A-M Systems 3000 Manuel d'instruction - Page 13

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Record Mode

In Record Mode, the inputs of the differential

amplifier U11 are switched by relay K2 (in

the off position), connecting them

differentially across the two electrodes in

order to amplify with a x50 gain the neural

activity appearing at the electrode-tissue

interface. In this mode relay K1 is off so that

the Stimulus leads do not feed noise into the circuit. A capacity compensation

circuit provides positive feedback through U7 to minimize the effect of electrode

and cable capacitance on recording and impedance measuring modes. The

differential output signal of U11 passes through the High Pass Filter U1, the

Notch Filter U5 if activated, and the Low Pass filter U3, in that order. Finally the

signal passes through the High Gain amplifier (U2), offering x1, x2, x10, x20,

x100, or x200 additional gain.

Stimulus Mode

In Stimulus Mode, the differential

inputs of the Probe amplifier U11 are

switched by K2 (in the on position) so

that they are across a 100Ω resistor

that is in series with

indifferent electrode lead. At the same

time, relay K1 to connect the stimulus

source at the

STIMULUS INPUT

from an isolated source passes through the

returning through the

voltage across the 100Ω resistor which is amplified by the differential amplifier U11

and passes through the rest of the recording circuit with including the adjustable gain

amplifier U2.

Impedance Mode

When in record Mode and the Impedance switch is

set to ON, the differential amplifier U11 is switched

across the two electrode leads by K2 (in the off

position). At the same time, relay K1 is on such

that the internal current source is connected to the

electrode leads. The current source generates a

2nA, 100 Hz square wave that passes through the electrodes, and the voltage that

develops is a measure of the electrode impedance. The output of is fed through the

recording circuitry including the adjustable gain stage U2.

The current source consists of several parts. A square wave is applied to an active

current source, which converts the square wave voltage to a square wave current of

2nA p-p at 100 Hz. The calibrated current source is connected to the electrode leads.

A-M Systems

, the

PROBE-

connector to the electrode leads. A stimulus current

lead and the 100Ω resistor. The current creates a

PROBE-

131 Business Park Loop, P.O. Box 850 Carlsborg, WA 98324

Telephone: 800-426-1306 * 360-683-8300 * FAX: 360-683-3525

E-mail: [email protected] * Website:

Probe +

Probe -

Probe +

Probe -

lead to the active electrode,

PROBE+

Probe +

Probe -

http://www.a-msystems.com

Output

Stim +

Output

Stim -

2 nA square wave

Output