Coded data generation or conversion – Analog to or from digital conversion – Analog to digital conversion
Reexamination Certificate
2000-09-20
2002-08-20
Williams, Howard L. (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Analog to digital conversion
C341S118000
Reexamination Certificate
active
06437723
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a signal processing circuit and a semiconductor integrated circuit, and more particularly, it relates to a signal processing circuit and a semiconductor integrated circuit processing a signal recorded in an optical disk such as a CD (compact disk).
2. Description of the Prior Art
In order to reproduce a signal recorded in an optical disk such as a CD or a CD-ROM, an analog RF (radio frequency) signal read from the optical disk is converted to a digital signal with reference to a prescribed slice level. In general, the data recorded in the optical disk is an EFM (eight to fourteen modulation) signal, which is so set that a dc component thereof is basically zero. Therefore, the aforementioned slice level in the digital conversion is controlled to reach a center voltage level of the analog RF signal.
FIG. 9
is a circuit diagram showing the structure of a conventional signal reproducing circuit for an optical disk, including a digital conversion part and a slice level control part converting the aforementioned analog RF signal to a digital signal.
A signal read from an optical disk by an optical pickup is amplified by an RF amplifier
51
, and supplied to an inversion input terminal of a comparator
53
through an input capacitor
52
for removing a dc component as an analog RF signal. The comparator
53
is a digital conversion part having a non-inversion input terminal supplied with a reference voltage Vref for comparing the aforementioned analog RF signal with the reference voltage Vref, converting the analog RF signal to a digital signal and outputting the same.
An end of a resistor
54
is connected between the capacitor
52
and the inversion input terminal of the comparator
53
, and a positive electrode of an integration capacitor
55
is connected to the other end of the resistor
54
so that the center voltage level of the analog RF signal is adjusted by charging/discharging the integration capacitor
55
.
A charge pump circuit
56
and a resistor
57
are provided between an output side of the comparator
53
and the positive electrode of the integration capacitor
55
. The charge pump circuit
56
controls charging/discharging of the integration capacitor
55
in response to the output level of the digital signal output from the comparator
53
. Thus, it follows that the charging quantity of the integration capacitor
55
is controlled in response to an average dc level of the output digital signal.
The integration capacitor
55
integrates the output of the comparator
53
through the charge pump circuit
56
and the resistor
57
, for operating the average value of the digital signal. This average value is added to the analog RF signal through the resistor
54
. Therefore, the center voltage level of the analog RF signal is adjusted in response to the voltage level of the positive electrode of the integration capacitor
55
, i.e., the average dc level of the digital signal so that the slice level follows the center voltage level of the analog RF signal.
However, the aforementioned conventional signal reproducing circuit must be provided with the capacitor
52
for removing the dc component and the resistor
54
, and hence the circuit area is disadvantageously enlarged to increase the cost. When the capacitor
52
and the resistor
54
are not built in the chip but externally provided, parasitic capacitances of the capacitor
52
and the resistor
54
are increased to result in difficulty in speeding up the operations.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a signal processing circuit and a semiconductor integrated circuit capable of implementing a function of adjusting a slice level with a small-scale circuit area while keeping the circuit at a high speed.
Another object of the present invention is to provide a signal processing circuit and a semiconductor integrated circuit capable of correctly detecting a dc component of an input signal.
A signal processing circuit according to an aspect of the present invention comprises an amplifier circuit amplifying an input signal, a conversion circuit converting an output from the amplifier circuit to a digital signal on the basis of a first reference value and a feedback circuit integrating the digital signal from the conversion circuit and feeding back the integrated digital signal as a second reference value of the amplifier circuit.
In this signal processing circuit, the amplifier circuit amplifies the input signal, the conversion circuit converts the output from the amplifier circuit to a digital signal on the basis of the first reference value, and the feedback circuit integrates the digital signal from the conversion circuit and feeds back the integrated digital signal as the second reference value of the amplifier circuit. Consequently, neither a capacitor for removing a dc component nor a resistor may be provided but it is possible to implement a function of adjusting a slice level with a small-scale circuit area while keeping the circuit at a high speed.
The amplifier circuit preferably amplifies the difference between the input signal and the second reference value. In this case, the difference between the input signal and the second reference value as fed back can be so amplified that the slice level can be properly controlled.
The amplifier circuit preferably includes at least two stages of amplifier circuits formed by a first amplifier circuit located on an input side and a second amplifier circuit located on an output side.
In this case, the first amplifier circuit can adjust the center voltage level of the input signal while the second amplifier circuit can amplify the input signal to a desired amplitude, so that the input signal can be amplified in high precision and output to the conversion circuit.
At least part of the amplifier circuit preferably includes a complete differential amplifier circuit, and one output of the complete differential amplifier circuit is preferably input in the conversion circuit as the first reference value.
In this case, the amplifier circuit can have a wide output range so that the amplification degree can be increased to operate the conversion circuit at a high speed and in-phase noise can be eliminated.
The feedback circuit preferably integrates the digital signal from the conversion circuit and feeds back the integrated digital signal to the first amplifier circuit.
In this case, the digital signal from the conversion circuit is integrated and fed back to the first amplifier circuit, whereby the center voltage level of the input signal can be adjusted in response to the level of the digital signal for properly controlling the slice level.
The feedback circuit preferably includes an integration capacitor and a charging/discharging circuit charging/discharging the integration capacitor in response to the level of the digital signal from the conversion circuit.
In this case, the charging/discharging circuit charges/discharges the integration capacitor in response to the level of the digital signal from the conversion circuit so that the center voltage level of the input signal can be adjusted in response to the level of the digital signal.
A signal processing circuit according to another aspect of the present invention comprises an amplifier circuit amplifying an input signal, a conversion circuit converting an output from the amplifier circuit to a digital signal on the basis of a first reference value and a detection circuit detecting a dc component of the signal not yet amplified by the amplifier circuit.
In this signal processing circuit, the amplifier circuit amplifies the input signal, the conversion circuit converts the output from the amplifier circuit to a digital signal on the basis of the first reference value, and the detection circuit detects the dc component of the signal not yet amplified by the amplifier circuit. Thus, it is possible to detect the dc component of the signal not yet subjected to amplification, i.e., the signal not yet subjecte
Otsuka Takeshi
Tani Kuniyuki
Wada Atsushi
Armstrong Westerman & Hattori, LLP
Sanyo Electric Co,. Ltd.
Williams Howard L.
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