- A
MPO
A IN
R
V
E
B
GND
A OUT
RMIC
VMIC
1
2
4
3
5
7
6
- B
B OUT
8
21K
R
E
GK509 DATA SHEET
Class A Amplifier with 2 DC Coupled
Gain Blocks & Schottky Diodes
FEATURES
• 100
µA typical current drain
• low noise and distortion
• 1.0 to 5 VDC operating range
• DC coupled stages
• Class A output stage
• Schottky diodes for MPO control
• variable transducer current
• 4 k
Ω microphone decoupling resistor
• 8 pin PLID®
• Chip ( 61 x 55 mils)
STANDARD PACKAGING
BLOCK DIAGRAM
All resistors in ohms, all capacitors in farads unless otherwise stated
DESCRIPTION
The GK509 is a Class A amplifier utilizing Gennum’s
proprietary low voltage JFET technology. It consists of a
single-ended, low noise inverting gain block, a Class
A output stage, an on-chip microphone decoupling
resistor , and a pair of Schottky diodes for symmetrical
peak clipping.
Block A typically has 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 GK509 is a Class A current drive.
It has a fixed reference voltage of typically 30 mV at pin 2
of the device. The current that flows in the transducer is the
ratio of the 30 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 2
to ground, thereby decreasing the equivalent emitter resistance
and increasing the current.
The GK509 also contains a pair of Schottky diodes in the
feedback configuration of the output stage, which provides
approximately 12 dB of MPO control.
Revision Date: January 2001
Document No. 510 - 69 -06
GENNUM CORPORATION P.O. Box 489, Stn. A, Burlington, Ontario, Canada L7R 3Y3 tel. +1 (905) 632-2996
Web Site: www.gennum.com
E-mail: hipinfo@gennum.com
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