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Hi !

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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.

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

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• Hi Kawa,

Do you mean that our customer don't need to do AC coupling between CVBS source and ADA4433-1 if GND is same?

What I meant here is if the output of the CVBS has known DC level is ground referenced like on the Figure 53 in the datasheet which is an output from the DAC, you can just use DC coupling.

What will happen if CVBS source output is 1Vpp but 0V bias?

The input voltage range of ADA4433 is 0 - 2.1V, if your signal is 0V biased the h-sync will be clipped.

Since 1Vpp signal is supposed to be input, is it OK to understand that 1.0 V bias is OK?

Yes, 1V bias is fine but not because your input signal is 1Vpp, you are just raising the biasing of your CVBS signal that will ensure that the sync tip will not be clipped at the input of the amplifier due to the input voltage range.

When deciding each constant, is there a point to consider other than the cutoff frequency and the bias voltage?

You also need to consider sag.

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?)

The location of the cutoff frequency should be set properly. It doesn't need to be 0.26Hz up to 4Hz I guess is fine depending on the refresh rate.

For the values of your components, try lowering it to R1 = 6.2kOhm, R2 = 2.7kOhm, your capacitor value is fine. Just make sure that R1 = R3, R2 = R4, and the capacitors should be equal too.

Let me know if you need any clarifications.

Regards,
Goz

• Hi Kawa,

Do you mean that our customer don't need to do AC coupling between CVBS source and ADA4433-1 if GND is same?

What I meant here is if the output of the CVBS has known DC level is ground referenced like on the Figure 53 in the datasheet which is an output from the DAC, you can just use DC coupling.

What will happen if CVBS source output is 1Vpp but 0V bias?

The input voltage range of ADA4433 is 0 - 2.1V, if your signal is 0V biased the h-sync will be clipped.

Since 1Vpp signal is supposed to be input, is it OK to understand that 1.0 V bias is OK?

Yes, 1V bias is fine but not because your input signal is 1Vpp, you are just raising the biasing of your CVBS signal that will ensure that the sync tip will not be clipped at the input of the amplifier due to the input voltage range.

When deciding each constant, is there a point to consider other than the cutoff frequency and the bias voltage?

You also need to consider sag.

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?)

The location of the cutoff frequency should be set properly. It doesn't need to be 0.26Hz up to 4Hz I guess is fine depending on the refresh rate.

For the values of your components, try lowering it to R1 = 6.2kOhm, R2 = 2.7kOhm, your capacitor value is fine. Just make sure that R1 = R3, R2 = R4, and the capacitors should be equal too.

Let me know if you need any clarifications.

Regards,
Goz

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