RECORDING APPARATUS PROVIDED WITH A WRITE DRIVER CIRCUIT

Abstract: A recording apparatus for recording an information signal on a magnetic record carrier is disclosed, comprising a write driver circuit and a magnetic write head (L>h<). The write driver circuit comprises a first voltage driver (4) and a second voltage driver (6). Further, a first current driver (40) and a second current driver (42) is available for driving the write head (L>h<).

Description: Recording apparatus provided with a write driver circuit. The invention relates to a recording apparatus for recording an information signal on a magnetic record carrier, the apparatus comprising: - an input terminal for receiving the information signal, - a write driver circuit and - a magnetic write head, the write driver circuit comprising - a first voltage driver having an input coupled to the input terminal of the apparatus, and an output coupled to a first terminal of the magnetic write head, - a second voltage driver having an input coupled to the input terminal of the apparatus and an output coupled to the second terminal of the write head, as well as to a write driver circuit for use in the recording apparatus. Write drivers of the voltage drive type are well known in the art. Reference is made in this respect to USP 4,853,800 (Dl in the list of related documents that can be found at the end of this description) and DE-A 2,735,498 (D2). There is a strong pressure, especially on hard-disk drive manufacturers, to increase bit density and to shorten access times. The current rate of increase in bit density (60 % per annum) is being sustained by a variety of technical improvements with a resulting increase in data rates of 40 % per year. In order to sustain this increase in data rates, the high frequency performance of the media, heads and electronics, in particular the write driver, have to increase at the same rate. Conventional write driver techniques, based on current driving, see D3, current steering, see D4, have severe speed limitations. These limitations result not only from poor high-frequency performance inside the driver, but also from limitations imposed by the head- amplifier combination. In addition to the poor high-frequency performance of thin-film write heads, these shortcomings have become a major limitation in the write process for magnetic recording. It is an object of the invention to further improve the recording characteristics of the recording apparatus The recording apparatus in accordance with the invention is characterized in that the first voltage dπver circuit compnses an output circuit of a seπes arrangement of an npn transistor and an impedance, coupled between a point of a first constant potential and the output of the first voltage dπver circuit, that the second voltage dπver circuit compnses an output circuit of a seπes arrangement of an npn transistor and an impedance, coupled between said point of a first constant potential and the output of the second voltage dπver circuit, the apparatus further compπsing - a first current dπver having an input coupled to the input terminal and an output coupled to said first terminal of the wπte head and - a second current dπver having an input coupled to the input terminal and an output coupled to said second terminal of the write head the invention is based on the recognition to combine voltage dπve and current dπve techniques in order to obtain an improved recording apparatus A voltage dπver is proposed for the reason that it does not only have a supeπor internal high-frequency performance but is also less sensitive to the performance limitations resulting from head-amplifier combinations Further, by adding a current dπver, preferably compπsing at least one transistor of the npn type, coupled between its output and the point of a second constant potential, which is the negative supply voltage, an improved behaviour can be obtained Both the current dπver as well as the voltage dπver have been realized by npn transistors npn transistors are much faster m their characteπstics. so that replacing the pnp transistor normally present m a current dπver circuit by a voltage dπver having an npn transistor in its output circuit speeds up the circuit significantly The wπte dπver proposed here has a major advantage in that it can be integrated in a chip area much smaller than that used for previous current dπvers The reduced chip area comes as a result of an improved architecture These and other aspects of the invention will become more apparent m the following figure descπption, in which figure 1 shows a pnnciple diagram of a wπte dπver circuit, provided with voltage dπvers, m which the voltage dπvers are dnven by a differential voltage source. figure 2 shows the pnnciple diagram of figure 1, in which the voltage dπvers are dnven by a voltage source implemented with a current source, figure 3 shows a elaborated version of the dπver circuit of figure 2, figure 4 shows the essential elements of the dnver circuit m accordance with the invention, and figure 5 a further elaborated version of the dπver circuit of figure 4 The wπte dπver circuit shown in figure 1 receives an input signal from a differential voltage source, indicated m figure 1 by the two voltage sources 1 and 2 that generate a voltage I w .R d /2, with the polaπties as shown in figure 1 The wπte dπver circuit compnses a first voltage dnver 4, a second voltage dπver 6. Figure 1 further show s the wπte head 8 dnven by the wnte dπver circuit The voltage dnvers each compnse a voltage follower 10a, 10b and a senes resistor Rd/2 Figure 2 shows how the voltage sources 1 and 2 can be implemented with a current source 12 and the resistors 2R b . The bandwidth of the wnte dπver circuit can be increased by adding capacitors C b across the voltage followers 10a and 10b and a corresponding resistor R b , as shown in figure 3. This results in an improvement of the step response of the wnte dnver circuit The addition of the capacitors C f across the resistors R d /2 m the output chain of the voltage dπvers improves the behaviour as well, m that it speeds up the response of the dπver circuit The voltage followers 10a and 10b can be realized m vanous ways, such as m the form of a class A voltage follower, or a class A/B voltage follower Figure 4 shows the essential elements of the wπte dπver circuit in accordance with the invention. The first voltage dπver compnses an npn transistor 40 and the impedance 42 in a senes connection between the positive supply voltage (+) and the output 46 A seπes connection of an impedance 44 and a current source 48 is provided between the positive (+) and negative (-) supply voltages The current source 48 is in the form of an npn transistor as well. The current dnver compnses an npn transistor 52 coupled between the output 46 and the negative supply voltage (-) The current dnver 52 could be considered to be coupled ' parallel with the current source 48 An equivalent circuit construction is shown for the πght hand side of the wnte dnver circuit An input signal supplied to the input terminal 44, which is m the form of a current having either a "high" current or a "low" current, such as a zero current, controls the voltage driver and the current driver in the following way. In response to a high current supplied to the input 44, a current flows through the current source 48, so that the voltage at the node 54 is "low". As a result, the voltage at the output 46 is low and the current driver 52 receives a current that flows through the head L H . In response to a "low" current supplied to the input 44, no current flows through the current source 48, so that the voltage at the node 54 is "high", and thus the voltage at the output 46 is high, resulting in a current running via the output 46 through the head L H - Further, when the input 44 receives a "high" current, the input 56 receives a "low" (no) current. As a result, the current that flows through the head L H runs from the positive supply voltage (+), via the transistor 40, through the head L H and via the transistor 58 to the negative supply voltage. And, when the input 44 receives a "low" current, the input 56 receives a "high" current. As a result, the current that flows through the head L H runs from the positive supply voltage (+), via the transistor 60, through the head L H and via the transistor 52 to the negative supply voltage. Figure 5 shows a further elaborated version of the only the left hand side of the write driver circuit of figure 4. From figure 5, it is clear that npn transistors are used in the output circuits of both the voltage driver and the current driver. This has the advantage over using pnp transistors in that npn transistors can cope with larger currents and are faster than pnp transistors. When using npn transistors, this implies a smaller chip surface area that is required for realizing the writer circuit. Further, the voltage drop across R /2 is reduced, for the reason that cuπent through the head L H is now (partly) taken up by the current source 52. Whilst the invention has been described with reference to preferred embodiments thereof, it is to be understood that these are not limitative examples. Thus, various modifications may become apparent to those skilled in the art, without departing from the scope of the invention, as defined by the claims. Further, the invention lies in each and every novel feature or combination of features. Related documents Dl USP 4,853,800 D2 DE-A 2,735,498 D3 H. Veenstra et al, "150 Mb/s write amplifier for hard-disk drives near rail-to-rail voltage swing", Proc. of the ESCIRC, 1995. D4 R . Reay et al, "A resonant switching write driver for magnetic recording", IEEE Jrnl of Solid-State Circuits, Vol. 32, no. 2, pp. 267-69, Febr. 1997.

Claims: CLAIMS: 1. A recording apparatus for recording an information signal on a magnetic record carrier, the apparatus comprising: - an input terminal for receiving the information signal, - a write driver circuit and - a magnetic write head, the write driver circuit comprising - a first voltage driver having an input coupled to the input terminal of the apparatus, and an output coupled to a first terminal of the magnetic write head, - a second voltage driver having an input coupled to the input terminal of the apparatus and an output coupled to the second terminal of the write head, characterized in that the first voltage driver circuit comprises an output circuit of a series arrangement of an npn transistor and an impedance, coupled between a point of a first constant potential and the output of the first voltage driver circuit, that the second voltage driver circuit comprises an output circuit of a series anangement of an npn transistor and an impedance, coupled between said point of a first constant potential and the output of the second voltage driver circuit, the apparatus further comprising - a first current driver having an input coupled to the input terminal and an output coupled to said first terminal of the write head and - a second current driver having an input coupled to the input terminal and an output coupled to said second terminal of the write head. 2. Recording apparatus as claimed in claim 1, characterized in that the first and second current drivers each comprise a transistor of the npn type, coupled between their output and a point of a second constant potential. 3. Recording apparatus as claimed in claim 1 or 2, characterized in that said first constant potential is the positive supply voltage of the write driver circuit. 4. Recording apparatus as claimed in claim 1 or 2, characterized in that said second constant potential is the negative supply voltage of the write driver circuit. 5. Recording apparatus as claimed in anyone of the preceding claims, characterized in that said first voltage driver is adapted to generate a first voltage signal at its output in response to the information signal having a first amplitude, the second current driver being adapted to generate a first current signal in response to said information signal having said first amplitude, said second voltage driver is adapted to generate a second voltage signal at its output in response to the information signal having a second amplitude, the first current driver being adapted to generate a second current signal in response to said information signal having said second amplitude. 6. Recording apparatus as claimed in claim 3 or 4, characterized in that the first and second current drivers are devoid of a transistor of the pnp type between their output and a second point of a second constant potential, said second constant potential having a polarity opposite to the polarity of the first constant potential. 7. Recording apparatus as claimed in anyone of the preceding claims, characterized in that the magnetic write head is of the thin film inductive type. 8. Recording apparatus as claimed in anyone of the preceding claims, characterized in that the first voltage driver comprises a series arrangement of an impedance and a switchable current source between said points of the first and the second constant potential, a node in the series connection between said impedance and said switchable cuπent source being coupled to the control electrode of the npn transistor in the first voltage driver. 9. Recording apparatus as claimed in claim 8, characterized in that the first current driver comprises a current source which is coupled in parallel with the current source of the first voltage driver. 10. Recording apparatus as claimed in claim 9, characterized in that the current source of the first voltage driver comprises an npn transistor and the current source of the first current driver comprises an npn transistor, the control electrodes of both npn transistors being interconnected. 11. Recording apparatus as claimed in anyone of the preceding claims, characterized in that the second voltage driver comprises a series arrangement of an impedance and a switchable current source between said points of the first and the second constant potential, a node in the series connection between said impedance and said switchable current source being coupled to the control electrode of the npn transistor in the second voltage driver. 12. Recording apparatus as claimed in claim 11, characterized in that the second current driver comprises a current source which is coupled in parallel with the current source of the second voltage driver. 13. Recording apparatus as claimed in claim 12, characterized in that the current source of the second voltage driver comprises an npn transistor and the current source of the second current driver comprises an npn transistor, the control electrodes of both npn transistors being interconnected. 14. Write driver circuit for use in a recording apparatus as claimed in anyone of the claims 1 to 13.

Inventors: DE JONG GERBEN W, LE LUAN, PIERAERTS ERIC, RAMALHO JOAO N V L, VOORMAN JOHANNES O, DE JONG, GERBEN, W., LE, LUAN, PIERAERTS, ERIC, RAMALHO, JOAO, N., V., L., VOORMAN, JOHANNES, O.
Applicants: KONINKL PHILIPS ELECTRONICS NV, PHILIPS SVENSKA AB, KONINKLIJKE PHILIPS ELECTRONICS N.V., PHILIPS AB
Application year: 1999
Main classification: G11B
IPC codes: G11B5, H03K17