Magnetic head write amplifier including current mirrors and switchable current sources
AssigneeU.S. Philips Corporation
InventorsJohannes O. Voorman, Hendrik J. Pothast, Ho W. Wong-Lam
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Abstract
An apparatus for recording on a magnetic record carrier includes a write amplifier comprising four current mirrors which are turned on two at a time by two switchable floating current sources connected between the input terminals of the current mirrors in order to produce a write current of alternating polarity through a write head. The high impedance at the terminals of the write head enables the common-mode voltage across the write head to be fixed at any desired voltage value by means of a common-mode circuit. The symmetrical structure further enables the parasitic capacitances at the write terminals to be neutralized by means of neutralizing capacitors.
Claims14
An arrangement for recording an information signal on a magnetic record carrier, comprising:
- a write head for recording information on the record carrier, and a write amplifier for driving the write head in response to the information signal, the write amplifier comprising:
- a first write terminal and a second write terminal, coupled to the write head;
- a first supply terminal and a second supply terminal for the connection of a supply voltage for the write amplifier;
- a first current mirror having a first current input terminal, a first current output terminal coupled to the first write terminal, and a first common current terminal connected to the first supply terminal;
- a second current mirror having a second current input terminal, a second current output terminal coupled to the second write terminal, and a second common current terminal connected to the first supply terminal;
- and
- current switching means for establishing a current path between the first current output terminal and the second supply terminal via the first write terminal and the second write terminal for a first value of the information signal and for establishing a current path between the second current output terminal and the second supply terminal via the first write terminal and the second write terminal for a second value of the information signal, wherein the current switching means comprise:
- a third current mirror having a third current input terminal, a third current output terminal coupled to the first write terminal, and a third common current terminal connected to the second supply terminal;
- a fourth current mirror having a fourth current input terminal, a fourth current output terminal coupled to the second write terminal, and a fourth common current terminal connected to the second supply terminal;
- a first switchable current source connected between the first current input terminal and the fourth current input terminal for supplying a first current for a first value of the information signal;
- and
- a second switchable current source connected between the second current input terminal and the third current input terminal for supplying a second current for the second value of the information signal.
A write amplifier circuit for a magnetic write head comprising:
- first and second write terminals for connection to respective terminals of the write head,
- first and second supply voltage terminals for the write amplifier circuit,
- first, second, third and fourth current mirrors each having a current input terminal, a current output terminal and a common terminal,
- first means coupling the common terminals of the first and second current mirrors to the first supply voltage terminal and the common terminals of the third and fourth current mirrors to the second supply voltage terminal,
- second means coupling the output terminals of the first and third current mirrors to the first write terminal and the output terminals of the second and fourth current mirrors to the second write terminal,
- a first switchable current source connected between the first current input terminals of the first and fourth current mirrors to provide a first current path that bypasses a write head when connected to said first and second write terminals, and
- a second switchable current source connected between the first input terminals of the second and third current mirrors to provide a second current path that bypasses a write head when connected to said first and second write terminals.
Dependencies are inferred from the claim text.