P
PureSine
Hello,
In many sensitive devices/ instruments which have a sensitive high
impedance section like a high impedance amplifier(10^12 Ohm or even
higher) or other high impedance signals, I've seen they are protected by
a metallic mold(mostly copper) that sits on top of sensitive parts and
tracks and is usually screwed to the PCB. Such metallic molds which are
specific to the shape of PCB seems very expensive. I wonder those of you
that are familiar with such protection do you think it is necessary ?
They are for protection against EMI but for instruments that have no
signal/Clock faster than a few hundreds of MHz, the EMI wavelength
should be fairly smaller than 30 Cm, So effective it would be to instead
of designing a board specific metallic mold for each high impedance
section, Just cutting copper or aluminum sheets approximately to the
size of sensitive area and then mount them on PCB using 5mm metallic
Spacers that are grounded. Well there is a 5mm gap but this method is
much cheaper and simpler and to the extent of theory that I know it
should stop all the EMIs that their wave length is higher than a few Cm
and it is translated to about 10 GHz.
Even harmonics of a few hundred MHz clock are very weak at such frequency.
What do you think ?
Regards.
In many sensitive devices/ instruments which have a sensitive high
impedance section like a high impedance amplifier(10^12 Ohm or even
higher) or other high impedance signals, I've seen they are protected by
a metallic mold(mostly copper) that sits on top of sensitive parts and
tracks and is usually screwed to the PCB. Such metallic molds which are
specific to the shape of PCB seems very expensive. I wonder those of you
that are familiar with such protection do you think it is necessary ?
They are for protection against EMI but for instruments that have no
signal/Clock faster than a few hundreds of MHz, the EMI wavelength
should be fairly smaller than 30 Cm, So effective it would be to instead
of designing a board specific metallic mold for each high impedance
section, Just cutting copper or aluminum sheets approximately to the
size of sensitive area and then mount them on PCB using 5mm metallic
Spacers that are grounded. Well there is a 5mm gap but this method is
much cheaper and simpler and to the extent of theory that I know it
should stop all the EMIs that their wave length is higher than a few Cm
and it is translated to about 10 GHz.
Even harmonics of a few hundred MHz clock are very weak at such frequency.
What do you think ?
Regards.
