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LM1881: Output delay

Depeng Man
Intellectual 2030 points
Part Number: LM1881

Hi team，

picture 1

picture 2

Figure 1 shows the output waveform of el1881 I used before,

Figure 2 shows the output waveform of lm1881mx,

The output waveform of lm1881mx has delay. My circuit is designed according to the reference circuit of the data table. How can I remove the delay?

Thank you！

BR,

James

  • 0
    TI__Intellectual 990 points

    Hello Depeng,

    1. Just to clarify, Figure 2 to TI's LM1881MX and Figure 1 refers to non-TI part: el1881?


    2. Regarding the reference circuit are you referring to the following?:


    3. Can you provide insight into your test above?
      1. From what I can see, the blue waveform is your input and the yellow waveform is your output. Can you specify where you are measuring the waveforms from the circuit above?
      2. Is this output (yellow waveform) taken from the "Composite Sync Output"?
      3. The delay seems to be approximately 80ns, can you verify this?

    Regards,
    Bill

  • 0 in reply to Bill Chieng
    TI__Intellectual 2030 points

    Hi Bill，

    Thank you for your quick reply.

    1) Figure 1 : EL1881CSZ Figure 2 : LM1881MX

    2) The reference circuit is correct.
    3) measuring the waveforms from the circuit above? : PIN 1 & PIN 2.
    4) Is this output (yellow waveform) taken from the "Composite Sync Output"? Yes, composite output.
    5) The delay seems to be approximately 80ns, can you verify this? Yes, that's about it.

    Best Regards

    James Man

  • 0 in reply to Depeng Man
    TI__Intellectual 990 points

    Hello James,

    Thanks for the clarification. At pin 2 of the device, do you have a chroma filter (low pass filter) as configured below?

    If so, do you have this configured in both EL1881CSZ and LM1881MX?

    I will notify your inquiry to the appropriate team. Please expect a response by 3/30/22.

    Regards,

    Bill Chieng

  • 0 in reply to Depeng Man
    TI__Intellectual 990 points

    Hello James,

    On page 7 of the LM1881's Datasheet, there is additional information about Composite Sync Output. One possible explanation for the output delay is the following low pass filter (indicated by the asterisks):

    The datasheet goes on to indicate that the delay between the Composite input and Composite output could be between 40ns to 200ns. From what the scope captured above (approximately 80 ns), this seems consistent according to the datasheet.

    Regards,

    Bill Chieng


    lm1881.pdf