Document No. 510 - 78 - 06
CORPORATION
Programmable Analog
Signal Processor
GP520A - DATA SHEET
Principle features of the preamp are the input impedance
100 k
and a gain of 14 dB.
The programmable filter block is composed of a low pass
and high pass filter which generates a range of high and
low pass corner frequencies. Although the control current
to this block varies linearly, linear to logarithmic conversion
is performed internally in order to adjust the corner frequencies
logarithmically. Both filters feature a 12 dB/octave rolloff
and unity gain.
The filters are followed by an AGC block. Up to 35dB of
adjustable gain is provided as well as programmable
threshold and release time. The attack time of the AGC
block remains fixed and is independent of the release
time. The output current is driven into the preamp of the
clipper, thus, the AGC converts a voltage input into a
current output and is therefore, a transconductance block.
The next stage is an electronic MPO control peak “clipper”
providing electronic clipping of the signal and setting of
the maximum output level. The clipper output is also a
transconductance block and drives a 40 k
resistor (R
OUT8
)
tied to the supply.
The input of the final stage is an inverting operational
amplifier. A feedback resistance of 240 k
is provided
internally and this final stage is thus configured as a
voltage drive output stage. The DC bias current through
the receiver is also programmable.
FEATURES
programmable parameters
- gain
- low pass filter
- high pass filter
- AGC threshold
- release time
- MPO
- receiver bias voltage
on-chip voltage regulator
typical gain 60 dB
voltage drive output stage
telecoil preamp
FUNCTIONAL BLOCK DIAGRAM
FULL WAVE
RECTIFIER
AVERAGING
CIRCUIT
THRESHOLD
AGC
Vcc
RF
LIN/LOG
CONVERTER
I
REF
LIN/LOG
CONVERTER
LIN/LOG
CONVERTER
R
2R
HP
FILTER
-
+
PREAMP
-
+
40K
R
IN14
10K
VOLTAGE
REGULATOR
R
R
14
13
9
18
15
19
22
24
26
27
1
3
5
7
8
10
11
17
I
BIAS
4
23
2
25
16
21
20
6
GND
I
HP
I
LP
I
REF
I
REL
I
THRESH
I
GAIN
I
CLIP
D
OUT
D
IN
C
OUT
B
OUT
B
IN
OUT
C
AGC
RIN
BOUT
BUIN
+
LP
FILTER
LPFB
HP
HPFB
A
OUT
V
CC
V
REG
A
IN
OUTPUT
+
-
R
OUT 8
12
P GND
C
COMP
31
30
C
CLIP
29
28
V
BIAS
50k
VC AMP
CLIPPER
All resistors in ohms, all capacitors in farads unless otherwise stated.
STANDARD PACKAGING
Chip (136 x 110 mils)
Au Bump
CIRCUIT DESCRIPTION
The GP520A is a programmable analog signal path IC
designed for use in hearing instruments. The GP520A’s
programmable parameters are adjusted by external
programming currents, such as generated by the GP521.
The GP520A provides a 2.5
μ
A reference current for use by
the GP521. Sixteen settings are possible in the GP521,
allowing the Programmable Current Sink (PCS) to sink
between 0 and 1.875 x
I
REF
.
The GP520A is composed of five functional blocks. The
input preamp, a filter block, the AGC block, MPO clipper
and the output stage.
Revision Date: May 1998
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