How do I use a quartz crystal in an oscillator?

Question

How can I get a quartz crystal to make square waves at 4.096MHz? So far I have the 4.096MHz quartz crystal and this schematic I saw:

enter image description here

Where can you find an amplifier with a single input and what voltage should I use?

Please tell us what you've got so far and what exact problem you ran in to. — jippie, Jul 22 '12 at 00:28

Oli Glaser · Accepted Answer · 2012-07-22T05:13:05.907

10

You can make a Pierce Oscillator similar to that shown in your question:

Pierce Oscllator

The "single input amplifier" is usually a simple CMOS inverting gate, like the 74HC7404 (6 inverters in one package), SN74HC14D (single inverter) or similar.
Voltage can be something within the operating range of the IC, such as 5V. You may need to add a series resistor to limit the crystal drive (you need to check the crystal datasheet for manufacturer recommendations)
Here is a circuit with typical component values:

Pierce Oscillator 2

Note the series R mentioned above. The above came from this Fairchild App Note which goes into some detail on the design process.

You can only pull the frequency of a crystal oscillator a very small amount, so you will need a 4.096MHz crystal. Either that or you will need to use something else such as a PLL.

edited Jul 22 '12 at 05:13

answered Jul 22 '12 at 05:03

Oli Glaser

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I wonder where is the input(VCC) and where is the output in "FIGURE 3. Typical Gate Oscillator" – Cristi Jul 22 '12 at 13:54
Vcc and GND to the gate are not shown. The output is at the right hand side of the gate (pointy side with circle) - you can buffer it with another gate if required as shown in your example. – Oli Glaser Jul 22 '12 at 14:02
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@Cristi: if Oli's answer answers your question you can accept, so that others know the problem is solved. The button with the check mark. – Federico Russo Jul 22 '12 at 15:07

score 3 · Answer 2 · answered Jan 29 '13 at 23:45

3

You can use an op amp in your circuit, ore use a 555 to generate square weaves

or do something like this:

enter image description here

answered Jan 29 '13 at 23:45

user12410214

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score 2 · Answer 3 · edited Jul 22 '12 at 10:01

Generally Xtals below 30MHz are fundamental parallel mode resonance like LC expect Q is 3K and high impedance 180deg phase shift at resonance. THis means you need negative feedback using an inverter not a series mode with a non-inverter. Try both buffered x1000 gain and unbuffered x10 gain inverter CMOS chips and ensure spurious harmonic oscillator modes are avoided.The Xtal Q has enough gain with CMOS gain of 10x to get a square wave when feedback R is high Z.

enter image description here

Let Rf = 1~10 MΩ to self bias input to Vcc/2 let Rs = 10kΩ and C1 = 30~47pF or so. Let C2 = 100~1000pF in series with Varicap cathode while anode is to ground for reverse bias V vs cap control. Choose 0~12Vdc control range for varicap (or more) and select C1 to tune centre F.

I know this is a lot to take in a short paragraph so ask a Q? or read up on parallel VCXO's.

Here is a simple reference to appreciate Crystals more.

http://ww1.microchip.com/downloads/en/devicedoc/31002a.pdf

How do I use a quartz crystal in an oscillator?

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