# [moved] How to design a crystall oscilator circuit using CMOS 40106 DESIGN

1. ## [moved] How to design a crystall oscilator circuit using CMOS 40106 DESIGN

Hi,

I need some help in designing this crystal oscillator circuit. I have attached the diagram. I want it to oscillate around 1MHZ.
How do i calculate the capacitor and resistor values values?
Can you please share the formulas

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2. ## Re: How to design a crystall oscilator circuit using CMOS 40106 DESIGN

The capacitor values come from the crystal manufacturers data sheet, if you use 33pF or 39pF it should work fine, the values are not particularly critical.
Likewise, use the resistor values for 5MHz, R1 will stay the same regardless of the frequency, it is just to provide some DC feedback for the inverter, R2 governs the feedback (drive) level to the crystal but using 5K should be fine to keep the level within a safe range.

Brian.

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3. ## Re: How to design a crystall oscilator circuit using CMOS 40106 DESIGN

Hi,

I want it to oscillate around 1MHZ.
The frequency is determined by the XTAL. If you use a 1MHz one, than you wonīt be able to 0.99MHz or 1.01MHz.

I agree with betwixt:
1M, 39pF, 5k should work.

Klaus

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4. ## Re: How to design a crystall oscilator circuit using CMOS 40106 DESIGN

Hi Klaus

I want to use an 8MHz crystal.
Would i still get it to oscillate at fo 1Mhz with provided values?

5. ## Re: How to design a crystall oscilator circuit using CMOS 40106 DESIGN

Hi,

--> read the XTAL datasheet (most reliable information)
--> use the recommended values (general recommendation. And your 8MHz isnīt far away from 10MHz in the table)

Klaus

6. ## Re: [moved] How to design a crystall oscilator circuit using CMOS 40106 DESIGN

The schematic has one major error: it is incorrectly showing a schmitt trigger inverter, whereas an unbuffered inverter is required for the crystal oscillator.

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7. ## Re: [moved] How to design a crystall oscilator circuit using CMOS 40106 DESIGN

I agree about unbuffered inverter. Other configuration like buffered inverter or ST inverter are likely to cause unstable operation or possibly oscillation on overtones.

The Epson Oscillation Circuit Design Guide is often quoted in this regard, various sources on the internet, e.g. http://read.pudn.com/downloads154/so...esignGuide.pdf

It's doesn't give values for 1 MHz but explains the design method. In addition, the total load capacitance is basically specified in the crystal data sheet, you keep it to achieve the nominal crystal frequency.

8. ## Re: How to design a crystall oscilator circuit using CMOS 40106 DESIGN

Originally Posted by thandana
Hi Klaus
I want to use an 8MHz crystal.
Would i still get it to oscillate at fo 1Mhz with provided values?