JPS6125057Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a magnetic reproducing circuit used in a magnetic recording/reproducing device or the like.

Conventionally, magnetic reproducing circuits have used the so-called peak detection method, which digitizes the information signal by inverting the output at each peak value of the information signal from the magnetic head, etc., or the so-called peak detection method, in which the information signal from the magnetic head, etc. reaches a certain reference value. The so-called level detection method was used to digitize the information signal by inverting the output at each input peak value.However, the peak detection method outputs an output at each input peak value, so it is prone to malfunction due to noise, and the level detection method Since the detection method outputs an output for each fixed level value of the input, both methods have their own drawbacks, such as the possibility of malfunctions when the output level of the magnetic head changes due to fluctuations in the running speed of the recording medium such as a magnetic card. It had

The present invention aims to eliminate these drawbacks and provide a magnetic reproducing circuit that is less susceptible to noise and operates stably even when the running speed of the recording medium changes.

Next, an embodiment of the present invention will be explained based on the drawings. 1 is a differential amplifier circuit, 2 is an integral type amplifier circuit that integrates an information signal input, and 3 is an integral type amplifier circuit 2 whose output is set to a specified voltage level. Level detection circuit to detect,
4 is a peak detection circuit that detects the input information signal at the peak of the waveform; 5 is a waveform shaping circuit that shapes the output of the peak detection circuit 4; The HD is a magnetic head that exchanges information with recording media such as magnetic cards. Both ends of the magnetic head HD are connected to the input end of the amplifier AMP1 through resistors R ₁ and R ₂ respectively, the non-inverting input end of the amplifier AMP1 is grounded through the resistor R _{3, and the inverting input end and output end are connected to the input end of the amplifier AMP1 through the resistor R 3} . Grounded by R ₄ . The output end of this amplifier AMP1 is commonly connected to one end of the capacitor _C1 and one end of the capacitor _C3 . The other end of capacitor C ₁ is resistor R ₄
Amplifier AMP whose non-inverting input is grounded via
A capacitor C 2 is connected between the inverting input terminal and the output terminal, and _an antiparallel circuit of diodes D ₁ and D ₂ is connected between the inverting input terminal and the output terminal. The diodes D ₁ and D ₂ are intended to stabilize the integral operation. The output terminal of the amplifier AMP2 is connected via a resistor R ₅ to the non-inverting input terminal of an amplifier AMP3 whose inverting input terminal is grounded, and this non-inverting input terminal is connected via a resistor R ₆ to the output terminal of the amplifier AMP3. ing. The other end of the capacitor _C3 is connected via a resistor _R7 , and the non-inverting input terminal is grounded via a resistor _R6 . It is connected to the inverting input terminal of amplifier AMP4, and a diode is connected between this inverting input terminal.
Anti-parallel circuits of D ₃ and D ₄ are connected. amplifier
The output terminal of AMP4 is connected to the inverting input terminal of amplifier AMP5, and the non-inverting input terminal of amplifier AMP5 is connected to resistor _R9 .
and is connected to its output terminal via a resistor _R10 . The output end of the amplifier AMP3 and the output end of the amplifier AMP5 are connected through a resistor R ₁₁ and a resistor R ₁₂ having the same resistance value, and the connection point between the resistor R ₁₂ and the resistor R ₁₃ is the opposite of the diodes D ₅ and D ₆ . It is connected to the inverting input terminal of the amplifier AMP4 via a parallel circuit, and is grounded via a resistor _R13 . These diodes D ₅ and D ₆ are intended to stabilize the feedback operation, and the resistor R ₁₃ is connected to the resistor R ₁₁ and the resistor R _12.
This is to compensate for the difference in resistance between the It goes without saying that the same operation can be obtained by using an anti-series circuit of Zener diodes in place of the anti-parallel circuit of diodes _D5 and _D6 .

The operation of this circuit configured in this way will be explained. The signal read out by the magnetic head HD is amplified by the differential amplifier circuit 1 and has a waveform as shown in FIG. When this signal is input to the integral amplifier circuit 2, the input signal is transmitted through the resistor R ₄ and the capacitor C ₂
The waveform is integrated by a time constant determined by , which compensates for fluctuations in the magnetic head reproduction output level due to fluctuations in card speed. for example,
When the running speed of the card suddenly slows down, the level of the waveform of the playback output of the head decreases as shown in Figure 2, but the value (area) of the integrated waveform that causes the width of the waveform to become wider is It does not change even if the speed changes. Therefore, the output level of the integrated output waveform obtained by integrating the reproduced output waveform of the head rises to a nearly constant value regardless of speed fluctuations, so if this integrated waveform B is input to the level detection circuit 3 and the level is detected, the card speed can be adjusted. Fluctuations in the reproduction output level of the magnetic head due to changes in the magnetic head are compensated for. This waveform is input to the level detection circuit 3 and the specified voltage level Vref is determined by the resistors R ₅ and R ₆ .
When the level is detected with The peak value of the waveform input to the peak detection circuit 4 is detected, and the waveform is further shaped by the waveform shaping circuit 5. When this waveform is connected through resistors R ₁₁ and R ₁₂ , a waveform like that is obtained. This waveform is applied to the inverting input terminal of the amplifier AMP4 of the repeater detection circuit 4 through the diodes _D5 and _D6 , and the operation of the repeater detection circuit 4 is stopped in the area shown by the hatched area. Therefore, even if there is a noise like the one shown in FIG. 2, since the operation of the peak detection circuit 4 is stopped at this time, this noise will not cause malfunction. This is a diode when the waveform signal is positive or negative.
Since a bias current is applied to the inverting input terminal of the amplifier AMP4 through _D5 and _D6 , the peak detection circuit 4 does not operate against noise, and when OV is present, the signal at the inverting input is also about 100 mV. Therefore, the diodes D ₅ and D ₆ are not conductive, so that no bias current flows and the peak detection circuit 4 is activated. Since no feedback current is flowing through the peak detection circuit 4 at this time, it operates with high sensitivity.

As mentioned above, the diodes D ₅ and D ₆ do not necessarily need to be provided, but if they are not provided, some current will flow even when the waveform signal is OV, resulting in malfunction. It will be accurate. It is desirable that the waveforms be symmetrical with respect to the OV and have the same size.

Since the present invention has the above-mentioned configuration, it is an extremely simple configuration, and a bias current is applied to the inverting input terminal of the amplifier except when the input signal is from the slice level to the peak level. It has the characteristic that it will not malfunction even if it happens. Also, since it is equipped with an integral amplifier circuit, it can compensate for fluctuations in the playback output level of the magnetic head due to fluctuations in the running speed of the magnetic card, fluctuations in recording density, etc., making it possible to perform accurate level detection. It also has excellent effects.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 is a waveform diagram showing the operating state of the circuit of FIG. 1. 2... Integral amplifier circuit, 3... Level detection circuit, 4... Peak detection circuit, 5... Waveform shaping circuit, _R11 , _R12 ... Resistor.

Claims (1)

[Scope of utility model registration request] an integrating amplifier circuit that integrates an input information signal; a level detection circuit that detects the output of the integrating amplifier circuit at a specified voltage level; a capacitor connected to the inverting input terminal of the amplifier; The peak detection circuit includes an anti-parallel circuit of diodes connected between input terminals and detects the information signal input at the peak of the waveform, and a waveform shaping circuit that shapes the output of the peak detection circuit. A magnetic reproducing circuit characterized in that the outputs of the level detection circuit and the waveform shaping circuit are combined and fed back to the inverting input terminal of the amplifier constituting the peak detection circuit.