Servo amplifier

A servo amplifier for supplying current to a D.C. servo motor, said servo amplifier including a control signal input;

• at each signal input;
• circuit means coupled to the signal inputs for creating an error signal between the control signal and the tach signal;
• a triangular wave generator for generating a triangular wave form;
• first means for summing the error signal with the triangular wave;
• means for modulating the resultant signal including first comparator means having one input for receiving the sum of the error signal and the triangular wave, another input connected to system common, and an output, inverting amplifier means for receiving and inverting said error signal, second means for summing the inverted error signal with the triangular wave, second comparator means having one input for receiving the sum of the error signal and the triangular wave, a second input connected to system common, and an output;
• tri-state drive logic circuitry having a first input for receiving a non-inverted signal and a second input for receiving an inverted signal and comprising a first invertor coupled to said first input, a second invertor coupled to said second output, a third invertor, the output of said first invertor being supplied to said third invertor for providing an output Q1, a fourth invertor also coupled to said second input and having an output Q2, a fifth invertor coupled to the output of said second invertor and having an otuput Q3, and a sixth invertor also coupled to said first input and having an output Q4;
• power transistors;
• and power transistor drive circuitry adapted to be coupled to said power transistors;
• said means for modulating being coupled to the output of said first and second summing means for supplying modulated signals form said outputs of said first and second comparator means to said first and second inputs of said tri-state drive logic circuitry, said tri-state drive logic circuitry having said Q1, Q2, Q3 and Q4 outputs coupled to said power transistor drive circuitry and said tri-state drive logic circuitry providing fast response to the error signals indicating a desired change in speed of the D.C. motor, and without over-shoot or hunting of the D.C. servo motor.