Need help to design a PCB

[houly]

Hello all,
I would have your opinion for a sensor application :

I would want to reduce the noise and also reduce the EMI effects
The sensor is deported from the PCB (about 20mm) for each connection. I’m wondering what is the best solution to protect the stage from EMI and noise ? a ring guard maybe ? a GND ring guard or a –5V ? Does the –5V reference should have a plane to reduce the impedance ?

For connection I would want to use insulated wire with shield is connected to the ground of the PCB (the other side should be unconnected) what do you think ?

here is the schematic :
**broken link removed**

 

[srizbf]

one suggestion is to use a shield wire for the sensor.
with a 2wire+shield , connect to sensor the 2 wires and
ground the shield -5v gnd.

in lt1964 have anothe 100nf ceramic between -5v and gnd.

since the frequency of sensor (usable) is not given , based on that some more can be incorporated.

 

[houly]

Hello and thanks for your reply.
So you suggest me to connect the shield of the sensor cable to the -5V plane ?
why is it better than connecting it to the ground ?
Why is it better than connecting it to the gard ring of the board (which is connected to the ground) ?

 

[kender]

Hello all,
I would have your opinion for a sensor application...

Sorry if I've missed it, but which type of sensor are you making a signal conditioning circuit for?
What kind of environment will the sensor work in?

- Nick

 

[houly]

Hello
It's a IR sensor that produce a variation of a resistor (typical value is 50 ohm). the sensor is placed in a metal box, the temperature is regulated by a compressor (the PWM of the motor induce a glitch in the preamp ! so I decided, for reducing this "noise" to put the preamp near the sensor (actually the preamp is deported by cables))
I'm not sure that is the good way to put the guard ring on a potential (-5V). I have a 4 layer PCB, the stackup is :

Top : signal
inner 1 : GND plane
inner 2 : power plane (supply of the op amp)
bottom : signal (but I finnaly no need to put signal, all signal should be placed on the TOP, so what is the best choice ? GND plane ? or leave it to no PCB tracks?


and I would put a local plane for the -5V on the top side, what do you think of it ? or does the common point of the sensor must be a plante like suggeted me srizbf ?
Does the case should be connected to the electrical GND ?

I have to make the choice tommorow so I hope that you could reply me today

thanks for your help