JPH0118488B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording head drive circuit used in a magnetic recorder such as a tape deck.

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording head drive circuit that stably drives a magnetic recording head with a constant current.

A conventional magnetic recording head drive circuit is constructed as shown in FIG. 1a or b.

The magnetic recording head drive circuit shown in FIG.
The signal current from the recording compensation circuit 1 that has passed through the magnetic recording head 6 and the bias current from the bias oscillator 5 that has passed through the variable resistor 4 are mixed at one end of the winding 7 of the magnetic recording head 6. It is driving 7. Note that 8 is a signal source.

However, the conventional drive circuit shown in FIG. 1a has many drawbacks as shown in (a) to (e) below.

(a) If the signal current does not flow to the variable resistor 4, the signal current I _S flowing to the winding 7 is I _S = A・V _S /
(R ₀ +Z _H ). Here A is recording compensation circuit 1
, V _S is the output voltage of the signal source 8 , R ₀ is the resistance value of the resistor 3 , and Z _H is the impedance of the winding 7 . The impedance Z _H of the winding 7 increases as the frequency increases, and even if the gain A and the voltage V _S are constant, the signal current I _S does not remain constant and decreases as the frequency increases. In other words, ideal constant current driving cannot be performed.

(b) Since the signal current _IS decreases as the frequency increases, the amount of high-frequency recording compensation must be greater than the amount of compensation for electromagnetic conversion loss caused by the magnetic recording head 6 and the magnetic tape. For this reason, the dynamic range of the recording compensation circuit 1 becomes narrow at high frequencies, causing distortion in the signal current at high input signals, and when mixed with the bias current, cross-modulation occurs due to the nonlinearity of the magnetic recording head 6. Distortion is likely to occur.

(c) If the resistance value R ₀ of resistor 3 is increased, the signal current I _S
becomes constant current. But the resistance value
If the output voltage level (V _S A) of the recording compensation circuit ₁ is not increased because the voltage drop due to R0 becomes large, the signal current I in the winding 7 will have the same value as before increasing the resistance value _R0 . _S will not flow. That is, even if the constant current property of the signal current I _S is obtained by increasing the resistance value R ₀ , the dynamic range of the recording compensation circuit 1 cannot be improved.

(d) Since the value of the resistance R ₀ is generally a fraction of the impedance of the winding 7 at the bias oscillation frequency, the bias current that has passed through the variable resistor 4 flows only through the winding 7. A bias signal trap circuit 2 is essential for this purpose.

(e) When using bias signal trap circuit 2,
Adjustment of the trap frequency is required, and the trap frequency is easily affected by temperature, and there is a large risk that the trap may shift due to changes in ambient temperature, resulting in deviation from the optimum bias current value.
Furthermore, since the bias signal trap circuit 2 is generally constructed using an inductor, it is likely to be coupled with leakage magnetic flux from a power transformer, etc.
worsens N.

Further, in the conventional magnetic recording head drive circuit shown in FIG. 1B, the signal current amplifier 9 having a constant voltage drive output section is configured as a current feedback amplifier. Therefore, the winding 7 of the magnetic recording head 6
The signal current I _S flowing through the current detection resistor 10 depends only on the parallel impedance of the resistance value of the current detection resistor 10 and the sum of the resistance values of the feedback resistors 12 and 13, and does not depend on the impedance of the winding 7. Therefore, in this drive circuit, the magnetic recording head 6, that is, the winding 7, is driven by an ideal constant current drive, which is different from the conventional circuit shown in (a) to (c) in FIG. The shortcomings will be eliminated.
In FIG. 1b, 11 is a bias signal trap circuit.

However, the circuit shown in FIG. 1b has the following drawbacks (f) to (l).

(f) When mixing the signal current and bias current at one end of the winding 7, use the signal current amplifier 9.
In order to prevent bias current from flowing into the output of the amplifier, a bias signal trap circuit 2 is required between one end of the winding 7 where the signal current and bias current are mixed and the signal current amplifier 9.

(g) Since a bias current as well as a signal current flows through the current detection resistor 10, a bias voltage is also induced at the connection point between the current detection resistor 10 and the other end of the winding 7. If this bias voltage is fed back to the input of the signal current amplifier 9, there is a possibility that cross-modulation distortion will occur between it and the signal current. Furthermore, unless the impedance of the bias signal trap circuit 2 at the bias frequency is infinite, it will affect the bias current flowing through the winding 7. For this purpose, a bias signal trap circuit 11 is required between one end of the current detection resistor 10 and the signal current amplifier 9.

(H) When the bias signal trap circuit 11 is present in the feedback loop of the signal current amplifier 9, the closed loop gain of the signal current amplifier 9 becomes maximum at the trap frequency. The steeper the slope of the attenuation characteristic of the bias signal trap circuit 11 is, the sharper the closed loop gain of the signal current amplifier 9 will be, the more likely the circuit will be unstable and oscillations will occur.

(li) A signal current and a bias current flow through the current detection resistor 10. In particular, the bias current that has passed through the winding 7 flows entirely through the current detection resistor 10 due to the presence of the bias signal trap circuit 11, resulting in a voltage drop proportional to the resistance value of the current detection resistor 10. Bias oscillation voltage required to flow the optimum bias current to winding 7
In order to keep V _B as small as possible, the voltage drop due to the current detection resistor 10 must be reduced, and the current detection resistor 10 is negligible compared to the impedance of the winding 7 at the bias frequency. must be small. Furthermore, the signal current flowing through the winding 7 is the resistance value of the current detection resistor 10, the resistance value of the feedback resistor 12+the resistance value of the resistor 13.
Since it is determined by the parallel impedance with the resistance value of
The dynamic range will increase. However, when the resistance value of the current detection resistor 10 becomes smaller, the feedback amount of the signal current amplifier 9 decreases and the closed loop gain increases. Since the feedback factor decreases as the frequency increases, the increase in closed-loop gain becomes more significant as the frequency increases. For this reason, (i) it becomes impossible to stabilize the gain; (ii) Nonlinear distortion associated with semiconductor elements cannot be sufficiently reduced. (iii) Frequency characteristics cannot be improved. 〓Problems such as noise not being reduced arise. Moreover, for this reason, it becomes difficult to include a recording compensation circuit in the signal current amplifier 9, and a recording compensation circuit must be constructed before the signal current amplifier 9.

(x) If the magnetic head is used for both recording and playback, the connection is switched between recording and playback. However, if the magnetic head 6 is inserted into the feedback loop of the signal current amplifier 9, both ends of the winding 7 will be lifted from the ground during recording. Therefore, the switching circuit for the winding 7 when switching between recording and playback becomes complicated. For example, when switching from the recording state to the playback state, both ends of the winding of the recording/playback magnetic head are once disconnected from the feedback loop of the signal current amplifier 9, one end is grounded, and the other end is connected to the input end of the playback compensation circuit. There must be.

(l) Since the winding 7 and its wiring material enter the feedback loop of the signal current amplifier 9, the closed loop gain has a sharp peak value at the resonant frequency determined by the inductance of the winding 7 and the distributed capacitance of the wiring material. have For this reason, the operation of the signal current amplifier 9 becomes unstable and oscillations are likely to occur.

The present invention has been made in consideration of the above-mentioned drawbacks, and is intended to eliminate the above-mentioned drawbacks by driving the winding of the magnetic head with a constant current and eliminating the need for a bias signal trap circuit.

The present invention will be explained below with reference to Examples.

FIG. 2a is a circuit diagram of an embodiment of the present invention.

In this embodiment, the transistor 2 that amplifies the input signal is
0, 21, a differential amplifier 27 consisting of a constant current source circuit 22, collector load resistors 23, 24, and diodes 25, 26, and a transistor 28 that constitutes a current mirror circuit together with the diode 26,
A collector load resistor 29 and a diode 30 of the transistor 28, a transistor 31 which forms a current mirror circuit together with the diode 25, and a transistor 32 which forms a current mirror circuit together with the diode 30 are connected in a complementary manner to drive the load 33 and transfer the output voltage to the transistor. Feedback impedance circuit 3 to the base of 21
a first constant current output stage 35 that feeds back via 4;
A transistor 36 that forms a current mirror circuit together with the diode 25, and a transistor 3 that forms a current mirror circuit together with the diode 30.
7 and magnetic recording head 6.
and a second constant current output stage 38 for driving the winding 7 of.

Therefore, the input signal voltage applied to the input terminal IN is amplified by the differential amplifier 27. Differential amplifier 27
The collector current of the transistor 20 constituting the transistor 3 constitutes the first constant current output stage 35.
1, and the collector current of transistor 21 constituting differential amplifier 27 is transferred to transistor 32 via transistor 28 and diode 30, thereby driving load 33. Further, the collector current of the transistor 20 constituting the differential amplifier 27 is transferred to the transistor 36, and the collector current of the transistor 20 constituting the differential amplifier 27 is transferred to the transistor 36.
The collector current of the transistor 21 constituting the transistor 21 is transferred to the transistor 37 via the transistor 28 and the diode 30, and the winding 7 is driven.

However, since the first and second constant current output stages 35 and 38 are configured with complementary connections consisting of emitter-grounded transistors 31, 32 and 36, 37, respectively, the output impedance is high and theoretically infinite, and the winding Line 7 will be driven with constant current. Therefore, in this embodiment, when only the signal current is amplified and mixed with the bias current I _B at the output terminal of the second constant current output stage 38, the bias current I _B is
8, but only into the winding 7 of the magnetic recording head 6. This eliminates the need for a bias current trap circuit.

Therefore, according to this embodiment, since the winding 7 is driven with a constant current, the above-mentioned drawbacks (a), (b), and (c) of the conventional magnetic recording head drive circuit are eliminated. Furthermore, according to this embodiment, since a bias signal trap circuit is not required, the above-mentioned (d), (e), and (f) in the conventional magnetic recording head drive circuit are eliminated.
The drawbacks of (g) and (h) are eliminated. Further, according to this embodiment, since the winding 7 is not inserted into the feedback loop of the signal current amplifier 9 as shown in FIG.
The drawbacks of (ri), (nu) and (ru) are eliminated.

Further, in this embodiment, two first and second constant current output stages 35 and 38 connected in parallel are used.
The winding 7 is driven by the output of the second constant current output stage 38, and the first constant current output stage 35 is used for gain control output. The load 33 is a load of the first constant current output stage 35 , the feedback impedance circuit 34 constitutes a feedback circuit of the first constant current output stage 35 , and the current flowing through the winding 7 is the load of the feedback impedance circuit 34 . It can also be changed by changing the impedance value. Furthermore, the current flowing through the winding 7 can also be changed by changing the impedance value of the load 33.

In this embodiment, by providing the first constant current output stage 35 for gain control in parallel with the second constant current output stage 38 and providing negative feedback as described above,
(i) It is possible to stabilize the gain, (ii) it is possible to sufficiently reduce the nonlinear distortion associated with semiconductor elements, and (iii) it is possible to improve the frequency characteristics and reduce noise. . Therefore, problems (i) to (i) out of the above-mentioned drawbacks (i) of the conventional magnetic head drive circuit are solved.

Furthermore, low-frequency compensation can be achieved by using, for example, a series-parallel circuit consisting of resistors R ₁ and R ₂ and a capacitor C ₁ as shown in FIG. 3a in the feedback impedance circuit 34, and as shown in FIG. 3b. High frequency compensation can be performed by using a series-parallel circuit consisting of resistors R ₃ and R ₄ , coil L ₁ and capacitor C ₂ as load 33.

Therefore, according to this embodiment, recording compensation and constant current driving can be performed simultaneously.

Further, in contrast to this embodiment, as a magnetic recording head drive circuit that simply drives the winding 7 with a constant current, a magnetic recording head drive circuit configured as shown in FIG. 4a without the first constant current output stage 35 can be considered. . However, the circuit shown in FIG. 4a does not have the first constant current output stage 35 that performs gain control, as is clear compared to the circuit of the embodiment of the present invention. The circuit can (i) stabilize the gain, (ii) sufficiently reduce nonlinear distortion associated with conductive elements, (iii) improve frequency characteristics, and reduce noise. It is not possible to obtain the effects that can be said to be reduced. Furthermore, it is difficult to insert a circuit for recording compensation into the magnetic recording head drive circuit shown in FIG. 4a, and the recording compensation circuit must be constructed before the magnetic recording head drive circuit shown in FIG. 4a. It will not happen.

Next, other embodiments of the present invention will be described.

FIG. 2b is a circuit diagram of another embodiment of the invention.

Another embodiment of the present invention includes transistors 40 and 41 for amplifying input signals, a collector load resistor 43,
44 and a constant current source circuit 45, and a transistor 48 which has a constant current source circuit 47 as a collector load and is driven by the collector output voltage of the transistor 40. A first constant current output stage 49 that drives a load 33 connected to A second constant current output stage 52 drives the winding 7 of the magnetic recording head 6, and a feedback impedance circuit 34 is connected between the collector of the transistor 48 and the base of the transistor 41.

The collector current of the transistor 51 increases or decreases according to the collector output voltage of the transistor 40 which amplifies the input signal, and the winding 7 is driven at a constant current by the current obtained by subtracting the collector current of the transistor 51 from the output current of the constant current source circuit 50. Ru. Also, load 3
3 is similarly driven by the first constant current output stage 49.

In this case as well, the winding 7 is driven by constant current, and the output impedance of the second constant current output stage 52 is high and theoretically infinite.
When mixing with the bias current at the output point of the second constant current output stage 52, the bias current does not flow into the second constant current output stage 52, but instead flows into the winding 7. Therefore, the bias signal trap circuit is not required, and the winding 7 is driven with a constant current, so that the conventional magnetic recording head drive circuit described in (a) to
The drawbacks of (l) will be resolved.

Further, a first constant current output stage 49 for gain control is provided in parallel with the second constant current output stage 52, and the gain can be adjusted by changing the impedance value of the load 33 and/or the impedance value of the feedback impedance circuit 34. That is, the value of the current flowing through the winding 6 can be changed.

Further, by using the impedance circuit shown in FIG. 3a for the feedback impedance circuit 34, for example, low frequency compensation can be achieved, and by using the impedance circuit shown in FIG. 3b, for example, for the load 33, high frequency compensation can be achieved. , recording compensation may also be performed within the circuitry of other embodiments of the present invention.

Further, as a magnetic recording head drive circuit for simply driving the winding 7 with a constant current, a magnetic recording head configured as shown in FIG. A driving circuit is considered. However, the circuit shown in FIG. 4b does not have the first constant current output stage 49 that performs gain control, as is clear compared to the circuits of other embodiments of the present invention. This is similar to the case in the circuit shown in Figure 4a for (i) the gain cannot be stabilized, (ii) the non-linear distortion associated with the semiconductor element cannot be sufficiently reduced, and (iii) the frequency characteristics It is not possible to improve the noise, and it is not possible to reduce the noise. Furthermore, a recording compensation circuit must be provided upstream of the magnetic recording head drive circuit shown in FIG. 4b.

Next, a modified example of one embodiment of the present invention will be described.

FIG. 5 is a circuit diagram of a modified embodiment of one embodiment of the present invention.

This modified embodiment uses a differential amplifier 27' in place of the differential amplifier 27 in the embodiment of the invention shown in FIG. 2a. The differential amplifier 27' includes a field effect transistor 2 instead of the transistors 20 and 21.
0', 21', diode-connected transistors 25', 26' are used in place of the diodes 25, 26, and the input signal current I _S and bias current I _B are added via adding resistors 55 and 56, respectively. , a voltage corresponding to the added current is applied to the gate of the field effect transistor 21'.
Also, the diode 30 is replaced by a diode-connected transistor 30'.

In this modified embodiment, the bias current I _B is
The addition is not performed at the output point of the constant current output stage 38, but is performed at the base side of the field effect transistor 21'. However, since the circuit of this modified embodiment is an inverting amplifier, the impedance at the inverting input terminal is theoretically zero, and there is no effect on other components caused by the addition of the signal current I _S and the bias current. It operates exactly as in one embodiment of the invention.

Furthermore, in the embodiments of the present invention, other embodiments, and modified embodiments of the embodiment of the present invention described above, the case where two constant current output stages, the first and second, are used is explained as an example. Of course, it is also possible to provide three or more constant current output stages, use some of the constant current output stages as gain control outputs, and use the other constant current output stages as drive outputs for the winding 7. As described above, according to the present invention, the magnetic recording head can be stably driven at a constant current, a bias signal trap circuit is not required, and recording compensation can be performed within the magnetic recording head drive circuit. Therefore, all the drawbacks of conventional magnetic recording head drive circuits can be eliminated.

Furthermore, the amount of high-frequency recording compensation is small, and the dynamic range is widened in the high-frequency region.

Furthermore, since the winding of the magnetic recording head is not connected in the feedback loop, the magnetic recording head drive circuit becomes unstable due to resonance caused by the inductance of the winding and the distributed capacitance of the wiring material to the magnetic recording head. The closed-loop gain can also be determined independently of the impedance of the windings of the magnetic recording head.

It also has the advantage of being easy to integrate into a circuit.

[Brief explanation of drawings]

FIGS. 1a and 1b are circuit diagrams of a conventional magnetic recording head drive circuit. FIG. 2a is a circuit diagram of a magnetic recording head drive circuit according to an embodiment of the present invention. FIG. 2b is a circuit diagram of a magnetic recording head drive circuit according to another embodiment of the present invention. FIGS. 3a and 3b are circuit diagrams showing an example of a feedback impedance circuit and a load in an embodiment of the present invention. FIGS. 4a and 4b are circuit diagrams of magnetic recording head drive circuits for comparison in order to explain the operation of one embodiment and another embodiment of the present invention. FIG. 5 is a circuit diagram of a magnetic recording head drive circuit in a modified embodiment of one embodiment of the present invention. 6...Magnetic recording head, 7...Winding of magnetic recording head, 20, 21, 28, 31, 32, 36,
37, 40, 41, 48, 51, 25', 26' and 30'...transistor, 22, 45, 47
and 50... constant current source circuit, 27, 46 and 27'... differential amplifier, 33... load, 34...
Feedback impedance circuit, 35 and 49...first constant current output stage, 38 and 52...second constant current output stage, 20' and 21'...field effect transistor.

Claims (1)

[Scope of Claims] 1. A magnetic recording head drive circuit using an AC bias method, in which a recording signal is amplified by a constant current amplifier, and the output of the constant current amplifier and the output from a bias oscillator are mixed in a magnetic recording head. a first constant current output stage driven by the output of the input stage; and a first constant current output stage driven by the output of the input stage and the first constant current output stage driven by the output of the input stage.
and a second constant current output stage connected in parallel to the constant current output stage, the output of the first constant current output stage drives a load, and the output of the first constant current output stage is driven by the output of the first constant current output stage. A magnetic recording head drive circuit characterized in that the constant current is fed back to the input stage through a feedback circuit, and the output of the second constant current output stage drives a winding of the magnetic recording head. 2. The porcelain recording head drive circuit according to claim 1, wherein the load is constituted by an impedance circuit having frequency characteristics to obtain recording compensation characteristics. 3. The magnetic recording head drive circuit according to claim 1, wherein the feedback circuit is constituted by an impedance circuit having frequency characteristics to obtain recording compensation characteristics.