Dynamic information storage or retrieval – Information location or remote operator actuated control – Selective addressing of storage medium
Reexamination Certificate
1999-03-09
2001-04-17
Neyzari, Ali (Department: 2651)
Dynamic information storage or retrieval
Information location or remote operator actuated control
Selective addressing of storage medium
C369S047150, C369S053200
Reexamination Certificate
active
06219310
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the field of optical digital information readers and more specifically to the field of processing signals produced by a radiation detector depending on a laser beam reflected from a rotating optical disk.
BACKGROUND OF THE INVENTION
An optical read/write apparatus is known from European Patent EP 508 522. The requirements imposed on the processing of the low frequency components and the high frequency components of the detected signal differ substantially. The position of the detector and the alignment of the optical system are controlled by a control signal derived from the low frequency components of the detected signal. For this, an accurate and offset-free amplification are important. For the high frequency components, from which the information signal is derived, a comparatively large bandwidth and a relatively constant group delay are required. The European Patent proposes an optical read/write apparatus in which, the high frequency components and the low frequency components are separated from one another by a filter having a resistor arranged between the common input terminal and the first input terminal; and having a capacitor arranged between the first input terminal and the second input terminal. Subsequently, the high frequency components and the low frequency components are processed separately.
U.S. Pat. No. 4,663,749 describes an optical read/write apparatus in which the low frequency components are amplified by a current amplifier whose input current also constitutes the bias current, as a result of which, an offset-free low frequency amplification is achieved. The high frequency signals are processed by a separate amplifier.
JP 12-79428 describes an optical read/write apparatus in which, signals from photodetectors are separated into high frequency components, and low frequency components and are subsequently amplified by operational amplifiers. The amplified low frequency signal is recombined with the high frequency signal.
U.S. Pat. No. 4,785,441 describes apparatus for achieving a reliable tracking in an optical read/write system. In this system the high frequency components are also processed separately from the low frequency components.
The above citations are hereby incorporated herein in whole be reference.
SUMMARY OF THE INVENTION
Consequently, there is a need for optical read/write apparatuses having a signal processing unit in which, high frequency components and low frequency components are separated from one another directly, after the output of the detector and are processed separately.
In order to cater to this, according to the invention, the apparatus of the type defined in the opening paragraph is characterized in that, apparatus M
III
for processing the high frequency components include a bias current source and a second current mirror, an input branch of the second current mirror and a current output terminal of the bias current source both being connected to the second input terminal of apparatus M
III
. The bias current source enables the second current mirror of apparatus M
III
to be biased to a value at which, a satisfactory bandwidth can be obtained without the operation of apparatus M
II
being affected thereby.
Apparatus M
II
are usually implemented as a self-biased amplifier, the current supplied by the detector also serving as bias current. This may lead to the input impedance of apparatus M
II
being dependent on the intensity of the current supplied by the detector. This affects the operation of apparatus M
I
, which in turn may result in crosstalk from the low frequency components to the high frequency components. It is an object of the invention to preclude such crosstalk. In a first embodiment, the current mirror of the apparatus M
II
includes an operational amplifier, a bias voltage source, and a first and a second semiconductor element, which operational amplifier has an inverting input, a non-inverting input, and an output, which semiconductor elements each include main electrodes, which define a main current path, and a control electrode, the control electrode of the first semiconductor element and the control electrode of the second semiconductor element being connected to one another, the current mirror of apparatus M
II
further includes a first input branch for transferring an input current, which first input branch connects the first input terminal to a first central terminal via the main current path of the first semiconductor element, the first main electrode of the first semiconductor element being connected to the first input terminal, which current mirror further includes a first output branch for transferring an output current, which first output branch connects the first central terminal to the first output terminal via the main current path of the second semiconductor element, the operational amplifier having one of its inputs connected to a voltage output terminal of the bias voltage source, the operational amplifier having its other input connected to the first main electrode of the first semiconductor element, and the operational amplifier having its output coupled to one of the other electrodes of the first semiconductor element. The effect of the operational amplifier is that apparatus M
II
have such a low input impedance that they do not have any significant influence on the operation of apparatus M
I
.
In another embodiment which also precludes crosstalk, apparatus M
II
have a comparatively high input impedance. In the other embodiment, the current mirror of the apparatus M
II
includes a first and a second semiconductor element, which semiconductor elements each include main electrodes, which define a main current path, and a control electrode, the control electrode of the first semiconductor element and the control electrode of the second semiconductor element being connected to one another, which current mirror includes a first input branch for transferring an input current, which first input branch connects the first input terminal to a first central terminal via the main current path of the first semiconductor element, which current mirror further includes a first output branch for transferring an output current, which first output branch connects the first central terminal to the first output terminal via the main current path of the second semiconductor element, the first semiconductor element and the second semiconductor element being connected to the first central terminal via a first resistive element and a second resistive element, respectively. However, since the input impedance is now substantially signal independent, allowance can be made for this in the choice of apparatus M
I
and, if desired, the input impedance can form part of apparatus M
I
.
Apparatus M
I
for separating high frequency components and low frequency components of the detected signal, give rise to a zero point in the signal transmission from the detector to apparatus M
III
for processing the high frequency components. The presence of the zero point is not of any significance for the transmission of the signal because the low frequency components do not contain any data information. However, the zero point does have an adverse effect on the flatness of the group delay response of the information signal. The object of a further embodiment is to mitigate this adverse effect. In the further embodiment, the current mirror in the apparatus M
II
has a further output terminal for supplying a further output current (I″
LF
) and the signal processing unit further includes apparatus M
IV
for coupling the apparatus M
II
to the apparatus M
III
, which apparatus M
IV
includes a third input terminal for receiving the further output current (I″
LF
) and a third output terminal for supplying to the second input terminal of the apparatus M
III
a current (%I″
LF
) which is related to the further output current. In this further embodiment, the low frequency component of the signal, which reaches the input of apparatus M
III
, is reconstructed, so that, the zero p
Biren Steven R.
Neyzari Ali
U.S. Philips Corporation
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