JPH04162257A - Digital information reading circuit for recording and reproducing device - Google Patents

Abstract

PURPOSE:To instantaneously secure reference potential without utilizing the spontaneous discharge of a capacitor by switching the time constant of a coupled time constant circuit through a switch in accordance with a change in input signal. CONSTITUTION:A coupled time constant circuit 10 constituted by successively connecting a capacitor 2, first resistor 3, and reference potential VN in series is connected to an input terminal 1 and a series circuit composed of a change- over switch 3 and second resistor 5 is connected in parallel with the resistor 3 so that the resistor 5 can be positioned between the switch 4 and reference potential VN. The switch 4 is connected to a control terminal 8. The time constant of the circuit 10 is switched through the switch 4 in accordance with a change in input signal produced when the input signal is changed from write signals to read signals, and so forth. When the time constant is switched in such way, potential variation from the reference potential VN can be canceled and the potential VN can be secured instantaneously without utilizing the spontaneous discharge of the capacitor 2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a digital information reading circuit for a recording/reproducing device using light, magnetism, or the like.

[Prior Art] As this type of information reading circuit, the one shown in FIG. 2 is generally known. In such a circuit, an information signal taken out from an information input/output section such as a light receiving element (not shown) is applied to an input terminal 9, and differentiated by a coupled time constant circuit 18 consisting of a capacitor 16 and a resistor 17. and input to the timer circuit 11. In this timer circuit 11, the timing of the information signal is controlled by a control terminal 14, and is input to an amplifier 12, where it is amplified to a predetermined level. The output of this amplifier 12 is sent to the next stage circuit (not shown) via the output terminal 13.

Next, the operation of such a circuit will be further explained in detail with reference to FIGS. 3A and 3B.

FIG. 3A shows an input signal, which is digital information, applied to the input terminal 9, and the area indicated by a indicates the read signal area,
The areas indicated by b indicate write signal areas.

Generally, the write signal area is larger than the read signal area a, and the signal level is also in the opposite direction. First, signals in the read signal area a are sequentially applied to the input terminal 9 and sent to the coupling time constant circuit 18. When the input of this signal is completed, the signal in the write signal area is similarly sent to the coupling time constant circuit 18. These signals are differentially processed by the combined time constant circuit 18 and enter the timer circuit 11 via point 15. The waveform transition of the output signal at point 15 at this time is as shown in FIG. 3B. In this figure, the output signals in areas C and d correspond to the input signals shown in the read signal area a and the write signal area I, respectively. As is clear from this figure, when moving from the write signal area to the read signal area a again, the signal that was averaged as shown in area C fluctuates greatly with respect to the reference potential VN as shown in area d. ing. This is because the capacitor 16 in the coupling time constant circuit 18 is held at a potential higher than the reference potential VN, and the power is different when reading and writing in the recording/reproducing device, and each output signal has an average value. This is due to the fact that it appears as a difference. When the signal of the read signal area a is inputted again in this state, it takes a time corresponding to the time constant determined by the capacitor 16 and the resistor 17 in order for the holding potential of the capacitor 16 to recover to the reference potential VN. I need. The recovery time at this time is shown as region e in FIG. 3B. When the signal shown in FIG. 3B is binarized by the next stage threshold circuit (not shown),
The judgment is made using the threshold value of level f. Since this level f is always lower than the signal in the area e, there is a problem in the threshold circuit that the information in the area e, that is, the signal input during the recovery time, is lost.

For this purpose, in the conventional circuit, as shown in FIG. 2, a timer circuit 1 and its control terminal 4 are provided at the next stage of the coupled time constant circuit 18. A signal indicating the end of the input of the write signal area is input to the control terminal 4, and a timer circuit 11 sets a certain waiting time. During this waiting time, the coupling time constant circuit 1
8, the capacitor 16 completes its natural discharge and reaches the reference potential V.
N and waits in preparation for inputting the next signal in the read signal area a.

[Problem to be solved by the invention] In the circuit using the timer circuit 11 described above, the timer circuit 1
Since the waiting time set by 1 is always required when moving from the write signal area to the read signal area a, the access time is limited by this time and the operation speed becomes slow. Furthermore, since the potential held in the capacitor 16 in the coupled time constant circuit 18 occurs in the form of natural discharge of the capacitor, the discharge time is not necessarily constant.

Therefore, the discharge time may be longer than the recovery time, and in this case, the input signal is lost during the excess time. Of course, in order to prevent this loss of input signals, the recovery time may be set longer, but this poses a problem in that the operation time becomes slower.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a digital information reading circuit for a recording/reproducing apparatus that does not cause input signal dropout when transitioning from a write signal area to a read signal area and is capable of high-speed operation.

[Means for Solving the Problems] A digital information reading circuit of a recording/reproducing device according to the present invention includes a capacitor and a first resistor, a coupling time constant circuit for differentiating input information, and the first resistor. a series circuit including a switch and a second resistor, which is connected in parallel to the resistor, and selectively makes the switch conductive or non-conductive in response to a change in input information to the coupled time constant circuit; The method is characterized by comprising means for switching the time constant of the coupled time constant circuit.

[Operation] In the reading circuit, the time constant of the coupling time constant circuit is switched via a switch in response to a change in the input signal, such as transition from a write signal to a read signal. By switching the time constant in this manner, fluctuations from the reference potential can be canceled without using the natural discharge of the capacitor, and the reference potential can be instantly secured.

[Embodiment] A digital information reading circuit of a recording/reproducing apparatus according to an embodiment of the present invention will be described below with reference to the accompanying drawings.

In FIG. 1 showing the circuit of the embodiment, the symbol ] indicates an input terminal connected to the output side of a light receiving element (not shown) that converts optical information from an information recording medium into electrical signal information. This input terminal l has a capacitor 2 and a first resistor 3,
A coupling time constant circuit 10 in which a reference potential VN is successively connected in series is connected. This first resistor 3 has
Either a series circuit consisting of the changeover switch 4 and the second resistor 5, or the second resistor 5 is connected in parallel so as to be located between the switch 4 and the reference potential VN. The resistance value R of the first resistor 3 and the resistance value r of the second resistor 5
is set to be R) r as described later. Further, the switch 4 is connected to a control terminal 8, and conduction and non-conduction are controlled by a signal from this terminal. The output side of the coupled time constant circuit 10 is connected to the input side of an amplifier 6 which amplifies the output signal from this circuit 0 to a certain level. The output side of the amplifier 6 is connected via an output terminal 7 to a threshold circuit (not shown) that binarizes the signal.

The operation of the reading circuit having the above configuration will be explained below.

With the switch 4 open, the third
Digital signals having waveforms as shown in the reading area a and the writing area s in Figure A are sequentially supplied to the input terminal 1 from the light receiving element. These signals are subjected to differential processing in the coupled time constant circuit 10 in the same manner as in the conventional example, and are output in waveforms as shown in regions g and h in FIG. 3C. At the end of the processing of the write area signal, the capacitor 2 holds a potential higher than the reference potential VN. At this time, a means (not shown) detects whether the input of the signal to the write area has ended, and this means transmits the detection signal K to the switch 4 via the control terminal 8, closing the switch 4. to make it conductive.

As a result of (2), the resistance value between the capacitor 2 and the reference potential VN becomes a parallel composite resistance value of the resistance value R of the first resistor 3 and the resistance value of the second resistor 5.

As described above, since both resistance values R and r are set to be R)r, the parallel combined resistance value is significantly lower than the resistance value R of the first resistor 3.

Therefore, the high potential of the capacitor 2 quickly drops to the reference potential VN as shown in FIG. 3C. Even if the input is shifted to the reading area a again in this state, the output signal will be at a stable level as shown in area 1. Therefore, even if the threshold voltage J is taken into consideration in the threshold circuit at the next stage, the data can be binarized accurately.

In the digital information reading circuit configured as described above, the switch 4 is closed by the detection signal K when moving from the write area to the read area a. As a result, the resistance value of the coupled time constant generating circuit 10 becomes the parallel combined resistance value of the two resistors 3.5, and becomes extremely low, and the potential of the capacitor 2 drops to the reference potential. The recovery time until this drop is extremely short and almost instantaneous since the natural discharge of the capacitor is not utilized at all. Therefore, access time is hardly affected by this recovery time, and high-speed operation is possible. Furthermore, since the recovery time is short, there is no fear that the next input signal in the reading area will be dropped.

[Effects] The digital information reading circuit of the recording/reproducing apparatus according to the present invention switches the time constant of the coupling time constant circuit via a switch in response to changes in the input signal. By switching the time constant in this way, the reference potential can be instantaneously secured without using the natural discharge of the capacitor.

There is no malfunction and high-speed operation is possible.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a digital information reading circuit of a recording/reproducing device according to an embodiment of the present invention, Fig. 2 is a circuit diagram showing a conventional digital information reading device, and Fig. 3A is a circuit diagram showing a digital information reading circuit of a recording/reproducing device according to an embodiment of the present invention. FIG. 3B is a diagram showing the waveform of the information signal, FIG. 3B is a diagram showing the waveform of the output signal from the coupling time constant circuit in the conventional reading circuit, and FIG. 3C is a diagram showing the waveform of the output signal from the coupling time constant circuit in the reading circuit of this embodiment. FIG. 2 is a diagram showing the waveform of an output signal. 1...Input terminal, 2...Capacitor, 3...First
resistor, 4... switch, 5... second resistor,
10... Combined time constant circuit. Applicant's agent Patent attorney Atsushi Tsuboi Figure 1 Figure 2

Claims (1)

[Claims] a coupled time constant circuit that includes a capacitor and a first resistor and differentiates input information; a series circuit that is connected in parallel to the first resistor and includes a switch and a second resistor;
Digital information reading of a recording/reproducing apparatus, comprising: means for selectively making the switch conductive or non-conducting in accordance with a change in input information to the coupling time constant circuit, and switching the time constant of the coupling time constant circuit. circuit.