oscillator circuitry

Started by Robert Imhoff March 24, 2004
I wanted to ask the hardware specialists if one should use special
high-frequency capacitors for the PLL and quartz circuit on the HCS12
or if multilayer "C0G" ceramic capacitors are ok? (the crystal is 4 MHz
and the PLL should run at 24 MHz, with a 9S12DT256C or similar, using
the Pierce oscillator)

Many thanks in advance!
Robert



Probably most important --

They should be low-loss at the frequency of operation, and

The crystal loading capacitors will somewhat affect the oscillator frequency
if they are not temperature stable.

I generally use small ceramic disks for crystal loading, consider low coef
of temperature if you are concerned about frequency. Silver mica types
should also work well.

For PLL bypass duty, silver mica or any quality bypass type will probably
OK. I wouldn't be afraid to at least "try" a monolithic bypass type. Bob Smith

--- Avoid computer viruses, Practice safe hex ---

-- Specializing in small, cost effective
embedded control systems --

http://www.smithmachineworks.com/embedprod.html Robert L. (Bob) Smith
Smith Machine Works, Inc.
9900 Lumlay Road
Richmond, VA 23236 804/745-1065
----- Original Message -----
From: "Robert Imhoff" <>
To: <>
Sent: Wednesday, March 24, 2004 10:11 AM
Subject: [68HC12] oscillator circuitry > I wanted to ask the hardware specialists if one should use special
> high-frequency capacitors for the PLL and quartz circuit on the HCS12
> or if multilayer "C0G" ceramic capacitors are ok? (the crystal is 4 MHz
> and the PLL should run at 24 MHz, with a 9S12DT256C or similar, using
> the Pierce oscillator)
>
> Many thanks in advance!
> Robert >
> --------------------To learn more
about Motorola Microcontrollers, please visit
> http://www.motorola.com/mcu
> o learn more about Motorola Microcontrollers, please visit
> http://www.motorola.com/mcu
>
> Yahoo! Groups Links >


Robert Imhoff <> wrote:

> I wanted to ask the hardware specialists if one should use special
> high-frequency capacitors for the PLL and quartz circuit on the HCS12

it will be hard to find capacitors bad enough to have noticeable
effect.

> or if multilayer "C0G" ceramic capacitors are ok? (the crystal is 4

C0G is pretty good, but don't bother to use X7R for the larger
capacitors in the PLL filter or for power supply decoupling.

> MHz and the PLL should run at 24 MHz, with a 9S12DT256C or similar,

The PLL filtering capacitors don't see 24MHz.

Oliver
--
Oliver Betz, Muenchen