Class D Preamp with
Anti-Aliasing Network
GS3018 - HYB DATA SHEET
FEATURES
鈥?incorporates GR504, 3 stage amplifer chip
鈥?designed to drive class D integrated receivers
鈥?adjustable symmetrical peak clipper for MPO
control
鈥?two low noise inverting preamplifiers
鈥?mid-supply referenced output stage
鈥?anti-aliasing filter network
STANDARD PACKAGING
鈥?Hybrid Typical Dimensions:
0.244 in x 0.102 in x 0.115 in
(6.20 mm x 2.59 mm x 2.92 mm)
Provisions have been made on the hybrid to allow the
manufacturer to increase or decrease this corner frequency
with the addition of a capacitor. As the class D receiver
utilizes a 100 kHz clock, lower harmonics of the frequency
may feed back into the system and interact with the
incoming signal from the microphone. Capacitors C5 and
C6 have been added to the hybrid to minimize this effect,
known as "aliasing".
Blocks A and B on the GR504 are low noise inverting
preamplifiers with an open loop voltage gain of typically
50 dB. Typically, the volume control potentiometer would
be placed around block A, and block B used either as a
Gain Trim stage or as a Telecoil amplifier. The voltage gain
of these two blocks is determined by the ratio of the input
resistance to the value of the feedback resistor. With
100 k鈩?potentiometer used as a feedback resistor for both
stages, block A would have a maximum gain of 20 dB, and
block B a gain of 26 dB.
Block C is a mid-supply referenced output stage designed
to drive class D receivers. It is typically capable of 670 mV
peak to peak output voltage swing and 14 dB of MPO
(Maximum Power Output) control with a 10 k鈩?MPO
potentiometer. The gain of the output stage is fixed at
typically 16 dB.
DESCRIPTION
The GS3018 contains Gennum's GR504 class D preamplifier
chip, six capacitors and one resistor. Capacitor C1 on the
hybrid, in conjunction with R
MIC
on the GR504 chip, form a
high pass filter which provides a very well regulated supply
voltage for the microphone. Resistor R1, capacitor C2 and
the output impedance of the microphone (鈮?4 k鈩? also form
a high pass filter with a corner frequency of approximately
240 Hz.
R
MIC
V
MIC
1
C1
4碌7
C2
IN
2
47n
C2
4
GR504
1
MGND
3
C3
68n
5
VC1
All resistors in ohms, all capacitors
in farads unless otherwise stated.
4
R
P1
C5
1n8
5
R
P2
C4
68n
C6
1n8
2A
10
9
8
7
6
3
R1
10k
2
-A
-B
5k
- C
9 V
B
10 OUT
GS3018
6
VC2
7
13
B
RIN
B
IN
15 16 12 11
B
OUT1
B
OUT2
C3 C
IN
MPO GND
8
14
FUNCTIONAL BLOCK DIAGRAM
Revision Date: May 1998
Document No. 521 - 09 - 03
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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