differential amp driver for AFE5801

Junwei,

Do you want diff in/diff out? Or single in/diff out?  What is your BW concerns?  Look into the THS4130 for fully-differential or the LMH6629 or LMe49990 for single-ended.

Chuck Smyth

Hi Chuck,

I want diff in/diff out. I have one more question, If I connect the ADC driver to the AFE5801 using DC couple, Can I connect the output of the driver directly to the input of the AFE5801, like the left bottom figure in the Ths4130 datasheet? Or I should put  some resistor or capacitor between them?

Thanks

Hi Junwei,

According to my experience with AFE5801, use AC coupling. Take a look on Fig.34 on page 18. This solution is APPROVED and works fine. Anyway, you can make some experiments, like placing on you PCB some 'dummy' resistors/capacitors. I often do it!! If resistors are useless, use 0 Ohm. Anyway, forget the resistors. For AC coupling use 10-100nF capacitors. The most important is the image quality!!  The PCB design has a VERY big influence on it!!  Minimum 6-layers PCB with a good GND is recommended.

Best Regards,

Mariusz

Hi Junwei,

If it's a new design, I strongly recommend AFE5808 !!

Regards,

Mariusz

Junwei,

Mariusz's answer is correct.  AC coupling is recommended, but worst case you can use a 0ohm and DC couple with Vcm.  Either way,  I would put a place for this series component. Also,  I recommend the AFE5808A as well, but this is analog TGC vs. AFE5801's digital TGC.

Thanks,

Chuck Smyth

Chuck, I agree with you. External analog TGC circuitry is much more convenient and flexible. And it's cheap!! Schematic is very simple:

[RAM(TGC curve)]=>DAC=>Integrating Amp.

8-bit DAC is enough even for a very sophisticated systems. DAC08 or any clone of it could be used, followed by any clone of TL08x.

And once again... For everyone who 'plays' with ultrasound: Multilayer PCB(6+ layers are welcome), digital LVDS signals should be routed close (+/-) with the equal length.

Trust me, the PCB design has a very big influence on the image quality.

Regards,

Mariusz

Dear Mariusz,

Following your experience, AC coupling is better for AFE5801. Right?

I want to use AFE5801 to build a 32-Channel  daughter board for positron emission tomography (PET),  eight daughter boards will connect to a mother board. I think a digital control is better. If I use analog TDC and there are some difference of the output of the DAC, I think the gain will be alight difference.

In the AFE datasheet, it says:

In the case of ac coupling, the external input capacitors form a high-pass filter with the internal bias resistors (5kΩ), so, the value of the capacitors should allow the lowest frequency of interest to pass with minimum attenuation. For the typical frequencies used in ultrasound (>1MHz) a value of 10nF or bigger is recommended.

If I use AFE5801 for PET signal, I think I need a frequency from very low frequency to some high frequency. I think I need to use a capacitor with big value. Right?

Thanks.

Junwei,

What frequencies are you looking at?

Thanks,

Chuck Smyth

Dear Smyth,

About 1KHZ to 100M?

Thanks.