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(ADA4433-1) To connect ADA4433-1 to ADI Video decodor

Hi !

I have some questions about ADA4433-1.

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Q1)

Our customer are planing to make evaluation board to change "single-CVBS" to "Diff-CVBS" to input ADV7281A-M.

To connect to ADI video decoder,  I think AC-coupling is necessary.

At ADA4433-1 datasheet page.22 Figure 55, there is "Difference Amplifier in a DC-Coupled Configuration" reference circuit.

Do you have "Difference Amplifier in a AC-Coupled Configuration" reference circuit?

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Q2)

Our customer will use like this.

"CVBS source" => "Single-CVBS" => "ADA4433-1" => "Diff-CVBS" => "ADV7281A-M"

Do our customer have to do AC-Coupling between "CVBS source" and "ADA4433-1"?

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Q3)

Do our customer have to do AC-Coupling between "ADA4433-1 source" and "ADV7281A-M"?

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Q4)

At ADA4433-1 datasheet Page.15, this is written.

Does this mean whether AC-coupled or DC-coupled, we do not change the connection of -IN and we need to bias with half the amplitude of + IN?

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Q5)

At ADA4433-1 datasheet Page.15, this is written.

Our customer are planing to use these value for each components.

C1 = 22uF

R1 = 62kOhm

R2 = 27kOhm (1V bias

*Fc = 0.26Hz.

How should they decide these value for each components?

Do you think that there is no problem with these values?

How should the cutoff frequency of the high-pass filter be taken into consideration while considering the NTSC signal frequency? (Does sag do not occur?)
Since 1Vpp signal is supposed to be input, is it OK to understand that 1.0 V bias is OK?
When deciding each constant, is there a point to consider other than the cutoff frequency and the bias voltage?

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Best ragards

Kawa

Parents
  • Hi Goz

    Thank you for your reply!

    Answering your first and third question you can refer on the Figure 22 of ADV7281 datasheet the AC coupling is necessary at the input of the device as a DC block. 

     

    => I understood that our customer should use AC-coupling between ADA4433-1 and ADV728x.

    AC coupling between the source and ADA4433-1 is essential, this ensures that any other DC bias by the CVBS source is blocked or removed before the amplifier.

    => I understood that our customer should use AC-coupling between CVBS source and ADA4433-1.

    It should be observed that the dc voltage bias at the inputs are equal so that the offset on the differential output of the amplifier will be on the same level, otherwise it will drift apart.

    => Sorry I couldn't understood what you said.

         " the dc voltage bias at the inputs are equal "

         Q1) What do you mean equal? Equal to something?

         " It should be observed that the dc voltage bias at the inputs are

           equal so that the offset on the differential output of the amplifier

           will be on the same level, otherwise it will drift apart. "

         Q2)Do you mean that the output offset will be equal to input bias voltage so we

               have to understand that maybe output offset level will drift little because

               the bias level is made by divide resister and the resister value will change by temperature?

    In a scenario where your input signal is 2Vpp, the offsets on each input should be 1V, we can compute for the values of the resistors based on what is suggested on the datasheet.

     

    This will give us R3 = 3.059kΩ. 

    => I understood.

    I think the values of your components are too large compared to the input impedance of the device. 

    => Q3)Which components are too large? C1?

    The resistor values of the biasing circuit should be equal for proper matching.

    => Q4)How do our customer decide resistor value of biasing which should be equal for proper matching?

               

         Q5)I suppose that AC coupling is necessary for ADA4433-1. 
                Can you tell me the recommended value of each value in the attached circuit diagram?

                Should our customer make like this?(R1 = R3, R2 = R4)

    Best regards

    Kawa

Reply
  • Hi Goz

    Thank you for your reply!

    Answering your first and third question you can refer on the Figure 22 of ADV7281 datasheet the AC coupling is necessary at the input of the device as a DC block. 

     

    => I understood that our customer should use AC-coupling between ADA4433-1 and ADV728x.

    AC coupling between the source and ADA4433-1 is essential, this ensures that any other DC bias by the CVBS source is blocked or removed before the amplifier.

    => I understood that our customer should use AC-coupling between CVBS source and ADA4433-1.

    It should be observed that the dc voltage bias at the inputs are equal so that the offset on the differential output of the amplifier will be on the same level, otherwise it will drift apart.

    => Sorry I couldn't understood what you said.

         " the dc voltage bias at the inputs are equal "

         Q1) What do you mean equal? Equal to something?

         " It should be observed that the dc voltage bias at the inputs are

           equal so that the offset on the differential output of the amplifier

           will be on the same level, otherwise it will drift apart. "

         Q2)Do you mean that the output offset will be equal to input bias voltage so we

               have to understand that maybe output offset level will drift little because

               the bias level is made by divide resister and the resister value will change by temperature?

    In a scenario where your input signal is 2Vpp, the offsets on each input should be 1V, we can compute for the values of the resistors based on what is suggested on the datasheet.

     

    This will give us R3 = 3.059kΩ. 

    => I understood.

    I think the values of your components are too large compared to the input impedance of the device. 

    => Q3)Which components are too large? C1?

    The resistor values of the biasing circuit should be equal for proper matching.

    => Q4)How do our customer decide resistor value of biasing which should be equal for proper matching?

               

         Q5)I suppose that AC coupling is necessary for ADA4433-1. 
                Can you tell me the recommended value of each value in the attached circuit diagram?

                Should our customer make like this?(R1 = R3, R2 = R4)

    Best regards

    Kawa

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