A-M Systems 1800 Manual - Halaman 9

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Overview

The Head Stage Probe, containing a high input impedance, low-noise, differential

amplifier, is connected to the Model 1800 through a 9-pin Input connector assigned to

each channel. The Mode Switch for each channel controls the input configuration of

the Probe attached to that channel as well as the operation of the subsequent stages of

the amplifier. In Record Mode, a combination of the Probe and the main circuit amplify

the signal which appears across the two electrodes attached to the Probe. In Stimulus

Mode, the signal at the Stimulus connector to be applied to the electrodes and the

Probe monitors the stimulus current by measuring the voltage developed across a 1 kΩ

resistor in series with the electrode. In Impedance Mode, an internally calibrated

current is passed through the Probe to one electrode, and the Probe monitors

electrode impedance by measuring the voltage that develops across the two

electrodes.

The signal from the Probe passes through the differential amplifier which has a unity

gain in Record and Stimulus Modes and a gain of x0.01 in Impedance Mode. The

signal then passes through the Low Cut-Off Filter and is increased by a factor of 10.

Next the signal enters the Notch Filter if it is activated. Finally the signal passes

through the High Cut-Off Filter which has a unity gain in Stimulus and Impedance

Modes and an adjustable gain controlled by the Gain Switch while in Record Mode

A-M Systems

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

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

E-mail: [email protected] * Website: http://www.a-msystems.com

Theory of Operation

Figure 2. Main circuit description and block diagram

*Only for impedance mode

**Only for record mode