The signal to noise ratio depends on the internal design of the operational (and
instrumentational) amplifier integrated circuits. The race of the smaller electronic
noise is a race of the semiconductor manufacturers. The designer can only choose
from the good amplifiers, from the leader semiconductor factories.
Ground topology
There is a general design method in the high gain amplifiers, what is applied in
LinearAmp, as well. Usually in the signal conditioner amplifiers (as in our amplifiers,
too, if optical isolators are not used) the Input GND, and Output GND points are
connected together internally. The ohmic resistance between them is less than 0.05
Ohms. However they are signed as different points, because in the interior of the
amplifier the ground network forms a linear topology, not a single-point GND (as it is
advised in the text-books). The suppression of the hum noise is better, if the ground
line follows the signal line linearly according to the increasing signal amplitudes from
the input to the output. To establish a single-point shielding ground is a good solution
at the output end of the signal ground line. Unfortunately the security ground wires
are also connected to the metal enclosures of the equipments. The security ground
wires are usually hum noise sources for the signal conditioner amplifiers (because
they usually drive some mains-frequency fault currents from other equipments, from
other rooms), but they must not be disconnected, they are compulsory to be used. If
you use a mains isolation transformer with symmetrical secondary coil, you can
eliminate the disadvantage of the security ground (if in your lab it is allowed to use,
please check the local rules). The Faraday-cage, metal parts in the Faraday-cage, the
oscilloscope, the PC, the Output GND of the amplifier, and the real, separated signal
ground line (coming from the earth directly, if it is available) should be connected to
this single-point shielding ground. But the ground point of the input circuitry should be
isolated from the shielding ground point (special care should be taken with the metal
parts close to the input in the Faraday-cage). The Input GND point of the amplifier is
used to provide a low impedance ground to the input circuitry only.
Connectors
The input and output connectors of LinearAmp amplifiers are standard BNC sockets.
Output GND is a 4-mm banana female connector. Output GND point is common to
the mains GND, the GND point of the Output BNC sockets and the metal parts of the
equipment case. The Input BNC sockets are isolated from the back plate. The Input
GND point is the GND point of the Input BNC socket(s).
