Telecoil Preamplifier
GC562 - DATA SHEET
FEATURES
鈥?direct coupled telecoil preamplifier
鈥?natural low frequency rolloff to reduce 50/60 Hz
hum pickup
鈥?low current consumption (typ 65
碌
A)
鈥?34 dB maximum gain
STANDARD PACKAGING
鈥?Chip (28 x 56 mils)
Au Bump
DESCRIPTION
The GC562 was designed to allow direct coupling of the
telecoil onto the preamplifier without the need of a capacitor.
The DC bias voltage at the output of the unity gain, inverting
preamplifier B, precisely matches that of the input of
preamp A. When the telecoil is placed between these two
pins, no DC current will flow through the coil as the potential
at both ends is equal. With stage B configured as unity gain,
its output appears as a virtual ground to AC signals. The lower
-3 dB corner frequency of the amplifier is set by the ratio of the
telecoil resistance to the inductance, given by the equation:
R
COIL
茠
L
=
(2蟺 L
COIL
)
With a gain set resistor from the input to output of
preamplifier A, a signal inductively coupled into the
telecoil via the telephone will produce a signal current to flow
through the resistor, thereby producing a voltage at the output
of the amplifier.
For stability reasons it is recommended that the telecoil
amplifier not be configured for more than 34 dB gain, or with
a feedback resistor larger than 100 k鈩?
V
B
2
T
REF
1
B
T
IN
3
-A
4
T
OUT
5
GND
FUNCTIONAL BLOCK DIAGRAM
Revision Date: September 1999
Document No. 520 - 93 - 02
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