Temeprature Compensated Oscillator

ul5255

Hi guys,
I have this temp. compensated 10MHz oscillator (0.1ppm) which I'd like to use to precisely clock
the Propeller (I do know that 10MHz clock input is slightly out of spec ...).

My question is this however:
The output of this oscillator is AC coupled at approx 2.4V V_pk_pk.
Can this be used to clock the Prop or do I need a biasing circuit which lifts the signal so it swings
from 0V to 2.4V (or up to 3.3V)?

Sapieha

Hi ul5255.

Use 7414 else like Schmitt trigger to buffer it

http://www.nxp.com/documents/data_sheet/74HC_HCT14.pdf

ul5255 wrote: »

Hi guys,
I have this temp. compensated 10MHz oscillator (0.1ppm) which I'd like to use to precisely clock
the Propeller (I do know that 10MHz clock input is slightly out of spec ...).

My question is this however:
The output of this oscillator is AC coupled at approx 2.4V V_pk_pk.
Can this be used to clock the Prop or do I need a biasing circuit which lifts the signal so it swings
from 0V to 2.4V (or up to 3.3V)?

ul5255

Thanks for the reply but I'm afraid the problem remains:
The 7414 data sheet lists as recommended operating conditions for Vi
0V as minimum. My little oscillator swings down to - 1.2V.
Also the max positive swing is just 1.2V which will not be recocnized
as logic high even if I run Vcc down to 2.0V, right?

Sapieha

Hi.

You have not posted any link to datasheet -- So I can't answer that

ul5255 wrote: »

Thanks for the reply but I'm afraid the problem remains:
The 7414 data sheet lists as recommended operating conditions for Vi
0V as minimum. My little oscillator swings down to - 1.2V.
Also the max positive swing is just 1.2V which will not be recocnized
as logic high even if I run Vcc down to 2.0V, right?

Ariba

Here are two possible circuits.
1) Lifts the AC signal to the middle of the 3.3V range with 2 resistors. The Osc mode of the Propeller must be XINPUT
2) Enables the inverter and feedback resistor inside the Oscillator circuit of the Propeller, so the AC signal is biased to the threshold voltage of the inverter input. Use XTAL3 or XTAL2 mode for this.


Andy

eldonb46

ul5255 wrote: »

Hi guys,
I have this temp. compensated 10MHz oscillator (0.1ppm) which I'd like to use to precisely clock
the Propeller (I do know that 10MHz clock input is slightly out of spec ...).

My question is this however:
The output of this oscillator is AC coupled at approx 2.4V V_pk_pk.
Can this be used to clock the Prop or do I need a biasing circuit which lifts the signal so it swings
from 0V to 2.4V (or up to 3.3V)?

ul5255

Here is a "search" of my Blogged adventure with a TCVCXO and the Propeller, part numbers and part sources are included within the blog.

Of course as with any blog, you really need to read the blog backwards to follow the project, and there are "Older Posts" of the beginning of the adventure (see link at bottom of each blog page).

http://wa0uwh.blogspot.com/search/label/TCVCXO

I hope this helps and inspire your efforts.

Regards,
Eldon - WA0UWH

jmg

Ariba wrote: »

2) Enables the inverter and feedback resistor inside the Oscillator circuit of the Propeller, so the AC signal is biased to the threshold voltage of the inverter input. Use XTAL3 or XTAL2 mode for this.

If the OP checks the value of the internal cap in his TCXO, then he may even be able to omit the 100pF, and simply join to XI
The effect of a 'large' internal value like 100nF would be a longer time to settle with the high feedback resistor.