Crystal Oscillator using SN74HC04 does not work !

[joeypc]

Hello Everybody,

I build this crystal oscillator circuit like the diagram below. When I use IC HD74HC04 of Hitachi Semiconductor or 74HC04 of NXP semiconductor (formerly Philips semiconductor). It works well. But when I use SN74HC04 of Texas Instruments. It does not work ! Could anyone give me any suggestion ? Thanks.

 

[jpanhalt]

Have you seen this: https://www.fairchildsemi.com/an/AN/AN-118.pdf

In particular, check out page 3, Figure 5a. Also, Figure 6 may be of interest to you. I realize the inverter in Fig. 6 is different.

John

 

[audioguru]

Maybe you have a fake or defective IC marked Texas Instruments. Try another one purchased from a genuine TI distributor.

 

[schmitt trigger]

For these types of oscillators to work reliably, they have to use unbuffered inverters, like the 74HCU04

https://www.ti.com/product/CD74HCU04?keyMatch=74hcu04&tisearch=Search-EN-Everything

the keyword here is reliably.

 

[audioguru]

I have never heard of a buffered inverter. I have also never heard of an unbuffered inverter, I thought they all were.
ON semi shows an ordinary 74HC04 inverter with three inverters in series to make it have high gain and be nice and slow.

 

[atferrari]

At least, referred to CMOS, it is a valid consideration.

You could read about, here.

 

[schmitt trigger]

Audioguru;
the U-version for inverters has been there since the beginning of the CMOS gates. It is used in applications where the inverter (essentially a single NMOS/PMOS complementary pair) requires to operate class A.
The DC bias to operate it in class A is provided by the 1 Meg resistor.
This is a requirement for crystal or tuning fork oscillators.

Buffered inverters (three cascaded NMOS/PMOS complementary pairs) should be used for ring (three gate) oscillators, hysteretic (schmitt trigger) oscillators, and other normal inverter functions.

 

[audioguru]

The ordinary old CD4069 and 74C04 inverters were not buffered. But nearly all the 4000 and 74C series gates and counters had buffered outputs.

 

[gary350]

I though you need a voltage across the crystal for it to work. Looks like a ground on both sides. How do you know it works? I found this circuit on the crystal oscillator circuit page. Many of those circuits dont work.

**broken link removed**

 

[schmitt trigger]

All of those circuit topologies do work, if the component values are correct for the crystal.
Crystals specify a certain capacitive loading. Read that from the data sheet.

The 32.768Khz units are not crystals per se but tuning forks. Although its model is similar to that of a crystal, they can be easily damaged with overdrive. I know, I've destroyed a few of them. A large value series resistor (300k in your schematics) or employing a lower supply voltage (1.5 to 3v) is required.

Please google "crystal oscillator". There is a ton of information, too much to discuss in a simple thread.

 

[RadioRon]

Are you building on a printed circuit board, on a solderless breadboard, on perf board with point to point wiring or what? Solderless breadboard adds a lot of capacitance to the terminals, which might impair function.

 

[Diver300]

Having made and designed crystal oscillators for a living for nearly 20 years, I found that you should always use unbuffered inverters as the main oscillator. You might want to add some resistance between pin 2 and the common point of C2 and the crystal.

You might be getting the crystal oscillating in 3rd overtone mode, at around 36 MHz. The propagation delay of the inverters is around 7 ns, which is short enough that you could get 3rd overtone oscillation.

If you have a look at **broken link removed** that has several application examples, mainly there because the unbuffered inverter is unlike most logic gates, in that it can be used as a linear device. The transfer characteristics are shown, and the much lower gain is what is wanted for a crystal oscillator.

Schmitt Trigger is perhaps overstating the difference between a watch crystal, usually at 32.768 kHz, and an AT-cut crystal, which is usually in the 4 - 50 MHz range. Both are quartz resonators, where the oscillation is mechanical. The frequency in both is mainly determined by the mass and stiffness of the quartz. The huge frequency difference between watch crystals and AT-cut crystals cannot be obtained by changing the dimensions alone. A 32.768 kHz AT cut crystal would be about 50 mm thick and would have to be around 1m in diameter, so watch crystals are made by making the quartz into tuning fork shapes, instead of plain disks. https://en.wikipedia.org/wiki/Crystal_oscillator#mediaviewer/File:Crystal_modes_multilingual.svg

Quartz crystals are made from quartz because it is a piezoelectric material. By simply adding electrodes to the mechanical resonator, the quartz converts the mechanical movement into electricity, (and vice-versa to keep the oscillation going) but the electrical power transfer is a tiny fraction of the mechanical energy, which is why crystals take thousands of cycles to start and stop, and why the electrical circuit can only have a tiny effect on the frequency.

 

[Tony Stewart]

The vendor sensitivity on bandwidth variations on HCMOS has existed since I started using them in 1973.

U unbuffered types have always been recommended for many reasons as SchmittTrigger and Diver300 indicated.

The series R is critical >=5V to avoid exceeding 50 uW losses in Xtal.
The U inverter has adequate linear gain of >=10
The 3 stage standard inverter has gain of 1000+ is excessive.

 

[audioguru]

An ordinary CD4069, CD4049 or 74C04 Cmos inverter has only one stage.

 

[Tony Stewart]

An ordinary CD4069, CD4049 or 74C04 Cmos inverter has only one stage.

CD4069 is not a valid part number but CD4069UB is valid bas with appropriate pakage suffix, which reinforces the notion of an unbuffered inverter for the purpose of XO's or lower latency inverters.

https://www.ti.com/lit/ds/symlink/cd4069ub.pdf

 

[audioguru]

I think the "U" in the CD4069UB part number is something new that was added because there is not and there never was one that has 3 stages and is buffered. Remember that RCA invented the 4000A series Cmos and the buffers were added later to fix problems but not on inverters.

 

[MrAl]

Hi,

I had constructed a two stage TTL type gate crystal oscillator with a 2MHz crystal back in the 1970's. It still works today.

I had also constructed a CMOS crystal oscillator (cant remember the frequency now) back in the 1990's and it stopped working one day, maybe a few months after first construction. When i replaced the CMOS with an HCT type, it always worked after that.

I never looked too deeply into either of these, but the two stage oscillator seemed better.

 

[Tony Stewart]

Hello Everybody,

I build this crystal oscillator circuit like the diagram below. When I use IC HD74HC04 of Hitachi Semiconductor or 74HC04 of NXP semiconductor (formerly Philips semiconductor). It works well. But when I use SN74HC04 of Texas Instruments. It does not work ! Could anyone give me any suggestion ? Thanks.

I wonder what voltage out you measured?

 

[moty22]

If you are using a breadboard expect strange things to happen because of the capacitance between the metal strips.
Crystal oscillators is a common cause for engineers to loose their hairs.

 

[Tony Stewart]

Decoupling caps and short wires are essential to prevent lost hairs. Grey Haired engineers do this without thinking.