Hardware Question

bambino

In a bread board enviroment I was able to get a Max1270 to produce a sample rate, from an Accelorometer, @ > 100K per second. When the ProtoBoard arrived I used the sme components from the Bread board to populate it. I am now having to implement digital filtering to get a decent signal from a sample rate of 45Ksps.
I have since taking out my bypass caps and replaced them with a 4.7uF and a .1uF per the Maxim datasheet for noisy circuits, and placed 5 Ohms·between the supply and VDD. I have checked continuity, shorts, opens, even wondered if Mars was conjuct with Scorpio.
Could bread board capacitance be such a loss to have caused all this. I'm using the same program as well, Just changed a couple contol pins!

scotta

Try tantalum caps...

bambino

The original setup used a 10uF filter cap, and I will go back to it, as it was a better signal than what I am getting now.
My app only requires 16Ksps, but my competition is hovering around 92Ksps.

I just can't believe the difference I'm seeing. Even on a home grown PCB using a 16 bit processor I was able to get clear signals at 90K.

mahjongg

perhaps you have a noisy ground plane because switching noise from the digital interface also "streams back" through the analog ground plane, causing noise beween the analog input signal and the analog ground pin of the MAX1270.

Try to seperate the analog and digital groundplanes, and only connect them together near the analog ground pin of the MAX1270.

Mahjongg.

bambino

Thanks Mahjongg,

Contrary to the datasheet, I have never connected them together at all, in any of the devices I've used the 1270 in. My sensor conditioner is in a different circuit with its own power supply and I use that gnd for my anolog ground. It gives me less of a 0 Offset problem. But you did give me an idea. In my app the max sets an inch above and two inchs below a transformer for a LCD screen. I am going to take it out of circuit and try it using a PC debug screen. I may have to redesign

bambino

The Transformer was causing some high frequency interferrence, but not the low frequency distortion.

I have taken the assembly down and am starting from scratch. By mounting the converter on a separate PCB, maybe I can get my signal back.
Thanks for all the input.