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INSTRUMENT OPERATION
Axopatch 200B, Copyright 1997-1999, Axon Instruments, Inc.
The very effective compromise solution adopted in the Axopatch 200B is to put an initial
gain of ten in front of the filter if the gain switch is set to 5 or more. The rest of the gain
amplification is after the filter.
The overload (OVLD) light illuminates if either the input to the filter or the output of the
final gain amplifier exceeds ±10 V for longer than the 100 µs. This signifies that the signal
output is being clipped and has become non-linear.
The electronic gain internal to the Axopatch 200B output section is twice the α value
shown on the gain switch. The reason is clear if you consider the output in the WHOLE
CELL configuration. To achieve the best compromise between noise and dynamic range,
the Axopatch 200B uses a 500 MΩ feedback resistor. The output of the current to voltage
converter is, therefore, 0.5 mV/pA. To simplify the daily mental scaling task for the user,
the headstage output is presented to the user as 1 mV/pA by including an additional two
times (x2) gain. In PATCH mode, the output of the differentiator is also 0.5 mV/pA and,
therefore, similar considerations apply.
Output BNCs
CELL CAPACITANCE TELEGRAPH
Puts out a voltage between 0 and 10 V that linearly specifies the whole-cell
capacitance between 0 and 100 pF (for β = 1; capacitance between 0 and 1000 pF
for β = 0.1). The voltage is 0 to -10 V if the WHOLE CELL capacitance switch is
turned off. If the WHOLE CELL CAP. switch is ON but the control is overridden
(e.g., by current-clamp mode) the telegraph output will be between 0 and +10 V.
DATA NOT VALID OUTPUT
Puts out a positive TTL voltage while the current output is blanked either during
reset or during external blanking via the blank activate input.
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