Evaluation and Compensation of Quantization Effect on Servo Performance for Hard Disk Drives

We investigated the quantization effect on the servo performance of a 1.8-in hard disk drive by changing the bits of the proposed quantizer model. We measured and analyzed the frequency response of the quantizer with different bits. The corresponding error rejection functions show that the poor rejection ability of the servo loop to low-frequency disturbances is caused by the quantizer in addition to the actuator pivot friction behavior. We propose a simple and low-cost scaling scheme to compensate the effect of the quantizer. With the compensation, the effect on the rejection ability is mostly due to the friction. Therefore, the effects from quantization and friction on the error rejection function can be differentiated, and the quantization and friction induced problems can be dealt with separately in the servo loop. In addition, through the proposed quantization model and measurement methodology, suitable bit resolution for the quantizer with and without the compensation can be identified.