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LM567C: LM567 - frequency stability

Serhii Dementii
Prodigy 70 points
Part Number: LM567C

LM567 - frequency stability

1. How to improve the stability of the internal oscillator frequency of the chip LM567 ?

2. How to connect to chip LM567 crystal oscillator ?

  • 0
    TI__Guru* 96591 points
    Hi Serhii,
    Can you expand on what you are trying to achieve with the LM567?

    Is the center frequency stability listed in the datasheet not accurate enough for your application?
  • 0
    Prodigy 70 points

    Hi Emrys,
    два устройства разработаны на чипе LM567. Первое устройство генерирует оптический сигнал. Второе устройство принимает сформированный оптический сигнал. У устройств нет других соединений, кроме оптических. Рабочая частота этих двух устройств составляет около 100 кГц.
    Частота сигнала должна быть стабильной в течение длительного времени. Однако дрейф частоты сигнала приводит к потере взаимодействия этих устройств. Это является причиной необходимости точно стабилизировать рабочие частоты этих двух устройств.
    Отсюда вопрос - как обеспечить стабилизацию частот этих устройств на чипе LM567 с помощью осциллятора - кристалла.

  • 0 in reply to Serhii Dementii
    Prodigy 70 points

    Hi,

    Tell me please to someone you can advise to address this issue?

  • 0 in reply to Serhii Dementii
    Prodigy 40 points

    Dear Mr. Dementii, if this could be of some help, we faced a similar problem.

    The LM567 is extremely sensitive to power supply fluctuations or ripple. We changed the power supply from PWM to a linear model and the frequency stability became very acceptable.

    Hope it helps.

    []s

    Marcellus

  • 0 in reply to Marcellus Pereira
    Prodigy 70 points
    Dear M-r Marcellus

    Thank you for your attention to my question. In this device, I installed a transformer power supply with a stabilizer plus provided additional stabilization with a Zenner diode and a capacitor. With food - it seems everything is ok.
    And yet the question is - is quartz frequency stabilization possible for this chip?

    Best regards, Serhii
  • 0 in reply to Serhii Dementii
    Prodigy 40 points
    Unfortunately, I don´t think it´s possible... I never saw this configuration.

    []s
    Marcellus
  • 0 in reply to Marcellus Pereira
    Prodigy 70 points
    All this works, but I did not find the answer to my question.
    Thank you for your attempt to help me.
    My best wishes..
  • 0 in reply to Serhii Dementii
    TI__Expert 5370 points
    Hello Serhii,

    anything else we can do to help you?

    Regards, Simon.
  • 0 in reply to Simon Damphousse
    Prodigy 70 points

    Hi, Mr Simon

    Thank you for your attention.

    But the answer to my question is missing.

    The question is still such - how to improve the stability of lm567 by using a quartz oscillator?

    Regards, Serhii.

  • 0 in reply to Serhii Dementii
    TI__Expert 5370 points
    Dear Serhii,

    The LM567 VCO is not designed as far as I can see to support a locking circuit to an external xtal. You will not be able just with an XO to lock the VCO on that XO.

    The touch tone decoder is not designed to have a PPM accuracy to decode the tone.

    If you are trying to generate a low frequency signal around 500 kHz from your XO, you may consider a divider?

    Can you tell me more about your application? I will likely have good device recommendation for you.
  • 0 in reply to Serhii Dementii
    TI__Expert 5370 points
    Dear Serhii,

    the VCO in the touch tone decoder is not designed imo to be locked onto an external XO with an external PLL. Pin 2 shows as a loop filter capacitor but it is a external access point for the IC not a tuning port imo. I am not able to see any tuning voltage spec or plot (something like frequency vs voltage).

    The decoder had BW setting to account for the frequency shift in the VCO.

    Do you intent to use the touch tone decoder as a touch tone decoder?

    The VCO on this device show to output frequency of 500 kHz or less. I assume your XO will be higher frequency so I am wondering if you could simply divide down that XO.

    could you tell me more about your application. I might have a good IC recommendation for you.

    Regards, Simon.
  • 0 in reply to Serhii Dementii
    TI__Expert 5370 points
    Dear Serhii,

    The touch-tone decoder chip is not designed imo to support the VCO on chip to be lcoked onto an texternal XO by mean of a PLL.

    The touch tone decoder provide enough BW for each tone so that the center frequency is not critical and no PPM accuracy is needed.

    Are you trying to use it for soemthing else than a touch tone decoder?

    Are you only interested in the VCO (max 500 kHz) to divide down from the XO (likely higher than 500 kHz)? Could you use a divider then instead of the VCO?

    Can you tell me more about your application?

    Regards, Simon.
  • 0 in reply to Serhii Dementii
    TI__Expert 5370 points
    Dear Serhii,

    The touch-tone decoder chip is not designed imo to support the VCO on chip to be lcoked onto an texternal XO by mean of a PLL.

    The touch tone decoder provide enough BW for each tone so that the center frequency is not critical and no PPM accuracy is needed.

    Are you trying to use it for soemthing else than a touch tone decoder?

    Are you only interested in the VCO (max 500 kHz) to divide down from the XO (likely higher than 500 kHz)? Could you use a divider then instead of the VCO?

    Can you tell me more about your application?

    Regards, Simon.
  • 0 in reply to Serhii Dementii
    TI__Expert 5370 points
    Dear Serhii,

    The touch-tone decoder chip is not designed imo to support the VCO on chip to be lcoked onto an texternal XO by mean of a PLL.

    The touch tone decoder provide enough BW for each tone so that the center frequency is not critical and no PPM accuracy is needed.

    Are you trying to use it for soemthing else than a touch tone decoder?

    Are you only interested in the VCO (max 500 kHz) to divide down from the XO (likely higher than 500 kHz)? Could you use a divider then instead of the VCO?

    Can you tell me more about your application?

    Regards, Simon.
  • 0 in reply to Serhii Dementii
    TI__Expert 5370 points
    Dear Serhii,

    The touch-tone decoder chip is not designed imo to support the VCO on chip to be lcoked onto an texternal XO by mean of a PLL.

    The touch tone decoder provide enough BW for each tone so that the center frequency is not critical and no PPM accuracy is needed.

    Are you trying to use it for soemthing else than a touch tone decoder?

    Are you only interested in the VCO (max 500 kHz) to divide down from the XO (likely higher than 500 kHz)? Could you use a divider then instead of the VCO?

    Can you tell me more about your application?

    Regards, Simon.