JPH05129853A - Semiconductor device - Google Patents

Abstract

PURPOSE:To prevent a cascade transistor provided in a read amplifier (RA), etc., from being electrostatically destroyed without increasing the input capacity by blocking a large current to flow to the emitter of the cascade transistor by impressing a serge voltage to the external terminal of a magnetic head driving integrated circuit without affecting the operating characteristic of the RA. CONSTITUTION:Between the emitters of cascade transistors T1 and T2 provided in the RA, etc., of the magnetic head driving integrated circuit and the bases or a high potential side power supply voltage VCC of the circuit, a pair of diodes D1 and D2 are provided while respectively coupling the anodes to the emitter of the cascade transistor T1 or T2 and coupling the cathodes to the base of the cascade transistor T1 or T2 or the high potential side power supply voltage VCC.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device,
For example, the present invention relates to a technology particularly effective for use in a magnetic head drive integrated circuit including a read amplifier.

[0002]

2. Description of the Related Art There is a magnetic disk device using a magnetic disk as a storage medium. These magnetic disk devices include a magnetic head drive integrated circuit including a write amplifier that applies a predetermined write current to the magnetic head and a read amplifier that amplifies the read signal.

A magnetic head driving integrated circuit including a read amplifier is described in, for example, Japanese Patent Application Laid-Open No. 60-201105.

[0004]

FIG. 3 shows a circuit diagram of a read amplifier RA developed by the inventors of the present invention prior to the present invention. In the figure, the read amplifier RA
Includes a pair of differential transistors T3 and T4. The non-inverted read signal RIT or the inverted read signal RIB of the magnetic head MH is supplied to the bases of these differential transistors via the corresponding external terminals, and the collector thereof has a pair of cascode transistors T1 or T2.
Are connected to the inverting output terminal ROB or the non-inverting output terminal ROT of the read amplifier RA, respectively. The inverting output terminal ROB or the non-inverting output terminal ROT is coupled to the non-inverting or inverting input terminal of the main amplifier MA (not shown), respectively. The cascode transistors T1 and T2 are
It functions as a so-called capacitance cut transistor, and acts to prevent the input capacitance of the read amplifier RA as viewed from the magnetic head MH side from increasing due to the relatively large input capacitance of the main amplifier MA. As a result, the read amplifier R
The high frequency characteristics of A are improved, and the data rate of the magnetic disk device is increased.

By the way, the differential transistors T3 and T4
As described above, since the base is coupled to the magnetic head MH via the external terminal of the magnetic head drive integrated circuit, a relatively large surge voltage may be applied. The surge voltage applied to the external terminal does not affect the input transistors T3 and T4 formed in a relatively large size so as to have a relatively large amplification factor, and is provided on the collector side of these input transistors. This causes electrostatic breakdown of the cascode transistors T1 and T2 formed in a small size. However, in the read amplifier RA of FIG. 3, the wiring between the emitters of the cascode transistors T1 and T2 and the collectors of the input transistors T3 and T4 is laid out to lengthen the wiring length, whereby the electrostatic capacitance of the cascode transistors T1 and T2 is increased. We have adopted a method to prevent destruction.

However, in the read amplifier RA of FIG. 3, the wiring length between the emitters of the cascode transistors T1 and T2 and the collectors of the input transistors T3 and T4 is lengthened, and conversely the input transistor T is reversed.
3 and T4 have large collector capacitances, and the magnetic head M
The input capacitance of the read amplifier RA when viewed from H increases. As a result, the high-frequency characteristic of the read amplifier RA is deteriorated, and there is a problem that the increase in the data rate of the magnetic disk device is limited.

An object of the present invention is to prevent electrostatic breakdown of a cascode transistor included in a read amplifier or the like without increasing its input capacitance. Another object of the present invention is to improve the reliability of the read amplifier and eventually the magnetic disk drive without sacrificing the high frequency characteristics and the data rate.

The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0009]

The outline of a typical invention among the inventions disclosed in the present application will be briefly described as follows. That is, between the emitter of the cascode transistor included in the read amplifier of the magnetic head drive integrated circuit and the base thereof or the power supply voltage on the high potential side of the circuit, its anode is coupled to the emitter of the cascode transistor and its cathode is connected to the cascode transistor. A pair of diodes are provided which are coupled to the high side power supply voltage of the base or circuit.

[0010]

According to the above means, the surge current is applied to the external terminal of the magnetic head drive integrated circuit without affecting the operation characteristics of the read amplifier, and the large current that tends to flow into the emitter of the cascode transistor. Can be blocked. As a result, electrostatic damage to the cascode transistor included in the read amplifier or the like can be prevented without increasing the input capacitance. As a result, it is possible to improve the reliability of the read amplifier and eventually of the magnetic disk device and the like without sacrificing the high frequency characteristics and the data rate.

[0011]

1 is a circuit diagram of a first embodiment of a read amplifier RA to which the present invention is applied. Based on the figure, the outline and characteristics of the configuration and operation of the read amplifier RA of this embodiment will be described. The read amplifier RA is mounted on the magnetic head drive integrated circuit of the magnetic disk device. The magnetic head drive integrated circuit further includes a write system circuit (not shown) that applies a predetermined write current to the magnetic head. The circuit element of FIG. 1 is formed on one semiconductor substrate such as single crystal silicon together with other circuit elements (not shown) of the magnetic head driving integrated circuit. In the following circuit diagrams, the illustrated transistors (in this specification, bipolar transistors are simply referred to as transistors) are not particularly limited,
All are NPN bipolar transistors.

In FIG. 1, the read amplifier RA of this embodiment includes a pair of differential transistors T3 and T4.
The magnetic head MH is connected to the bases of these differential transistors via corresponding external terminals of the magnetic head drive integrated circuit.
Non-inverted read signal RIT or inverted read signal RI
B is supplied to each of them, and the common-coupled emitters of the same are connected to the low-potential-side power supply voltage VE of the circuit via the constant current source S1.
Bound to E. The collectors of the differential transistors T3 and T4 are the corresponding cascode transistors T1 or T2.
Is connected to the inverting output terminal ROB or the non-inverting output terminal ROT of the read amplifier RA, respectively, and is further connected to the high potential side power supply voltage VCC of the circuit via the corresponding load resistor R1 or R2. The high-potential-side power supply voltage VCC of the circuit is not particularly limited, but is a positive power-supply voltage such as + 5V, and the low-potential-side power supply voltage VEE of the circuit is -5.
It is a negative power supply voltage such as 2V.

Non-inverting output terminal ROT of read amplifier RA
A main amplifier MA (not shown) of the magnetic head driving integrated circuit is coupled to the and the inverting output terminal ROB. Also,
The bases of cascode transistors T1 and T2 are coupled to the circuit ground potential. As a result, the differential transistors T3 and T4 form a differential amplifier circuit, amplify the non-inverted read signal RIT and the inverted read signal RIB output from the magnetic head MH, and output the non-inverted output terminal ROT of the read amplifier RA. And the inverted output terminal ROB. Further, the cascode transistors T1 and T2 function as so-called capacitance cut transistors, and act to prevent the input capacitance of the read amplifier RA from increasing due to the relatively large input capacitance of the main amplifier MA. As a result, the high frequency characteristics of the read amplifier RA are improved and the data rate of the magnetic disk device is increased.

In this embodiment, the read amplifier RA
Has a cascode transistor T
1 and T2 includes a pair of diodes D1 and D2, respectively, which are coupled to the emitters and whose cathodes are coupled to the bases of these transistors, respectively. As aforementioned,
The bases of the input transistors T3 and T4 are connected to the magnetic head MH via the corresponding external terminals of the magnetic head drive integrated circuit.
And a relatively large surge voltage may be applied. The positive surge voltage applied to these external terminals is transmitted to the emitters of the cascode transistors T1 and T2 via the base-collector capacitances of the input transistors T3 and T4. At this time, the diodes D1 and D2 are turned on, and a large current due to the surge voltage is prevented from flowing into the emitters of the cascode transistors T1 and T2. As a result, electrostatic breakdown of the cascode transistors T1 and T2 can be prevented, and the reliability of the read amplifier RA and eventually the magnetic disk device can be improved.

Incidentally, in a normal state in which the surge voltage is not applied to the external terminal of the magnetic head driving integrated circuit, the diodes D1 and D2 are reverse biased and are turned off. Therefore, the provision of these diodes does not affect the operation characteristics of the read amplifier RA, and the effect of reducing the input capacitance by the cascode transistors T1 and T2 is not lost.

FIG. 2 shows a circuit diagram of a second embodiment of the read amplifier RA to which the present invention is applied. Since this read amplifier RA basically follows the embodiment of FIG. 1, description will be added only to portions different from this.

In FIG. 2, the read amplifier RA of this embodiment includes a pair of diodes D3 and D4 provided between the emitters of the cascode transistors T1 and T2 and the high potential side power supply voltage VCC of the circuit. In these diodes, the level of the surge voltage transmitted from the external terminal of the magnetic head drive integrated circuit to the emitters of the cascode transistors T1 and T2 via the base-collector capacitances of the input transistors T3 and T4 is the high-potential-side power supply voltage VCC.
When the potential of the cascode transistors T1 and T2 exceeds the potential of + 5V, ie, + 5V, the surge voltage prevents a large current from flowing into the emitters of the cascode transistors T1 and T2. As a result, the read amplifier R of this embodiment is
Even in A, the same effects as those of the embodiment of FIG. 1 can be obtained, and the reliability of the read amplifier and eventually the magnetic disk device can be improved without sacrificing the high frequency characteristics and the data rate.

As shown in the above two embodiments, by applying the present invention to a semiconductor device such as a magnetic head drive integrated circuit including a read amplifier, the following operational effects can be obtained. That is, (1) between the emitter of the cascode transistor included in the read amplifier of the magnetic head driving integrated circuit and the base thereof or the high-potential side power supply voltage of the circuit, its anode is coupled to the emitter of the cascode transistor and its cathode is By providing a pair of diodes that are coupled to the base of the cascode transistor or the power supply voltage on the high-potential side of the circuit, surge voltage is applied to the corresponding external terminals of the magnetic head drive integrated circuit and flows into the emitter of the cascode transistor. The effect that an attempted large current can be blocked is obtained. (2) According to the above item (1), it is possible to prevent an electrostatic breakdown of the cascode transistor included in the read amplifier without increasing the input capacitance thereof. (3) According to the above items (1) and (2), it is possible to improve the reliability of the read amplifier and eventually the magnetic disk device without sacrificing the high frequency characteristics and the data rate.

Although the invention made by the present inventor has been specifically described based on the embodiments, the invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say. For example, in FIGS. 1 and 2, the read amplifier RA may receive only the non-inverted read signal RIT or the inverted read signal RIB, and the differential amplifier circuit does not have to be a basic configuration. The specific circuit configuration of the read amplifier RA is not restricted by these examples, and the polarity and absolute value of the power supply voltage, the conductivity type of the transistor, and the like can adopt various embodiments.

In the above description, the case where the invention made by the present inventor is mainly applied to a magnetic head drive integrated circuit including a read amplifier which is the field of application which is the background of the invention has been described, but the invention is not limited to this. Without
For example, the present invention can be applied to various types of integrated circuit devices including a read amplifier that is formed as a single unit or a similar read amplifier. The present invention can be widely applied to a semiconductor device including at least a cascode transistor and a system including such a semiconductor device.

[0021]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows. That is, between the emitter of the cascode transistor included in the read amplifier of the magnetic head drive integrated circuit and the base thereof or the power supply voltage on the high potential side of the circuit, its anode is coupled to the emitter of the cascode transistor and its cathode is connected to the cascode transistor. By providing a pair of diodes that are coupled to the power supply voltage on the high potential side of the base or circuit, surge voltage is applied to the corresponding external terminals of the magnetic head drive integrated circuit or the like to try to flow into the emitter of the cascode transistor. It is possible to prevent a large current from flowing. This allows
The electrostatic breakdown of the cascode transistor included in the read amplifier or the like can be prevented without increasing the input capacitance. As a result, it is possible to improve the reliability of the read amplifier and eventually of the magnetic disk device and the like without sacrificing the high frequency characteristics and the data rate.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a read amplifier to which the present invention is applied.

FIG. 2 is a circuit diagram showing a second embodiment of a read amplifier to which the present invention is applied.

FIG. 3 is a circuit diagram of a read amplifier developed by the inventors of the present application prior to the present invention.

[Explanation of symbols]

RA ... Read amplifier, MH ... Magnetic head, MA
... Main amplifier. T1 to T4 ... NPN type bipolar transistor, D1 to D4 ... Diode, R1
~ R2 ... Resistor, S1 ... Constant current source.

Claims (3)

[Claims] 1. An input transistor having a base for receiving a predetermined input signal, a cascode transistor provided between a collector of the input transistor and an output terminal of the circuit, and an anode thereof coupled to an emitter of the cascode transistor. A semiconductor device comprising: an amplifier circuit including a cathode whose cathode is coupled to a base of the cascode transistor or a high-potential side power supply voltage of the circuit. 2. The input signal comprises non-inverted and inverted input signals, and the amplifier circuit includes a pair of the input transistor, cascode transistor and diode provided corresponding to the non-inverted and inverted input signals. The semiconductor device according to claim 1, which includes: 3. The semiconductor device is a magnetic head drive integrated circuit of a magnetic disk device, and the amplifier circuit is a read amplifier included in the magnetic head drive integrated circuit. The semiconductor device according to claim 2.