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Posts Tagged ‘simple crystal oscillator’

Oscillator astable multi-vibrator with Crystal controller

Oscillator circuit of this nature.Often used as a clock circuit.This circuit uses a million crystal frequency control with stability.And a circuit that does not use the capacitor or Inductor all.
Each transistor to work, the amplifier with feedback. The Q2 transistors to circuits with a gain equal to 1.The gain of the transistor Q1, as a function of the resistance of the crystal, while the resonance.
By default, the resistance will be less than 22K.This is the feedback resistance of the circuit. Therefore, the gain of the circuit Q1, it is higher than one.
Output from a square wave circuit.The size of the signal depends on the voltage input to the circuit.This circuit can oscillate from birth 3 KHz up to 10MHz.

Safe Oscillator For Watch Crystals

This circuit was developed to allow watch crystals to be used in an existing CMOS oscillator circuit that was to run from a 12V supply. The problem is that these crystals only work up to a supply voltage of about 6V. Any more than that and the crystal will be over-driven, causing it to shatter. This circuit solves the problem by using LEDs 1 & 2 and a 470nF capacitor (C3) to limit the drive to the crystal to about 4V peak-to-peak. Note that it may be necessary to adjust C1 & C2 to ensure reliable start-up and stable oscillation with some crystals. However, the C1:C2 ratio should be maintained. As a bonus, the two LEDs both glow, giving a visual indication that the oscillator is working.

The relatively high values used here for capacitors C1 & C2 will load the crystal, which means that the oscillator will run at less than the nominal crystal frequency (32.768kHz).
Author: Duncan Graham – Copyright: Silicon Chip Electronics
Read more : http://www.extremecircuits.net/2010/06/safe-oscillator-for-watch-crystals_14.html

Switchable Output Crystal Oscillator

This oscillator circuit permits crystals to be electronically switched by logic commands. The circuit is best understood by initially ignoring all crystals. Furthermore, assume that all diodes are shorts and their associated 1kO resistors open. The two 1kO resistors at the non-inverting input of IC1 (LT1016) set the output to half the supply, ie, +2.5V. The RC network from the output to pin 3 sets up phase-shifted feedback and the circuit looks like a wide-band unity gain follower at DC. When crystal X1 is inserted (remember, D1 is temporarily shorted) positive feedback occurs and oscillation commences at the crystal’s resonant frequency.
If D1 and its 1kO resistor are then considered to be part of the circuit, oscillation can only continue if logic input A is biased high. Similarly, the circuit can only operate at crystal X2’s frequency if logic input B is high. Additional crystal/diode/1kO resistor branches permit logic selection of the crystal frequency. For AT cut crystals about a millisecond is required for the circuit output to stabilise due to the high Q factors involved. Crystal frequencies can be as high as 16MHz before propagation delays in the comparator prevent reliable operation.

Read more : http://www.extremecircuits.net/2010/05/switchable-output-crystal-oscillator.html