鈩?/div>
microphone decoupling resistor
DESCRIPTION
The GC509 is a Class A amplifier utilizing Gennum鈥檚 proprietary
low voltage JFET technology. It consists of two single-
ended, low noise inverting gain blocks, a Class A output
stage, and an on-chip microphone decoupling resistor.
Blocks A and B typically have an open loop voltage gain of
56 dB, with the closed loop gain set by the ratio of the
feedback resistor to the source impedance. It is recommended
that the maximum closed loop gain be 20 dB lower than the
open loop gain. All blocks of the device are internally bias
compensated, preventing any DC current flow via external
feedback resistors. Without this compensation, audible
scratchiness would be present during changes in volume
control settings.
The output stage of the GC509 is a Class A current drive.
It has a fixed reference voltage of typically 55 mV at pin 8
of the device. The current that flows in the transducer is the
ratio of the 55 mV reference voltage and the on-chip emitter
resistor (R
E
). To increase the bias current in the transducer,
simply place an external R
E
resistor from pin 8 to ground,
thereby decreasing the equivalent emitter resistance and
increasing the current.
STANDARD PACKAGING
鈥?10 pin MICROpac
鈥?10 pin PLID
廬
鈥?10 pin SLT
鈥?Chip (61 x 55 mils)
Au Bump
V
B
V
MIC
5
R
MIC
6
21K
4
A IN
-A
-B
-C
7
8
R
E
C OUT
R
E
2
3
10
B OUT
9
C IN
1
GND
A OUT B IN
All resistors in ohms, all capacitors in Farads unless otherwise
stated
BLOCK DIAGRAM
Document No. 510 - 70 - 3
GENNUM CORPORATION P.O. Box 489, Stn A, Burlington, Ontario, Canada L7R 3Y3
Japan Branch: A-302, M i yamae Vi l l age, 2鈥?0鈥?2 M i yamae, Suginami鈥搆u, Tokyo 168, Japan
tel. (905) 632-2996 fax: (905) 632-5946
tel. (03) 3334-7700
fax (03) 3247-8991
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