts used...

Light touch variable delay circuit

vl.U no mantle base current. Open cut II:, n is also turned off when the touch when the metal...

DC motor armature series resistance one way operation start dynamic braking circuit

Circuit shown in Figure 3-196. The circuit has a resistance level start, under voltage relay KAz...