JPS6243870A - Switching circuit for filter - Google Patents

Abstract

PURPOSE:To prevent a switching noise from being generated by using a field effect transistor (TR) as a switch element changing over the characteristic of a filter correcting the output waveform differences of an inner track and the outer track of a disc recording medium. CONSTITUTION:A series circuit comprising a capacitor C5 and a source-drain of a field effect TR FET is inserted between both ends of a capacitor C4 of a filter circuit comprising capacitors C1-C4, resistors R1-R3 and inductors L1, L2. A signal read from a reproducing head 1 is inputted to a filter circuit via a buffer 2. In this case, the FET is subjected to a switch control for conduction/cut-off by the switching signal (a) corresponding to the position of the reproducing head 1 depending whether the reproduction track of a floppy disc is an inner track or an outer track so as to change over the filter characteristic in the filter circuit. Even when a voltage based on the switching signal (a) is fed to the gate of the FET, since a current hardly flows to the gate, no noise is applied to the reproducing signal.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to an inner track and a seventh outer track output when reproducing recorded information using a disk type recording medium, for example, a magnetic disk (floppy disk). This invention relates to improvements in circuits used to correct waveform differences.

(Technical background of the invention and its problems) The present applicant has discovered that when reading information by rotating a digitally recorded floppy disk, if the floppy disk is driven at the same rotational speed, the linear velocity of the inner track and outer track is Because of the difference in the filter circuit characteristics, we have developed a technology that changes the characteristics of the filter circuit using the following circuit configuration.

In FIG. 2, ■ is a magnetic head that reproduces signals from the floppy disk when reading data, 2 is a buffer to which the signal read from the reproduction head 1 is added, and between the buffer 2 and the reading circuit 3, A filter circuit is provided to which the signal from the buffer 2 is input.

The filter circuit is designed to obtain the desired waveform from the signals inputted from the 8-fa 2 through two signal lines using the following elements connected in series and in parallel.One signal line is connected to a capacitor. C3, resistor R1 and inductor L1
However, the other signal line has a capacitor C2 and a resistor R2.
and inductor L2 are connected in series. A capacitor C3 is connected to each connection point of R1, R2 and inductors L+, L2 so as to be parallel to the two signal lines, and a capacitor C4 is connected to both ends of the output ends of inductors L, L2. Resistors R3 are connected in parallel, and one ends of capacitors C6 and C7 are connected to both ends of the capacitor C4, respectively. The other ends of these capacitors C6 and C7 are connected to transistors Q7. The collectors of Q2 are each connected, and the emitters of each are grounded. In addition, each transistor Q1
．． A switching signal a is applied to the base of Q2 for switching via an inverter 4 and resistors R5 and Ra, respectively.

This switching signal a is used to switch the filter due to the difference in frequency during reproduction between the inner track and the outer track, that is, the change in linear velocity. The capacitor C4 is outputted as
Controls whether or not to add 6 and 07. That is, the dry transistor Q1. Switching signal a is between the collector and emitter of Q2.
When the capacitors C6 and C7 are connected in series and in parallel to the capacitor C4, the static capacity increases. In other words, [・ransistor QI
, when the voltage applied to Q2 becomes high level due to the switching signal a, the base circuit becomes BE and current is passed between the collector and the emitter, and the capacitors C6 and 07 are connected to the capacitor C4.
Synthetic vinegar 1: volume is connected in parallel. On the other hand, when a low level voltage is applied to the bases of transistors Q+ and Q2, the collector and emitter are in a high impedance state yE, and the parallel circuit of the capacitor C4 part of the filter circuit is , is switched to the value of the capacitance fi1 of the capacitor C4.

The readout circuit 3 to which the signal obtained through such a filter circuit is added differentiates the signal input from the filter circuit with a desired waveform, further shapes the waveform, and converts it to "0". It is converted into a pulse signal corresponding to a digital code of "1".

In this way, the filter circuit described in 1-1 filters out the DC voltage and high-frequency waveforms that are unnecessary for continuous data output and outputs the filter to the readout circuit 3, and also switches the filter characteristics depending on the position of the playback head l, so that the floppy disk Corrects the difference in output waveform between the inner track and outer track.

By the way, if the configuration is such that the parallel circuit constant of the filter circuit provided between the reproducing head 1 and the readout circuit 3 is switched,
A single readout circuit 3 can read out both the inner track and the outer track without malfunction, and moreover, it requires less mounting space than when the switching circuit is configured with mechanical switching elements such as relays, and it also prevents mechanical deterioration. This is advantageous in that there is no induced noise caused by the recording element.

However, in the above configuration, transistor Q5. There is a drawback that the current that flows when Q2 is turned on acts as noise, and noise is added to the reproduction signal from the reproduction head 1.

(Object of the Invention) An object of the present invention is to provide a switching circuit that can prevent the generation of noise when switching a filter using a transistor between reproduction of an inner track and reproduction of an outer track of a disk-type recording medium. .

(Summary of the Invention) The present invention is characterized in that a field effect transistor is used as a switching element for switching filter characteristics in order to correct the output waveform difference between the inner (rack) and outer track of a disk-type recording medium.

(Embodiments of the Invention) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the configuration of an embodiment of the present invention, and similarly to FIG. 2, capacitors C3 to C4, resistors R7 to R3,
Inductor L1. A case is shown in which L2 is applied to a filter circuit configured as each element, and the same components as in FIG. 2 are denoted by the same reference numerals, and detailed explanation thereof will be omitted.

As shown in FIG. 1, in this example, the filter circuit is connected across the capacitor C4, which is connected in parallel to the input signal; or inserted. A voltage is applied to the gate of the field effect transistor FET from the terminal of the switching signal a via the inverter 4 and the resistor R4 for switching. In this field effect transistor FET, the electrostatic field td of the capacitor C4 is
The capacitance of the capacitor C5 is controlled to be switched between a state where the capacitance is added and a state where it is separated, and the filter characteristics are switched between inner track reproduction and outer track reproduction.

Next, the switching operation of the switching circuit having the above configuration will be explained.

The signal read from the reproducing head 1 is input to the filter circuit via the buffer 2. In this case, in the filter circuit, the field effect transistor FET is controlled to be turned on or off by a switching signal a as a control signal corresponding to the position of the playback head 1 depending on whether the playback track of the floppy disk is an inner track or an outer track. By this, the filter, especially 1, is switched. That is, when a high-level voltage is applied to the gate of the field effect transistor FET, a conductive state 78 is established between the drain and source of the field effect transistor FET. When the drain and source of the field effect transistor FET become conductive, capacitor C5 is inserted in parallel with capacitor C4, so the electrostatic field of capacitor C5 is connected in parallel, and the capacitor of the filter circuit The capacitance of the parallel circuit at C4 increases, thereby switching the filter characteristics. In this way, in the switching circuit that performs switching using the field effect transistor FET, even if a voltage based on the switching signal a is applied to the gate of the field effect transistor FET, almost no current flows through this gate. As in the case shown in the figure, the current that flows when the transistor is turned on acts as noise, and this does not add to the reproduction signal from the reproduction head l as noise.

Conversely, when a low-level voltage is applied to the gate of the field effect transistor FET, the field effect transistor FET is in a high impedance state with the source and drain cut off based on the switching signal a at that time. It has become. Therefore, in the parallel circuit portion, capacitor C5 is separated from capacitor C4, so at this time, the capacitance value is only that of capacitor C3.

In this way, by switching the filter characteristics using the field effect transistor FET, the parallel circuit constant of the filter circuit can be switched without causing noise generation, and the difference in output waveform between the inner track and the outer track of the floppy disk can be corrected. Then, the signals obtained through the filter circuit during reproduction of the inner track and the 7th outer track are subjected to differential processing in the readout circuit 3, further converted into a rectangular wave signal by a zero port comparator, etc., and the rectangular wave signal is further pulse-shaped. Since this pulse waveform is correctly determined by the host computer, reading can be performed without malfunction.

It should be noted that the present invention is not limited to the configurations of the embodiments 1) and 2). For example, in the configuration shown in FIG. 2, each transistor Q1. Replace Q2 with field effect transistors, and replace capacitor C4 with capacitor Ce,
Cy may be added or separated. In this case, even if a voltage based on the switching signal 1a is applied to the gate of the field effect transistor, almost no current flows through the gate, so that, as in the embodiment described above, the transistors Q, ,
The effect of avoiding the influence of noise due to the current flowing when Q2 is on can be obtained. Furthermore, when the configuration of the embodiment shown in FIG. 1 is used, the following advantages can also be obtained. That is, transistor Q1. of FIG. Instead of replacing Q2 with a field effect transistor, the number of parts can be reduced, especially when replacing Q2 with one field effect transistor FET and capacitor C5, as shown in Figure 1, to configure a circuit that switches the parallel circuit constant. can do.

(Effects of the Invention) According to the present invention, a field effect transistor is used as a switching element in a circuit that switches the parallel circuit constant of a filter in order to correct the output waveform difference between the inner track and the outer track of a disk type recording medium. By using this, there is no problem of mechanical deterioration or induced noise compared to switching with mechanical contacts such as relays, and the control radio waves used to switch the constants of the elements will not be added to the reproduced signal as noise. . Therefore, digital signals can be reproduced without being affected by noise.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, and FIG. 2 is a circuit diagram showing the configuration when transistors are used as switching elements. 1----------1 playback head, 2--1-------- buffer, 3-1--1 read circuit, 4-------- inverter, 01~Cs---111 capacitor, R7-R4---1 resistor, L+, L2 -m-inductor, FET---1 field effect transistor.

Claims (1)

[Claims] A circuit that obtains a reproduced signal from a disk-type recording medium through a filter and switches the characteristics of the filter in order to correct the difference in output waveform between an inner track and an outer track, and a switching device used to switch the characteristics. A filter switching circuit characterized in that a field effect transistor is used as an element.