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Created page with " The amplifier implements closed-loop current control for each transmitter coil. The amplifier accepts a sinusoidal signal reference from the Signal Generator. The circuit is..."
The amplifier implements closed-loop current control for each transmitter coil. The amplifier accepts a sinusoidal signal reference from the Signal Generator. The circuit is constructed from two individual amplifier stages.
# A closed loop high-speed amplifier
# A class B current amplifier stage
==Closed-loop current amplifier==
A high-speed feedback amplifier achieves closed loop control of the emitter coil current. By ensuring a stable alternating current amplitude exists it can be assumed that the associated time-varying magnetic field amplitude is constant too. The LM7171 high speed operational amplifier is used for this design. The amplifier circuit design is shown below. [[File:Highspeedamp.png|350px|frame|Closed loop topology for controlling the current in the emitter coils]]
* <math>R_f</math> is the sense resistor (typically 1 ohm). The voltage dropped across this resistor is used as feedback for the amplifier
* <math>L_t</math> and <math>R_t</math> are the series resistance and inductance of the emitter coil. <math>L_t</math> is typically 75μH for the square coil design. <math>Rt</math> is typically 2.9Ω
* <math>R_c</math> and <math>C_c</math> form a compensation network for the amplifier. his network maintains amplifier stability and prevents excessive ringing. Anser EMT uses an <math>R_c</math> of 5kΩ and <math>C_c</math> of 70nF.
