High frequency track and hold full-wave rectifier

Details High frequency track and hold full-wave rectifier High frequency track and hold full-wave rectifier

1999-04-19

2003-11-25

Hudspeth, David (Department: 2651)

Dynamic magnetic information storage or retrieval

General processing of a digital signal

Head amplifier circuit

Reexamination Certificate

active

06654192

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates in general to circuits for processing analog signals, and, more particularly, to a rectifier integrated circuit.
BACKGROUND OF THE INVENTION
In many applications it is necessary to monitor the amplitude of a high frequency signal, i.e., >10 MHz, received at a certain input in order to optimize the signal reception. Frequently, the devices of servo loops that implement the necessary optimization adjustments are digitally controlled. This implies the need for converting an analog signal representative of the amplitude of the high frequency input signal into a digital value.
A typical example of a signal amplitude detector for the control loop of a numerical servo actuator is used to align the read/write heads of a mass memory device, such as a hard disk drive (HDD) of a personal computer. The amplitude of the signals originating from the distinct heads represent a measure of the head alignment on the respective disk tracks. Therefore, the analog signal representing the amplitude of the high frequency signal is fed to an analog/digital converter, whose output is used to control the positioning motor of the heads.
The amplitude of a high frequency signal may be determined using a peak detector. Normally, it uses an operational amplifier to store the maximum level of the input signal on a capacitor. However, due to the relatively high frequency of the signals (>10 MHz), relatively high performance in terms of slew rate is required from the operational amplifier. This often requires unacceptably high power consumption and large size components A further drawback of this approach is the limited noise rejection and the disturbances that eventually cause errors in the output digital stream. A known alternative approach includes detecting the amplitude by rectifying the signal, followed by an integration.
The rejection of noise is noticeably improved because the noise is minimized by the integration. A typical full-wave rectifier and an integrating capacitor are used. The input voltage is converted into a current by the operational amplifier and the current is rectified by a common diode bridge and integrated on the output capacitor However, to obtain an adequate precision, the requirements of pass band and gain (GBW) of the operational amplifier are severe.
The article titled: “A CMOS Rectifier-Integrator for Amplitude Detection in Hard Disk Servo Loops”, by Michel S. J. Steyaert, et al.; IEEE Journal of Solid-State Circuits, Vol. 30, No 7, July 1995, describes a rectifier-integrator CMOS circuit for a high frequency signal, particularly suited to act as an amplitude detector in HDD servo loops. Even in this case, the operational amplifier must satisfy the pass band and gain requisites which are particularly demanding. In general, by assuming that a sinusoidal input signal has a frequency F
0
, the system requires an analog pass band larger than 2*F
0
.
The trend in many applications is to handle higher and higher frequency signals, e.g., >10 MHz originating from HDD heads. This imposes an adjustment in the operating characteristics which generally implies a greater power consumption, and also imposes the need to achieve a high precision which generally requires a relatively large area of integration on silicon.
SUMMARY OF THE INVENTION
Confronted with the aboved described increasing difficulties to meet the requirements of amplitude detector circuits for high frequency signals, a system according to the present invention is based on the use of a so-called Track&Hold circuit (T&H) and on a known bistable circuit commonly known as an ECL latch.
This system is functionally controlled by a dedicated timing circuit that derives appropriate control signals for the T&H and the ECL latch from a master clock signal, and of an analog amplifier multiplexed by way of multiplexing control signals provided by the same bistable circuit. This circuit contains information on the sign of the output signal of the multiplexed analog amplifier to the input of which is fed the signal output by the Track&Hold stage.
The invention is particularly effective, but not exclusively, in servo loops for reading data from disks, typically in hard disk drives (HDD) of personal computers.


REFERENCES:
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patent: 5483393 (1996-01-01), Mento et al.
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Texas Instruments application report for TRF3040 Frequency Modulator/Synthesizer Jun. 1999.*
Steyart, M.S., A CMOS Rectifier-Integrator for Ammplitude Detection in Hard Disk Servo Loops, IEEE Journal of Solid-State Circuits, vol. 30, No. 7, Jul. 1995, pp. 743-751.

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