A CMOS rectifier-integrator for amplitude detection in hard disk servo loops

In this paper a CMOS alternative amplitude detection system is presented. It is designed as an alternative for the, bipolar, amplitude detection in hard disk servo systems. The amplitude is detected by converting the input voltage to a current, rectifying the current, and integrating it on a capacitor. For this a new OTA topology and a rectifier cell are designed. This circuitry is expanded with a very linear current mirror and an automatic offset compensation system to cope with technology spread. The measured accuracy of the amplitude detector is 0.2% (9 b). This makes the circuit suitable for implementation in state-of-the art hard disk systems with very high track densities and very short access times. Because the circuit is realized in standard CMOS it is a further step toward CMOS only hard disk electronics. Because the circuit operates from a single 3 V power supply and has limited power consumption it can be used in battery powered systems