Adaptive Highpass Filter
with Independent Gain Block
GR581 DATA SHEET
FEATURES
• unity gain 12 dB/oct. highpass Butterworth filter
• adaptive frequency range from 200 Hz to 2 kHz
• rectifier threshold set to 82 dBSPL (adjustable)
• low noise, typically 2.6
µ
V
• 300
µ
A typical current drain
• operates from 1.1 to 3 VDC
• preamplifier with 56 dB open loop gain
DESCRIPTION
The GR581 is a level-sensitive, adaptive highpass filter
comprised of a current controlled highpass filter, a half- wave
rectifier, a voltage regulator for microphone bias and a separate
preamplifier.
The internal rectifier senses the long term average signal level
and controls the filter response by setting the control current
of the filter. The rectifier sensitivity, with respect to the input
signal, can be increased by placing the internal preamplifier
(A) before the filter section of the GR581. The preamplifier has
an internal 265 kΩ feedback resistor from its input to output, to
facilitate in setting the gain.
An increase of 20 dB above the rectifier threshold will
automatically increase the corner frequency one decade
above the initial corner frequency. The filter will only allow an
increase in corner frequency of one decade, regardless of
further increases in the input signal level.
It is recommended that the attack and release times be set to
30 ms and 90 ms respectively. The average time period of a
speech frame is about 15 ms which is not long enough to
activate the filter, however long term average noise, which can
have time periods greater than 30 ms, will activate the filter
(providing that the amplitude is above the rectifier threshold).
The GR581 is an improved version of the LS581adaptive high
pass filter and has an identical pinout.
PACKAGING
• 10 pin MICROpac
• 10 pin PLID®
• Chip (73 x 59 mils)
VB
2
1
VREG
VREG
+
-
A IN
6
-A
RECTIFIER
10k
265k
5
A OUT
CA
9
CB
8
3
7
4
RECT IN GND RECTCAP
10
B
B OUT
All resistors in ohms, all capacitors
in farads unless otherwise stated.
FUNCTIONAL BLOCK DIAGRAM
Revision Date: January 2001
Document No. 520 - 60 - 05
GENNUM CORPORATION P.O. Box 489, Stn A, Burlington, Ontario, Canada L7R 3Y3 tel. (905) 632-2996 fax: (905) 632-2814
Gennum Japan Corporation: C-101, Miyamae Village, 2-10-42 Miyamae, Suginami-ku, Tokyo 168-0081, Japan tel. (03) 3334-7700 fax:(03) 3247-8839
GENNUM [ GENNUM CORPORATION ]
