JPS63127404A - Magnetic recording and reproducing circuit - Google Patents

Abstract

PURPOSE:To reduce the input conversion noise of a differential amplifier by providing a single reproducing circuit, which is conventionally shared among heads, correspondingly to each of individual heads to eliminate a need of a diode provided in the differential amplifier for head switching. CONSTITUTION:Two constant current sources consisting of transistors (TR) Q9a and Q10a, TRs Q9b and Q10b, and diodes Q6a-Q8a and Q6b-Q8b for reproducing circuit are provided correspondingly to magnetic heads Ha and Hb. A signal SLDE which selects the head Ha or Hb and a signal WG which indicates the recording or reproducing state are supplied to a control circuit 4 of constant current sources for reproducing circuit, and each constant current source is controlled by the circuit 4. Leak current preventing diodes D11a-D12b whose number is equal to that of heads Ha and Hb are provided between pairs of emitters of TRs Q9a and Q10a and Trs Q9b and Q10b for reproducing circuit and a current supply line to prevent the leak current of the counter- electromotive force due to switching of conduction of TRs Q9a-Q10b, and the leak current is prevented by leak current preventing diodes D13a-D13b commonly connected to emitters.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording/reproducing circuit, and particularly to improving the input conversion noise of a reproducing circuit section in a magnetic recording/reproducing circuit such as a floppy disk drive.

[Conventional technology]

A conventional magnetic recording/reproducing circuit for a floppy disk having two sets of magnetic heads is shown in FIG. In the figure, WG is a signal for instructing the recording state or reproduction state, 5IDE is a signal for selecting the magnetic heel or do, and Ha.

Hb is a magnetic head, l is a control circuit for the center tap circuit, and in response to the above-mentioned WG double signal and 5IDE signal, transistors Q1. ．． Q,,,Q,,
, Q, b and resistance RIII+ Rlb+ Rtsr R
Along with zb, the center tap terminals 1a and lb are selected.

Further, WRDATA is a recording signal, 2 is a control circuit for a recording circuit, and Q, , Q are transistors forming a recording differential pair, which are repeatedly turned on and off by the control circuit 2. 3 is a constant current source for the recording circuit, Q is a resistor R3, and the transistor Q3. This is a transistor for determining the current value flowing through Q4.

D0~D,. , , D, b'-"D, , are diodes constituting a diode matrix switch circuit, and the voltage values under each condition of the center tap terminals 1a and 1b, that is, recording/reproducing 1 selected side head non-selected side head It is controlled by the voltage value of each condition, and performs circuit control in each state.These diodes are usually connected to D0 to D
! Is (Dab~Dab) is an NPN transistor collector-base direct connection type, p9m, DI (1
m (Dwb, pl.,) is formed of a PNP l-transistor collector-base direct connection type.

The reverse withstand voltage of each diode is approximately 7V for the NPN structure.
In the case of SPNP structure, it is about 30V or more.

4 is a constant current source for the reproduction circuit, Q, , Q are transistors controlled by this, R4 and R5 are resistors, Dll
+ otz are diodes for leakage current prevention, which will be described later, and R7 to RI! is the resistance, Q,,Q,. Q is a transistor pair that constitutes a regenerative differential amplifier.

is a transistor for determining the current value flowing through the differential amplifier together with the resistor R.

Next, the operation will be explained.

First, regarding head selection and switching between recording and playback,
Each transistor Q Im is controlled by the center tap circuit control circuit 1 which receives the 5IDE signal and the WG double signal.
+ Q + b + Q z * * Q t
b on, o.

This is done by controlling the voltage values of the center tap terminals 1a and lb. For example, when head Ha is selected, the voltage at terminal 1a is: (power supply voltage Vcc) (saturation voltage of Qg-) during recording, (saturation voltage of Qg-), and (resistor R1,
(any voltage applied to) - (V■ of Qt). However, vmE is the voltage between the base and emitter of the transistor. Further, at this time, the voltage of the non-selected terminal 1b becomes OV.

Furthermore, when head Hb is selected, the above is reversed.

Next, during recording, the recording circuit control circuit 2 and the recording circuit constant current source 3 are operated by the WG double signal,
As a result, the transistors Ql and Q< forming the differential pair repeatedly turn on and off each other in response to the -RDATA signal. The current value flowing at this time is a constant current determined by the transistor QS and the resistor R3 as described above.

Furthermore, during this recording, the constant current source 4 for the reproducing circuit is inoperative, and the transistors Qh and Qt connected thereto are
, Qa are made non-conductive.

Next, during reproduction, the process is opposite to that during recording, and the constant current [4] for the reproduction circuit is operated by the WC signal.

The recording circuit constant current source 3 is made non-conductive. A reproducing circuit for reading recorded data in this case will be described next.

The minute playback output signal from the head is passed through the diode D axis (
Dab), Dto-(DI.,) and is input to a differential amplifier composed of transistors Q9 and Q+o, where it is amplified. The bias of the circuit is the constant current source of the transistors Q, , Q, the voltage of the center tap terminal 1a (lb) during reproduction, and the resistor R? , R1.

In a circuit configured in this way, when transistor Q or Q4 changes from conductive to non-conductive due to the WRDATA signal during recording, the inductance of the magnetic head causes L・(di/dt) (where i is the transistor Q
, a back electromotive force of the value of the current flowing through the magnetic head is generated at the magnetic head terminal. The value of this back electromotive force is particularly problematic in devices for floppy disks (the value is large for floppy disks), and varies depending on the values of L and l. may reach several times the value. When such a back electromotive force is generated at the magnetic head terminal, this causes a resistance R.
? , (Rs) to vce, and the base-collector resistance Rz of transistor Q9 (Ql.)
A leakage current will flow to vcc through (R+t). Therefore, to prevent this, diode D2++
This is because Dl2 is provided. This diode Dt
l+DZZ is typically the PNP structure described above.

However, in this conventional circuit, since the diodes Dz+ and D2□ are provided, the transistor Q9.

The base resistance of QIo increases. For this reason, the input equivalent noise of the differential amplifier of the reproducing circuit becomes large, and the performance of recording and reproducing deteriorates, resulting in problems such as, for example, the inability to reproduce minute signals.

The conventional circuit will now be considered in more detail. now,
When considering a differential amplifier as shown in FIG. 3, generally the equal input noise eni of the differential amplifier is eni=2
2q IeΔf (Re+(rb' +RG)/β
)2°2kT(RE+rb・)Δ, ]+. rb' is the base spreading resistance of the amplification stage NPN) transistor, and usually bL of the NPN) transistor.
is about several ohms. Further, Δf is the signal bandwidth, Re is the emitter resistance of the transistor Tr itself, and β is the current amplification degree.

In the conventional reproducing circuit shown in Fig. 2, the above-mentioned rb' is equivalently the operating resistance of CDq-) + (base spread resistance of Q9)
corresponds to Diode D1. The operating resistance when a current of 100μA is passed through is (q/kT)/100μA#260Ω. Also, the base spread resistance of a transistor (usually NPN) is several Ω.
That's about it.

From the above, it is possible to reduce the equal input noise by reducing rb' in the formula for eni above. Therefore, while preventing leakage current due to back electromotive force by some means, the diode D'111+ ( Dqb)
, D.I. , , (D, .b) can be deleted, it is considered that the input equivalent noise level of this reproducing circuit can be reduced.

Focusing on the above points, a magnetic recording/reproducing circuit capable of solving the above-mentioned problems has already been developed by the applicant of the present invention, and this will be explained using FIG. 2. That is, this configuration eliminates the resistors Ry, Re and diodes D2□ Dl2 in FIG. 2, and instead uses the diodes DIll DI□ (first diode pair) as the differential transistor Q! of the regeneration circuit. , Ql
. The above-mentioned problem is solved by providing the collector between the collector and the load resistor.

However, in such a configuration, when a back electromotive force is generated in the magnetic head, the base-emitter of HA (Hll)-〇→R7→R1°→Q. Emifta → Base-HA
A leakage current is generated through (Hl) and the write characteristics are deteriorated. To prevent this, diode D9
−． D.I. m+Dqb+Dlab is provided. Note that this diode D, □ Dl. ,,D,b
,D. 5 is the aforementioned PNP type diode.

[Problem that the invention seeks to solve]

In this way, in the magnetic recording/reproducing circuit developed by the applicant, the diodes D9-(Dqb), Dl,1(
Dlab), transistors Q9.
Q. The base resistance of increases. As a result, the input equivalent noise of the differential amplifier of the reproducing circuit becomes large (ie, the recording/reproducing performance deteriorates, resulting in problems such as the inability to reproduce weak signals, for example).

The present invention has been made in view of the above problems, and an object of the present invention is to provide a magnetic recording/reproducing circuit that can further improve the input-referred noise of the differential amplifier in the reproducing circuit section.

[Means for solving problems]

Therefore, in the magnetic recording/reproducing circuit according to the present invention, a single reproducing circuit, which was conventionally shared by each head, is provided for each individual head, so that differential amplification transistors in the reproducing circuit can be used for head switching. The diode provided at the base of the differential amplification transistor is removed, and a diode for leakage current prevention is provided between the emitter of each differential amplification transistor and the current supply path.

[Effect]

In this invention, since a reproducing circuit is provided for each head, a diode for head switching is not required, and the input equivalent noise of the differential amplification transistor of the reproducing circuit is reduced. Furthermore, leakage current due to the deletion of the diode is prevented by a leakage current blocking diode provided between the emitter of the differential amplification transistor and the current supply path, thus further reducing the input equivalent noise of the reproducing circuit. I can do it.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a magnetic recording/reproducing circuit according to an embodiment of the present invention, and in the figure, the same reference numerals as in FIG. 2 indicate the same parts. In this embodiment, the leak prevention diode Dq**Dvb+D+oa+D+o2 in the conventional example is removed, and two sets of amplifier circuits for the reproduction circuit and constant current sources for the amplifier circuits are provided, and are controlled by the 5IDE signal and the WG double signal. In addition, a leakage prevention diode (second diode pair) is connected between the emitter of the amplification transistor of the regeneration circuit and the current supply path of the differential amplifier.
+D++b*I)za +D14. It was designed to provide a. Note that the above-mentioned PNP structure is normally used as the structure of this diode.

Next, the effects will be explained.

In this embodiment, as described above, a reproducing circuit is provided corresponding to each head, and a diode for switching the reproducing circuit is not required.
) connected in series to the base of the transistor:
- Since the code is removed, the equivalent input resistance becomes smaller. Therefore, the input equivalent noise of the reproducing circuit can be reduced. Note that during recording, Qij (Q6b), Q, -(Q
, b) The constant current circuit of Qm-(Q'sb) is inactive, and no leakage occurs from this path.

Note that although the above embodiment is a case in which two sets of magnetic heads are provided, it can also be applied to a case in which one set or two or more sets of heads are provided.

〔Effect of the invention〕

As described above, the magnetic recording/reproducing circuit according to the present invention has the effect of further reducing the noise of the reproducing amplifier during reproducing while preventing the back electromotive current generated in the magnetic head during recording.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a magnetic recording/reproducing circuit according to an embodiment of the present invention, FIG. 2 is a diagram showing a conventional magnetic recording/reproducing circuit developed by the applicant, and FIG. 3 is a diagram showing a differential amplifier, etc. FIG. 3 is a diagram for explaining input noise. In the figure, ) (a, Hb are magnetic heads, Q3゜Q4 are amplification transistors for the recording circuit, Q9.Q10 are amplification transistors for the reproduction circuit, DIlm. D, , b, D, □, Dltb are for leak prevention. Diode (first diode pair), D+3a + I) 11
% r Dlam + Dr4b is a leak prevention diode (second diode pair).

Claims (1)

[Claims] (1) In a magnetic recording/reproducing circuit comprising a recording/reproducing head and a recording circuit having a pair of differential transistors, a difference between the same number of reproducing circuits as the heads, each directly connected to the recording/reproducing head, and the reproducing circuit. The same number of recording and reproducing heads are provided between the collector pair of the dynamic amplification transistor and the load resistor,
A first pair of diodes for preventing leakage current caused by back electromotive force generated by switching conduction and non-conduction of the differential transistor, and a pair of emitters of differential amplification transistors of the regeneration circuit and a current supply path. A second transistor is provided in the same number as the recording/reproducing head to prevent leakage current caused by a back electromotive force generated by switching between conduction and non-conduction of the differential transistor.
A magnetic recording/reproducing circuit comprising: a pair of diodes, wherein a reproduction output is taken out from a connection point between the load resistor and the first pair of leakage current prevention diodes.