SN74LVC1G04: Attemp to Build an Oscillator Circuit with an Inverter

Yuanchen Zhu

Part Number: SN74LVC1G04
Other Parts Discussed in Thread: SN74LVC1G14, SN74LVC1GU04, SN74LVC1404, SN74LVC1GX04

Tool/software:

Dear TI Experts or Gurus,

We attempted to build a basic oscillator circuit of 24MHz crystal with a CMOS inverter as shown below, but somehow we cannot get the frequency that was expected to be 24MHz. Instead, we have got a square wave signal with a weird frequency of about 268kHz. And we tried to tune load capacitors low to 10pF or high to 20pF, but both found no luck.

And we are quite sure that the 24MHz crystal component itself has no issue to output in a normal condition. Any suggestion on how we should carry on or is there anything we should take care for this inverter alone?

Really appreciate if someone can shed some light on this probelm.

Regards,

Yuanchen

4 months ago

0 Clemens Ladisch 4 months ago

Guru 317480 points

You have selected the part number SN74LVC1G04, but the schematic shows two other part numbers. Please confirm what parts you are actually using.

Where exactly have you been measuring this signal?

Please show your board layout.

0 Yuanchen Zhu 4 months ago in reply to Clemens Ladisch

Intellectual 425 points

Hello, Clemens.Thanks for your quick reply. Part number of U7 there is a typo, it is meant to be SN74LVC1G04. And for the part of U8 there we have tried both SN74LVC1G04 and SN74LVC1G14 (a Schmitt-Trigger inverter), did not get any good result in either case.

Please see above screenshot of layout. We've taken measurements from a MCX connector (RF3) and also input of U8 there. Would add decoupling capacitors for 3.3V power rail next time, though. Please point out anything else that you would be concerned for this problem. Thanks again. Feel really curious that where this could go wrong.

Regards,

Yuanchen

+1 Clemens Ladisch 4 months ago in reply to Yuanchen Zhu

Guru 317480 points

U7 is used as an analog amplifier. There is no typo, only an unbuffered inverter like the SN74LVC1GU04 works in this place.

There are integrated devices like the SN74LVC1GX04 or SN74LVC1404.

0 Yuanchen Zhu 4 months ago in reply to Clemens Ladisch

Intellectual 425 points

Really thanks for pointing out that.

0 cuiping miao 4 months ago

Prodigy 11 points

https://www.ti.com.cn/cn/lit/pdf/zhca048 CMOS 非缓冲反向器在振荡器电路中的使用,希望能帮到你

0 Albert Xu1 3 months ago in reply to cuiping miao

TI__Mastermind 38925 points

Thank you for linking the app note. I will mark this as closed.

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SN74LVC1G04: Attemp to Build an Oscillator Circuit with an Inverter