JP2543211B2 - Read circuit of magnetic recording / reproducing apparatus - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a read circuit of a magnetic recording / reproducing apparatus for writing and reading with the same magnetic head, and more particularly to noise reduction of the read circuit.

2. Description of the Related Art Conventionally, the circuit configuration of FIG. 3 or 4 has been adopted as a read circuit of a magnetic recording / reproducing apparatus for writing and reading with the same magnetic head.

In FIG. 3, both ends of the magnetic head 32 having a common terminal are connected to the output end of the writing circuit 37.
A diode 33 having a cathode connected to one end of 32 is forward-conductive by a constant current source 35 connected to the anode.
The diode 34 having the cathode connected to the other end of the magnetic head 32 is electrically connected in the forward direction by the constant current source 36 connected to the anode. The anodes of the diodes 33 and 34 are connected to the base input of the differential amplifier 31, and the magnetic head 32
The reproduced signal reproduced by the above is input to the differential amplifier 31 through the diodes 33 and 34, and the amplified reproduced signal is taken out from the output terminal thereof.

In the conventional example of FIG. 4, the diodes 43 and 44 connected to both ends of the magnetic head 42 are the diodes 33 and 44 of FIG.
Since it functions similarly to FIG. 3 except that the connection direction is different from that of 34, the circuit operation will be described mainly with reference to FIG.

First, in FIG. 3, when writing data to the magnetic recording medium, the write circuit 37 is activated and the current amplified by the write circuit 37 is applied to both ends of the magnetic head 32.
Write data to the magnetic recording medium. At this time, the magnetic head
Since a large voltage swing is applied across both ends of 32, there is a risk of damaging low voltage circuits, so diodes 33, 34
Is provided for the purpose of protecting the input part of the differential amplifier 31,
The one with high reverse breakdown voltage is adopted.

Next, when reading data from the magnetic recording medium, the write circuit 37 is turned off. Then, the constant current source 35,3
Diode 33, which is conducting in the forward direction by the bias of 6,
34 transmits the weak reproduction signal read by the magnetic head 32 to the input end of the differential amplifier 31, and the amplified reproduction signal is transmitted to the differential amplifier.
Take out from the output end of 31.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the above conventional configuration, a constant bias current is constantly applied to the diodes 33 and 34 by the constant current sources 35 and 36, and the diode 33,
Conduct 34 forward. At this time, the bias current also flows into the magnetic head 32, so if the bias current is set to a large value, an erroneous write operation will be performed on the magnetic recording medium, so the bias current of the diodes 33 and 34 is suppressed to a small value. It was On the other hand, since the internal resistance of the diode shows a characteristic that changes nonlinearly with the bias current,
Diodes 33, 34 that conduct in the forward direction with a small bias current
Has a large internal resistance and becomes a factor of signal loss when transmitting the signal of the magnetic head 32 to the differential amplifier 31. Further, since the impedance when the magnetic head 32 (signal source) side is viewed from the differential amplifier 31 side becomes large, it becomes a factor of increasing noise and causes a problem that the SN ratio of the read circuit is deteriorated.

The present invention solves such a problem, and an object thereof is to reduce the noise of a read circuit of a magnetic recording / reproducing apparatus.

Means for Solving the Problems In order to solve the above problems, a read circuit of a magnetic recording / reproducing apparatus of the present invention is connected to both ends of a magnetic head having both ends connected to an output end of a write circuit. A differential amplifier to which an input signal is inputted to the pair of input terminals through the first and second diodes, and a first amplifier which constantly applies a bias current to both ends of the first diode so as to conduct the first diode in the forward direction. A first constant current source, and third and fourth constant current sources that constantly apply a bias current to both ends of the second diode so as to conduct the second diode in the forward direction. is there.

Operation With this configuration, without applying DC current to the magnetic head,
The bias current given to the first and second diodes can be increased, the internal resistance of the diode having the non-linear characteristic can be reduced, and the loss of the signal input to the differential amplifier can be reduced, while the noise generated from the diode can be reduced. , SN ratio can be improved.

Embodiment An embodiment of the read circuit of the magnetic recording / reproducing apparatus of the present invention will be described below with reference to FIG.

FIG. 1 is a diagram showing a circuit configuration of essential parts of a magnetic recording / reproducing apparatus according to an embodiment. In FIG. 1, 11 is a differential amplifier, and 12 is a differential amplifier.
Is a magnetic head with a common terminal, 13 and 14 are diodes, 1
5 to 18 are constant current sources, and 19 is a writing circuit. You.

As shown in FIG. 1, both ends of the magnetic head 12 are connected to the output end of the writing circuit 19, the cathode of the diode 13 and the cathode of the diode 14 are connected to each of the both ends, and the anodes of the diodes 13 and 14 are different from each other. Connected to the input terminal pair of the dynamic amplifier 11, the diode 13 is constantly biased by the constant current source 15 and the constant current source 17 to conduct in the forward direction, and the diode 14 is constantly biased by the constant current source 16 and the constant current source 18. It is configured so that it conducts in the forward direction.

Then, at the time of recording, the write circuit 19 is activated, the signal amplified by the write circuit 19 is applied to both ends of the magnetic head 12, and data is written to the magnetic recording medium. At the time of reproduction, the writing circuit 19 is turned off. Then, the magnetic head 12 reads the data of the magnetic recording medium, and the read weak reproduction signal is passed through the diodes 13 and 14 to the differential amplifier 1
The reproduced signal amplified and transmitted to the pair of input terminals 1 is taken out from the output terminal of the differential amplifier 11.

Next, the SN ratio of the read circuit will be described. The bias of the diode 13 causes a constant current to flow from the constant current source 15 to the anode, and the constant current source 17 draws a constant current from the cathode, while the bias of the diode 14 causes a constant current to flow from the constant current source 16 to the anode. Since the constant current source 18 draws a constant current from the cathode, the bias current given to the diodes 13 and 14 can be increased without giving a direct current to the magnetic head 12. This makes it possible to reduce the internal resistance of the diodes 13 and 14 having nonlinear characteristics, reduce the loss of the signal input to the differential amplifier 11, reduce the noise generated from the diodes, and reduce the SN ratio of the read circuit. Can be improved.

Next, FIG. 2 is a circuit configuration showing another embodiment of the present invention, but the connection directions of the diodes 23 and 24 are different from the configuration of FIG. 1, and the constant current sources 25 to 28 are set accordingly. The configuration is similar to that of the embodiment shown in FIG.

As described above, according to the present invention, the bias current applied to the first and second diodes is increased without applying a direct current to the magnetic head, and the first and second diodes having the nonlinear characteristics are provided. It is possible to reduce the internal resistance, reduce the loss of the signal input to the differential amplifier, reduce the noise generated from the diode, and improve the SN ratio of the read circuit.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of an embodiment relating to a read circuit of a magnetic recording / reproducing apparatus of the present invention, FIG. 2 is a circuit configuration diagram for explaining another embodiment, and FIGS. FIG. 3 is a diagram showing a circuit configuration of a main part of the magnetic recording / reproducing apparatus of FIG. 11,21 …… Differential amplifier, 12,22 …… Magnetic head, 13,14,2
3,24 ... Diode, 15-18,25-28 ... Constant current source, 19,
29 …… Writing circuit.

Claims (1)

(57) [Claims] 1. A magnetic head having both ends connected to the output end of a write circuit, and a differential amplifier having an input signal input to a pair of input terminals through first and second diodes connected to both ends of the magnetic head. , A first and a second constant current source that constantly supplies a bias current to both ends of the first diode so as to make the first diode forward-conductive, and a second constant current source for making the second diode forward-conductive. A read circuit of a magnetic recording / reproducing apparatus comprising: a third diode; and a third constant current source for constantly applying a bias current to both ends of a second diode.