XTAL question about capacitors

[super]

XTAL question..

Dear all:
For general xtal output terminal are shunt 2 cap to ground and connect to IC pin xtal1 and xtal 2, but in this circuit have another method.
who can explain this circuit and c512,c513,c514 function?

Thanks,
Best regards.

 

[FvM]

Re: XTAL question..

The circuit is specified in various NXP tuner chip datasheets without detailed explanation. Basically two aspects have to be considered:
- The crystal must be operated with the specified load capacitance to achieve the correct frequency.
- The requirements of the oscillator circuit must be met. The NXP circuit is apparently different from ususal inverter oscillators,
a few hints can be found in datasheets.

Generally, I guess that keeping the external oscillator circuit fully differentially reduces both, possible emissions from the XTAL
oscillator and susceptibility to interferences. So it looks like NXP applied some optimizations that have been missed yet by
other chip designers.

 

[erikl]

XTAL question..

Additional advantage - IMHO - is lower power dissipation of the XTAL (reduced oscillation amplitude). Modern miniature crystals have rather low power dissipation values.

 

[super]

XTAL question..

Dear FvM,Erikl:
Ok,I see.This structure is possiable to reduce emissions from the XTAL and susceptibility to inter and power dissipation.

Thanks.