AD9957 DAC Power supply filtering Circuit

Hi there,

It would be best to use ferrite bead to these pins of the AD9957

1. AVDD (Pin 74 to 77 and Pin 83)

These are 3.3V DAC power supplies that typically consume about 28mA. At a minimum, a ferrite bead should be used to isolate these from other 3.3 V supplies, with a separate regulator being ideal.

2. AVDD (Pin 3)

This 1.8 V supply powers the REFCLK multiplies (PLL) and consumes about 7mA. For applications demanding the highest performance with the PLL enabled, this supply should be isolated from other 1.8 V AVDD supplies with a separate regulator. For less demanding applications, this supply can be run off the same regulator as Pin 89, Pin 92 with a ferrite bead to isolate Pin 3 from Pin 89, and Pin 92. 

3. AVDD (Pin 6)

This pin can be grouped together with the DVDD 1.8V supply pins. For the highest performance, a ferrite bead should be used for isolation, with a separate regulator being ideal.

4. AVDD (Pin 89 and 92)

This 1.8 V supply the REFCLK input consumes about 15mA. The supply can be run off the same as Pin 3 with a ferrite bead to isolate Pin 3 from Pin 89 and 92. At the minimum, a ferrite bead should be used to isolate these from other 1.8V supplies. However, for applications demanding highest performance, as separate regulator is recommended.

We do not have particular part number for the ferrite bead but we recommend to use low Q-beads. You can also check  on  this thread .

Regards,

Jules

Hi,

We are Operating The DAC with 1Ghz Sampling Clock.

The Thread You suggested says:

"you have to use beads that have high impedance on that frequency range."

IF We had 4 options:

1. 200 Ohms @1000MHz 

2. 400 Ohms @1000MHz 

3. 600 Ohms @1000MHz 

4. 800 Ohms @1000MHz 

Which Will Be the Good?

Hi,

We are Operating The DAC with 1Ghz Sampling Clock.

The Thread You suggested says:

"you have to use beads that have high impedance on that frequency range."

IF We had 4 options:

1. 200 Ohms @1000MHz 

2. 400 Ohms @1000MHz 

3. 600 Ohms @1000MHz 

4. 800 Ohms @1000MHz 

Which Will Be the Good?

Hello,

To reduce high frequency noise, the bead must be in the resistive region; this is especially desirable for electromagnetic interference (EMI) filtering applications. The component acts like a resistor, which impedes the high frequency noise and dissipates it as heat. The resistive region occurs after the bead crossover frequency (X = R) and up to the point where the bead becomes capacitive.

With this, I suggest the 800 ohms @ 1000Mhz. You have to use beads that have high impedance on that frequency range.

This application note AN-1368 regarding Ferrite Bead Selection and Design will also help you more.

Regards,

Jules