Appeal No. 96-0517
Application 08/264,473
14. A playback circuit for a magnetic head comprising
an initial-stage amplifying means [base-grounded
transistor amplifier 22] for amplifying an output signal
from a magneto-resistive head,
voltage-to-current converting amplifying means [70]
supplied with an output signal of said initial-stage
amplifying means, said voltage-to-current converting
amplifying means having input/output characteristics
represented by an exponential function,
a capacitor [26] connected to an output terminal of
said voltage-to-current converting amplifying means, and
feedback means for feeding back an output of said
voltage-to-current converting amplifying means to an
input side of said initial-stage amplifying means.
This claim reads in similar fashion on the alternative
embodiment shown in Figure 19, which replaces the base-
grounded transistor 22 of Figure 14 with an emitter-grounded
transistor 22 (Spec. at 26:16-18). The circuits of Figures 14
and 19 reduce the capacitor charging/discharging as follows:
[F]or the starting of the amplifier operation by turning
on of the power source as mentioned above, or the head
switching, the input voltage Vi is increased and the
transconductance gm of the voltage-current converting
amplifier (gm amplifier) 70 is increased to enable the
quick charging/discharging of the capacitor 26, whereas,
for usual playback or the steady-state operation, the
input voltage Vi is decreased to lower the
transconductance gm. Besides, since changes in
transconductance gm are small in the vicinity of Vi = 0
under steady state condition, only small changes in the
frequency response are incurred even if more or less
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Last modified: November 3, 2007