JPH11144386A - Signal processing circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress influence of noise contained in a CD-RW signal, when it is amplified, at the time of inputting the CD-RW signal (a signal reproduced from a re-writable CD-ROM) which is small in signal quantity against the CD- ROM signal (a signal reproduced from a read only CD-ROM). SOLUTION: In the case of reproduction of a CD-ROM signal, a switch 11 selects a CD-ROM signal (terminal 9) to which the signal quantity is close to a CD-RW signal attenuated by a resistance R2, R3; in the case of reproduction of a CD-RW signal, it selects unattenuated CD-RW signal (terminal 7). A wide band amplifier consists of a resistance R4, Gm amplifier 13, buffer 15, resistance R5, switch 23, and a low pass filter(LPF) element C1 like a capacitor. In the case where the CD-RW signal is inputted, the switch 23 is turned on, the LPF element C1 is incorporated in the wide band amplifier to limit its band. In this case, the wide band amplifier cuts the high frequency noise (noise mixed by wiring 3 and a PC board pattern 5) contained in the CD-RW signal, amplifies the CD-RW signal, and outputs it.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing circuit for processing a first input signal or a second signal having a smaller signal amount than the first input signal.

[0002]

2. Description of the Related Art FIG. 6 shows a first configuration of a conventional signal processing circuit. The optical pickup 1 is a read-only CD-
The signal is reproduced from the ROM, and the signal (CD shown in FIG.
-ROM signal). Or optical pickup 1
Reproduces a signal from a rewritable CD-ROM,
At this point, a signal (CD-RW signal) shown in FIG. 8 is output. C
The D-RW signal is a signal of about １ ／ of the signal amount of the CD-ROM signal.

A signal reproduced by the optical pickup 1 is supplied to a resistor R1 via a wiring 3 and a PC board pattern 5.

The other end of the resistor R 1 is connected to a terminal 7. Further, an attenuator formed by connecting resistors R2 and R3 in series is connected between the other end of the resistor R1 and the reference voltage VREF. Ratio R2 of resistance values of resistance R2 and resistance R3: R3
= 3: 1. The connection point between the resistors R2 and R3 is connected to the terminal 9.

The signal output from the optical pickup 1 is a CD-
In the case of a ROM signal, the signal amount of the CD-ROM signal appearing at the terminal 9 is determined by the signal output from the optical pickup 1 being a CD-R.
In the case of the W signal, it approaches the signal amount of the CD-RW signal appearing at the terminal 7.

The switch 11 is such that the optical pickup 1 has a CD
When outputting the −RW signal, the terminal 7 is selected, and when the optical pickup 1 outputs the CD-ROM signal, the terminal 9 is selected. The switch 11 is connected to one end of the resistor R4. The other end of the resistor R4 is connected to the inverting input terminal of the Gm amplifier 13. The non-inverting input terminal of the Gm amplifier 13 is connected to a fixed voltage. The output terminal of the Gm amplifier 13 is connected to the input terminal of the buffer 15. The output terminal of the buffer 15 is connected to the output terminal 17. RF (high frequency) by Gm amplifier 13 and buffer 15
Configure the amplifier.

[0007] A resistor R5 is connected in parallel with the inverting input terminal of the Gm amplifier 13 and the output terminal of the buffer 15.
The resistor R4, the Gm amplifier 13, the buffer 15, and the resistor R5 constitute a wideband amplifier. With the values of the resistors R4 and R5,
The gain of a broadband amplifier, especially an RF amplifier, is determined.

The CD-ROM output signal and the CD-RW output signal at the output terminal 17 (point B) are as shown in FIG.

FIG. 7 shows a second configuration of a conventional signal processing circuit. The difference from FIG. 6 is that a phase compensation element 19 composed of a resistor R6 and a capacitor C2 connected in series is connected between the output terminal of the Gm amplifier 13 and the reference voltage VREF.

The waveforms of the CD-ROM signal and the CD-RW signal at point A output from the optical pickup 1 and the CD-ROM output signal and CD-RW signal at the output terminal 17 (point B)
The waveform of the output signal is as shown in FIG.

[0011]

In the wiring 3 and the PC board pattern 5, noise of a system clock (about 30 MHz) and a high frequency band (20 MHz or more) jump into the CD-ROM signal and the CD-RW signal. The CD-ROM signal containing noise is once attenuated by the attenuator,
Since the signal is amplified by the broadband amplifier, the influence of noise on the CD-ROM output signal at the point B shown in FIGS. 8 and 9 is small.

However, since the amount of the CD-RW signal output from the optical pickup 1 is small, the noise that has entered cannot be ignored, and the noise is amplified together with the CD-RW signal by a broadband amplifier. The influence of noise on the CD-RW output signal at the point B shown in FIG. 9 increases, and there is a problem that the S / N ratio of the CD-RW output signal deteriorates.

Accordingly, the present invention firstly provides a method for amplifying a second input signal when a second input signal having a smaller signal amount than the input signal is input, thereby reducing noise included in the second input signal. It is an object to provide a signal processing circuit capable of suppressing the influence.

[0014]

(First configuration example) An input terminal to which a first input signal or a second input signal having a smaller signal amount than the first input signal is supplied; Attenuating means for connecting the signal amount of the first input signal to the second input signal, and selecting the output of the attenuating means when the first input signal is supplied, When an input signal is supplied, switch means for selecting the input terminal, first resistor means having one end connected to the switch means, and high-frequency amplifier means connected to the other end of the first resistor. A second resistor connected in parallel to the high-frequency amplifier, and a second resistor connected to the input terminal.
And a low-pass filter element connected in parallel to the second resistor when the input signal is supplied.

(Second Configuration Example) An input terminal to which a first input signal or a second input signal having a smaller signal amount than the first input signal is supplied, and the first input signal is connected to the input terminal, Attenuating means for bringing the signal amount of the input signal closer to the second input signal, and when the first input signal is supplied,
A switch for selecting the input terminal when the output of the attenuation unit is selected and the second input signal is supplied; a first resistance unit having one end connected to the switch unit; G whose input terminal is connected to the other end of the resistor
m amplifier means, buffer means having an input terminal connected to the output terminal of the Gm amplifier means, second resistance means connected between the input terminal of the Gm amplifier means and the output terminal of the buffer means, First phase compensation element means connected to the output terminal of the Gm amplifier means, and when the second input signal is supplied to the input terminal, the first phase compensation element means is connected in parallel to the first phase compensation element means. And a second phase compensating element means.

[0016]

FIG. 1 shows a configuration of a signal processing circuit according to a first embodiment of the present invention. The optical pickup 1 is
The signal is reproduced from the read-only CD-ROM, and the signal (CD-ROM signal) shown in FIG. Alternatively, the optical pickup 1 is a rewritable CD-ROM
From the signal (CD-RW) shown in FIG.
Signal). The CD-RW signal is a signal of about １ ／ of the signal amount of the CD-ROM signal.

The signal reproduced by the optical pickup 1 is supplied to the resistor R1 via the wiring 3 and the PC board pattern 5.

The other end of the resistor R1 is connected to a terminal 7. Further, an attenuator formed by connecting resistors R2 and R3 in series is connected between the other end of the resistor R1 and the reference voltage VREF. Ratio R2 of resistance values of resistance R2 and resistance R3: R3
= 3: 1. The connection point between the resistors R2 and R3 is connected to the terminal 9.

The signal output from the optical pickup 1 is a CD-
In the case of a ROM signal, the signal amount of the CD-ROM signal appearing at the terminal 9 is determined by the signal output from the optical pickup 1 being a CD-R.
In the case of the W signal, it approaches the signal amount of the CD-RW signal appearing at the terminal 7.

The switch 11 selects the terminal 7 when the optical pickup 1 outputs a CD-RW signal in response to a control signal input to the terminal 21, and the optical pickup 1
-To output a ROM signal, select the terminal 9. The switch 11 is connected to one end of the resistor R4. Resistance R
4 is connected to the inverting input terminal of the Gm amplifier 13. The non-inverting input terminal of the Gm amplifier 13 is connected to a fixed voltage. The output terminal of the Gm amplifier 13 is connected to the input terminal of the buffer 15. The output terminal of the buffer 15 is connected to the output terminal 17. Gm amplifier 1
3 and the buffer 15 constitute an RF (high frequency) amplifier.

A resistor R5 is connected in parallel with the inverting input terminal of the Gm amplifier 13 and the output terminal of the buffer 15.
A selector of the switch 23 is connected to one end of the resistor R5, and one end of an LPF element C1 such as a capacitor forming a low-pass filter (LPF) together with the resistor R5 is connected to the selector of the switch 23. The other end of the LPF element C1 is
It is connected to the other end of the resistor R5.

The resistor R4, the Gm amplifier 13 and the buffer 15
, The resistor R5, the switch 23, and the LPF element C1 constitute a wideband amplifier. The values of the resistors R4 and R5 determine the gain of the wideband amplifier, especially the RF amplifier. According to the control signal input to the terminal 21, the input signal of the broadband amplifier is
In the case of a CD-ROM signal, the switch 23 is turned off and the CD
In the case of the -RW signal, the switch 23 is turned on.

When the switch 23 is off, the frequency characteristics of the wideband amplifier are as shown in FIG. 3A, and when the switch 23 is on, the frequency characteristics of the wideband amplifier are as shown in FIG. Bandwidth is limited.

As before, the system clock (about 30 MHz) and the high frequency band (20 MHz or more) are applied to the CD-ROM signal and the CD-RW signal reproduced by the optical pickup 1 while passing through the wiring 3 and the PC board pattern. ) Is mixed.

Since the CD-ROM signal containing noise is once attenuated by the attenuator and then amplified by the wide band amplifier, the CD-R signal at the output terminal 17 (point B) as shown in FIG.
The effect of noise on the OM output signal is small. CD-R
The high-frequency noise included in the W signal is cut off because the broadband amplifier limits the band of the amplification action, and the influence of the noise on the CD-RW output signal at the output terminal 17 (point B) as shown in FIG. Becomes smaller.

FIG. 2 shows the configuration of a signal processing circuit according to a second embodiment of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals, and detailed description is omitted.

The switch 23 and the LPF element C1 in FIG.
Omitted. Instead, a resistor R6 and a capacitor C2 are connected between the output terminal of the Gm amplifier 13 and the reference voltage VREF.
Are connected in series.
Further, a phase compensation element 31 in which a resistor R7, a capacitor C3, and a switch 33 are connected in series is connected in parallel to the phase compensation element 19.

The resistor R4, the Gm amplifier 13 and the buffer 15
, The resistor R5, and the phase compensation elements 19 and 33 constitute a wideband amplifier. According to the control signal input to the terminal 21, the switch 33 is turned off when the input signal of the broadband amplifier is a CD-ROM signal, and the switch 33 is turned on when the input signal is a CD-RW signal.

When the switch 33 is off, the frequency characteristics of the wideband amplifier are as shown in FIG. 3A, and when the switch 33 is on, the frequency characteristics of the wideband amplifier are as shown in FIG. Bandwidth is limited.

As in the prior art, the CD-ROM signal (signal at point A in FIG. 5) reproduced by the optical pickup 1 and the C-ROM signal
The D-RW signal (the signal at point A in FIG. 5) includes the wiring 3 and the PC
While passing through the board pattern, the system clock (30M
Hz) and high-frequency band (20 MHz or more).

Since the CD-ROM signal containing noise is once attenuated by the attenuator and then amplified by the wide band amplifier, the CD-R signal at the output terminal 17 (point B) as shown in FIG.
The effect of noise on the OM output signal is small. CD-R
The high-frequency noise included in the W signal is cut off because the wide band amplifier limits the band of the amplifying operation, and the influence of the noise on the CD-RW output signal at the output terminal 17 (point B) as shown in FIG. Becomes smaller.

1 and 2, the resistor R4 may be connected to the non-inverting input terminal of the Gm amplifier 13, and the inverting input terminal of the Gm amplifier 13 and one end of the resistor R5 may be connected to the reference voltage VREF.

[0033]

As described above, according to the present invention, when amplifying a CD-RW signal, the influence of noise (particularly, noise in a high frequency band) included in the CD-RW signal can be suppressed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of a signal processing circuit of the present invention.

FIG. 2 is a diagram illustrating a configuration of a signal processing circuit according to a second embodiment of the present invention;

FIG. 3 is a diagram illustrating frequency characteristics of the wide band filters of FIGS. 1 and 2;

FIG. 4 is a diagram showing a waveform of a CD-ROM signal and a waveform of a CD-RW signal at a point A in FIG. 1 and a waveform of a CD-ROM output signal and a waveform of a CD-RW signal at a point B;

5 is a diagram showing a waveform of a CD-ROM signal and a CD-RW signal at point A in FIG. 2 and a waveform of a CD-ROM output signal and a CD-RW signal at point B.

FIG. 6 is a diagram illustrating a first configuration of a conventional signal processing circuit.

FIG. 7 is a diagram illustrating a second configuration of a conventional signal processing circuit.

8 is a diagram showing a waveform of a CD-ROM signal and a CD-RW signal at a point A in FIG. 6, and a waveform of a CD-ROM output signal and a CD-RW signal at a point B.

9 is a diagram showing a waveform of a CD-ROM signal and a CD-RW signal at point A in FIG. 7 and a waveform of a CD-ROM output signal and a CD-RW signal at point B.

[Explanation of symbols]

1 ... optical pickup, 3 ... wiring, 5 ... PC
Plate pattern, 11 switch, 13 Gm amplifier, 15 buffer, 19 phase compensation element, 3
1 ... phase compensation element, R1, R2, R3, R4, R
5, R6, R7... Resistors, C1... Low-pass filter (LPF) elements such as capacitors, C2, C3.
・ Capacitor.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Ryuichi Yamashita 3-3-9, Shimbashi, Minato-ku, Tokyo Inside Toshiba Abu E Co., Ltd. (72) Inventor Hiroshi Osuka 3-chome, Shimbashi, Minato-ku, Tokyo No. 9 Toshiba Abu E Co., Ltd.

Claims (3)

[Claims] 1. An input terminal to which a first input signal or a second input signal having a smaller signal amount than the first input signal is supplied, and a signal of the first input signal connected to the input terminal Attenuating means for bringing an amount closer to the second input signal; and when the first input signal is supplied, selecting an output of the attenuating means, and when the second input signal is supplied,
Switch means for selecting the input terminal; first resistor means having one end connected to the switch means; high-frequency amplifier means connected to the other end of the first resistor; and parallel to the high-frequency amplifier means Connected second resistance means, when the second input signal is supplied to the input terminal,
A signal processing circuit comprising: a low-pass filter element connected in parallel to the second resistor. 2. An input terminal to which a first input signal or a second input signal having a smaller signal amount than the first input signal is supplied, and a signal of the first input signal connected to the input terminal. Attenuating means for bringing an amount closer to the second input signal; and when the first input signal is supplied, selecting an output of the attenuating means, and when the second input signal is supplied,
Switch means for selecting the input terminal; first resistor means having one end connected to the switch means; Gm amplifier means having an input terminal connected to the other end of the first resistor; and Gm amplifier means. Buffer means having an input terminal connected to an output terminal of the Gm amplifier means, second resistance means connected between an input terminal of the Gm amplifier means and an output terminal of the buffer means, and connection to an output terminal of the Gm amplifier means. When the second input signal is supplied to the input terminal,
A signal processing circuit comprising: a second phase compensating element connected in parallel with the first phase compensating element. 3. The method according to claim 1, wherein the first input signal is a signal reproduced from a read-only CD-ROM, the second input signal is a signal reproduced from a rewritable CD-ROM, 3. The system according to claim 1, wherein a system clock and a high-frequency band noise are mixed before the first and second input signals are supplied to the input terminal. A signal processing circuit as described.