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The other major part of the integrated control card is the amplifier. The amplifier takes relatively weak signals from the motion processor, phases them for the given motor and application, and amplifies them. The motor command from the motion processor is either a PWM signal, a +/- 10V analog signal, or a pulse and direction signal. Servo motors generally use the first two methods, while step motors use the latter.

A newer variation for analog motor output is SPI (Serial Peripheral Interface) format. In this scheme the motion processor outputs a 16 bit signed motor command on a digital serial line. This method is useful because a number of D/A (digital to analog) converter ICs and other amplifier controllers directly accept it. Compared to the traditional +/- 10V analog scheme, this method is an improvement because it avoids conversion to analog on both ends, a noise and cost-inducing process.

Depending on the architecture of the motion processor, commutation may be done in the amplifier, or it may be done by the motion processor. It should be noted that only brushless DC motors require commutation. If the amplifier is to perform the commutation, then the motion processor sends a single phase signal for each motor, and the amplifier uses Hall sensors to distribute the power to the correct motor coil. If the motion processor performs the commutation, then it sends multiple motor signals per motor (one for each motor phase) and the amplifier does not have to perform any commutation. Using the motion processor to perform commutation has the advantage that it can perform more advanced motor control techniques such as sinusoidal commutation and field oriented control because the motion processor “sees” all the signals from the motor, including the encoder data stream, while the amplifier only “sees” the motor currents.

Another important consideration for amplifier design is whether or not current control, also called torque control, will be used. Current control means that there is an additional control layer between the motion processor and the motor which measures the actual current through each phase of the motor and adjusts the drive voltage to match the desired current (from the motion processor) to the actual current measured in the motor. Current control generally increases the bandwidth of the motor, which means it can react more quickly to outside disturbances, and thus is a must for high end applications such as machine tools. Lower power and/or lower performance applications may consider not using a current loop as long as some type of over current protection is included to protect against short circuits at the motor.