True voltage follower in current clamp mode
One of the fundamental features we have incorporasted into the Optopatch
is the ability to perform true current clamping. The standard patch
clamp has performance limitations that are often detectable in practice. For
a true 
current clamping circuit the headstage amplifier
needs to be connected as a voltage follower, with the current provided by
a voltage source connected to a resistor. To approximate to a true current
source, the value of the current-passing resistor should be high compared
with the load resistor, so that the voltage at the amplifier input remains
low compared with the current-passing drive voltage, since the current flow
is actually given by the difference between these two voltages. With the optical
current-passing method, this condition is met automatically, but when a resistor
is used, the equivalent effect can be obtained by adding the input voltage
to the current-passing command voltage, as shown in the schematic below.
Further information on true current clamp can be found in our technical section.
